7.1 Epistasis, Codominant, Multiple, Autosomal and Sex linked Alleles Flashcards
Define epistasis
One allele will affect or mask the phenotype of a second allele by affecting the expression of the second allele
Define dominant epistasis
Dominant allele at one gene locus masks the expressions of alleles at a second gene locus
Define recessive epistasis
Two recessive alleles at one gene locus will mask the expression of alleles at a second gene locus
What ratios are typically associated with dominant epistasis?
12:3:1 and 13:3
What ratios are typically associated with recessive epistasis?
9:3:4
How does epistasis affect metabolic pathways?
For each enzyme, dominant allele produces functional protein and the recessive allele produces non-functional protein
Enzyme one converts the precursor molecule into the intermediate molecule
Enzyme two converts intermediate molecule into final molecule
Enzyme one has to be functional for enzyme two to work
What would happen if enzyme one was inactive?
Build up of precursor and reduction in intermediate and final
What would happen if enzyme two was inactive?
Build up of intermediate and reduction of precursor and final
Define co-dominant alleles
Two alleles, equally as dominant so are both expressed in the phenotype
Describe the genotypes and subsequent phenotypes for co-dominant alleles
Homozygous for the first allele, homozygous for the second allele and heterozygous
Both alleles always expressed so forms three characteristics
How should co-dominant alleles be represented in a genetic diagram?
Instead different letters as subscripts on a letter than represents the gene
Define multiple alleles
A gene that has more than two alleles but only two are present in the cell because there only two homologous chromosomes
Define sex linkage
Alleles for characteristics that are carried on the sex chromosomes
Why might sex-linked characteristics not be preset on the Y chromosome?
It’s smaller and carries less information so the alleles on the X chromosome might not have a corresponding homologous section on the Y chromosome
What makes sex-linked characteristics different to co-dominant alleles?
They are dominant and recessive
If the male has no corresponding homologous section, more likely to express the recessive trait
How should sex-linked alleles be represented in a genetic diagram?
Chromosomes written as X and Y and alleles written in subscript
Define carrier
A person possesses the allele for a recessive characteristic but does not express it
Define autosome
Any chromosome that isn’t a sex chromosome
Define autosomal linkage
Any alleles for different characteristics carried on the same autosome
How many pairs of autosomes do humans have compared to sex chromosomes?
22 pairs of autosomes
1 pair of sex chromosomes
What do all the genes on a single chromosome form in autosomal linkage? What benefit does this have?
Form a linkage group and will stay together as long as chiasmata doesn’t occur
Makes tracking of characteristics through genetic crosses easier and in some instances more predictable
