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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
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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 C1
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 = A BB = B AO = A BO = B AB = AB OO = O Four blood type phenotypes Sometimes written IA IB 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
Environment and Inheritance • 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
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
Sex-linked Inheritance 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
Sex-linked Inheritance 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?
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 sons are color blind ½ of the daughters are normal 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
