pob ii: class 3 (dominance, additivity, and linkage)

why are some alleles dominant or recessive?

dominance

one allele is dominant over the other, phenotype reflects the dominant allele

• doesn’t exist in homogeneous because two alleles are the same

segregation of alleles

during meiosis, one of the parent alleles is sorted into each haploid cell

If proteins do things in cells, and one allele of a gene e.g. makes more protein, or more functional protein, than another → what should we see?

we should see something intermediate between them in hte parents

• this is called additivity (it’s the default for most traits)

  • think of “averages” rather than “adding”

• how most allele works

• ex. the heterozygote has a phenotype in between two homozygote ones

codominance

phenotypes from both parents are present

ex. the alleles of enzyme make two different products from same substrate → in heterozygote both substrates will be made

how to approach questions about domiance

ask yourself what would happen in the heterozygote