Genetics Beyond Mendel

Incomplete Dominance Phenotype is a blend of the alleles An intermediate is seen Four o’clocks Homozygous Red Heterozygous Homozygous White Sometimes written: C and C 1

Incomplete Dominance - Humans Hair Follicles –Curly hair is homozygous recessive –Straight hair is homozygous dominant –Heterozygous individuals have wavy hair

Incomplete Dominance - Humans Cholesterol Gene –Homozygous dominant – Very high cholesterol –Heterozygous – high cholesterol –Homozygous recessive – normal cholesterol

Multiple Allele Traits More than two alleles for a trait Only two forms are inherited Can have co-dominance Can have a hierarchy of dominance –hair color in mice determined by a single gene with alleles for black, brown, agouti, gray, albino agouti > black > brown > albino.

Codominance Both alleles are expressed at the same time Roan horse appears grey but has a mixture of white and black hairs Hybrid camellia

Blood Types Multiple Alleles (3) and Co dominant A, B, O alleles produce: AA = ABB = B AO = ABO = B AB = ABOO = O Four blood type phenotypes Four blood type phenotypes Sometimes written I A I B i Sometimes written I A I B i

Polygenic Inheritance More than one set of alleles controls a trait Skin color has three different sets Effect is additive

Environment and Inheritance Gene expression is influenced by the environment Chemicals, temperature, pH levels, radiation, nutrition can all be factors Himalayan rabbits – fur changes color with exposure to cold

Turtles –Sex determined by temperature of eggs –Males produced at lower incubation temperatures than females –At temperatures around 30 degrees Celsius only female turtles arise Lizards and crocodilians –Females produced at lower temperatures, males at higher temperatures Environment and Inheritance

Gender Inheritance Due to one set of chromosomes in humans XX = female XY = Male One X must come from mother Sperm can donate an X or Y Sex is determined at fertilization

Sex-linked Inheritance Sex linked traits: – –Genes that are carried by either sex chromosome – –Y linked genes appear on Y chromosome – –X linked genes appear on the X chromosome Only men inherit Y chromosomes – –Only ones to inherit Y-linked traits Men and women both inherit X chromosomes – –Both can get the X-linked traits

Males – Genes on the X chromosome that do not code for gender are expressed Even recessive genes No corresponding gene on the Y chromosome. Sex-linked Inheritance

Females – Recessive allele on one X chromosome is masked by a dominant allele on the other Women are frequently carriers of X-linked traits but rarely have them expressed in their own phenotypes. Sex-linked Inheritance

X chromosome carries coat pigment genes One X chromosome randomly becomes deactivated. The active X chromosome determines the color in that particular cell

A human female "carrier“ heterozygous for sex- linked trait causing red-green color blindness (recessive) marries a normal male What proportion of their male progeny will have red-green color blindness? Sex-linked Inheritance

Genotype of parents Mother: heterozygous for red green color blindness Father: homozygous dominant on X no allele on Y ½ of the daughters are carriers ½ of the daughters are normal ½ of the sons are color blind ½ of the sons are normal

The two most noted X linked genetic disorders are hemophilia and color blindness

Pedigree Diagram Visual chart of a family’s genetic history

Pedigree Diagram