Extending Mendel Genetics:

Other Genetic Variations:Dominance variations -

• complete, incomplete, codominance

Polygenetic & Multiple Alleles

Pleiotropy

Epistasis

CodominanceBoth 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 DominanceIn some cases, an intermediate phenotype is shownNeither allele is dominantIn 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 TypesMultiple Alleles (& codominance): Blood Types

___________

___________

___________

___________

Type B Blood

Type AB Blood

Type O Blood

Type A Blood

IBIB or IBi

IAIB

ii

IAIA or IAi

10%

4%

46%

40%

Blood Test Phenotype Genotype Population

If a dad is heterozygous for Type B blood anda mom is heterozygous for Type A blood…Create a Punnett Square to determine the blood types of their children.

If a dad is heterozygous for Type B blood anda mom is heterozygous for Type A blood…Create a Punnett Square to determine the blood types of their children.

IB i

IA

i

IAIB IAi

IB i i 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?

Blood Typing

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 orsickle cell allele (S) = AS and they do manifest some sickling in low-oxygen environments.

http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html

Heterozygous AdvantageThe 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 beforethe protozoan’s life cycle is complete, thus eradicating the disease.

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, 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 ________)

Because they have enough red blood cells that arenot sickled and can adequately carry oxygen.

Malaria mosquito

PointVal Glu

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 ofMelanin, due to genetics, mosaicism, disease or injury.

Blue & Green

Brown & Hazel

Crossing over during mitosis can cause mosaicism

Colorblindness

Hemophilia

Hairy Ear

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 - x-linked

Hairy Ears - y-linked

PolygenicIn 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 & PolygeneticLabrador Retriever GeneticsBlack 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)

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