2009
Ivanhoe Girls’ Grammar School
Year 10
Genetics
NAME:__________________________
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Learning Outcomes
Describe the genetic basis of inheritance.
Indicators
This is evident when the student is able to:
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explain that the variation that exists between organisms can be explained by information inherited
from a previous generation.
explain that chromosomes are the carriers of genetic information and occur in pairs in a body cell
explain that chromosomes are made up of DNA, which codes for an organism’s characteristics
identify a gene as a section of a chromosome that produces phenotypic characteristics in organisms
explain that the gene for a particular characteristic may occur in different forms or alleles
identify that alleles are found on homologous chromosomes
explain that the chromosome number within a species is consistent
explain the process of mitosis as a means of cell growth and repair in multicellular organisms
explain that as a result of meiosis gametes (ova and sperm) are formed which possess only one set of
chromosomes
compare the outcome of mitosis and meiosis in relation to genetic inheritance
explain that fertilisation results in a complete set of chromosomes in the cells of the offspring
distinguish between the terms homozygous (pure breeder) and heterozygous (hybrid)
distinguish between the different types of autosomal inheritance:
(a) complete dominance
(b) incomplete dominance
(c) co-dominance
(d) multiple alleles
explain how chromosomes determine the sex of a child
describe that genes carried on the sex chromosomes are inherited with those determining the sex of
the individual
chart the outcome of simple monohybrid crosses, including complete, incomplete dominance and
co-dominance
explain the genetic basis of the human ABO blood system
explain pedigrees by tracing the inheritance of one characteristic resulting from ‘dominant’ or
‘recessive’ genes
identify ways in which inheritance can be manipulated by human intervention
define the following terms: allele, carrier, chromosome, co-dominance, complete dominance,
deoxyribonucleic acid (DNA), diploid, dominant, double helix, gamete, gene, genetics, genotype,
haploid, heterozygous, homozygous, incomplete dominance, karyotype, meiosis, mitosis,
mutation, nucleus, pedigree, phenotype, recessive, sex chromosome.
IT skill development
 copying and saving to the school server
 e-mailing files to teacher
 internet
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HUMAN
VARIATION
Overview
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People vary in their appearance.
Members within a family are more alike than those from different families.
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A complete instruction manual for human development is found within the nucleus of every cell.
This information is coded for in DNA.
DNA (deoxyribonucleic acid) is a long molecule similar in shape to a twisted rope ladder (double
helix). The sides of the ladder are composed of alternating sugar and phosphate units. The rungs are
made of paired bases. Adenine pairs with thymine and cytosine pairs with guanine. The instructions
for development are coded in the order of the bases.
A section of DNA that codes for one particular characteristic is called a gene.
Genes are linked together to form chromosomes.
The number of chromosomes in cells of organisms of the same species is usually the same.
Eg human cells all have 46 chromosomes.
In human cells the chromosomes are paired. Paired chromosomes (homologous) carry the same genes
but the alleles for these genes may be different.
An allele is an alternative form of a gene. For example the gene for the CFTR protein is found on the
7th pair of chromosomes. It has 2 possible alleles, one coding for normal CFTR protein and one coding
for an abnormal protein which leads to cystic fibrosis.
Because human chromosomes are paired, each cell has 2 pieces of information for every gene.
Cells that contained paired chromosomes are diploid and cells that only have one of each type of
chromosome are haploid.
The last pair of human chromosomes are called sex chromosomes. In females cells these
chromosomes are matching and are called X chromosomes. In males they are not matching. Males
have one X chromosome paired with a smaller y chromosome.
Meiosis is a nuclear division that results in the production of ova and sperm that contain only one of
each pair of homologous chromosomes.
Ova and sperm are haploid. (They contain only one allele for each gene)
When a sperm fertilises an ovum the new cell is diploid. In this way each child inherits one allele for
each gene from her mother and one from her father.
The new cell is the first cell of the new child. It divides by mitosis to produce cells that are identical to
the first cell.
Cell growth occurs by mitosis.
The alleles that a child inherits from her parents are called her genotype.
If both alleles for a particular characteristic are the same she is homozygous, if they are different she is
heterozygous.
How the alleles are expressed is the child's phenotype.
Expression depends on the gene’s pattern of inheritance, how it interacts with other genes and its
interaction with the environment.
determined by
DNA
STRUCTURE
organised into
KARYOTYPE
inherited through
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MEIOSIS
FERTILISATION
MITOSIS
determines
INDIVIDUAL’S
GENOTYPE
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expression depends on
1 PATTERN OF
INHERITANCE
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-complete dominance
-incomplete dominance
-co-dominance
-multiple alleles
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2 GENE
INTERACTION
3 ENVIRONMENT
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Early experiments were carried out by Gregor Mendel.
In complete dominance heterozygous individuals have the same phenotype as one of the homozygous
forms.
In incomplete dominance the heterozygous phenotype is between both homozygous forms.
In co-dominance both phenotypes are expressed in the heterozygous individual.
The human ABO blood system shows both dominance and co-dominance expression
It is the male that determines the sex of a child.
½ the sperm produced by males contain an X chromosome and 1/2 contain a Y chromosome.
The Y chromosome is smaller than the X chromosome and so carries fewer genes.
A characteristic that is X linked does not have an allele on the y chromosome.
There is a greater chance of a male showing an X linked recessive disorder as only one allele for the
disorder is required for the disorder to be expressed.
A female can have an X linked recessive disorder but it is less likely as she must have 2 copies of the
recessive allele.
PHENOTYPE
tracked by
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Used to follow the inheritance of characteristics over many generations
PEDIGREES
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Work Sequence - Student
Lesson
Activity
Reference
Genetics
Overview
Video:
GATTACA
Basic
Genetics
Activity:
Classy
Characteristic
s
Set up Barley
Practical 1
Glossary
Pg 3-7
GATTACA
questions Pg 89
Pg 10-11
Pg 12
Pg 54
6-7
Activity:
Making a
Monster
Pg. 16
Complete the
table
8-9
Types of
autosomal
inheritance
Pg. 13-15:
Types of
autosomal
inheritance.
Genetics
problems Pg
22-25
1-3
4
5
Extension Mendel
Complete
dominance
Blood
Groups
10
10 Science.1
Barley
practical
5
Notes/commen
ts
Introduction to
genetics
Complete table
& questions
Homework
Activity Making a Child
Pg 18
Use
chromosomes
to create a
monster
Complete
questions
http://library.think
quest.org/20465/m
endl.html
http://www.sonic.
net/~nbs/projects/
anthro201/
http://www.biolog
y.arizona.edu/men
delian_genetics/pr
oblem_sets/mono
hybrid_cross/mon
ohybrid_cross.htm
l
http://www.dnaftb
.org/dnaftb/4/conc
ept/index.html
http://gslc.genetics
.utah.edu/units/bas
ics/blood/
Practical
exercise 1:
Genetic Barley
Pg 54
Collate
individual and
class results
and discuss
questions
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9-10
Pedigrees
Using
pedigrees Pg.
26-29
http://www.dnaftb
.org/dnaftb/13/con
cept/index.html
11-13
Introduction
to the
structure of
DNA.
Genes &
Chromosomes
Pg 30-35
Practical
Exercise 2:
DNA
Extraction Pg
55-56
Activity:
Building a
DNA model
Questions:
Genes &
Chromosomes
Pg 34
Students write
report during
class. Not
assessed
Extension
Activity - How
to extract DNA
from anything
living?
http://gslc.genetics
.utah.edu/units/act
ivities/extraction
14-15
Cystic
fibrosis
practical
Karyotypes
Human
Chromosome
s
16-17
Start research
Assessed
Practical
Activity:
karyotypes Pg.
36-40
Human
Chromosomes
Homework:
Access the
website and
karyotype 3
people then
diagnose their
genetic
disorder.
