Expression of an organisms genotype, and its interaction with the environment
What is an allele?
Different versions of a gene found at the same locus on a chromosome
How many alleles per gene do diploid organisms carry?
Two.
What is a dominant allele?
An allele whose characteristic will always appear in the phenotype, so only one is needed
What is a recessive allele?
An allele whose characteristic only appear in the phenotype if no dominant allele is present, meaning two must be present
What is meant by codominant alleles?
Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together
What is meant by homozygous and heterozygous?
Homozygous - both alleles are dominant, or both alleles are recessive
Heterozygous - one allele is dominant, one is recessive
Define monohybrid inheritance?
Where one phenotypic characteristic is controlled by a single gene
Define dihybrid inheritance?
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
What is meant by sex-linkage?
When an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual
Why are males more likely to express a recessive sex-linked allele?
Most sex-linked alleles are located on the X chromosome. Males only get one copy of this allele, so will express this characteristic even if it's recessive. Since females have XX chromosomes this is less likely.
What is meant by autosomal linkage?
When two or more genes are located on the same autosome (non-sex chromosome). The genes are unlikely to be separated by crossing over during meiosis so are often inherited together
What is meant by epistasis?
When two non-linked genes interact, with one gene either masking or supressing the other
Define the two types of epistasis?
Recessive epistasis - when two homozygous recessive alleles mask expression of another allele
Dominant epistasis - when one dominant allele masks expression of multiple other alleles
How can we use a chi-squared test in relation to genetics?
We can compare expected phenotypic characteristics with observed ratios to test our understanding of how different genes or alleles are inherited