Bio 2100: Extending Beyond Mendel (10/14)

Vocabulary practice flashcards covering non-Mendelian inheritance patterns including multiple allelism, codominance, incomplete dominance, incomplete penetrance, environmental effects, epistasis, and sex linkage.

Origin of homologous chromosomes

In a sexually reproducing diploid species, the two homologous chromosomes in a pair originate from two different parents (one maternal and one paternal).

Origin of sister chromatids

Two identical copies of a single replicated chromosome that originate from one parent.

Origin of non-sister homologous chromatids

Chromatids belonging to opposite homologous chromosomes within a pair, which originate from two different parents.

Origin of two non-homologous chromosomes

Any pair of different chromosomes in a diploid cell, which can originate from either one parent or two different parents.

Multiple allelism

The existence of three or more alternative allele forms of a given gene within a population, such as the $I^A$, $I^B$, and $i$ alleles determining ABO blood types.

Codominance

A pattern of inheritance in which the phenotypic effects of both alleles are fully and simultaneously expressed in a heterozygote, as seen in individuals with genotype $I^A/I^B$ having type AB blood.

Type O blood group

The ABO blood phenotype produced by the genotype $i/i$, producing antibodies against both A and B antigens, capable of donating blood safely to types O, A, B, and AB, but only receiving blood from type O.

Type AB blood group

The ABO blood phenotype produced by the genotype $I^A/I^B$, producing no ABO antibodies, capable of safely receiving blood from types O, A, B, and AB, but only donating blood to type AB.

Incomplete dominance

A form of gene expression where the heterozygous phenotype is an intermediate blend between the two homozygous parental phenotypes, illustrated by four-o'clock plants where crossing dark purple and white flowers produces light purple flowers.

Incomplete penetrance

A phenomenon where some individuals carrying a particular pathogenic or dominant genotype fail to express the corresponding clinical phenotype, such as in autosomal dominant polydactyly.

Environmental effects (gene expression)

The modulation of gene expression or phenotypic outcome by external environmental factors, as demonstrated by temperature-sensitive coat color pigmentation in Himalayan rabbits.

Epistasis

A genetic interaction in which the allele or alleles of one gene mask or alter the phenotypic expression of alleles at a second, independent gene locus.

White Leghorn ($CC\,II$)

A chicken breed with white plumage because the dominant inhibitor allele ($I$) prevents expression of the pigment allele ($C$).

White Wyandotte ($cc\,ii$)

A chicken breed with white plumage because the homozygous recessive allele ($cc$) fails to produce pigment, even though no dominant inhibitor ($I$) is present.

$13:3$ phenotypic ratio

A modified $9:3:3:1$ dihybrid $F_2$ ratio resulting from dominant inhibitory epistasis in fowl, where only genotypes of the form $C\_\,ii$ display colored feathers ($\frac{3}{16}$) and all other genotypes are white ($\frac{13}{16}$).

Sex-linked genes

Genes residing specifically on sex chromosomes (such as the human X or Y chromosome) rather than autosomes, giving rise to unique sex-dependent inheritance patterns.

Reciprocal cross

A pair of genetic crosses in which the phenotypes/genotypes of the male and female parents are swapped to test whether an inherited trait is autosomal or sex-linked.

X-linked inheritance in Drosophila melanogaster

The inheritance mode discovered by Thomas Hunt Morgan where crossing white-eyed females ($w\,w$) with red-eyed males ($w^+\,Y$) produces all red-eyed females ($w^+\,w$) and all white-eyed males ($w\,Y$), demonstrating that the eye color gene is on the X chromosome.