http://www.biolog
y.arizona.edu/hum
an_bio/activities/k
aryotyping/patient
_c/13c-13.html
18
A question of
sex
19-20
Meiosis,
fertilisation
and mitosis
Animations
A boy or girl?
Pg. 41-42
Chromosome
number
questions Pg
43
Meiosis and
Mitosis Pg. 4445
Extension Video: Fight to
be male
http://www.biolog
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y.arizona.edu/cell
_bio/tutorials/cell
_cycle/cells3.html
http://www.biolog
y.arizona.edu/cell
_bio/tutorials/mei
osis/page3.html
21-22
Activity:
Modelling
mitosis
Research
Stem cells
Video
Looks at
cloning stem
cells for
treatment of
paralysis?
(Christopher
Reeve)
Stem cells
overview http://gslc.genet
ics.utah.edu/uni
ts/stemcells/
Pg. 46-48
Revision
activity
Genetically
modified
foods
23
24
Rikki Lake
Activity
Revision
25
Test
Research in
groups
Revision
worksheets Pg
. 49-52
ASSESSMENT
Task
Name of Activity
Due
Practical & Assignment
Genetics Problems
Cystic fibrosis practical
Worksheets will be done in
class under test conditions a minimum of 5 will be done
during the unit
Completed and
submitted during the
lesson
Total
Test
10 Science.1
%
assessment
80-90%
10-20%
100%
Done under test conditions in
class
7
100%
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Handout 4
REPRODUCTION
CELLS – CHROMOSOMES - DNA
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DVD: GATTACA
Hardly a day seems to go by without some researchers
claiming to have discovered the gene for this condition or the
gene for that affliction. If we are to believe researchers,
everything from obesity and myopia to homosexuality and
manic depression can be attributed to our genetic make-up.
Humanity, as we know it, seems to be reduced to a genetic sequence.
Of course, if the sum of our being can be attributed to genetics, then it only follows that it can be
engineered. That is the premise behind the sci-fi thriller GATTACA. Set in a "not-so-distant future"
(as the opening credits inform us), GATTACA deals with a future where it is possible to genetically
engineer all these "defects" out of newborn children. As a parent, you can request that your children
will not one day be afflicted by any debilitating heart diseases or other illnesses.
Obviously people genetically engineered this way will have an edge in the workplace over those who
are not. And thus the plot of GATTACA: Ethan Hawke, one of the genetically have-nots in this brave
new world (called "in-valids" in the movie) wants to desperately become an astronaut, but obviously
cannot because of his untampered-with birth. He thus begins a deception by posing as a so-called
"valid" to become an astronaut at a major space exploration company. He does this by "borrowing" the
blood, urine, hair and skin cells of a "valid" who has been crippled in an accident to pass the numerous
tests one have to undergo to get and stay in the training course. But then a murder occurs at the
company, some of his real hair gets picked up and soon the Ethan Hawke character is the prime
suspect. Can he maintain his deception when the human body sheds several million cells each day every single one of them betraying his true identity?
Questions to consider:
1. What characteristics did the parents screen out of their second child?
2. Why does the Ethan Hawke character clean his keyboard obsessively every day?
3. What is present in the blood, urine, hair and skin cells of the potential astronauts that is regularly
tested at the institute?
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4. DNA analysis is used for a number of purposes in the film. State the different purposes.
5. What do you think is an appropriate use of DNA testing?
6. What characteristics, if any, do you think should be screened out of a baby’s DNA?
7. Summarise the reasons for and against the testing of DNA.
Reasons ‘for’ testing DNA
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Genetics Wheel
Characteristic
Alternative forms
Handedness
Left-handed
Right-handed
Ear lobe shape
Attached ear lobe
Hanging ear lobe
Type of joints
Double jointed
Not double jointed
Length of second toe
Longer than big toe
Shorter than big toe
Tongue-rolling
Can roll tongue
Cannot roll tongue
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11
Class
Class
member 1 member 2
Family
Family
member 1 member 2
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Genetic Wheel Questions.
1 What do you notice about the characteristics of different students in the class?
2 What can you conclude about the characteristics of people in your family?
3 Are there any characteristics which appear to be inherited together?
4 If the wheel contained more characteristics, what difference would it make to the results?
5 Calculate the percentage frequency for the ear lobe shapes in the class.
5b. Would the same frequency exist in the broader population?
5c. Would the results for your family be similar or different from those for the class?
Explain.
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TYPES OF AUTOSOMAL INHERITANCE
If a gene is located on an autosome (a non- sex chromosome), then autosomal inheritance exists.
Remember it is the gene rather than the trait that is found on the chromosome.
The following three examples look at various types of autosomal inheritance. In each case flower
colour is considered.
a)
1. COMPLETE DOMINANCE
If this type of inheritance exists what offspring would be produced if two heterozygous
individuals mated?
R = Red flower allele
r = White flower allele
Female
P. PHENOTYPES:
RED FLOWERS
P. GENOTYPES:
Male
x
RED FLOWERS
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
b)
What offspring would be produced if a homozygous red individual is mated with a
homozygous white individual ?
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2. INCOMPLETE OR PARTIAL DOMINANCE
R = Red flower allele
r = White flower allele
Note the symbols used to represent the alleles. If incomplete dominance exists, the heterozygote has a
different phenotype from either of the homozygotes. There are 3 different phenotypes for this type of
inheritance.
a)
What offspring would be produced if two heterozygous individuals mated?
Female
Male
P. PHENOTYPES:
P. GENOTYPES:
Rr
x
Rr
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
Both alleles in the heterozygous plant are fully expressed in the phenotype.
b)
What offspring would be produced if a homozygous red individual is mated with a
homozygous white individual ?
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3. CO-DOMINANCE
This example deals with the inheritance of hair colour in cattle.
CR = Red hair
CW = White hair
CR CW =Red and white hair (roan)
a)
If co-dominance existed what offspring would be produced if two heterozygous individuals
mated?
Female
Male
P. PHENOTYPES:
P. GENOTYPES:
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
b)
What offspring would be produced if a homozygous red individual is mated with a
homozygous white individual ?
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SUMMARY
In all the examples below we are looking at a flower colour gene. The alleles are:
R = red flower and r = white flower
Complete Dominance
Female
Male
P. PHENOTYPES:
x
P.:GENOTYPES
RR
x
rr
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES
Incomplete Dominance
Female
Male
P. PHENOTYPES:
x
P.:GENOTYPES
RR
x
rr
Female
gametes
Male gametes
F1. GENOTYPES:
F1. PHENOTYPES:
Codominance
Female
Male
P. PHENOTYPES:
x
CRCR
P. GENOTYPES:
x
CrCr
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
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Activity: Making a monster
Chromosome
Number
Gene
Alleles
Pattern of
Inheritance
Alleles of
organism
Phenotype
of organism
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
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Activity: Making a child
Stick your egg and sperm combinations here.
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Making a Child
1. Complete the following table for each of the zygotes that you have generated.
Ova and
sperm
Sex chromosomes
and sex
Child
Genotype
Phenotype
1
2
3
4
5
6
7
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Questions for Analysis
1a.
Which of the sex chromosomes is/are found in the egg cells?________________
1b.
Which of the sex chromosomes is/are found in the sperm cells?______________
1c.
Which parent determines the sex of the baby? Explain your answer. __________
______________________________________________________________________
______________________________________________________________________
Look carefully at the egg and sperm for individual 1.
2a.
What were the genotypes of the mother and father for the face shape gene?
______________________________________________________________________
______________________________________________________________________
2b.
