Transcript Extending Mendel Genetics

Extending Mendel Genetics:
Other Genetic Variations:
Dominance variations • complete, incomplete, codominance
Polygenetic & Multiple Alleles
Pleiotropy
Epistasis
Codominance
Both alleles can be expressed
For example, red cows crossed with white will generate roan cows.
Roan refers to cows that have red coats with white blotches. (RW)
Questions:
1. What is this type of inheritance called?
2. Why is is called that?
3. What genotype is used to depict a red cow, white cow,
and a roan cow?
Tasks:
1. Using a Punnett Square, mate a red bull  with a white cow,
to determine the F1 generation’s genotype and phenotype.
2. Determine the F2 generation:
a. Genotypes
b. Phenotypes
Incomplete Dominance
In some cases, an intermediate phenotype is shown
Neither allele is dominant
In Snapdragons, flower color can be red, pink, or white.
The heterozygous condition results in pink flowers (or an
intermediate trait)
R1R1
R2R2
R1R2
Questions:
1. Why is this considered Incomplete Dominance?
2. The trait you’re looking at is?
3. What are the three alleles for Snapdragon flower color?
Tasks:
1. Cross a white Snapdragon with a red Snapdragon and
determine the genotype and phenotype ratios of the
F1 generation.
2. Cross two pink Snapdragons and determine the
genotype and phenotype ratios of the F2 generation.
3. Cross a red Snapdragon with a pink Snapdragon
and determine the genotype and phenotype ratios of the F3 generation.
Multiple Alleles (& codominance): Blood Types
Blood Test
Phenotype
Type B Blood
___________
Genotype
IBIB or IBi
Population
10%
Type AB Blood
___________
IAIB
4%
Type O Blood
___________
ii
46%
Type A Blood
___________
IAIA or IAi
40%
Blood Typing
If a dad is heterozygous for Type B blood and
a mom is heterozygous for Type A blood…
Create a Punnett Square to determine the blood types
of their children.
IB
i
IA
IAIB
IAi
i
IB i
ii
1. What are the blood types of the children?
2. Which child(ren) can the mom donate to?
3. Which child(ren) can the dad donate to?
4. Who can get blood from everyone in the
family (the universal recipient)?
5. Who can donate blood to everyone in
the family (the universal donor)?
6. Who in the family cannot get blood
from any family member? Why?
Sickle Cell and Codominance
Homozygous for normal hemoglobin allele (HBA) receive a normal hemoglobin
allele from each parent and do not have any sickled RBC’s: AA
Homozygous for mutant or sickle cell hemoglobin allele (HBS) receive a
Sickle cell allele from each parent and are said to have sickle cell disease: SS,
Resulting in abnormal, sickle-shaped RBC’s.
Heterozygous receive one normal hemoglobin allele (A) and one mutant or
sickle cell allele (S) = AS and they do manifest some sickling in low-oxygen
environments.
Heterozygous Advantage
The protozoan that causes Malaria (and it deposited via mosquitos) has an
affinity to sickled cells and starts its life cycle in those cells rather than
the normal RBC’s, but sickled cells are short-lived 10-20 days and die before
the protozoan’s life cycle is complete, thus eradicating the disease.
http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html
Pleiotropy (resulting in multiple seemingly unrelated effects) in Sickle Cell Disease
1. Sickle Cell Anemia is a genetic disorder caused by
one wrong DNA base, CAT instead of CTT,
Val rather than ________
Glu
making amino acid ______
Point mutation.
This called a _______
2. Why are people who are heterozygous for sickle
cell generally healthy?
Because they have enough red blood cells that are
________________________________________
not sickled and can adequately carry oxygen.
3. What disease are people who carry the sickle cell trait immune to (heterozygous advantage)?
Malaria (which is caused by a protozoan parasite passed on by a ________)
mosquito
_________
Pigments (displaying Multiple Alleles) = Polygenetics
i.e. skin, eyes, hair
GeneTree Eye Color Inheritance Chart:
(Number of dominant alleles shown below each eye color)
0
1
2
3
3-4
4
5
6
In anatomy, heterochromia refers to a difference in coloration
usually of the iris, but also of hair & skin.
Eye color is determined primarily by the concentration
and distribution of melanin (a pigment).
Heterochromia is a result of the relative excess or lack of
Melanin, due to genetics, mosaicism, disease or injury.
Crossing over during mitosis can cause mosaicism
Brown & Hazel
Blue & Green
Colorblindness
Red-Green color blindness = sex (X) linked
Trichromats - blue/yellow color blindness is not sex-linked, rather it’s autosomal, on the 7th chromosome)
Hemophilia
Hemophilia - x-linked
Hairy Ear
Hairy Ears - y-linked
Polygenic
In cats, the gene that controls the color of coat spots is located
on the X-Chromosome – expressing (or not) either black or
orange or possibly both if there are 2 X chromosomes.
Calico cats are white with patches of black & orange.
Tortoiseshell cats are black & orange with sparse to no patches of
white.
These conditions happens because one X chromosome may
have the allele for gold patches, while the other X may have
the allele for black patches.
Since females have 2 X chromosomes, they can have two different color
patches. If you see a cat with 3 colors: white black, and orange, it’s almost
certain it’s a female. What condition in humans would give a male XXY?
Multiple Alleles & Polygenetic
Labrador Retriever Genetics
Black is dominant (B) to chocolate (b)
Yellow is (ee) recessive epistatic (when present, it
blocks the expression of the black and chocolate alleles)
Genotype
BBEE
BbEE
BBEe
BbEe
bbEE
bbEe
Phenotype
Questions:
1. What in the genotype is unique to the
yellow lab?
2. What does epistatic mean?
3. What color lab would you expect with
BB or Bb? And with bb?
Task: Determine the number of black,
chocolate, and yellow labs produced
from a black female and a yellow male.
(BbEe x bbee)
Hint: Set it up like a two trait Punnett Square
(16 offspring)
BBee
Bbee
bbee
Drosophila fruit fly lab
Students enter as a guest.
http://sciencecourseware.org/vcise/drosophila/
1. Order a wild type (red-eyed) female and mate it with a white-eyed vestigial wing size male,
2. View shopping cart and check out
3. Go to the lab - observe F1 generation (record the phenotypes, genders, #’s)
4. Create an F2 generation with the F1 flies (record the phenotypes, genders, #’s)
5. Take the quiz