Chapter 3- Genetics

True breeding/pure breeding

Refers to organisms that will produce offspring identical to themselves if they self-pollinate.

Principle of segregation

States that each individual has two alleles for a trait and these alleles segregate during the formation of gametes.

Principle of independent assortment

States that alleles of different genes assort independently of one another during gamete formation.

Test cross

A genetic cross between an individual showing a dominant phenotype but unknown genotype and a homozygous recessive individual.

Incomplete dominance

A genetic situation in which one allele does not completely dominate another allele, resulting in a new phenotype.

Co-dominance

A condition in which both alleles for a gene are fully expressed, leading to a phenotype that shows both traits.

Recessive lethality

Occurs when an individual inherits two copies of a recessive allele that results in death.

Incomplete penetrance (versus 100% penetrance)

Incomplete penetrance refers to a genotype not always being expressed in the phenotype, unlike 100% penetrance where the genotype always manifests.

Variable expressivity

Describes the range of phenotypes associated with a particular genotype.

Pleiotropy

Occurs when a single gene influences multiple, seemingly unrelated phenotypic traits.

Polygenic trait

A trait that is controlled by multiple genes.

Epistasis

Interaction between genes where the effect of one gene is dependent on the presence of one or more 'modifier' genes.

Epistatic

Refers to a gene that masks the effect of another gene.

Hypostatic

Refers to a gene whose effect is masked by the presence of an epistatic gene.

Null hypothesis

Baseline expectation from prior knowledge or assumptions before conducting an experiment or making observations.

Chi-square value

A statistical value calculated to determine the significance of the differences between expected and observed data.

χ2 = ∑(o-e)2/e

Formula used to calculate the chi-square value in statistical analysis.

p-value

The probability that the differences between expected and observed data are due to random chance.