What were the phenotypes of the mother and father for the face shape gene?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
2b.
How do you know this? _____________________________________________
______________________________________________________________________
______________________________________________________________________
3.
Could all these eggs and sperm come from the same mother and father respectively?
Explain your answer.
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
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Solving Genetic Problems
Using the 7 step method
1.
2.
3.
4.
5.
6.
7.
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Genetics problems
For each of the following show your working.
Q1.
Two people are carriers (ie. are heterozygous) of the inherited autosomal recessive disease
Hurler syndrome. They have a child.
a)
What is the chance that the child will be unaffected by Hurler syndrome? Use the
symbols: H = Normal allele and h = Hurler syndrome allele.
Female
P. PHENOTYPES:
Normal (Carrier)
P. GENOTYPES:
Male
x
Normal (Carrier)
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
Hurler syndrome causes death in childhood. Affected children are mentally retarded, have
changes in the bones leading to dwarfism, and as a result of the abnormal biochemistry in
Hurler syndrome children, the corneas of their eyes become cloudy.
b)
The first child of these two people is diagnosed as have Hurler syndrome. The couple
has a second child. What is the chance that this child will also suffer from the disease?
Explain.
c)
Can this couple have a baby that will be homozygous normal? What is the chance of
this occurrence?
d)
Another couple is both carriers for Hurler syndrome. They have a family of four
children. How many of these children would have Hurler syndrome? Explain.
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Q2.
In humans, brown eyes (B) are dominant to blue eyes (b). Suppose a blue-eyed man marries a
brown-eyed woman whose father was blue eyes. What proportion of their children would you predict
would have blue eyes?
P. PHENOTYPES:
Female
Brown eyes
P. GENOTYPES:
x
Male
Blue eyes
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
Q3.
Mr and Mrs Miller have two sons. What is the probability that their third child will be a boy?
Q4.
In humans, it is found that a blonde haired individual mated with a black haired individual will
produce brown haired children. Explain this in terms of phenotypes and genotypes.
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Q5.
If the litter resulting from the mating of two short-tailed cats contains three kittens without
tails, two with long tails and six with short tails, what would be the simplest way of explaining
the inheritance of tail length in these cats? Show genotypes and include a cross. (This is an
example of incomplete dominance.)
Female
P. PHENOTYPES:
Short tail
P. GENOTYPES:
Male
x
Short tail
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
Q6.
In snapdragons, red flower colour (R) and white flower colour (r) produce pink when in a
heterozygous state (Rr). Predict flower colour in plants that are crossed as follows:
(a) Homozygous dominant (RR) and heterozygous (Rr).
Female
P. PHENOTYPES:
Red flowers
P. GENOTYPES:
Male
x
Pink flowers
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
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(b) Both heterozygous (Rr).
P. PHENOTYPES:
Female
Pink flowers
P. GENOTYPES:
x
Male
Pink flowers
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
Q7.
Coat colour of the Shorthorn breed of cattle represents a classical example of co-dominant
alleles. In some cells one allele operates and in other cells the other allele is expressed. Red is
governed by the genotype CR CR, roan (a mixture of white and red hairs) by CRC W, and white
by C WC W.
a) When roan Shorthorns are crossed amongst themselves, what genotypic and phenotypic
ratios are expected among their offspring?
Female
P. PHENOTYPES:
Roan
P. GENOTYPES:
Male
x
Roan
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
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b) If a red Shorthorn bull is crossed with a white cow, what genotypic and phenotypic ratios
would you expect among their offspring?
Female
P. PHENOTYPES:
White
P. GENOTYPES:
Male
x
Red
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
Q8.
The Palomino horse is a golden colour with lighter mane and tail. A pair of co-dominant
alleles (CD and CG) is known to be involved in the inheritance of these coat colours. Genotypes
homozygous for the CD gene are chestnut coloured (reddish), heterozygous genotypes are
Palomino coloured, and genotypes homozygous for the CG gene are almost white and called
cremello.
a) From matings between Palominos, determine the expected Palomino: non-Palomino ratio
among their offspring.
Female
P. PHENOTYPES:
Palomino
P. GENOTYPES:
Male
x
Palomino
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
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b) What kind of mating will produce only Palominos?
An example of co-dominance and dominance/ recessiveness
The ABO blood typing gene in humans has three alleles. IA, IB and i. The IA allele is
dominant to the i allele, the IB allele is dominant to the i allele and the IA and IB alleles are
co-dominant.
Phenotype
Blood type A
Blood type B
Blood type AB
Blood type O
Q. 9
Q10.
Genotype
= IA, IA or IA i
= IB, IB or IB i
= IA IB
= ii
A man has blood type AB.
a)
What is his genotype?
b)
In terms of the ABO gene, how many different kinds of sperm can he produce?
A man produces a sperm containing the “i allele” of the ABO gene.
a)
Could this man have been blood type O? Explain.
b)
Could he have been blood type A? Explain.
c)
Could he have been blood type AB? Explain.
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Q11. If a man with blood type B, one of whose parents had blood type O, marries a woman with
blood type AB, what will be the theoretical probability of their children having blood type B? Show a
cross.
Female
Male
P. PHENOTYPES:
Blood type AB
P. GENOTYPES:
x
Blood type B
x
Female
gametes
Male gametes
F1 GENOTYPES:
F1 PHENOTYPES:
ANSWER:
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Q12. A purple-flowered pea plant is crossed with a white-flowered pea plant. All the F1 plants produce
purple flowers .When the F1 plants are crossed to each other, 401 of the F2 plants have purple flowers
and 131 have white flowers.
What are genotypes of the parents and F1 generation?
Q13. In tomatoes red fruit colour is dominant to yellow. Suppose a tomato plant homozygous for red
is crossed with one homozygous for yellow. Determine the appearance of the:
a. the F1
b. the F2
c. the offspring of a cross of the F1 back to the red parent
d. the offspring of a cross of the F1 back to the yellow parent
14. A red-fruited plant, when crossed with a yellow-fruited one, produces progeny about half of
which are red-fruited and half are yellow-fruited. What are the genotypes of the parents?
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15.
In guinea pigs rough coat (R) has dominant expression over smooth coat (r). A rough coated
guinea pig is bred to a smooth one, giving 8 rough and 7 smooth in the F1.
a.
What are the genotypes of the parents and their offspring?
b.
If one of the F1 animals is mated to its rough parent, what progeny would you expect?
16.
Purple flowers have dominant expression over white flowers in the Jimsonweed. When a
particular purple-flowered Jimsonweed is self-pollinated, there are 28 purple-flowered and 10
white-flowered progeny. What proportion of the purple-flowered progeny are true-breeding?
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Pedigrees
A pedigree is a family tree showing a line of descent. It can be used to trace the occurrence of
inherited traits in parents and offspring through a number of generations. Pedigrees are valuable tools
in genetic counselling. It allows a pattern of inheritance to be traced throughout generations of a
family. This can allow identification of the genetic disease and advice can be made available on the
probability of a couple having an affected child. Cystic fibrosis is an example of a recessive genetic
disease. Huntington's chorea is an example of a dominant genetic disease.
By convention, circles represent females and squares, males. A line between a square and a circle
represents a union and a line down indicates offspring from the union. Filled in symbols represent
individuals displaying the phenotype being studied.
Dominant Inheritance
In pattern 1, the son and father are both affected. This is a reasonable indication that the characteristic
is dominant. An affected offspring must have at least one affected parent if the phenotype is dominant.
Features of pedigrees of a dominant trait are:

