Unit 5 – Other forms of inheritance Non-Medelian Inheritance Not all traits are simply dominant or recessive, with only 2 possible alleles.

Incomplete Dominance = BLENDING in heterozygotes Neither allele is dominant over the other, so individuals with a heterozygous genotype show a blended phenotype somewhere in the middle. (i.e. red + white=pink) Use different letters to represent each possible allele (instead of Rr use RW since there is not dominant or recessive allele) Examples: feather color in chickens, flower color such as roses or snapdragons.

EXAMPLE: ◦ Red flowers x White Flowers = Pink flowers Choose letters to represent each phenotype Red = RR White = WWPink = RW Cross a red parent with a white parent & give phenotype and genotype ratios of offspring.

Phenotype ratio: 100% Pink Genotype ratio: 100% heterozygous

Phenotype: 25% Red 25% White 50% Pink Genotype: ◦ 25% Homo Red ◦ 25% Homo White ◦ 50% Hetero. RRRW WW R W RWRW

Co-dominance = TOGETHER or SPOTTED – both traits are FULLY and SEPARATELY expressed Co means together, and BOTH alleles are dominant so they show up together. Ex: hair color in humans, fur color in cattle. Use different letters to represent each possible allele (instead of Bb use BW since there is not dominant or recessive alleles)

Sample cross…black and white fur in cows. BB = Black WW = White BW = Black AND White hairs together Cross a cow and a bull that have black and white hairs.

BBBW WW BW B W Phenotype: 25% Black, 25% white, 50% black and white Genotype: 25% homozygous black, 25% homozygous white, 50% Hetero

Human Blood Types: Use both co- dominance and regular dominant/recessive. A and B are co-dominant. O is recessive. Multiple alleles: when more than two alleles for the trait exist in the population. Use the chart to help with crosses.

Cross a person who is homozygous for type A blood with a person who has type AB blood. AA AB A A A B Phenotype Ratio: 50% Type A, 50% Type AB Genotype Ratio: 50% Homozygous Type A, 50% AB Heterozygous Type AB

Sex-Linked: Use sex chromosomes and alleles. Some disorders are carried on the X chromosome. Examples of these disorders are color blindness, and hemophilia.

Only females can be carriers (heterozygous) because they have two X chromosomes Males either have the allele (and hence show the trait) or they don’t. Males only get 1 X, so whatever they inherit on that 1 X is what you see.

When doing Punnett Squares, you must first use sex chromosomes (XX for female, XY for male) then assign letters to the trait and put them as superscripts on the sex chromosomes. B = normal vision, b = color blind. Cross a heterozygous normal vision female with a normal vision male. (First cross sex chromosomes, then put on alleles and cross them).

Phenotype: 50% Normal vision females 25% Normal vision males 25% Color Blind males Genotype: 25% X B X b (Carrier) 25% X b Y 25% X B X B 25% X B Y

Sex-Influenced Traits Sex influenced traits are also autosomal, meaning that their genes are not carried on the sex chromosomes. What makes these traits unusual is the way they are expressed differently phenotypically in the two genders (can be influenced by things like hormones). Example: pattern baldness

Polygenic Traits Traits produced by two or more genes. ◦ Example: Human skin color

Multiple Alleles Multiple alleles are when there are more than 2 forms of a gene. Ex: human blood type (ABO), human hair colors. HBr = brown HBd = blonde hR = red hbk = black The possible genotypes and phenotypes: HBdHBd or HBdhbk = blonde HBdHBr = mousy brown HBdhR = strawberry blonde HBrHBr or HBr hbk = brown HBrhR = auburn hRhR or hRhbk = red hbkhbk = black

You Practice Cross a black hair parent with a blond hair parent whose mother had black hair. P = hbk hbk x HBdhbk HBdhbk hbkhbk hbk HBd hbk Phenotype: 50% Blond, 50% Black Genotype: 50% HBdhbk, 50% hbkhbk

X-Inactivation In mammals, males receive one copy of the X chromosome while females receive two copies. To prevent female cells from having twice as many gene products from the X chromosomes as males, one copy of the X chromosome in each female cell is inactivated randomly in each cell.