Module 7: Genetics, populations, evolution and ecosystems

7.1 Inheritance

Gene

A sequence of DNA that codes for a specific polypeptide (protein). It is found at a specific locus.

Allele

A version of a gene. Different alleles may produce different phenotypes.

Locus

The specific, fixed position of a gene on a chromosome.

Genotype

The alleles an organism has for a particular gene or genes - the genetic constitution/makeup of an organism.

Phenotype

The observable characteristics of an organism, determined by genotype and environment.

Homozygous

Both alleles for a gene are the same.

Heterozygous

Two different alleles are present for a gene.

In heterozygous individuals, the dominant allele is expressed in the phenotype.

Dominant allele

Expressed in the phenotype even if only one copy is present.

Recessive allele

Only expressed when there is no dominant allele present.

Codominant

Both alleles are expressed in the phenotype if present.

Diploid

A cell with two sets of chromosomes (one from each parent).

Haploid

A cell with one set of chromosomes (single chromosomes).

Epistasis

When one gene affects or masks the expression of another gene at a different locus.

Sex Linkage

When a gene is located on a sex chromosome (usually the X chromosome in humans).

Autosomal Linkage

When two or more genes are located on the same autosome (non-sex chromosomes) and are inherited together.