An affected offspring must have at least one affected parent

Heterozygous individuals will be affected

Two affected parents can produce an unaffected child (both parents would be heterozygous)

Trait cannot reappear in future generations.
Recessive Inheritance
In pattern 2, the daughter is affected but neither parent is. This can only happen if the characteristic is
recessive and the offspring are homozygous, e.g. bb. Both parent must be heterozygous, Bb. Features
of pedigrees of a recessive trait are:

Two unaffected patents can have an affected offspring

Heterozygous individuals will be unaffected

Two affected parents will always have an affected child.

Trait can skip a generation and then reappear in future generations.
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Reference: Core Biology Practical, Kate Mudie and Judith Brotherton p4.21
Pedigrees
One form of expression of a characteristic may be prominent in certain families. Its inheritance is
often illustrated by using family trees or pedigrees
Symbols used in family tree diagrams include:
Pedigree problems
Part A
A pedigree for the recessive pattern of inheritance of albinism is shown in Fig. 1
Use the pedigree answer the following questions.
Key:
Albino - a–
Normal - A
1
Figure 1 Pedigree for albinism
How many males and females in the pedigree are albino?
2
When two albino parents have children, are all their children albinos?
3
In the second generation a male albino married a ‘normal’ woman and they had three ‘normal’
children. If they had another child, what is the probability that it would be albino?
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Part B
Huntingtons disease is a progressive, neurological condition caused by an allele with dominant
expression. The pedigree of a family with this condition is shown below
Key
A
1
2
3
Insert genotypes for as many people as you can in this pedigree.
Does this condition skip a generation?
If a person has the condition, what can be deduced about their parents?
3
If person A were to have another child, what is the probability that this child would have the
condition?
Part C
Key
Look at the pedigree in Figure 3 and then answer these questions about it.
1
3
4
5
12
6
13
2
7
8
9
10
14
11
_
15
Figure 3 Family pedigree showing the inheritance of night blindness, a condition in which it’s difficult
to see in dim light. The condition is controlled by a single pair of alleles, the allele for night blindness
being dominant
1
Using B as the symbol for the night-blindness allele (dominant) and b for the normal allele
(recessive), write down the possible genotypes of all the people in the chart.
2
Explain in words how you know the genotype of person 1.
3
How are persons 13 and 15 related to each other?
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4
How do you know the genotypes of 13 and 15?
5
If 13 and 15 should marry, what is the chance that any of their children will be night-blind?
Explain your answer.
6
If 14 and 15 marry, what is the chance of any of their children having night-blindness? Explain
your answer.
Part D
Examine the family pedigree below. It illustrates the pattern of inheritance of right- (R) and lefthandedness (r) in a particular family. Familiarise yourself with the key before answering the questions.
1
Which characteristic, left- or right-handedness, is dominant in humans, and which is recessive?
___________________________________________________________________________________________
2
Write down the phenotypes and genotypes for each of the following individuals.
Individual
Phenotype
Genotype
A
B
C
D
F
H
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3
a
Write down the phenotype for individuals E and G.
_______________________________________________________________________________________
b
List the possible genotypes for the individuals E and G.
_______________________________________________________________________________________
c
Explain how it is that you can be sure of the genotype for D but not for E or G.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
4
Suppose individual F married a left-handed woman and they have three children—two girls and a boy.
a
Draw a pedigree to illustrate the phenotypes for this family. Beneath each individual write down the
genotype for that person.
b
Explain how you can be sure of the genotypes of each individual.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Part E
A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a
blue-eyed woman whose father and mother were brown-eyed. The couple had a blue-eyed son.
Of the individuals mentioned, can you be sure of their genotypes? What genotypes are possible
for the others. State your reasoning.
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Genes and chromosomes and DNA
“The book of life”
Our genetic information, sometimes described as the ‘Book of Life’, can be
thought of as being made up of two volumes. Each volume of the book is
contributed to a person by one of their parents.
So in your ‘Genetic Book of Life’ (Figures 1.1 & 1.2):
• One volume was inherited from your Mum and one from your Dad
• Both volumes contain 23 chapters each, and together are equivalent to the
23 pairs of chromosomes present in your body cells that contain your genetic
information
• The 23 chapters (ie. chromosomes) are made up of a variable number of
pages (ie. genes)
• Women’s chromosomes are described as 46 XX; men’s as 46,XY
• A mother passes 23 chromosomes to her child through her egg and a father
passes 23 chromosomes through his sperm
• The chromosomes consist of two very long thin strands of DNA chains
twisted into the shape of a double helix and are located in the nucleus (the
‘control centre’) of our body cells
• The chromosomes consist of long strands of genes.
• Since the chromosomes come in pairs, the genes also come in pairs.
• In each of the approximate 20,000 genes there is a piece of genetic
information which guides our growth, development and health and is in the
form of a chemical code, called the genetic code.
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What is DNA?
We all know that humans give birth to humans, elephants only give birth to little
elephants, giraffes to giraffes, dogs to dogs and so on for every type of living creature.
But why is this so?
The answer lies in a molecule called deoxyribonucleic acid (DNA), which contains the
biological instructions that make each species unique. DNA, along with the instructions it
contains, is passed from adult organisms to their offspring during reproduction.
Where is DNA found?
DNA is found inside a special area of the cell called the nucleus. Because the cell is very
small, and because organisms have many DNA molecules per cell, each DNA molecule
must be tightly packaged. This packaged form of the DNA is called a chromosome.
DNA spends a lot of time in its chromosome form. But during cell division, DNA unwinds
so it can be copied and the copies transferred to new cells. DNA also unwinds so that its
instructions can be used to make proteins and for other biological processes.
