Genetics and Punnett Squares - Vocabulary

Vocabulary flashcards covering key genetics concepts from the lecture notes, including Punnett squares, Mendelian genetics, and common exceptions.

Punnett square

A diagram that shows the possible gametes, genotypes, and phenotypes of offspring from a cross, along with the associated probabilities.

Genotype

The genetic makeup of an organism—the specific alleles it carries (e.g., TT, Tt, tt).

Phenotype

The observable traits or characteristics of an organism, determined by its genotype and environment.

Homozygous dominant

Having two dominant alleles for a gene (e.g., TT).

Homozygous recessive

Having two recessive alleles for a gene (e.g., tt).

Heterozygous

Having one dominant and one recessive allele for a gene (e.g., Tt).

Dominant allele

An allele that is expressed in the phenotype when present, often masking the recessive allele in a heterozygote.

Recessive allele

An allele whose effect is masked in a heterozygote and is usually expressed only in homozygous recessive individuals.

Genotypic ratio

The relative proportions of the different genotypes (e.g., TT:Tt:tt = 1:2:1 in a monohybrid cross).

Phenotypic ratio

The relative proportions of observable traits among offspring (e.g., 3:1 for tall:short in a simple dominance cross).

Law of Segregation

During gamete formation, the two alleles for a gene separate so each gamete carries one allele.

Law of Independent Assortment

Genes on different chromosomes assort independently during gamete formation, producing various allele combinations.

Dihybrid cross

A cross examining two traits at once, often resulting in a 9:3:3:1 phenotypic ratio under complete dominance.

FOIL method

A method (First-Outer-Inner-Last) to list all possible allele combinations for two genes in a dihybrid cross.

Codominance

A pattern where both alleles are fully expressed in the phenotype (e.g., AB blood type expresses both A and B antigens).

Incomplete dominance

A pattern where neither allele dominates completely, yielding an intermediate phenotype (blending).

Pleiotropy

When one gene influences multiple, seemingly unrelated traits.

Epistasis

When the expression of one gene masks or modifies the expression of another gene.

Polygenic inheritance

A trait controlled by many genes, often producing continuous variation (e.g., height, skin color).

Autosomes

Chromosomes 1 through 22 that are the same in both sexes.

Sex chromosomes

Chromosome pair 23 (X and Y) that determines sex; females are XX, males are XY in humans.

X-linked recessive

Traits on the X chromosome that are more commonly expressed in males; females can be carriers.

Color blindness

An X-linked recessive disorder affecting red-green color perception due to cone abnormalities in the retina.

ABO blood types

Blood type determined by codominant IA and IB alleles and recessive i; phenotypes A, B, AB, and O.

Calico cats (sex-linked trait)

Calico coloration in cats results from X chromosome inactivation in heterozygous females, a sex-linked trait.

Crossing over

Exchange of genetic material between homologous chromosomes during meiosis, affecting linkage.

Linkage

Genes located close together on the same chromosome tend to be inherited together unless separated by crossing over.