BIOLOGY 30
Unit C-2: Genetics
GENERAL OUTCOME #2
Students will explain the basic rules and processes associated with the transmission of genetic characteristics.
PART A – INTRODUCTORY TERMINOLOGY
TERM
Heredity
DEFINITION
Genes
Alleles
Genotype
Phenotype
Homozygous
Heterozygous
Dominant
Recessive
EXAMPLE #1: Height (Tall or Short)
EXAMPLE #2: Eye Color (Brown or Blue)
EXAMPLE
PART B – GREGOR MENDEL: THE GENETIC PIONEER
C2.1k – students will describe the evidence for dominance, segregation, and the independent assortment on different chromosomes, as
investigated by Mendel.
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
Who Was Gregor Mendel?
Mendel’s Experiment
Pea Plants: Traits Observed
CASE A – SEED SHAPE
Cross
P1
(parental)
F2
(second filial generation)
Pollination
Phenotype #1
Phenotype #2
Result
F1
(first filial generation)
CASE B – FLOWER COLOR
Cross
Pollination
Phenotype #1
Phenotype #2
Result
P1
F1
(parental)
(first filial generation)
F2
(second filial generation)
Based on the results of Mendel’s experiments, attempt to answer the following:
SEED SHAPE
Trait
Dominant or
Recessive?
P1 Generation
Homozygous or
Heterozygous?
F1 Generation
Homozygous or
Heterozygous?
F2 Generation
Homozygous or
Heterozygous?
P1 Generation
Homozygous or
Heterozygous?
F1 Generation
Homozygous or
Heterozygous?
F2 Generation
Homozygous or
Heterozygous?
Round
Wrinkled
FLOWER COLOR
Trait
Dominant or
Recessive?
Purple
White
A Closer Look…
MENDEL’S LAWS OF HEREDITY
#1 – Law of Unit Characteristics
#2 – Law of Dominance
#3 – Law of Segregation
#4 – Law of Independent Assortment
PART C – MONOHYBRID CROSSES
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
A cross where only
is involved. For example,
.
EXAMPLE #1
A geneticist crosses two pea plants based on seed shape (round or wrinkled). Both parents are heterozygous.
Phenotypic Ratio
Genotypic Ratio
EXAMPLE #2
A homozygous orange cat is crossed with a heterozygous brown cat. Show the results of this cross using a Punnett square
and identify the resulting phenotypic ratio.
EXAMPLE #3
A homozygous yellow-bellied frog is crossed with a heterozygous red-bellied frog. Show the results of this cross using a
Punnett square and identify the resulting phenotypic ratio.
EXAMPLE #4
Using a Punnett square, determine the expected phenotypic and genotypic ratio for the progeny (offspring) of a cross
between a pea plant that is homozygous for the white allele for flower color and a pea plant that is homozygous for the
red allele.
TEST CROSSES
A test cross is performed to determine the
identify if a parent is
. More specifically, it is used to
or
The individual used in the test cross is a
.
crosses with the unkown genotype.
In sheep, white fur is dominant to black fur. A farmer wants to know if his white sheep is a purebred or a
hybrid.
Scenario #1 – Homozygous Dominant
What do you notice about the offspring?
Scenario #2 – Heterozygous Dominant
What do you notice about the offspring?
IN SUMMARY…
If all progeny exhibit the
If at least one offspring exhibits the
trait, then the unknown parent must be
trait, then the unknown parent must be
.
.
EXAMPLE #1
In rams, white coat color is dominant over black coat color. A newly born black ram has a white mother, however
breeders do not know if the mother is a purebred or hybrid. Based on this information, what is the genotype of the
newborn’s mother? Prove your answer by showing two test crosses.
PART D – MULTIPLE ALLELES
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
C2.4k – students will explain the relationship between variability and the number of genes controlling a trait
Multiple alleles refers to a trait that has more than two alleles.
Any individual within a population can carry a maximum of two alleles, however the population itself may have more.
Must be given a dominance hierarchy.
CASE STUDY #1 – BLOOD TYPING
Four Blood Types
A, B, AB, O
Three Alleles
IA, IB, i
Dominance Hierarchy
IA = IB > i
Blood Type
O
(Type A and Type B are equal, however they are both dominant over Type O)
Genotype(s)
AB
A
B
EXAMPLE #1
Steven is homozygous for type A blood. Sherry is type O blood. After marriage, Sherry gives birth to a baby girl. Using a
Punnett square, state the possible blood types of the newborn.
