genetics

genetics

the science of heredity and of the mechanisms by which traits are passed from parents to offspring

heredity

the passing of genetic traits from parent to offspring

true-breeding

describes organisms or genotypes that are homozygous for a specific trait and thus always produce offspring that have the same phenotype for that trait

P generation

parental generation, the first two individuals that mate in a genetic cross

F1 generation

the first generation of offspring obtained from an experimental cross of two organisms

F2 generation

the second generation of offspring, obtained from an experimental cross of two organisms; the offspring of the F1 generation

dominant

in genetics, describes an allele that is fully expressed whenever the allele is present in an individual

recessive

in genetics, describes an allele that is expressed only when no dominant allele is present in an individual

law of segregation

Mende's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

law of independent assortment

the law that states that genes separate independently of one another in meiosis

allele

one of the alternative forms of a gene that governs a characteristic, such as hair color

genotype

the entire genetic makeup of an organism; also the combination of genes for one or more specific traits

phenotype

an organism's appearance or other detectable characteristic that results from the organism's genotype and the environment, example: the person has brown eyes or lobed ears

homozygous

describes an individual that has identical alleles for a trait on both homologous chromosomes (GG or gg)

heterozygous

describes an individual that has two different alleles for a trait (Gg)

probability

the likelihood that a possible future event will occur in any given instance of the event; the mathematical ratio of the number of times one outcome of any event is likely to occur to the number of possible outcomes of the event

monohybrid cross

a cross between individuals that involves one pair of contrasting traits (Aa x AA, a is the single trait)

Punnett square

a graphic used to predict the results of a genetic cross

genotypic ratio

the ratio of the genotypes that appear in offspring

complete dominance

a relationship in which one allele is completely dominant over another

codominance

a condition in which both alleles for a gene are fully expressed

dihybrid cross

a cross between individuals that have different alleles for the same gene (AAbb x AaBB, A and B are the two traits)

phenotypic ratio

the ratio of phenotypes that appear in the offspring

Meiosis

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes.

Carrier

A person who has one recessive allele for a trait, but does not have the trait.

Gene

A segment of DNA on a chromosome that codes for a specific trait

homologous chromosomes

Chromosomes that have the same sequence of genes, that have the same structure, and that pair during meiosis.

egg

female gamete created in Meiosis

sperm

male gamete created in Meiosis