Researchers refer to DNA found in the cell's nucleus as nuclear DNA. An organism's
complete set of nuclear DNA is called its genome.
Besides the DNA located in the nucleus, humans and other complex organisms also have
a small amount of DNA in other cell structures known as mitochondria. Mitochondria
generate the energy the cell needs to function properly.
In sexual reproduction, organisms inherit half of their nuclear DNA from the male parent
and half from the female parent. However, organisms inherit all of their mitochondrial
DNA from the female parent. This occurs because only egg cells, and not sperm cells,
keep their mitochondria during fertilization.
What is DNA made of?
DNA is made of chemical building blocks called nucleotides. These building blocks are
made of three parts: a phosphate group, a sugar group and one of four types of
nitrogen bases. To form a strand of DNA, nucleotides are linked into chains, with the
phosphate and sugar groups alternating.
The four types of nitrogen bases found in nucleotides are: adenine (A), , thymine (T),
guanine (G) and cytosine (C). The order, or sequence, of these bases determines what
biological instructions are contained in a strand of DNA. For example, the sequence
ATCGTT might instruct for blue eyes, while ATCGCT might instruct for brown.
Each DNA sequence that contains instructions to make a protein is known as a gene.
The size of a gene may vary greatly, ranging from about 1,000 bases to 1 million bases
in humans.
The complete DNA instruction book, or genome, for a human contains about 3 billion
bases and about 20,000 genes on 23 pairs of chromosomes.
What does DNA do?
DNA contains the instructions needed for an organism to develop, survive and
reproduce. To carry out these functions, DNA sequences must be converted into
messages that can be used to produce proteins, which are the complex molecules that
do most of the work in our bodies.
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How are DNA sequences used to make proteins?
DNA's instructions are used to make proteins in a two-step process. First, enzymes read
the information in a DNA molecule and transcribe it into an intermediary molecule called
messenger ribonucleic acid, or mRNA.
Next, the information contained in the mRNA molecule is translated into the "language"
of amino acids, which are the building blocks of proteins. This language tells the cell's
protein-making machinery the precise order in which to link the amino acids to produce
a specific protein. This is a major task because there are 20 types of amino acids, which
can be placed in many different orders to form a wide variety of proteins.
Proteins
Although DNA is the carrier of genetic information in a cell, proteins do the bulk of the
work. Proteins are long chains containing as many as 20 different kinds of amino acids.
Each cell contains thousands of different proteins: enzymes that make new molecules
and catalyze nearly all chemical processes in cells; structural components that give
cells their shape and help them move; hormones that transmit signals throughout the
body; antibodies that recognize foreign molecules; and transport molecules that
carry oxygen. The genetic code carried by DNA is what specifies the order and number
of amino acids and, therefore, the shape and function of the protein.
Who discovered DNA?
The German biochemist Frederich Miescher first observed DNA in the late 1800s. But
nearly a century passed from that discovery until researchers unraveled the structure of
the DNA molecule and realized its central importance to biology.
For many years, scientists debated which molecule carried life's biological instructions.
Most thought that DNA was too simple a molecule to play such a critical role. Instead,
they argued that proteins were more likely to carry out this vital function because of
their greater complexity and wider variety of forms.
The importance of DNA became clear in 1953 thanks to the work of James Watson,
Francis Crick, Maurice Wilkins and Rosalind Franklin. By studying X-ray diffraction
patterns and building models, the scientists figured out the double helix structure of
DNA - a structure that enables it to carry biological information from one generation to
the next.
What is the DNA double helix?
Scientist use the term "double helix" to describe DNA's winding, two-stranded chemical
structure. This shape - which looks much like a twisted ladder - gives DNA the power to
pass along biological instructions with great precision.
To understand DNA's double helix from a chemical standpoint, picture the sides of the
ladder as strands of alternating sugar and phosphate groups - strands that run in
opposite directions. Each "rung" of the ladder is made up of two nitrogen bases, paired
together by hydrogen bonds. Because of the highly specific nature of this type of
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chemical pairing, base A always pairs with base T, and likewise C with G. So, if you
know the sequence of the bases on one strand of a DNA double helix, it is a simple
matter to figure out the sequence of bases on the other strand.
DNA's unique structure enables the molecule to copy itself during cell division. When a
cell prepares to divide, the DNA helix splits down the middle and becomes two single
strands. These single strands serve as templates for building two new, double-stranded
DNA molecules - each a replica of the original DNA molecule. In this process, an A base
is added wherever there is a T, a C where there is a G, and so on until all of the bases
once again have partners.
In addition, when proteins are being made, the double helix unwinds to allow a single
strand of DNA to serve as a template. This template strand is then transcribed into
mRNA, which is a molecule that conveys vital instructions to the cell's protein-making
machinery.
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Genes, Chromosomes & DNA notes
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Questions: Genes and Chromosomes and DNA
1. In the book of life, what are the two volumes and where do they come from?
2. How many chapters are there? In the analogy what do the chapters refer to?
3. What is the full name of DNA?
4. What structure do the chemical building blocks of DNA have?
5. What are the 4 building blocks in DNA?
6.
What are the base pairing rules?
7.
Draw the opposite complementary DNA strand for the following DNA strand
AAT CGA CCT GAT CCG
8. What is found on the chromosomes?
9. What is the human genome?
10. What is a gene?
11. Where are genes located?
12. How many genes are thought to be in humans?
14. What information is on a gene?
15. Name 5 of the types of proteins found in cells.
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Structure of DNA
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Human Chromosomes
Introduction
All of the cells in the human body, except for the reproductive cells, have 23 pairs of chromosomes.
One set of chromosomes comes from a person's mother, and the other from a person's father. One pair
