1. Multiple alleles (more than 2 alleles for gene in

population)

Example: Blood Groups Karl Landsteiner 1900’s

Chromosome 9 I gene

Modified Mendelian Ratios Ch. 13

ABO blood system = polymorphic I gene

Blood type genotypeA IAIA or IAi

B ?

AB IAIB

O ii

What is the mechanism of inheritance of A, B, AB, O?

Autosomal or sex chromosome?

Which two alleles are codominant?

Which allele is recessive?

Example

A child has type O blood. The mother of the child has Type B blood. What could the blood types of the f IBi

ii

A,B,O carbohydrate antigens

Bombay phenotype A man IAIA (Type A) and a woman of type IAIB have

a child with type O blood. How??

I gene encodes glycotransferasesGlycotransferases add sugar group to glycolipid

H gene encodes the glycolipid antigen

HH IAI A Hh IAIi

2. Incomplete dominance

Example: snapdragons

Allelic symbols do not specify dominance

CR = red color

Cw = white color

CR CR X Cw Cw

3. Codominance

Each allele encodes separate gene

product distinct in heterozygote

L gene for human blood cell surface protein

LM = M antigen LMLN x LMLN

LN = N antigen 1M

A man with the M bloodtype has a child with a woman of the MN bloodtype

Expected ratio of offspring?

4. Lethal alleles

MM = normal spineMM’ = manx cat (no

tail)M’M’ = lethal

Cross two manx, what is ratio of phenotypes in offspring?How do breeders obtain manx cats?

Lethal alleles in humans

Tay Sach disease tt is fatal

Huntington disease HH is fetal lethal Hh causes death ~ age 50.

5. Penetrance % individuals that exhibit

phenotype corresponding to genotype

Polydactyly, dominant

Pp pp

5,5 6, 5 6, 6

6. Expressivity =the extent to which a trait is exhibited

Piebald spotting

Human piebald trait autosomal dominant defect in melanocyte development mutation in the KITgene, which encodes cell surface receptor tyrosine kinase

http://dermatlas.med.jhmi.edu/derm/indexDisplay.cfm?ImageID=386927278

Both sisters have same genotype

Incomplete penetrance AND expressivity NF-1 = Neurofibromatosis1

(1/4000, 17q11.2)

(350 kb gene, 60 exons)

Autosomal dominant trait NN and Nn with 50- 80% penetrance

Variable expressivity

Mild form tumors on nerve CT coverings, skin, eyes, organs, face

speech, blood pressure, spine curvature, headaches

Gene expression also affected by: Sex (baldness) Temperature (melanin in Siamese cats) Chemicals (PKU) Diet (height, cancer)

A product of one gene influences, or masks, the expression of another gene(s)

Modification of dihybrid cross ratioAaBb X AaBb 9:3:3:1

7. Epistasis- gene product interactions

Epistasis in labrador retrievers B and E color genes (labs)

B black b brown

E color e no color (yellow)

ee is epistatic

Cross two double heterozygotes

Phenotypes of parents?

Phenotypes of offspring? ratio?

The genotype rrpp gives roosters a single comb.R-P- gives a walnut comb. rrP- gives a

pea comb, R-pp gives a rose comb.

Determine the ratio of phenotypes in the F2 generation of the following cross

P ?

F1 ?

F2 ?

ROSE PEA

SINGLE WALNUT

Epistasis in Cats

W = white w = not white B = black b = brown

Mate 2 heterozygous cats

What is the expected ratio?

8. Polygenic traits

Vary continuously Weight, height, IQ

Example: CAD is a multifactorial trait affected by

Obesity, diabetes, high blood pressure, high levels of LDL-cholesterol, and gum disease

Although CAD runs in families, does not show Mendelian inheritance patterns

CAD occurs more often in men Risk higher among US African Americans than

Caucasians or Asians >200 genes identified

LDLR and familial hypercholesterolemia (dominant)

Influenced by many genes and environmental factorsPredisposition genes + environment

Cleft palate and identical twins, colon cancer may run in families

4. Dominance series – C series/ rabbits

c+ = full color cch = chinchilla (hypomorphic)

ch = himalayan (hypomorphic)

c = albino (apomorphic allele = nonfunctional)

Chinchilla

Himalayan Albino

Genotype phenotype?

cch cch

cch ch

ch c

c+ cch

c+ = full color cch = chinchilla (hypomorphic)

ch = himalayan (hypomorphic)

c = albino (apomorphic allele = nonfunctional)