CH 4 - Single-Gene Inheritance

These flashcards cover fundamental vocabulary regarding Huntington Disease, Mendelian laws of inheritance, gene mutations, and genetic analysis techniques based on the lecture notes.

Huntington Disease

A condition beginning in early adulthood that causes uncontrollable movements and changes in behavior/cognition with death $10$ to $20$ years later due to a dominant gene.

Juvenile Huntington Disease

People who have Huntington Disease under the age of $20$.

Monogenic

A trait caused by a mutation in a single gene.

Single-Gene Predictability

The ability to deduce the probability that a person has inherited a trait based on how they are related to an affected relative.

Single-Gene Tests

Tests where all cells harbor the mutation if a person has inherited it.

Genetic Disease “Fixability”

The concept that a genetic disease may be fixable by compensating for abnormal instructions.

Modes of Inheritance

The pattern in which a gene variant passes from generation to generation; it may be dominant or recessive, autosomal, or X- or Y-linked.

Autosomal Dominant

A mode of inheritance in which one autosomal allele causes a phenotype, affecting males and females without skipping generations, such as in Huntington Disease.

Autosomal Recessive

A mode of inheritance requiring two autosomal alleles to cause a phenotype, affecting males and females and capable of skipping generations, such as in Cystic Fibrosis (CF).

De Novo

The term for a dominant mutation arising anew.

Mendelian Traits

Single-gene traits and diseases.

Gregor Mendel

Known as the “Father of genetics,” he derived two laws of inheritance determining trait transmission through breeding pea plants.

Dominant Traits

One trait that masks another.

Recessive Traits

The masked traits that are not visible when a dominant allele is present.

Heterozygotes

Individuals that hide one expression of a trait that then reappears when crossed with another heterozygote.

Law of Segregation

Mendel’s first law, stating that the alleles of a gene are distributed into separate gametes during meiosis.

Homozygous

Having two identical alleles of a gene.

Heterozygous

Having two different alleles of a gene.

Compound Heterozygote

An individual with two different recessive alleles in the same gene.

Wild Type Phenotype

The most common phenotype in a population for a particular gene.

Mutant Phenotype

An allele that differs from the most common allele in a population and alters the phenotype.

Monohybrid Cross Genotypic Ratio

The ratio derived from a monohybrid cross, expressed as $1TT:2Tt:1tt$.

Punnet Square

A diagram that follows and combines parental gene contributions to offspring.

Test Cross

Breeding an individual of unknown genotype with a homozygous recessive individual to deduce the unknown genotype from the offspring's traits.

Eumelanin

Melanin that is dark brown or black.

Pheomelanin

Melanin that is red-yellow.

Melanocytes

Cells that produce melanin.

Melanosomes

Structures in the outermost layer of the iris where melanin pigment is stored.

OCA2

A gene on chromosome $15$ that confers eye color by controlling the maturation of melanosomes.

HERC2

A second gene on chromosome $15$ that controls the expression of the OCA2 gene.

Consanguinity

Blood relatives having children together.

Loss-of-Function

A term describing recessive traits because the recessive allele usually prevents the production of the corresponding protein.

Gain-of-Function Mutation

Typically a dominant mutation that alters the encoded protein by introducing a new activity, such as in Huntington Disease.

Manifesting Heterozygote

A heterozygous individual who develops symptoms under certain circumstances.

Law of Independent Assortment

Mendel’s second law, stating that for two genes on different chromosomes, the inheritance of one gene does not influence the inheritance of the other.

Dihybrid Cross

Breeding individuals that are heterozygous for two different traits.

Product Rule

The principle that the chance of two independent events occurring equals the product of their individual chances (e.g., $\frac{1}{4}$ chance of rr and $\frac{1}{4}$ chance of yy equals $\frac{1}{16}$ chance).

Pedigrees

Charts used to display family relationships and depict which relatives have specific phenotypes or genotypes.

Conditional Probability

Occurs when an offspring’s genotype depends on the parents’ genotypes, which may not be obvious from their phenotypes.

Candidate Genes

Gene variants whose malfunction might explain specific symptoms of De Novo mutations.

Ratio for One-Gene Mendelian Inheritance

A $3:1$ phenotype ratio.

Ratio for Two-Gene Mendelian Inheritance

A $9:3:3:1$ phenotype ratio.

Family Exome Analysis

The process of sequencing the protein-coding regions of the genome for a patient and their biological parents to identify mutations (autosomal dominant if new)