Genetics and Patterns of Inheritance

Vocabulary practice flashcards covering Mendelian and non-Mendelian genetics, monohybrid and dihybrid crosses, ABO blood types, X-linked inheritance, pedigrees, and practice problem terminology.

Monohybrid Cross

A cross between two heterozygotes that each carry two different alleles for a gene, typically producing a $3:1$ offspring phenotype ratio.

Mendel's Dihybrid Cross

A mating event between two organisms that are each heterozygous for two separate genes, commonly analyzed using the FOIL method.

Homozygous

An individual or genotype possessing two identical alleles for a specific gene (such as $RR$, $rr$, $I^A I^A$, or $ii$).

Heterozygous

An individual or genotype possessing two different alleles for a specific gene (such as $Rr$ or $I^A i$).

Genotype

The specific genetic composition of someone's genes.

Phenotype

The observable physical traits or characteristics of an organism, which can arise from more than one genotype.

Complete Dominance

An inheritance pattern in which only one allele in the genotype is expressed and observed in the phenotype.

Incomplete Dominance

A non-Mendelian inheritance pattern where neither allele is completely dominant over the other, causing the alleles to mix together so that a mixture or intermediate blend is seen in the phenotype (such as pink $Rr$ petunias from red $RR$ and white $rr$ parents).

Codominance

A non-Mendelian inheritance pattern where traits from both alleles in the genotype show up simultaneously in the offspring, meaning both alleles are expressed (such as roan cattle displaying both red and white hair, or type $AB$ blood).

Mendel's Law

The principle that paired unit factors (genes) must segregate equally into gametes so that offspring have an equal likelihood of inheriting each factor, resulting in gametes that carry only one allele for a gene.

ABO Gene

The gene responsible for building antigens on red blood cell membranes, featuring alleles $I^A$ (type A antigen), $I^B$ (type B antigen), and $I^C$ (no antigen).

Type AB Blood

A blood type resulting from the codominant genotype $I^A I^B$ that can receive blood from everyone.

Type O Blood

A blood type resulting from the homozygous genotype $ii$ with no antigens on the red blood cell surface; it can donate blood to everyone but can only receive blood from type O.

Rh Factor

A specific protein located on the surface of red blood cells; blood type is designated as positive (+$) if the protein is present and negative (-$$) if it is absent.

X-Linked Gene

A gene located on the X chromosome.

Hemizygous

Having only one copy of an X-linked gene, typical of human males who possess one X chromosome and one Y chromosome.

Crisscross Inheritance

A pattern of inheritance in which male and female phenotypes switch from one generation to the next.

Autosome

Any chromosome that is not a sex chromosome.

Autosomal Dominant Allele

An allele on a non-sex chromosome that is expressed in both homozygotes and heterozygotes.

Autosomal Recessive Allele

An allele on a non-sex chromosome that is expressed only in homozygotes.

Hemophilia

A non-Mendelian, sex-linked recessive disorder that prevents platelets from clotting blood, which is more commonly expressed in $XY$ genotypes than $XX$.

Pedigree

A diagram used to track an inherited trait across generations, using circles for females, squares for males, shaded shapes for tracked traits, and half-shaded shapes for carriers.

Roan

A blending coat color phenotype in cattle possessing both red and white hair, resulting from a mating involving red ($RR$) and white ($rr$) alleles.

X-Linked Colorblindness

A sex-linked trait in humans carried on the X chromosome, where $X^N$ represents the normal vision allele and $X^n$ represents the recessive colorblind allele.

Non-Mendelian Traits

Traits that do not follow traditional Mendelian rules, meaning the dominant allele does not always simply mask the recessive allele.