Single Gene Inheritance and Genetics Principles

This set of vocabulary flashcards covers key genetic concepts include single gene inheritance patterns, probability rules, human genetic diseases, and non-Mendelian gene interactions based on the lecture transcript.

Locus

The specific physical location of a gene on a chromosome.

Allele

A version of a gene; at a single locus with two alleles, one is typically dominant and one is recessive.

Homozygous Dominant

A genotype consisting of two dominant alleles (e.g., $AA$).

Homozygous Recessive

A genotype consisting of two recessive alleles (e.g., $aa$).

Heterozygous

A genotype consisting of one dominant allele and one recessive allele (e.g., $Aa$).

Law of Independent Assortment

Mendel's law stating that tetrads (homologous chromosome pairs) align independently on the metaphase plate during Meiosis I, ensuring the alignment of one tetrad does not influence another.

Tetrads

Homologous chromosome pairs that align independently on the metaphase plate during Meiosis I.

Haploid ($n$)

The cellular state of gametes, meaning they contain only one allele per locus and cannot have two alleles for the same gene (e.g., a gamete cannot be $HH$).

Test Cross

A cross used to determine the genotype of an individual expressing a dominant phenotype by crossing them with a known homozygous recessive partner.

Starch Branching Enzyme ($SBE1$)

An enzyme encoded by the $R$ allele that allows starch to branch, filling the seed and creating a round phenotype.

Stay-Green ($SGR$)

An enzyme encoded by the $Y$ locus that breaks down green pigment (chlorophyll) as a seed matures; loss-of-function alleles result in green seeds.

Rule of Multiplication

A probability rule used for independent events where the probability of both events occurring is found by $\text{Prob(A AND B)} = \text{Prob(A)} \times \text{Prob(B)}$.

Rule of Addition

A probability rule used when an event can occur in two or more mutually exclusive ways, calculated by $\text{Prob(A OR B)} = \text{Prob(A)} + \text{Prob(B)}$.

Pedigree

A family history diagram where squares represent males, circles represent females, and colored shapes indicate individuals affected by a trait.

Carriers

Healthy heterozygotes ($Aa$) who possess one recessive disease allele and can pass it on to offspring.

Huntington’s disease

A dominant genetic disease caused by a gain-of-function mutation resulting in nerve cell damage.

Achondroplasia

A dominant form of dwarfism caused by a hyperactive $FGF$ protein that inhibits bone growth.

Incomplete Dominance

An inheritance pattern where neither allele is completely dominant, resulting in a blended phenotype in heterozygotes, such as pink snapdragons ($Rr$).

Codominance

An inheritance pattern where both alleles are fully expressed in the heterozygote, as seen in ABO blood types.

Multiple Alleles (Polymorphism)

The existence of many possible alleles for a single locus within a population, even though an individual only carries two (e.g., $I^A, I^B, i$).

Polygenic Traits

Traits controlled by many genes, such as human height which is influenced by over 800 genes, leading to a continuous distribution.

Pleiotropy

A phenomenon where a single gene affects multiple seemingly unrelated traits.

Epistasis

A gene interaction where the expression of one gene masks or interferes with the expression of another gene.

Recessive Epistasis

A gene interaction resulting in a $9:3:4$ phenotype ratio where homozygous recessive alleles at one locus (e.g., $ee$ in Labradors) mask the expression of another locus.

Duplicate Recessive

A gene interaction resulting in a $9:7$ ratio where two genes are in the same pathway and a mutation in either gene leads to the same recessive phenotype.

Redundancy

A gene interaction resulting in a $15:1$ ratio because two genes perform the same function, meaning only the double homozygous recessive ($aabb$) shows the mutant phenotype.