Biological Basis of Inheritance and Mendelian Genetics

A set of vocabulary flashcards covering the biological basis of inheritance, Mendelian genetics, laws of segregation and independent assortment, and basic genetic problem-solving terminology.

Diploid ($2n$)

Human somatic cells containing homologous pairs of chromosomes.

Homologous Chromosomes

Chromosome pairs (one from the maternal parent, one from the paternal parent) that carry the same genes at the same loci.

Homozygous Alleles

Identical versions of a gene on both homologs, such as $B$ and $B$.

Heterozygous Alleles

Different versions of a gene on homologous chromosomes, such as $B$ on the maternal chromosome and $b$ on the paternal chromosome.

Meiosis

The process that reduces the diploid ($2n$) state to the haploid ($n$) state to produce gametes (sperm and egg).

Fertilization

The fusion of haploid gametes that results in the formation of a diploid zygote, restoring homologous pairs.

Blending Theory

A prior biological theory suggesting that offspring were a uniform intermediate blend of their parents, such as a black dog and white dog producing a gray dog.

$$Pisum sativum$$

The scientific name for the pea plant model system used by Gregor Mendel.

Self-fertilization

A mating technique in plants where pollen from anthers is transferred to the ovules of the same flower.

Cross-fertilization

A mating technique involving the transfer of pollen from the anthers of one plant to the ovules of a different plant.

Antagonistic Traits

Discontinuous variation where traits are "either/or," such as seeds being either yellow or green with no intermediate blending.

Phenotype

The observable physical appearance or functional trait of an organism, such as flower color.

Genotype

The specific genetic makeup or combination of alleles an individual possesses, such as $PP$, $Pp$, or $pp$.

Dominant Allele

An allele that is expressed over another when both are present, typically denoted by an uppercase letter.

Recessive Allele

An allele whose phenotype is hidden when a dominant allele is present, typically denoted by a lowercase letter.

Homozygous Dominant

A genotype possessing two dominant alleles, represented as $PP$.

Homozygous Recessive

A genotype possessing two recessive alleles, represented as $pp$.

Heterozygous

A genotype possessing one dominant and one recessive allele, represented as $Pp$, with no such thing as "heterozygous dominant" or "heterozygous recessive."

Mendel’s Law of Segregation

The principle that every individual carries two alleles for each gene, and these alleles separate into different gametes during gamete formation.

P Generation

The parental generation in a genetic cross, typically involving pure-breeding (homozygous) individuals.

$F_1$ Generation

The first filial generation resulting from a $P$ generation cross; in Mendel's purple vs. white cross, all were heterozygous ($Pp$) with a purple phenotype.

$F_2$ Generation

The second filial generation resulting from crossing two $F_1$ heterozygotes ($Pp \times Pp$).

Monohybrid Cross Phenotypic Ratio

The $3:1$ ratio (three dominant to one recessive) observed in the $F_2$ generation.

Monohybrid Cross Genotypic Ratio

The $1:2:1$ ratio ($1$ $PP$ : $2$ $Pp$ : $1$ $pp$) observed in the $F_2$ generation.

Test Cross

A procedure used to determine an unknown genotype of a dominant phenotype by crossing the unknown individual with a homozygous recessive ($pp$) individual.

Mendel’s Law of Independent Assortment

The principle that the segregation of alleles for one gene occurs independently of the segregation of alleles for another gene.

Dihybrid Cross

Tracking two genes on different chromosomes simultaneously, which results in a $9:3:3:1$ phenotypic ratio in the $F_{2}$ generation if independent assortment occurs.

Metaphase I

The stage of meiosis where random alignment of homologous chromosome pairs (tetrads) on the metaphase plate provides the meiotic basis for independent assortment.

Carriers

Healthy heterozygous genotypes ($Ff$) in human genetics that possess one recessive allele for a condition, such as cystic fibrosis, but do not display the disease phenotype.