Genetics ch. 3: Extensions to Mendel's laws

what observations were shown to not follow Mendel’s rules?

- no definitively dominant or recessive alleles

- more than two alleles exist

- multiple genes involved in one trait

- gene-environment interactions

Pleiotropy

one gene contributes to several distinct and seemingly unrelated characteristics

complete dominance

hybrid resembles one of the two parents

incomplete dominance

hybrid resembles neither parent

codominance

hybrid shows traits from both parents

allele frequency

the percentage of gene copies for one allele and are unique to a pair of alleles

wild type

the more common form of a trait found in nature (denoted with a +)

rare allele

aka mutant allele… this allele is not common in nature

monomorphic

gene with only one common wild-type allele (mostly exists in one form)

polymorphic

gene with more than one common wild-type allele (mostly exists in multiple forms)

common variants

high frequency alleles of polymorphic genes

novel phenotypes

two genes interacting to determine one trait that has never been seen in the organism’s lineage

epistasis

one allele at one gene masks the phenotype alleles of another gene

epistatic allele

the “masker”. can be dominant or recessive

hypostatic allele

the gene that is “masked”. can be dominant or recessive

what causes phenotypic variance?

- effects of modifier genes

- effects from the environment

- pure chance

modifier gene

alters the phenotypes produced by the alleles of other genes. can have major or subtle effects

phenocopy

phenotype arising from an environmental agent that mimics the effect of a mutant gene

discontinuous traits

gives clear cut “either-or” phenotypic differences between alternative alleles

continuous traits

are determined by segregating alleles of many genes that interact together and with the environment