of chromosomes is known as the sex chromosomes. The sex chromosomes of a female consist of two
X chromosomes. A male has an X and a Y sex chromosome. If a person does not have the exact
number of chromosomes, or if one of the chromosomes is not fully formed, the person will have what
is known as a genetic disorder. Very few genetic disorders can be successfully treated by doctors.
This activity will give you the opportunity to examine human chromosomes.
During mitosis, the chromosomes become short and thick and are easy to identify. Each pair of
chromosomes has a distinctive shape and appearance. Scientists can take a picture of the
chromosomes and then match the pairs to display a complete set of human chromosomes. The pairs
are usually arranged size to form a complete picture of the chromosomes. This picture is called a
karyotype.
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Activity : Karyotypes
Aim
To determine the sex and chromosome condition of an individual using a karyotype.
Method
Clear a work space on your desk or table. Carefully cut out the chromosomes shown. Now try to
match chromosomes by their size and appearance. Tape the pairs together on a separate piece of
paper. Start with the largest chromosomes and work toward the smallest. If the chromosomes are
from a male, you will be left with two unmatching chromosomes, a medium size X chromosome and a
small Y chromosome
Tape the sex chromosomes at the bottom of your page.
Discussion and conclusion
1
Do you think this individual is a male or a female? Why?
2
Do all of the chromosomes match up?
3
How many of the chromosomes are involved in the inheritance of the gender of an individual?
4
Based on your observations, do you think the person has a genetic disorder? Why or why not?
5
Downs syndrome is due to an extra chromosome 21. Why do most embryos with extra
chromosomes not survive until birth?
Evaluation
6
What were some problems you ran into when trying to match the chromosomes?
7
When you are finished matching the chromosomes as best you can, compare your karyotype
with your classmates. Did your classmates match the same chromosomes that you did?
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Homework
Determine the problem for each of the karyotypes shown in the link below:
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html
Patient A: _____________________________________________________________
Patient B: _____________________________________________________________
Patient C: _____________________________________________________________
Karyotype results
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NOTE: a stain is often used to give chromosomes a banded appearance. This helps in their
identification. The banding pattern does not represent individual genes but regions of that may contain
hundreds of genes.
This page has been left blank.
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Reference: Biology for Life, MBV Roberts p33, ASEP Genetics p51 Advanced Biology, Mary Jones and Geoff Jones p135
A boy or a girl?
The cells of an adult human
contain 46 chromosomes (23
pairs). One pair is called sex
chromosomes because they
determine the individual's sex.
There are two types of sex
chromosome: a long one known as
the X chromosome, and a short
one known as a Y chromosome.
Males contain an X and a Y
chromosome, whereas females
contain two X chromosomes.
Sperm which males produce in
their testes contain only one of
these two chromosomes, either an
X or a Y. This is because they are
formed by meiosis. In fact, of all
the sperm formed, half will
contain an X and half a Y. On the
other hand, all the ova which
females produces in their ovaries
will contain an X chromosome.
This is shown in the top part of
Figure 1.
When fertilisation occurs, the
ovum may be fertilised by either
an X containing sperm or a Y
containing sperm. If fertilisation is
random, as it's believed to be,
there is an equal chance of either
happening. If an X sperm fertilises
the ovum the zygote will contain
two X chromosomes and this will
develop into a female. On the
other hand if a Y containing
sperm fertilises the ovum, the
zygote will contain an X and a Y
chromosome and will develop into
a male. This is shown in the
bottom part of
Figure 1.
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Genetic disorders involving the sex chromosomes
Condition
Sex
chromosomes
Incidence
Jacob’s Syndrome
XYY,XYYY
1 in 7500 live
male births
Klinefelter’s
Syndrome
XXY,XXXY,
XXXXY
1 in 1000 live
male births
Turner’s Syndrome
XO
1 in 5000 live
female births
Super Female
XXX, XXXX,
XXXXX
1 in 1200 live
female births
Normal Male
XY
Normal Female
XX
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Greater than
1/2 of live
births
Less than 1/2
of live births
48
Phenotype
Tall and sometimes aggressive.
Very tall, sometimes develop
breasts (20%) and usually
infertile.
Short stature, infertile, shieldlike chest and webbed neck.
Apparently normal female
(XXX) or low
fertility/intelligence (XXXX
and XXXXX).
Normal Male
Normal Female
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Chromosome number questions
Sperm and ova contain precisely half the number of chromosomes typically found in body cells.
The number of chromosomes found in somatic cells of several mammals is shown below:
Diploid
Human
Brush-tailed possum
Mouse
American opossum
Killer whale
Haploid
46
20
40
22
44
Q1.
Which animal has 20 chromosomes in a sperm?
Q2.
Which has 23 chromosomes in a mature sperm?
Q3.
Which has 22 in a mature sperm?
Q4.
Which has 10 chromosomes in a mature sperm?
Q5.
How many number 9 chromosomes do you have in each body cell? Explain.
Q6.
How many number 9 chromosomes did you inherit from your mother? Explain.
Q7.
How many sex chromosomes do you have in your body cells? What kind are they?
Q8.
What sex chromosome did you inherit from your mother?
Q9.
What sex chromosome did you inherit from your father?
Q10.
The diploid number of the red kangaroo is 20. What is the haploid number of this species?
Q11.
The cat has a diploid number of 38. How many chromosomes would be expected in each of the
following cells of a cat?
a)
A bone marrow cell;
b)
A skin cell;
c)
An egg cell;
d)
A fertilised egg;
e)
A cell from a developing embryo.
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MITOSIS AND MEIOSIS
When normal body cells (somatic cells) divide, they must reproduce exactly the same number if
chromosomes (46), so that the new cells are exactly the same. This cell division is called mitosis.
When egg and sperm cells are made, they must be produced with only 23 chromosomes. Cells in the
ovary and in the testes carry out this division to produce daughter cells with half the number of
chromosomes. This type of cell division is called meiosis.
1.
In what cells of the body would mitosis occur? Give 3 examples.
2.
In what cells of the body would meiosis occur? Give 2 examples.
3.
Compare meiosis and mitosis.
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
Number of times the chromosomes duplicate

