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

Unit 5 – GeneticsOther 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

You PracticeCross 2 pink flowers

RR RW

RW WW

R W

R

W

Phenotype: 25% Red, 25% White, 50% Pink

Genotype: 25% Homozygous Red, 25% Homozygous White, 50% 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 BW

BW WW

B W

B

W

Phenotype: 25% Black, 25% white, 50% black and white Genotype: 25% homozygous black, 25% homozygous white,

50% Hetero

You PracticeCross a white cow with a black

bull.

BW BW

BW BW

W W

B

B

Phenotype: 100% Black and White Hairs

Genotype: 100% Heterozygous

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 AA

AB AB

A A

A

B

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

You PracticeCross type O blood, with

heterozygous type B blood.

Bi Bi

ii ii

i i

B

i

Phenotype: 50% Type B, 50% Type O

Genotype: 50% Heterozygous Bi, 50% Homozygous Recessive

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

You PracticeCross a carrier female with a

colorblind male and give the genotype and phenotype %.

XBXb XbXb

XBY XbY

XB Xb

Xb

Y

Phenotype: 25% Normal Vision Carrier Female 25% Colorblind Female 25% Normal Vision Male 25% Colorblind Male

Genotype: 25% XBXb, 25% XbXb, 25% XBY, 25% XbY

Sex-Linked Pedigree

Multiple AllelesMultiple 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 PracticeCross a black hair parent with a

blond hair parent whose mother had black hair.

P = hbk hbk x HBdhbk

HBdhbk HBdhbk

hbkhbk hbkhbk

hbk hbk

HBd

hbk

Phenotype: 50% Blond, 50% BlackGenotype: 50% HBdhbk, 50% hbkhbk

PolygenicPolygenic traits are the result of the

interaction of several genes (2 or more genes) Poly = many, Genic = “genes”

Examples: human skin color, human eye color