Unit 5: Heredity & The Mendelian Model

Gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA.

Locus

The specific physical location of a gene on a chromosome.

Allele

Alternative versions of a gene that may produce distinguishable phenotypic effects.

Genotype

The genetic makeup, or set of alleles, of an organism.

Phenotype

The observable physical and physiological traits of an organism.

Homozygous

Having two identical alleles for a given gene.

Heterozygous

Having two different alleles for a given gene.

P Generation

The parental generation in a genetic cross.

F1 Generation

The first filial, hybrid offspring arising from a P generation cross.

F2 Generation

The offspring resulting from interbreeding of the F1 generation.

Law of Segregation

States that the two alleles for a heritable character segregate during gamete formation.

Anaphase I

The stage in meiosis when homologous chromosomes separate.

Monohybrid Cross

A cross between heterozygotes for a single character.

Phenotypic Ratio

The relative number of different phenotypes in the offspring.

Genotypic Ratio

The relative number of different genotypes in the offspring.

Multiplication Rule

Used to determine the probability that two independent events will occur together.

Addition Rule

Used to determine the probability that any one of two or more mutually exclusive events will occur.

Law of Independent Assortment

States that each pair of alleles segregates independently during gamete formation.

Dihybrid Cross

A cross between individuals heterozygous for two characters.

Chi-Square Test

A statistical test used to determine if there is a significant difference between observed and expected frequencies.

Null Hypothesis (H0)

States that there is no significant difference between observed and expected frequencies.

Degrees of Freedom (df)

The number of categories minus one used in the Chi-Square Test.

Observed Number (o)

The actual data collected in an experiment.

Expected Number (e)

The expected data based on Mendel's ratios.

Critical Value

The value used to determine if the observed chi-square statistic is significant or not.

Linkage

The tendency of genes located close together on a chromosome to be inherited together.

Dominant Allele

An allele that masks the effect of a recessive allele in a heterozygote.

Recessive Allele

An allele whose effect is masked by a dominant allele in a heterozygote.