Genetic Crosses: Definitions

Gametes

Haploid sex cells capable of fusion.

Alleles

Different forms of the same gene.

Locus

The position of a gene on a chromosome.

Dominant allele

Prevents the recessive allele from working.

Recessive allele

Is prevented from working (being expressed) by the dominant allele.

Phenotype

The physical make up (appearance) of an organism when gene is physically expressed.

Genotype

The genetic make-up of an organism.

Homozygous

When two alleles are the same.

Heterozygous

When the two alleles are different.

Progeny

The offspring produced.

Monohybrid crosses

Involve the study of one characteristic.

Dihybrid crosses

Involve the study of two characteristics.

Incomplete dominance

Both alleles are expressed (Neither allele is dominant or recessive with respect to the other).

Pedigree study

A diagram showing the genetic history of a group of individuals.

Somatic cell

All the body cells except the reproductive cell.

Autosomes

All the non sex chromosomes.

Law of segregation (Mendel's first law)

Inherited characteristics are controlled by pairs of factors which separate from each other at gamete formation where only one is found in each gamete.

Law of independent assortment (Mendel's second law)

When gametes are formed either of a pair of factors is equally likely to combine with either of another pair of factors.

Linkage

When genes are located on the same chromosome.

Sex linkage

When a characteristic is controlled by a gene on the X chromosome.