Genetics: The Basic Principles of Heredity Chapter 12

Comprehensive vocabulary flashcards covering basic heredity, Mendelian principles, molecular genetics terminology, and human inheritance patterns including sex-linkage and blood groups.

Gregor Mendel

A 19th-century monk (1822–1884) who began the scientific study of inheritance by breeding pea plants to identify inheritance patterns.

Heredity

The transmission of genetic information from parent to offspring, which generally follows predictable patterns.

Genetics

The science of heredity.

True-breeding organisms

Organisms that are genetically pure for a specific trait, meaning they will only produce offspring with that same trait when mated with another true-breeding organism for that trait.

Hybrids

Offspring produced from the mating of two genetically different true-breeding parents.

Pisum sativum

The scientific name for the garden pea plants Mendel used in his inheritance studies.

Phenotype

The physical appearance of an organism.

Genotype

The genetic makeup of an organism.

P generation

The parental generation, consisting of genetically pure individuals with two different phenotypes.

F1 generation

The first generation of offspring, all of which look alike and resemble one of the two parents; these individuals are considered hybrids.

F2 generation

The second generation of offspring, resulting from a cross between two $F1$ individuals or by self-pollination of an $F1$ individual.

Dominant trait

A hereditary factor that masks the expression of a hidden (recessive) trait in the $F1$ generation when both are present in the same individual.

Recessive trait

A hereditary factor whose expression is hidden in the $F1$ generation but can reappear in the $F2$ generation.

Alleles

Different forms of a particular gene (such as $T$ and $t$) that occupy corresponding loci on homologous chromosomes.

Locus

The specific site a gene occupies on a chromosome; plural is loci.

Homozygous

An individual that carries two identical alleles for a specific locus, such as $TT$ or $tt$.

Heterozygous

An individual that carries two different alleles for a specific locus, such as $Tt$..

Mendel’s Principle of Segregation

The principle stating that during meiosis, alleles for one locus separate from each other so that each haploid gamete contains only one allele for each locus.

Monohybrid Cross

A cross between parents that takes into account alleles at only one locus, typically resulting in a $3:1$ phenotypic ratio in the $F2$ generation.

Dihybrid Cross

A cross between parents that takes into account alleles at two different loci.

Punnett Square

A grid-based method used to predict the genotypes and phenotypes of offspring from a genetic cross.

Mendel’s Principle of Independent Assortment

The principle stating that alleles of different loci are distributed randomly into gametes during meiosis, and the segregation of one set of alleles does not affect another.

Product Rule

Also known as the multiplication rule, it states that the probability of two independent events occurring together is calculated by multiplying the probabilities of each event occurring separately.

Autosomes

The 22 pairs of chromosomes in humans that are not sex chromosomes.

Sex Chromosomes

The pair of chromosomes ($X$ and $Y$ in mammals) that determine the sex of an individual; females are $XX$ and males are $XY$.

SRY gene

A gene on the $Y$ chromosome that acts as a genetic switch causing testes to develop in a fetus.

Incomplete Dominance

An inheritance pattern where the heterozygote exhibits a phenotype that is intermediate between the two homozygotes.

Codominance

An inheritance pattern where the heterozygote simultaneously expresses the phenotypes of both homozygotes, such as in the $AB$ blood type.

ABO Blood Group Alleles

The three alleles ($IA$, $IB$, and $i$) that control blood types, where $IA$ and $IB$ are codominant to each other and both are dominant over $i$.

X-linked genes

Genes located on the $X$ chromosome; females have two alleles for these genes while males have only one and will express whatever allele they possess.