Mendel's Experiments and Heredity

A comprehensive set of vocabulary flashcards covering Mendel's experiments, laws of inheritance, and extensions of Mendelian genetics based on the provided lecture notes.

Johann Gregor Mendel

Considered the father of genetics, he was an Austrian monk who set the framework for genetics by conducting methodical, quantitative analyses of garden peas.

Genetics

The science of heredity.

Model system

A system with convenient characteristics used to study a specific biological phenomenon to be applied to other systems.

Continuous variation

A distribution of phenotypes in which offspring appear to be a blend of their parents' traits, resulting from the action of many genes determining a characteristic like human height.

Blending theory of inheritance

An incorrect hypothetical process asserting that original parental traits were lost or absorbed by blending in the offspring to produce an intermediate physical appearance.

Discontinuous variation

The inheritance of traits in distinct classes, such as violet versus white flowers, where traits maintain their distinctness and do not blend.

$$Pisum \, sativum$$

The scientific name for the garden pea, which naturally self-fertilizes and was the species used in Mendel’s seminal work on inheritance.

True-breeding

Highly inbred organisms that always produce offspring that look like the parent.

Hybridizations

The process of mating two true-breeding individuals that have different traits.

P0

The parental generation one, representing the plants used in first-generation crosses.

F1

The first filial generation, or the first generation of offspring resulting from a cross of the parental generation.

F2

The second filial generation, produced when F1 offspring are allowed to self-fertilize naturally.

Trait

A variation in the physical appearance of a heritable characteristic.

Reciprocal cross

A paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross.

Dominant traits

Traits that are inherited unchanged in a hybridization, concealing the presence of another trait.

Recessive traits

Traits that become latent or disappear in the F1 offspring of a hybridization, only to reappear in the F2 generation at a ratio of approximately 3:1.

Empirical probability

A mathematical measure of likelihood calculated by dividing the number of times an event occurs by the total number of opportunities for the event to occur.

Theoretical probability

A measure of likelihood calculated by dividing the number of times an event is expected to occur by the total possible outcomes.

Product rule

A rule of probability stating that the probability of two independent events occurring together can be calculated by multiplying the individual probabilities of each event.

Sum rule

A rule of probability stating that the probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities.

Alleles

Gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes.

Phenotype

The observable traits expressed by an organism.

Genotype

An organism’s underlying genetic makeup, consisting of both physically visible and non-expressed alleles.

Homozygous

A diploid organism that has two identical alleles for a given gene on their homologous chromosomes.

Heterozygous

A diploid organism that has different alleles for the gene being examined.

Incomplete dominance

A pattern of inheritance in which the heterozygote exhibits a phenotype that is intermediate between the homozygous phenotypes, such as pink flowers from red and white parents.

Codominance

A variation of inheritance in which both alleles for the same characteristic are simultaneously and equally expressed in the heterozygote, such as MN blood groups in humans.

Wild type

The most common phenotype or genotype among natural populations, often abbreviated with a plus ($+$) sign, considered the standard or norm.

X-linked

A description of a gene that is present on the X chromosome but not on the Y chromosome.

Hemizygous

The condition of having only one allele for any X-linked characteristic, making descriptions of dominance and recessiveness irrelevant for males in XY systems.

Recessive lethal

An inheritance pattern in which an allele is only lethal in the homozygous form and the heterozygote may be normal or have an altered non-lethal phenotype.

Dominant lethal

An inheritance pattern in which an allele is lethal in both the homozygote and the heterozygote, such as the Huntington allele in humans.

Law of segregation

Mendel's postulate stating that paired unit factors (genes) must segregate equally into gametes such that offspring have an equal likelihood of inheriting either factor.

Law of independent assortment

Mendel's postulate stating that genes do not influence each other with regard to the sorting of alleles into gametes, and every possible combination of alleles for every gene is equally likely.

Dihybrid cross

A cross between two true-breeding parents that express different traits for two characteristics, resulting in a phenotypic ratio of 9:3:3:1.

Test cross

A technique used to determine whether an organism expressing a dominant trait is a heterozygote or a homozygote by crossing it with a homozygous recessive organism.

Linked genes

Genes that are located physically close to each other on the same chromosome and are more likely to be inherited as a pair, violating the law of independent assortment.

Recombination (crossover)

The process by which homologous chromosomes exchange linear segments of genetic material during the first division of meiosis.

Epistasis

An interaction between genes where one gene masks or interferes with the expression of another gene, such as pigmentation in mice or seed shape in shepherd’s-purse.