Unit 4 Genetics

Alleles

different variants of a gene.

Alleles map to

the same locus on individual chromosomes.

Allelic

individual has two variants (Gg) of a gene so, the two genes are..

Non-Allelic

individual has two copies/identical (GG or gg) of a gene so, the two genes are..

Wild type

the phenotype of the most common form of a species as it occurs in nature.

Null allele

a mutant allele with the effect of either the absence of gene product or the absence of gene product function due to a loss-of function mutation; most behave as recessive

e+/e+; +/+

homozygous color

e/e

homozygous recessive (ebony)

e+/e; +/e

heterozygous

R1 and R2

alternative alleles of gene R (flower colors)

IA, IB, and IO

alternative alleles of gene I (blood types)

nine of the 100+ alleles of the white locus in Drosophila

w+, w, wa, wcf, wbl, we, wis, wch, wDZL

incomplete dominance (partial dominance)

neither one of the two contrasting traits is dominant; the phenotype of heterozygous individuals is an intermediate of the two contrasting traits.

incomplete penetrance

identical known genotypes yield <<100% penetrance: should have color but some are showing the recessive phenotype (no color).

variable expressivity

Identical known genotypes with an expressivity effect yield range pf phenotypes. 100% penetrance but all have color that are showing in different ways

Flies that are homozygous for this show different degrees of eye size reduction.

recessive eyeless mutant allele.

Complete penetrance

Identical known genotypes yield 100% expected phenotype

Constant expressivity

Identical known genotypes with no expressivity effect yield 100% expected phenotype.

Penetrance

the frequency with which individuals of a given genotype manifest at least some degree of the trait

Expressivity

the degree or range in which a phenotype for a given trait is expressed.

Pleiotropy

a condition in which a single mutation causes multiple phenotypic effects.

Marfan syndrome

results from an autosomal dominant mutation in fibrillin.

Fibrillin

a gene that codes for a connective tissue protein present in many tissues in the body.

Essential Gene

defined as a gene that is necessary for growth and survival, and its absence results in lethality.

A (agouti) is an..

essential gene.

A^Y (yellow) is a ….

dominant, pleiotropic, and recessive lethal mutant allele.

The inheritance of plumage color patterns in mallard ducks depends on the three alleles of the M locus:

M^r: restricted

M: mallard (wild type)

m^d: dusky

M^r (restricted) is dominant over and .

mallard and dusky

M (mallard) is dominant over _.

dusky

Codominance

a mode of inheritance in which the phenotypic effects of two allelic genes are fully and simultaneously expressed in heterozygous individuals.

Type A (IA) dominant

Erythrocytes (red blood cells) with type A surface antigens and plasma with anti-B antibodies

Type B (IB) dominant

Erythrocytes (red blood cells) with type A surface antigens and plasma with anti-A antibodies

Type AB (IA and IB are co-dominant)

Erythrocytes (red blood cells) with type A and type B surface antigens and plasma with neither anti-A not anti-B antibodies.

Type O (Io recessive-null allele)

Erythrocytes (red blood cells) with neither type A not type B surface antigens, but plasma with both anti-A and anti-B antibodies.

Epistasis

occurs when the effect of one gene masks or modifies the effect of another, non-allelic gene.

Complementation

occurs when two parents that exhibit a recessive phenotype can yield offspring that exhibit the dominant phenotype for the character.