EXAMPLE #2
John and Cindy have a child with an unknown blood type. John is type A blood (his father is type AB and his mother is
type O). Both of Cindy’s parents are type O. Using a Punnett square, state the possible blood types of John and Cindy’s
child.
Fruit Fly Eye Color – Page 608-609, Practice Question #1
Rabbit Coat Color – Page 612, Question #1
PART E – INCOMPLETE DOMINANCE
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
C2.4k – students will explain the relationship between variability and the number of genes controlling a trait
Incomplete Dominance occurs when two alleles are equally dominant but interact to produce a new phenotype.
(offspring exhibit a new phenotype that neither parent has)
CASE STUDY #1 – FLOWER COLOR IN SNAPDRAGONS
In snapdragons, when a red flower is cross-pollinated with a white flower, all offspring are pink.
Let C stand for flower color.
CrCr  Red Flowers
CwCw  White Flowers
CrCw  Pink Flowers
With the aid of a Punnett square, incomplete dominance can be proven by crossing red and white flowers.
EXAMPLE #1
A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver. The color of blahblah
birds is determined by just two alleles.
a) What are the genotypes of the parent blahblah birds in the original cross?
b) What is/are the genotype(s) of the silver offspring?
c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?
Horse Coat Color – Page 612, Question #2
PART F – CO-DOMINANCE
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
C2.4k – students will explain the relationship between variability and the number of genes controlling a trait
Co-Dominance occurs when two alleles are equally dominant, but both alleles are expressed equally at the same time.
CASE STUDY #1 – SHORTHORN CATTLE
When a red bull crosses with a white cow, the resulting offspring are roan (some red hair, some white hair).
Let H stand for hair color.
HrHr  Red Bull
HwHw  White Cow
HrHw  Roan Calf
EXAMPLE #1
Show the Punnett square results of a roan cow mating with a red bull.
PART G – LETHAL GENES
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
The presence of an allele in the homozygous condition results in the death of the individual.
CASE STUDY #1 – FUR COLOR IN MICE
Let F stand for fur color.
FF  Normal Color
FyF Yellow Color
FyFy  Die Before Birth
PART H – DIHYBRID CROSSES
C2.2k – students will compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incompletely
dominant, and co-dominant alleles.
C2.4k – students will explain the relationship between variability and the number of genes controlling a trait
Dihybrid crosses deal with two different genes or traits. For example, eye color and hair color.
More On….Mendel’s Law of Independent Assortment
Mendel confirmed his hypothesis about the independent assortment of genes by performing dihybrid crosses. In these
crosses, he noticed that genes assort independently. One gene does not influence the inheritance of another.
EXAMPLE: SEED COLOR AND SHAPE
Yellow Round Seed (YyRr)
Possible Gametes – F.O.I.L.
Yellow
Green
Round
Wrinkled
Dihybrid Punnett Square
A cross between two heterozygous yellow, round seeded plants.
A genotypic ratio for any dihybrid heterozygous cross is:
9 Dominant Dominant
3 Dominant Recessive
3 Recessive Dominant
1 Recessive Recessive
A Parent is said to be ______________________________ if it produces only one type of gamete. It is Homozygous.
YYRR is true breeding for ______________________ and _________________.
yyrr is true breeding for ______________________ and __________________.
EXAMPLE #1
YYrr x yyRR
EXAMPLE #2
YYRR
x
yyRR
DIHYBRID ASSIGNMENT
GENE INTERACTION
Some traits are regulated by
.
. They are said to be
Genes that
with the expression of other genes are called
.
EXAMPLE – Coat Color in Dogs
B = black
b = brown
W = no pigment (white)
w = pigment
1. Perform a cross between a heterozygous white dog and a black dog.
2. Perform a cross between a brown dog and a black dog.
**The trait for dog coat color is polygenic.
** The alleles w/W for pigment are epistatic.
DIHYBRID ASSIGNMENT - #10
PART I – The Chromosomal Theory of Inheritance
Mendel did his study of ___________________ without any knowledge of
______________________________________________________________________________.
Years after the invention of the __________________ chromosomes were discovered.
After studying chromosomes, how they divide and their make-up
The _________________________ Theory was created:
1.
2.
3.
4.
PART J – Sex Linked Traits
Morgan and American _________________ used ___________________ to study Mendel’s work on
inheritance.
Why Fruit Flies????
1.
2.
3.
4.
