Chapter 8 Bio

Genetics

The study of heredity.

Mendel's Experiments

Foundation for genetics established by Johann Mendel before the identification of chromosomes or genes.

Genes

Basic functional units of heredity that can be replicated, expressed, or mutated. They are carried on chromosomes.

Model system

A system with convenient characteristics used to study a specific biological phenomenon.

Continuous variation

The range of small differences seen among individuals in a characteristic, such as human height.

Discontinuous variation

Variation among individuals where each shows one of two or a very few distinguishable traits.

Alleles

Gene variants that arise by mutation and exist at the same relative locations in homologous chromosomes.

Phenotype

Observable traits expressed by an organism.

Genotype

An organism's underlying genetic makeup, consisting of visible and non-expressed alleles.

Law of dominance

In a heterozygote, one trait will conceal the presence of another trait for the same characteristic.

Monohybrid cross

Fertilization between two true-breeding parents differing by only one characteristic.

Punett square

A tool to determine probabilities by predicting potential outcomes of fertilization events.

Law of segregation

Paired unit factors (genes) segregate equally into gametes, giving offspring equal likelihood of inheriting either factor.

Test cross

Crossing a dominant expressing organism with a homozygous recessive organism for the same characteristic.

Law of independent assortment

Genes do not influence each other regarding the sorting of alleles into gametes; combinations are equally likely.

Dihybrid cross

A cross between two true-breeding parents expressing different traits for two characteristics.

Incomplete dominance

When one allele appears in the phenotype of a heterozygote to the exclusion of another.

Codominance

Both alleles for the same characteristic are simultaneously expressed in a heterozygote.

Linked genes

Genes located physically close on the same chromosome that are inherited together.

Linkage

The tendency of genes located close to each other on the same chromosome to be inherited as a pair.