Unit 5 – Other forms of inheritance
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Unit 5 – Other forms of inheritance Not all traits are simply dominant or recessive, with only 2 possible alleles. Incomplete Dominance = BLENDING in heterozygotes.

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Unit 5 – Other forms of inheritance

Not all traits are simply dominant or recessive, with only 2 possible alleles.


Incomplete dominance blending in heterozygotes
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 = RRWhite = 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)



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
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

  • Maleseither 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 females25% Normal vision males

25% 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.

A

A

A

B

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

Genotype Ratio: 50% AA, 50% AB


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