Unit 5 – Other forms of inheritance

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 = WW Pink = RWCross a red parent with a white

parent & give phenotype and genotype ratios of offspring.

Phenotype ratio: 100% PinkGenotype 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 = BlackWW = WhiteBW = Black AND White hairs togetherCross a cow and a bull that have black and white hairs.

BB BWBW WW

B W

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.

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 males25% Color Blind males Genotype: 25% XBXb (Carrier) 25% XbY 25% XBXB 25% XBY

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 AAAB AB

A A

A

B

Phenotype Ratio: 50% Type A, 50% Type ABGenotype Ratio: 50% AA, 50% AB