Number of times the nucleus divides

Number of daughter cells produced by the process

Number of chromosomes in the new daughter cells

Daughter cells produced are identical/non-identical to parent cell
http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/
page3.html
50
http://www.biology.arizona.edu/cell_bio/t
utorials/cell_cycle/cells3.html
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Comparison of Meiosis and Mitosis
Meiosis
Mitosis
Similarities
Differences
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Activity: “Rikki Lake” Genetics
The Scenario
Sick of her usual ‘who is the father?’ show format, Rikki Lake has decided to present definite sets of
parents and get her audience to use punnet squares to match kid to their parents. On the following
sheets the parents and their characteristics are presented. Your task is to match the correct child to
their parents. “Go Rikki!”
Part 1 – The 5 characteristics
You will be matching the children to their parents using the following five characteristics:
Table 1
Phenotype
Ability to roll
Can’t roll tongue
Brown
Blue
Widow’s peak
No widow’s peak
Free ear lobes
Attached ear lobes
Non-red hair
Red hair
Characteristic
Tongue rolling
Eye Colour
Widow’s peak
Ear lobes
Hair colour
Genotype/s
TT or Tt
tt
BB or Bb
bb
WW or Ww
ww
FF or Ff
ff
HH or Hh
hh
1. List which phenotype is dominant for each characteristic. (Hint: check the genotypes.)
2. Identify the homozygous recessive form for hair colour and eye colour.
Part 2 – Meet the parents
In the tables below each parent has been listed with their phenotypes and genotypes.
Jane’s phenotype
Can’t roll tongue
Blue eyes
No widow’s peak
Attached ear lobes
Red hair
Jane’s genotype
tt
bb
ww
ff
hh
Martin’s phenotype
Able to roll tongue
Blue eyes
No widow’s peak
Attached ear lobes
Non-red hair
Martin’s genotype
TT
bb
ww
ff
Hh
3. Below punnet squares have been set out for the first couple (Jane and Martin).These should be
copied into your books and used for each couple. Give the resulting phenotypes and genotypes for
each cross and couple.
Punnet square crosses for Jane and Martin
Tongue rolling
t
t
T
T
Possible children’s phenotypes: ___________________
Possible children’s genotypes: ____________________
Eye colour
b
b
b
b
Possible children’s phenotypes: ___________________
Possible children’s genotypes: ____________________
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Ear lobes
f
f
f
f
Possible children’s phenotypes: ___________________
Possible children’s genotypes: ____________________
Widow’s peak
w
w
w
w
Possible children’s phenotypes: ___________________
Possible children’s genotypes: ____________________
Hair colour
H
h
h
h
Possible children’s phenotypes: ___________________
Possible children’s genotypes: ____________________
Couple Number 2: Sholene and Bob
Sholene’s phenotype
Able to roll tongue
Blue eyes
Widow’s peak
Free ear lobes
Red hair
Sholene’s genotype
TT
bb
WW
FF
hh
Bob’s phenotype
Can’t roll tongue
Blue eyes
No widow’s peak
Attached ear lobes
Red hair
Bob’s genotype
Tt
Bb
Ww
Ff
Hh
Glen’s phenotype
Can’t roll tongue
Brown eyes
Widow’s peak
Attached ear lobes
Non-red hair
Glen’s genotype
Tt
Bb
WW
Ff
HH
Joe’s phenotype
Can’t roll tongue
Brown eyes
Widow’s peak
Attached ear lobes
Non-red hair
Joe’s genotype
Tt
BB
Ww
Ff
Hh
Couple Number 3: Cherise and Glen
Cherise’s phenotype
Able to roll tongue
Brown eyes
Widow’s peak
Free ear lobes
Non-red hair
Cherise’s genotype
Tt
BB
Ww
FF
HH
Couple Number 4: Glory and Joe
Glory’s phenotype
Able to roll tongue
Brown eyes
No widow’s peak
Attached ear lobes
Non-red hair
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Glory’s genotype
TT
Bb
ww
ff
HH
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Part 3 – Meet and Match the Children
Each of the following four children belongs to one of the above sets of parents.
Mobi’s phenotype
Can roll tongue
Blue eyes
Widow’s peak
Free ear lobes
Red hair
Mobi’s genotype
Tt
bb
Ww
Ff
hh
Shakula’s phenotype
Can roll tongue
Brown eyes
No widow’s peak
Attached ear lobes
Non-red hair
Shakula’s genotype
TT
BB
ww
ff
HH
Neesha’s phenotype
Can roll tongue
Blue eyes
No widow’s peak
Attached ear lobes
Red hair
Neesha’s genotype
Tt
bb
ww
ff
hh
Rajah’s phenotype
Can’t roll tongue
Brown eyes
Widow’s peak
Free ear lobes
Non red hair
Rajah’s genotype
tt
Bb
Ww
Ff
HH
4. Use the information you have recorded in Part 2 to decide which child belongs with which set of
parents. Give reasons for your choices.
Source: Fiona Trapani, Craigeburn Secondary College
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Revision : Worksheet 1
1.
One parent has dimples, and comes from a family which all have dimples (assume pure
breeding). The other parent does not have dimples. Will their children have dimples? Assume
that ‘dimples’ is usually dominant over ‘no dimples’.
2.
a)
In another family if two parents have dimples, will all their children have dimples?
b)
If neither parent has dimples, will any of their children have dimples?
3.
a)
Dark hair is dominant over red hair. If two parents have red hair, what colour hair will
their children have?
b)
If one parent is heterozygous for dark hair, and the other has red hair, what will be the
genotypes and phenotypes of their children?
4.
5.
In the garden-pea, white flower (p) is recessive to purple flower (P)
a)
What is the phenotype of a Pp plant?
b)
What is the genotype of a plant with white flowers?
c)
What is the genotype of a plant with purple flowers?
Assume that white colour is dominant over yellow colour in squash.
Pollen from the anthers of a heterozygous white-fruited plant is placed on the pistil of a
yellow-fruited plant. Show, using ratios, the genotypes and phenotypes you would expect the
seeds from this cross to produce.
6. In human beings, the allele for brown eyes is usually dominant over the allele for blue eyes.
Suppose a blue-eyed man married a brown-eyed woman whose father was blue-eyed. What
proportion of their children would you predict to have blue eyes?
7.
If a brown-eyed man married a blue-eyed woman and they have ten children, all brown-eyed,
can you be certain that the man is homozygous? If the eleventh child has brown eyes, will that
prove what the father’s genotype is?
8.
A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a
blue-eyed woman whose father and mother were both brown-eyed. The couple has a blueeyed son. For which of the individuals mentioned can you be sure of the genotype? Draw a
pedigree showing all possible genotypes.
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9.
10.
Suppose that radishes have two alleles for shape - RL for long, and RR for round.
a)
What is the genotype of a long radish?
b)
What is the genotype of a round radish?
c)
What is the phenotype of a radish with an RL RR genotype?
d)
What genotypes could be expected in the offspring of a cross between two oval
radishes?
d)
If a plant with oval radishes is crossed with a plant bearing long radishes, what could
the F1 be like?
There is incomplete dominance inheritance for feather colour in Andalusian fowls.
Choose appropriate allele symbols.
a)
What colour would you expect the offspring of a white hen and a black rooster to be?
b)
If these offspring were crossed among themselves, is it possible for all the next
generation to be black?
c)
11.
What would the offspring of a black Andalusian rooster with a grey hen look like?
If the litter resulting from the mating of two short-tailed cats contains three kittens without
tails, two with long tails, and six with short tails, what would be the simplest way of explaining
the inheritance of tail length in these cats? Show genotypes.
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Revision : Worksheet 2
1
One half of a section of the double helix ‘ladder’ is shown below. The bases adenine, guanine, cytosine and
thymine are abbreviated to A, G, C and T respectively. Draw the complementary strand, complete with the
correct base pairs.
Strand A
Strand B
A
C
A
G
T
2
Write down the number of genes for each characteristic, either one or two, that are found in each of the
stages of reproduction below.
Male sex cells are called sperm. Female sex cells are
called eggs. Sperm and eggs are formed by the
process known as mitosis/meiosis.
number of
genes __________
number of
genes __________
Sex cells carry one gene for each characteristic. They
are said to be haploid/diploid.
At fertilisation the sperm nucleus and the egg
nucleus fuse.
number of genes __________
There are now two genes for each characteristic in the
fertilised egg cell—one from each parent. The egg is
haploid/diploid. The egg grows and divides into a
zygote by mitosis/meiosis.
number of genes __________
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Revision Worksheet 3
Rule a line between the dots to match each definition with the correct word. Start the lines from the dots. The letter that
each line passes through gives the answer to the question at the bottom of the page.
1
Thread-like structures of genetic material
found in the nucleus of cells.


