6 Genetic Risk Assessment of Single Gene Inherited Conditions

Vocabulary flashcards focusing on key concepts, definitions, pedigree symbols, probability rules, and genetic principles in single gene inheritance.

Principle of Segregation

A Mendelian law stating that sexually reproducing organisms possess genes that occur in pairs, and only one member of each pair is transmitted to a given offspring.

Principle of Independent Assortment

A Mendelian law stating that genes located at different genetic loci are transmitted independently of one another during gamete formation.

Dominant Allele

An allele that exerts its phenotypic effect in both homozygous ($HH$ or $AA$) and heterozygous ($Hh$ or $Aa$) forms, masking recessive alleles.

Recessive Allele

An allele whose phenotypic effects are masked by a dominant allele, becoming observable only when present in the homozygous form ($hh$ or $aa$).

Phenotype

The physically or clinically observed characteristics of an individual, resulting from the interaction of their genotype with environmental factors.

Genotype

An individual's genetic constitution at a particular locus.

Phenylketonuria (PKU)

An autosomal recessive metabolic disorder caused by mutations in the phenylalanine hydroxylase ($PAH$) gene, leading to an inability to metabolize phenylalanine.

Pedigree

A diagrammatic representation showing relationships among family members and tracking the transmission of traits or diseases across generations.

Proband

The first affected individual in a family who is diagnosed or brings the family to medical attention, designated in a pedigree chart by an arrow.

First-Degree Relatives

Family members related at the parent-offspring or sibling level.

Second-Degree Relatives

Family members removed by one additional generational step, such as grandparents, grandchildren, aunts, uncles, nieces, and nephews.

Third-Degree Relatives

Family members removed by two generational steps beyond first-degree relatives, such as first cousins and great-grandchildren.

Allele

Alternate forms of a gene at a specific chromosomal locus, inherited from each parent.

Autosomal Chromosome

Any chromosome other than a sex chromosome ($X$ or $Y$).

Homozygous

Having two identical alleles at a particular genetic locus.

Heterozygous

Having two different alleles at a particular genetic locus.

Multiplication Rule

A probability rule stating that if two events are independent, the probability of obtaining a given outcome in both trials is the product of their individual probabilities.

Addition Rule

A probability rule stating that the probability of obtaining either one outcome or another mutually exclusive outcome is calculated by adding their individual probabilities together.

CFTR Gene

The cystic fibrosis transmembrane regulator gene, which encodes a chloride ion channel and whose mutations cause cystic fibrosis.

Hardy-Weinberg Principle

A mathematical law establishing that gene and genotype frequencies in a large, randomly mating population remain constant in the absence of selection ($p + q = 1.0$ and $p^2 + 2pq + q^2 = 1.0$).

Fetus

In humans, the unborn young from the end of the eighth week after conception to birth.

Female Biological Symbol

Standard botanical/biological symbol used in pedigree charts to designate a female individual.

Male Biological Symbol

Standard botanical/biological symbol used in pedigree charts to designate a male individual.

Dihybrid Cross Phenotypic Ratio

The expected $9:3:3:1$ ratio of phenotypic outcomes produced by crossing two individuals heterozygous at two unlinked autosomal loci ($AaDd \times AaDd$).