Chapter 4: Extensions of Mendelian Inheritance

Vocabulary flashcards covering key terms and definitions from Chapter 4: Extensions of Mendelian Inheritance.

Simple Mendelian inheritance

Classic single-gene inheritance following Mendel’s laws (dominant/recessive pattern).

Penetrance

Proportion of individuals with a genotype who actually express the phenotype; measured at the population level.

Expressivity

Range or degree of phenotype expressed by individuals with the same genotype.

Incomplete dominance

Heterozygote phenotype is intermediate between the two homozygotes (e.g., pink flowers from red and white).

Heterozygote advantage

Heterozygotes have higher fitness than either homozygote, increasing their reproductive success.

Codominance

Heterozygotes express both alleles’ phenotypes simultaneously (e.g., AB blood type).

X-linked inheritance

Inheritance pattern of genes on the X chromosome; males are hemizygous and often more affected.

Sex-influenced inheritance

Allele is dominant in one sex and recessive in the other; autosomal and influenced by sex hormones.

Sex-limited inheritance

Trait occurs in only one sex; hormones/developmental pathways restrict expression.

Lethal alleles

Alleles that can cause death; often recessive and involve essential genes.

Wild-type allele

Prevalent, functional allele in a population that encodes normal protein and phenotype.

Mutant allele

An allele altered by mutation, often defective or loss-of-function; usually rare.

Loss-of-function allele

Mutant allele that reduces or abolishes normal gene function.

Gene dosage effect

Phenotype depends on the amount of gene product produced; 50% may or may not suffice.

Up-regulation

Increase in expression of a normal allele to compensate for loss of function.

Gain-of-function mutation

Mutant allele that changes the protein to gain a new or abnormal function.

Dominant-negative mutation

Mutant protein antagonizes the normal protein, reducing overall function.

Haploinsufficiency

Dominant phenotype caused by a single functional copy being insufficient to maintain wild-type traits.

ABO blood group system

Blood groups determined by ABO antigens on red blood cells; IA, IB, i alleles.

IA allele

Allele that produces A antigen on red blood cells.

IB allele

Allele that produces B antigen on red blood cells.

i allele

Allele with no surface antigen (O allele).

Pleiotropy

One gene influencing multiple, seemingly unrelated phenotypic traits.

Environmental effects on gene expression

Environment can modify gene expression and phenotype (e.g., PKU or animal adaptations).

Gene interactions

Two or more genes influence the outcome of a single trait.

Epistasis

One gene’s alleles mask or modify the phenotypic effects of another gene.

Complementation

Offspring from different recessive lines show wild-type phenotype, indicating different genes.

Huntington disease

Autosomal dominant neurodegenerative disease with late onset (typically 30–50 years).

Duchenne muscular dystrophy (DMD)

X-linked recessive muscular dystrophy; primarily affects males.

Pseudoautosomal inheritance

Genes on X and Y show autosomal-like inheritance pattern despite sex chromosomes.

Reciprocal cross

Crosses in which parental sexes are swapped to test for sex-specific inheritance effects.

Gene knockout

Laboratory deletion of a gene to study its function; may show no phenotype due to redundancy.

Gene duplication

Presence of two or more gene copies; duplicates (paralogs) can compensate for each other.

Paralog

Related genes within the same genome arising from gene duplication.

Psittacofulvin

Pigment produced in parakeets that contributes to feather coloration.

Eumelanin

Dark pigment (melanin) contributing to black/brown coloration in feathers.

Feather coloration in parakeets

A gene-modification example showing how genotype combinations affect face/feather pigments.