Fundamentals of Genetics
Chapter 9
Black – write it down
Green – don’t write it down
Blue – its up to you
Red – key term
Genetics Goals
• Be able to explain the relationship
between genes, alleles, and traits
• Be able to distinguish between a species’
genotype and phenotype
• Be able to use a Punnett square to
calculate the probability of each phenotype
and genotype given a set of parents
• Know the three laws of genetics
2-25-10
What is Genetics?
• the scientific study of heredity;
characteristics and how they are inherited,
for ex. nose shape.
UMBUKU Lizard
LIGER
ZEEDONK
Gregor Mendel
-
Austrian Monk, famous for
his work with pea plants.
Father of Genetics
chose traits that did not
appear to blend
the first to follow single traits
from generation to generation
• trait - specific
characteristic that varies
from one individual to
another
• true-breeding (purebred) plants - always
produce offspring
identical to themselves.
• Hybrids - offspring from
parents with different
traits.
•
Alleles - different forms
of a gene
Genes – a short segment
of DNA on a
chromosome; contains
the instructions for a
single trait
Molecular genetics –
the study of the structure
and function of
chromosomes and genes
The Principle of Dominance
• Dominant alleles always expressed
– Ex: brown eyes are dominant.
• 2 brown alleles = brown eyes
• 1 brown allele and 1 blue allele =
brown eyes
• Recessive alleles - only
expressed if both
alleles are recessive
– Ex: blue eyes are recessive
• 2 blue alleles = blue eyes
• Law of Segregation
Each individual has a pair of factors
controlling each trait, one inherited from
each biological parent.
During the formation of gametes (sex cells)
these two factors separate. Only one
ends up in each sex cell.
• The Law of Independent Assortment
genes for different traits can separate on
their own during the creation of gametes
Ex 1: The heterozygous parents of the F1 generation
have two alleles for the gene in question, and can pass
one or the other, but not both, to their offspring.
heterozygous parent
gametes
gene
A
a
Homologous chromosomes
A
a
Ex. 2: the homozygous parents in the P generation can
pass one kind of allele to their offspring.
homozygous parent
gametes
gene
A
A
Homologous chromosomes
A
A
• Homozygous –
both alleles of a
pair are alike (BB)
– Purebred
• Heterozygous –
two alleles in the
pair are different
(Bb)
– Hybrid
• Genotype – genetic makeup (BB,
Bb, bb)
• Phenotype – physical characteristic
(eyecolor, haircolor etc.)
Students
should use
book here
Genetic Generations
• P generation –
pure-bred parents
are crossed
• F1 generation –
offspring of P
generation selfpollinate
• F2 generation –
offspring of the F1
generation
RR
rr
pollen
Parental
generation (P)
pollen
cross-fertilize
true-breeding,
purple-flowered
plant
true-breeding,
white-flowered
plant
Rr
First-generation
offspring (F1)
Punnett Squares
• Diagram used to
predict genetic
crosses.
• Individuals with
identical alleles are
called homozygous
• Individuals with
different alleles are
called heterozygous
How to use Punnett Squares
1.
2.
3.
4.
Key: use a letter to represent each allele
Cross: the genotypes of the parents.
Punnet square
Write the genotype: list all possible
genotypes, then the fractions and
percents shown in the Punnet square
5. Phenotypes: show all, with fractions and
percents.
Probability & Genetics
• Probability - likelihood that something will
happen.
– used to predict the outcomes of genetic
crosses
– ex: penny – 2 possible outcomes, heads or
tails
3.1.10
Predicting Results in
Monohybrid crosses
• Monohybrid – only one characteristic is studied
– Mono means one
• Genotypic Ratio – ratio of the genotypes in
offspring
• Phenotypic ratio – ratio of offspring’s phenotypes
• Testcross – individual of unknown genotype is
crossed with a homozygous recessive individual
• Monohybrids have 2 possible phenotypes, 3
possible genotypes
Trait 1: Dominant-Recessive
- Dominant trait - shows up if
present
- Recessive trait - shows up if
dom. trait not present
- Dominant trait – capitalize
- Ex: R for red
- Recessive trait – lowercase
- Ex: r for white
- 3 genotypes, 2 phenotypes
Trait
Seed
shape
Seed
color
Pod
shape
Pod
color
Dominant form
Recessive form
smooth
wrinkled
yellow
green
inflated
constricted
green
yellow
purple
white
at leaf
junctions
at tips of
branches
tall
(1.8 to
2 meters)
dwarf
(0.2 to 0.4
meters)
Flower
color
Flower
location
Plant
size
Trait 2: Incomplete Dominance
one allele is not completely dominant over the other.
