Mendels postulates - intro to genetics

Mendel's Postulates

Principles established by Gregor Mendel stating that genes are passed down in pairs as discrete units (alleles), that alleles segregate independently during gamete formation, and that dominant alleles mask recessive ones.

Segregation (Principle of Segregation)

Mendel’s first law stating that allele pairs separate (segregate) during gamete formation, so that each gamete carries only one allele for each gene.

Independent Assortment

Mendel’s second law stating that genes for different traits segregate independently of one another during gamete formation, provided the genes are on separate chromosomes or far apart on the same chromosome.

Dominant Allele

An allele that expresses its phenotypic trait even when present in a single copy (heterozygous state).

Recessive Allele

An allele whose phenotypic effect is masked in a heterozygote and is only expressed when two copies are present (homozygous recessive).

Homozygous

Having two identical alleles for a particular gene (e.g., $WW$ or $ww$).

Heterozygous

Having two different alleles for a particular gene (e.g., $Ww$).

Hemizygous

Having only a single copy of a gene for a diploid organism—typically used for genes on sex chromosomes or for transgenic individuals with a single inserted transgene copy.

Genotype

The genetic makeup or allele combination of an organism (e.g., $WwGg$).

Phenotype

The observable physical or biochemical characteristics of an organism, resulting from its genotype and environment (e.g., round yellow seeds).

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Locus (pl. Loci)

The specific physical location of a gene or DNA sequence on a chromosome.

True-Breeding Line

A group of genetically identical individuals that consistently offspring with the same phenotype when self-pollinated over generations.

Monohybrid Cross

A genetic cross between two individuals involving one trait or gene locus.

Dihybrid Cross

A genetic cross between two individuals involving two traits or gene loci.

Testcross

A cross between an individual of unknown dominant genotype and a fully recessive tester (homozygous recessive) to determine whether the unknown individual is homozygous or heterozygous.

Self-Pollination / Selfed

The fertilization of a plant by pollen from the same flower or another flower on the same plant.

Punnett Square

A diagram used to predict the genotypes and phenotypes of a cross between organisms of known genetic makeup.

Forked-Line Method

A probability-based branching method used to calculate the expected frequencies of genotypes or phenotypes in multi-gene crosses without a large Punnett square.

Progeny

The offspring produced by a mating or cross.

Wildtype

The standard, non-mutant phenotype or genotype most commonly found in natural populations.

Transgene

A gene or genetic material that has been transferred naturally or by genetic engineering techniques from one organism to another.