Unit 5 – Other forms of 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

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

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

Human Blood Types: Use both co- dominance and regular dominant/recessive. A and B are co-dominant. O is recessive. 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% AA, 50% AB