Extending Mendel Genetics:

1
Extending Mendel Genetics

• Other Genetic Variations
• Dominance variations -
• complete, incomplete, codominance
• Polygenetic Multiple Alleles
• Pleiotropy
• Epistasis

2
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 generations genotype and
phenotype. 2. Determine the F2 generation a.
Genotypes b. Phenotypes
3
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 youre 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.
4
Multiple Alleles ( codominance) Blood Types
Blood Test
Phenotype
Genotype
Population
IBIB or IBi
10
Type B Blood
___________
4
IAIB
___________
Type AB Blood
46
ii
___________
Type O Blood
Type A Blood
40
___________
IAIA or IAi
5
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
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?
IAIB
IAi
IA
i
IB i
i i
6
Sickle Cell and Codominance Homozygous for
normal hemoglobin allele (HBA) receive a normal
hemoglobin allele from each parent and do not
have any sickled RBCs 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 RBCs. 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
RBCs, but sickled cells are short-lived 10-20
days and die before the protozoans life cycle is
complete, thus eradicating the disease.
http//www.pbs.org/wgbh/evolution/library/01/2/l_0
12_02.html
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Pleiotropy (resulting in multiple seemingly
unrelated effects) in Sickle Cell Disease
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1. Sickle Cell Anemia is a genetic disorder
caused by one wrong DNA base, CAT instead of
CTT, making amino acid ______ rather than
________ This called a _______ mutation. 2.
Why are people who are heterozygous for sickle
cell generally healthy? ____________________
____________________ 3. What disease are
people who carry the sickle cell trait immune to
(heterozygous advantage)? _________ (which
is caused by a protozoan parasite passed on by a
________)
Val
Glu
Point
Because they have enough red blood cells that
are not sickled and can adequately carry oxygen.
Malaria
mosquito
9
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
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Colorblindness
Red-Green color blindness sex (X) linked
Trichromats - blue/yellow color blindness is not
sex-linked, rather its autosomal, on the 7th
chromosome)
Hemophilia
Hemophilia - x-linked
Hairy Ear
Hairy Ears - y-linked
11
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, its
almost certain its a female. What condition in
humans would give a male XXY?
12
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 Phenotype BBEE BbEE BBEe
BbEe bbEE bbEe BBee Bbee bbee
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)
13
Drosophila fruit fly lab
Students enter as a guest. http//sciencecoursewar
e.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