- Colors mix because neither is completely dominant
- Both letters for genotype are capitalized
- 3 genotypes, 3 phenotypes
RR – Red, RW – Pink, WW – White
Ex: Pink flower X Pink flower
produce
White-, pink-, and red-flowers
in a 1:2:1 ratio
3.2.10 p 184
Incomplete
dominance
example
R1R1 or RR = red R2R2
or WW = white
R1R2 or RW = pink
(there are multiple ways
of writing the genotype;
we will only use the
capital letters like the
previous slide)
Trait 3: Codominance
Both alleles
contribute
to the
phenotype.
Examples:
Black cat x white cat = black
and white cat
Roan horse
Red cow X White Cow = Roan Cow
Dihybrid Cross
- Two pairs of
contrasting
traits
Ex: color and
shape for peas
3.4.10
Punnett Squares:
Monohybrid & Dihybrid Crosses
Use the FOIL method:
First
Outer
Inner
Last
http://nature.ca/genome/04/041/041_e.cfm
Example Dihybrid Cross
• In guinea pigs, the allele for short hair (S)
is dominant to long hair (s), and the allele
for black hair (B) is dominant over the
allele for brown hair (b). What is the
probable offspring phenotype ratio for a
cross involving two parents that are
heterozygotes for both traits?
Example Dihybrid
•
•
•
•
•
Short hair = dominant = SS or Ss
Long Hair = recessive = ss
Black coat = dominant = BB or Bb
Brown coat = recessive = bb
SsBb x SsBb (gametes done by the FOIL
method: First, Outer, Inner, Last)
– SB, Sb, sB, sb and SB, Sb, sB, sb
Answer the Question
• What is the probable offspring phenotype
ratio for a cross involving two parents that
are heterozygotes for both traits?
– 9/16 Black, short coats
– 3/16 Black, long coats
– 3/16 Brown, short coats
– 1/16 Brown, long coats
March 5, Friday
• Review: chromosomes
• sex linked genes
• pedigrees
http://www.biology.arizona.edu/Mendelian_genetics/problem_sets/sex_link
ed_inheritance/sex_linked_inheritance.html
Chapter 12: Inheritance
Patterns and Human Genetics
Chromosomes
Autosomes
- non-sex chromosomes.
- Humans have 22 pairs
Sex Chromosomes
- Genetic information that determines gender
of organism; humans have 1 pair
- Females XX
- males XY
Karyotype
22 pairs of Autosomes
+
1 pair sex
chromosomes
=
a total of 23 pairs
Objectives for X-linked traits:
• Know males have sex-linked traits more
often and why
• Know what a carrier is
• calculate inheritance using Punnett square
• give examples
Traits covered so far:
On Autosomes
1: Dominant-Recessive traits
2: Incomplete Dominant traits
3: Codominant traits
Now:
On Sex Chromosome
4: X-linked traits
Trait 4: X-linked Traits
• X-linked recessive traits more common in
males
• Female carrier has a recessive allele
hidden by the dominant allele
• Ex:
– Baldness
– Hemophilia
– Color blindness
Examples:
Healthy is dominant (A = normal vision):
• Female: XAXA, XAXa, XaXA - 75%
• Male: XAY – 50%
Diseased is recessive (a = colorblind)
• Female: XaXa - 25%
• male XaY – 50%
ColorBlindness
When would a female have a sex linked
trait?
http://74.125.47.132/search?q=cache:rWFtNrPOFNoJ:www.austincc.edu/mlt/mdfund/mdfund_unit2pedi
gree_genetics.ppt+sex+linked+traits+worksheet&cd=7&hl=en&ct=clnk&gl=us
Pedigree
A diagram that shows how a trait is inherited
over several generations
Pedigree
• Circles – stand for females
• Squares – stand for males
• Colored circle or square – affected by
recessive trait
• Half filled in - carrier
Trait 5: Multiple Alleles
- determined by a single gene that has at least four
different alleles.
Ex: rabbit fur, blood types, parakeet color
You will need to learn the blood types
Genotype
AO
http://nobelprize.org/educational_games/medicine/landsteiner/index.html
BO
AB
OO
http://www.biology.arizona.edu/human_bio/problem_sets/blood_types/markers.html
YYBB or YyBb
yyBB or yyBb
YYbb or Yybb
yybb
Trait 6: Polygenic traits
– Several genes control the trait (more than two alleles)
Ex: Skin color in humans.