gene
2
Package of genetic information coding for a
particular characteristic of an organism.


genotype
3
Chemical substance from which
chromosomes are composed.


homozygous
4
Cell division that results in cells with the
same number of chromosomes as the parent
cell.


chromosome
5
The genetic make-up of an organism.


DNA
6
Chemical units that pair up to make DNA.


dominant
7
A trait that can skip a generation.


bases
8
An organism that has two identical alleles
for a particular characteristic.


mitosis
9
The gene that is exhibited as a physical trait
over another that is not exhibited.


recessive
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Practical
Investigations
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Practical Exercise 1 Genetic Barley
Background
Many of the early investigations into patterns of inheritance were carried out using plants. Mendel’s
famous pea plants were well documented in the 1800’s, and are now well known today.
The genetics of a number of more common plant species is also well known. In this activity you will
observe inheritance patterns in barley. The character being investigated is seedling colour. The
alternate phenotypes are green seedlings and albino seedlings (which lack the green pigment
chlorophyll). The seeds used in this activity are the result of the cross Aa x Aa. ‘A’ represents green
pigment production and ‘a’ represents lack of pigment production. In barley seeds, green seedling is
the dominant phenotype over the albino seedling.
Aim
To study the relative effects of heredity on barley seeds with respect to pigmentation.
Materials- per group
1 petri dish
Permanent marker
Cotton wool-sufficient to cover base of both dishes
Forceps
H2O wash bottle
Barley seeds: 20
Method
Day 1
1. Label the petri dishes on the side with your initials, using a permanent marker.
2. Fill the bottom of each dish with cotton wool and soak with water. During the course of the
experiment, the cotton wool must be kept moist and not allowed to dry out.
3. Place 20 seeds on each petri dish and replace the lid.
Day 6 and Day 10
1. By now, at least half of the seeds should have germinated. Each young barley plant consists of
white or colourless roots and a tiny shoot. Usually the roots appear first, but in this experiment,
you are concerned only with the shoot. Some of the seedlings will have green shoots, and some
will have yellowish (‘albino’) shoots
2. Count the number of green and albino shoots in each dish. Do not count seedlings in which the
shoots have not yet broken through. Both partners should do the count to confirm the results.
Recount if there is any discrepancy.
Results
Green
Albino
Seedling Colour
Total
% Albino
% Green
Group
Class
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Discussion & Conclusion
1. From the information provided above, what would you expect the colour of the plants to
be? Use a punnet square and show the complete cross.
2. Using the class and group results, calculate the simplest ratio of green to albino seedlings.
Which result is the most reliable? Why?
3. How well do the class results match with what the theory predicts? Comment on any
similarities or differences.
4. What is the genotype of the albino seedlings?
5. Why do the albino seedlings not survive?
6. What are the possible genotypes of the green seedlings? Explain.
Conclusion
What did you learn about a cross between heterozygotes from this practical?
What did you learn about sample size from this experiment?
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Practical Exercise 2: DNA Extraction
Aim
To extract DNA from the cells of raw wheat germ
Materials
●
●
●
●
●
●
●
1 teaspoon raw wheat germ
1 ml detergent
20 ml alcohol
20 ml of hot water (50 -60)
methylene blue
microscope
methylene blue
●
●
●
●
●
●
test-tube rack
50 ml test tube
dropping pipette
measuring cylinder
stirring rod
slide and coverslip
Method
Part A
1. Place 1 gram or 1 teaspoon of raw wheat germ in a 50 ml test tube.
2. Add 20 m; of hot tap water and mix constantly with glass rod for 3 minutes.
3. Add 1 ml of detergent and mix gently every minute for 5 minutes. Try not to create foam.
4. Use an eyedropper, pipette, or piece of paper towel to remove any foam from the top of the
solution.
5. Tilt the test tube at an angle. SLOWLY pour 15 ml of alcohol down the side so that it forms a layer
on top of the water/wheat germ/detergent solution. Do not mix the two layers together. DNA
precipitates at the water-alcohol interface. Therefore, it is crucial to pour the alcohol very slowly so
that it forms a layer on top of the water solution. If the alcohol mixes with the water, it will become
too dilute and the DNA will not precipitate.
6. Let the test tube, beaker or jar sit for a few minutes. White, stringy, filmy DNA will begin to appear
where the water and alcohol meet.
7. Use a glass or paper clip hook or a wooden stick to collect the DNA.
Part B
1. Place some of the DNA on a microscope slide. Stain with 1 drop of methylene blue. Cover with a
coverslip.
2. View under low, then high power.
Results and Discussion
1. Write a detailed description of the material floating at the top of the test-tube after adding the
alcohol.
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1. Draw and label a diagram of the high power view of the DNA.
3. Why is detergent used in the experiment?
4. What is the purpose of the alcohol?
5. If the DNA was extracted from a sheep’s liver, what would you expect it to look like?
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GLOSSARY
allele
autosome
carrier
chromosome
codominance
deoxyribonu
cleic acid
(DNA)
diploid
dominant
double helix
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gamete
gene
genetics
genotype
haploid
heterozygous
homozygous
homologous
pairs
incomplete
dominance
karyotype
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meiosis
mitosis
mutation
nucleus
pedigree
phenotype
recessive
sex
chromosome
somatic
cells
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