(CIE A2 Biology) Phenotypic variation (based on SaveMyExams revision notes)

Phenotype

The observable characteristics of an organism.

Phenotypic variation

The difference in phenotypes between organisms of the same species.

Genotype

The genetic constitution of an organism.

Genetic variation

The small differences in DNA base sequences between individual organisms within a species population.

Discontinuous variation

Variation that occurs where qualitative differences fall into distinct, non-overlapping categories.

Continuous variation

Variation characterized by quantitative differences that form a range of values between two extremes.

Independent assortment

The random alignment of chromosomes during metaphase I leading to different combinations of alleles in gametes.

Crossing over

The exchange of genetic material between non-sister chromatids during prophase I.

Mutation

A random change in the DNA base sequence that generates a new allele.

Polygenes

Multiple genes that together influence a phenotype in a cumulative manner.

Additive effect of genes

When different alleles at various loci combine to produce a cumulative effect on a phenotype.

Homozygous

An organism with two identical alleles for a given gene.

Heterozygous

An organism with two different alleles for a given gene.

ABO gene

The gene that determines blood group in humans.

Sickle cell anaemia

A genetic condition caused by a recessive allele that affects the shape of red blood cells.

Environmental factors

External conditions, such as sunlight, nutrients, and temperature, that can affect an organism's phenotype.

Gamete

A reproductive cell (sperm or egg) that carries genes to the next generation.