aBc
aBC
Abc
AbC
ABc
ABC
abc
abC
ABC
AABBCC AABBCc AABbCC AABbCc AaBBCC AaBBCc AaBbCC AaBbCc
ABc
AABBCc
AbC
AABbCC AABbCc AAbbCC AAbbCc AaBbCC AaBbCc AabbCC AabbCc
Abc
AABbCc
aBC
AaBBCC AaBBCc AaBbCC AaBbCc aaBBCC aaBBCc aaBbCC aaBbCc
aBc
AaBBCc
AaBBcc
AaBbCc
AaBbcc
aaBBCc
aaBBcc
aaBbCc
aaBbcc
abC
AaBbCC
AaBbCc
AabbCC
AabbCc
aaBbCC
aaBbCc
aabbCC
aabbCc
abc
AaBbCc AaBbcc AabbCc Aabbcc aaBbCc aaBbcc
http://biology.clc.uc.edu/Courses/Bio105/geneprob.htm
aabbCc
aabbcc
AABBcc
AABbcc
AABbCc
AAbbCc
AABbcc
AAbbcc
AaBBCc
AaBbCc
AaBBcc
AaBbcc
AaBbCc
AabbCc
AaBbcc
Aabbcc
Review
• Know this about the 6 Traits:
• 1: Dominant-Recessive traits – only one trait is
expressed
• 2: Incomplete Dominant traits – traits are
mixed (red + white = pink)
• 3: Codominant traits – both traits are shown
separately (patches)
• 4: X-linked traits – on X-chromosome, if
recessive, occurs most often in males
• 5: Multiple Alleles - single gene, but at least 4
alleles; know how to find blood type
• 6: Polygenic – more than one gene
WHAT IS A
MUTATION?
March 8
A Mutation is:
A change in the
nucleotide-base
sequence of a
gene or DNA
molecule
Objectives:
• Recognize germ cell & somatic cell
mutations
• Differences between chromosome & point
mutations
• Know why mutations are important, & be
able to give examples of mutations
• Germ cell mutation – occurs in gametes,
can be inherited
• Somatic-cell mutations – take place in
body cells, affect the organism; not
inherited. Ex: skin cancer, leukemia
• Lethal mutations – cause death, often
before birth.
Chromosome mutations
Deletion- piece of a chromosome breaks off
Inversion – chromosome segment breaks off, flips around
and reattaches
Translocation – piece of a chromosome breaks off and
reattaches to a nonhomologous chromosome.
Nondisjunction – chromosome fails to separate from its
homologue during meiosis
Point mutations
Substitution – one nucleotide is replaced with another
Insertion mutation - one or more nucleotides is added
Frameshift mutation – deletion or insertion of nucleotides,
makes later amino acids change
Disorders
•
•
•
•
Down syndrome: trisomy 21 (47)
Klinefelter syndrome: XXY (47)
Turner’s syndrome: X (45)
Cri du chat – deletion in chromosome 5.
mental retardation, early death
• Oculotaneous albinism – caused by
mutation in one of four genes
• Pick one example for your notes
Some scientists credit mutations with being the driving force behind
evolution, by which they mean progressive changes through which
organisms, especially humans, become more advanced. Unfortunately
for these scientists, mutations tend to either be a loss of information
(frameshift mutation), an extra copy of pre-existing information, or rarely
a small, random and benign (non-harmful) change in DNA. Most
mutations are far from benign, and are the source of various birth
defects, genetic illnesses and cancer.
“Oculocutaneous albinism 2” caused by mutation in a gene on chromosome 15
Albinism is the result of a loss of genetic information, specifically pigments
or coloring
Animals or people born with additional body parts – additional copies of
pre-existing information
END GENETICS
Cloning
• http://learn.genetics.utah.edu/content/tech/
cloning/clickandclone/
http://www.youtube.com/watch?v=IUKslRdPvbY&feature=related
• http://www.youtube.com/watch?v=zP2m95
JAD4g&feature=related
• http://www.sumanasinc.com/webcontent/a
nimations/content/mendel/mendel.html
http://www.nburlington.com/ourpages/users/alanoue/Bio_handouts.htm#Genetics
http://web.archive.org/web/19971023004508/http://nesen.unl.edu/methods/biodemo.html#demo13
http://www.upt.pitt.edu/ntress/Bio1_Lab_Manual_New/molecular_biology_exercises.htm
http://www.apsnet.org/education/feature/ancientdna/top.htm
• Mosaicism http://www.vivo.colostate.edu/hbooks/gene
tics/medgen/chromo/mosaics.html
http://learn.genetics.utah.edu/
Mosaicism
a pattern of development in which an organism consists of two sets of cells that differ according to which X
chromosome is activated.
• Heterochromatic
eyes
• Fred and Wilma both have smooth
hairlines. Their daughter, Pebbles,
has a pointed (“widow’s peak”)
hairline. Which is dominant: smooth
or pointed hairline? How do you
know?
• Penelope has small, attached
earlobes. Armando has larger, free
earlobes. All four of their children
have large, free earlobes. Which is
dominant: free or attached
earlobes? How do you know?