When crossing male and female _________ he got different ratios than would be expected from a normal
_____________________ cross.
He also discovered that __________ flies contained __________________ chromosomes and ___________
that wasn’t completely homologous. __________ flies had ____________________________________.
From his work he believe that fruit fly eye colour was a gene that was carried on the _________________;
he called this gene a ______________________ gene.
REWIND……. Let’s Remember What We Have Already Learned
Remember How to Read a Karyotype??
Is this individual male or female? How do you know?
Which chromosomes are autosomal chromosomes?
Which chromosomes are sex chromosomes?
Does this individual have any non-disjunction disorders?
Back to the Fruit Flies:
Use Big X’s to represent the genes found on the ________________________.
_________ = Red Eyes in Fruit Flies
_________ = White Eyes in Fruit Flies
Cross a Homozygous Dominant Female and a White-Eyed Male:
P1 Female Genotype: _________
Phenotypic Ratio >>
P1 Male Genotype: _________
Next…… Cross an F1 Female and an F1 Male
F1 Female Genotype: _________
F1 Male Genotype: _________
Phenotypic Ratio >>
Show all Work!!
Sex-Linked Traits PRACTICE 1:
Hemophelia is a sex linked recessive
disorder. What are the expected
phenotypic ratios among the children of a
women whose father was a hemophiliac
and whose husband is normal?
Sex-Linked Traits PRACTICE 2:
X-linked dominant hypophosphatemic rickets, also known as vitamin d-resistant rickets can cause bone
deformity and result in a short stature or bow leggedness. A mother suffering from this disorder has a father
who was normal and mother who was bow-legged. She has a child with a man who is normal.
a. State the potential genotypes of the child using a Punnett square.
PART K – Sex Determination
The difference between a male and a female is caused by the presence or absence of the
__________________.
Female cells also differ in another way, the presence of a __________________________
or ______________________.
In Female cells on ______ becomes ____________ but which X chromosome varies from cell to cell.
Example 1: Calico Cats
-
Males - XBY = Black XOY = orange
Females - XBXB = Black
XOXO = Orange
XBXO = Calico black and orange patches – orange patches contain cells in which XB is inactive
black patches contain cells in which XO is inactive
Not much gene information is carried on the ______________________________.
However, it does carry a gene called _________________________________.
This gene stimulates the production of ______________________ in the 6th and 7th week of pregnancy.
PART L – Sex Influenced Traits
Sex hormones exert a powerful influence on how some genes will be _____________ themselves.
These genes are not carried on the _______________________; they are __________________________
influenced by the hormones produced in the individual
Example 1: Pattern Baldness in Males
B1 = allele for Baldness, Dominant over B2(normal) in males, but recessive to B2 (normal) in females
Genotypes
B1B1 or B1B2
B2B2 or B2B1
Phenotypes
_____________ Male
Bald Female
_____________ Female
Normal Male
DIPLOMA DEMO
PART M – Probability
EXAMPLE #1
AaBb x AaBb
What is the probability of an offspring being AABB?
EXAMPLE #2
In humans, the disease galactosemia is inherited as a recessive trait. An unaffected woman whose father had the
disorder intends to marry an affected man whose grandfather was galacosemic. What is the probability of having an
affected child?
PRACTICE #1
Huntington’s Disease is a rare, fatal disease that usually develops in middle age. It is caused by a dominant
allele. A PHENOTYPICALLY normal man learns that his father developed the disorder, however his mother
was unaffected. Furthermore, his sister was recently screened and it was determined that she would not
develop the disease.
a. What is the probability the man will develop the disorder?
b. If the man develops Huntington’s disease and marries an unaffected woman, what is the probability that
they will have a daughter who develops the disease?
PRACTICE #2
When a fruit fly of Genotype Mm Nn Oo is mated to another fruit fly of identical genotype. What is the
probability of the off spring having the following genotypes:
a.
b.
c.
MM Nn OO
mm NN Oo
Mm Nn Oo
DIPLOMA DEMO
Feather colour in parakeets is controlled by two genes. For one pigment gene, the B allele produces
blue colour and the b allele does not produce any colour. For the other pigment gene, the Y allele
produces yellow colour and the y allele does not produce any colour. Any genotype containing at least
one B allele and one Y allele will produce a green parakeet.
1. Which of the following parental genotypes could produce offspring with the four different colour
patterns?
A.
B.
C.
D.
