Genetics

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Biology

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Autosomal Dominant Inheritance

Dominant gene located on 1 of the autosomes

Letters used are upper case ie BB or Bb

Affected individuals have to carry at least 1 dominant gene (heterozygous or homozygous)

Passed onto males and females

Every person affected must have at least 1 parent with the trait

Does not skip generations

E.g. Huntington’s disease, Marfan syndrome

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Autosomal Dominant- Marfan syndrome

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Autosomal Recessive Inheritance

The recessive gene is located on 1 of the autosomes

Letters used are lower case ie bb

Unaffected parents (heterozygous) can produce affected offspring (if they get both recessive genes ie homozygous)

Inherited by both males and females

Can skip generations

If both parents have the trait then all offspring will also have the trait. The parents are both homozygous.

E.g. cystic fibrosis, sickle cell anaemia, thalassemia

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Autosomal Dominant/ Recessive Problems

Cross a pure breeding, black coated guinea pig with a pure breeding, white coated guinea pig. Given that, in guinea pigs, black coat colour is dominant to white coat colour, determine the genotypes and phenotypes of the first and second generation offspring.

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Incomplete dominance

In a heterozygous organism, neither gene is dominant, both genes are expressed equally

Capital letters used for both alleles

Snap dragons- red = RR, white= WW, pink = RW

Cows- brown = BB, white= WW, roan=BW

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Incomplete dominance

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Incomplete dominance problems

In Andalusian chickens, the black Andalusian character is incompletely dominant to the white-splashed Andalusian character. The heterozygous condition produces blue Andalusian chickens. Determine the genotypes and phenotypes of the F1 and F2 generations if a pure breeding, black Andalusian is crossed with a pure breeding, white-splashed Andalusian.

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Co- dominance