Chapter 13: Observing Patterns in Inherited Traits

Dominant

Refers to an allele that masks the effect of a recessive allele paired with it in heterozygous individuals.

Genotype

The particular set of alleles that is carried by an individual’s chromososmes.

Heterozygous

Genotype in which homologous chromosomes have different alleles at the same locus.

Homozygous 

Genotype in which homologous chromososmes have the same allele at the same locus.

Hybrid

A heterozygous individual.

Locus

A gene’s location on a chromosome.

Phenotype 

An individual’s observable traits.

Recessive

Refers to an allele with an effect that is masked by a dominant allele on the homologous chromosome.

Law of segregation

A diploid cell has teo copies of every gene that occurs on its homologous chromosomes. Two alleles at any locus are distributed into separate gametes during meiosis.

Monohybrid Cross 

Cross between two individuals identically heterozygous for alleles of one gene; for example, Aa x Aa.

Punnett Square

Diagram used to predict the genotypic and phenotypic outcomes of a cross

Testcross

Method of determining the genotype of an individual with a dominant phenotype: a cross between the individual and another individual know to be homozygous recessive.

dihybrid cross

Cross between two individuals identically heterozygous for alleles of two genes; for example AaBb xAaBb.

Law of independent assortment 

During meiosis, alleles at one gene locus on homologous chromosomes tend to be distributed into gametes independently of alleles at other loci.

Linkage group

A set of genes whose alleles do not assort independently into gametes.

Codominance

The full and separate phenotypic effects of two alleles are apparent in heterozygous individuals. 

Epistasis

Form of polygenic inheritance in which the effect of an allele on a trait masks the effect of a different gene. Incomplete dominance, one allele is not fully dominant over another, so the heterozygous phenotype is an intermediate blend between the two homozygous phenotypes.

Multiple allele sytem 

Gene for which three or more alleles persist in a population at relatively high frequency. 

Peiotropic

Refers to a gene that affects multiple traits.

Polygenic inheritance 

Pattern of inheritance in which the form of a single trait is collectively determined by alleles of several genes. 

Continous Variation 

Range of small differences in a trait.