BBYy
BbYY
BbYY
Bbyy
x
x
x
x
BbYy
Bbyy
bbyy
bbYy
2. What is the probability of obtaining a blue parakeet when two green heterozygous parakeets are
crossed?
A.
B.
C.
D.
0
3/16
1/4
9/16
Cystic Fibrosis is the most common genetic disorder among Caucasians, affecting one in 2000
Caucasian children. The cystic fibrosis allele results in the production of sticky mucus in several
structures, including the lungs and exocrine glands. Two parents who are unaffected by the disorder
can have a child with the disorder.
A girl and both her parents are unaffected by the disease. However, her sister is affected by cystic
fibrosis.
3. Which term best describes the allele for
cystic fibrosis?
A.
B.
C.
D.
X-linked
Recessive
Dominant
Co-Dominant
4. The genotypes of the mother and father are
A.
B.
C.
D.
both homozygous
both heterozygous
homozygous and heterozygous, respectively
heterozygous and homozygous, respectively
NUMERICAL RESPONSE:
These parents, who are unaffected by cystic fibrosis, are planning to have another child. What is the
percentage probability that their next child will be affected by cystic fibrosis? ____________________
PART N – Pedigrees
What is a Pedigree?
EXAMPLE
INHERITANCE PATTERN
In order to correctly analyze a pedigree, you must understand inheritance patterns in order to determine the
genotypes of the affected and unaffected individuals.
For example…
If the inheritance pattern is Autosomal Dominant, then the disorder is carried an on autosome and all affected
individuals carry a dominant allele.
If the inheritance pattern is Autosomal Recessive, then the disorder is carried on an autosome and all affected
individuals exhibit the recessive allele.
If the inheritance pattern is X-Linked Dominant, then the disorder is carried on the X chromosome and all affected
individuals carry a dominant allele (XHXH, XHXh, XHY).
If the inheritance pattern is X-Linked Recessive, then the disorder is carried on the X chromosome and all affected
individuals carry a recessive allele (XhXh, XhY).
INHERITANCE PATTERN FLOW CHART
Are there more males affected than females?
YES
NO
X-Linked Recessive
Does the trait skip a generation?
YES
Autosomal Recessive
NO
Do all affected males have affected daughters?
YES
X-Linked Dominant
NO
Autosomal Dominant
Identify the inheritance pattern in each pedigree below.
PRACTICE #1
1. Identify the inheritance pattern.
2. Number the generations and the
individuals
3. If III.6 has a child with a
heterozygous woman, what is
the probability that they will
have a boy who is affected?
PRACTICE #2
1. Identify the inheritance pattern of this pedigree.
2. What is the probability that II.2 and II.3 will have another daughter who is affected?
3. If I.1 and I.2 end their relationship, and I.3 and I.4 end their relationship, what is the probability that I.2
and I.3 would have two children, a boy who is affected and a girl who is unaffected, should they meet
each other and fall in love?
PEDIGREE AND PROBABILITY ASSIGNMENT
PART O – Gene Linkage and Crossing Over
Because there are
located on
most likely to be
, they are said to be
together because they are not
and are
during
.
Linked genes are influenced by
, which can impact how they will be
.
If
occurs between
, new combinations of alleles in the
gamete chromosome will result.
The
two genes are located together on a chromosome, the
they will be inherited together.
The
that crossing over will
two genes are located together on a chromosome, the
them.
What is a RECOMBINANT?
Frequency of Crossing Over can be expressed as a percentage using the following formula:
Using crossover frequency data, GENE ORDER can be MAPPED on a CHROMOSOME.
For Example:
Crossover Frequency
1%
12 %
Map Units Apart
1
12
DRAWING CHROMOSOME MAPS – DETERMINING GENE ORDER
EXAMPLE #1
Crossover frequencies between 3 genes are as follows:
A  B = 12%
B  C = 7%
A  C = 5%
What is the order of the 3 genes?
EXAMPLE #2
If there were 50 recombinant phenotypes out of 250 total offspring, what is the map distance between the
linked genes?
PRACTICE:
Page 641, Question #3
ASSIGNMENT: Gene Mapping Worksheet
Page 640, Gene Mapping Case Study
PART P – Genetics: Science, Technology, and Society
Using the notes shared with you, please complete the following graphic organizer by summarizing key points.
Genetic Screening
Gene Therapy
Gene Mapping
Selective Breeding
Human Genome Project
ASSIGNMENT FOR REINFORCEMENT: Review the 3 articles included in the share and summarize the
key points of each article. Include this in your homework log.