Unit 5 – Other Forms of Inheritance

Not all traits are simply dominant or recessive, with only ______possible alleles.

1. ______= BLENDING in heterozygotes

·  ______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 ______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 = RW

Sample Cross…

Cross a red parent with a white parent & give phenotype and genotype ratios of offspring.

R R

W

W

Phenotype Ratio= ______Pink

Genotype Ratio= ______heterozygous

You practice:

Cross two pink flowers and give the genotype and phenotype ratios of their offspring.

2. ______= TOGETHER or SPOTTED – both traits are FULLY and SEPARATELY expressed

·  Co means together, and ______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 Rr use RW 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.

B W

BB / BW
BW / WW

B

W

Phenotype: ______

Genotype: ______

You practice: Cross a white cow with a black bull. Give the genotype and phenotype ratios of the offspring.

3. Human Blood Types/Multiple Alleles: Use both co-dominance and regular dominant/recessive.

·  A and B are co-dominant. O is recessive.

·  Use the chart to help with crosses.

*Note: You may use the letter subscripts when doing Punnett crosses, OR just use the letters (i.e. A, B, O)

Cross a person who is homozygous for type A blood with a person who has type AB blood.

A A

A

B

Practice: Cross someone with Type O blood with someone who is heterozygous for type B blood.

3. (cont) Multiple alleles are when there are more than ______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. Give phenotypes and genotypes

4. Polygenic traits are the result of the interaction of several ______(2 or more genes)

Poly = ______, Genic = ______

Examples: human skin color, human eye color

5. 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. Since females have 2 copies of the X chromosome, the dominant allele will cancel out the recessive allele. 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.

Practice Cross:

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% XBXb (Carrier)

25% XbY

25% XBXB

25% XBY

Practice: Cross a carrier female with a colorblind male and give the genotype and phenotype ratios of the offspring.

Sex-Linked Pedigree

6. Sex influenced traits are also ______, meaning that their genes are not carried on the sex chromosomes.

These traits are influenced by ______. They can be influenced by hormone production.

Example: pattern baldness due to testosterone.


What is the probability that you will be bald if your father is homozygous and balding, and your mother is homozygous and not balding?

7. 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 ______randomly in each cell.