Principles of Inheritance and Variations

Comprehensive vocabulary flashcards covering the principles of inheritance, Mendelian laws, non-Mendelian inheritance patterns, linkage, and sex determination based on the provided notes.

Genetics

A branch of biology that deals with the study of inheritance and variations.

Variation

The degree of difference between parent and progenies.

Inheritance

The process by which characters are passed from parents to offsprings; it is the "Basis of Heredity."

Sahiwal cows of Punjab

A breed made by artificial selection and domestication of ancestral wild cows.

Character

A general feature studied in heredity, such as hair colour or eye colour.

Trait

The specific expression of a character, such as blue eyes or black eyes.

Gene

A coding fragment of DNA that expresses itself by making RNA and protein; Mendel referred to these as "factors."

Allele (Allelomorphs)

Slightly different forms of a gene, such as the allele for tallness and the allele for dwarfness.

Dominant trait

The trait that can express itself in both homozygous ($TT$) and heterozygous ($Tt$) conditions, often denoted by a capital letter.

Recessive trait

The trait which cannot express itself in the presence of a dominant trait and is only expressed in homozygous condition ($tt$).

Homozygous

A genetic condition where both alleles are the same, such as ($TT$) or ($tt$).

Heterozygous

A genetic condition where both alleles are different, such as ($Tt$).

Phenotype

The physical expression of an individual's visible characters, such as being tall or dwarf.

Genotype

The genetic constitution of a character, such as whether a tall plant is pure ($TT$) or heterozygous ($Tt$).

Gregor Mendel

The father of Genetics who conducted hybridization experiments on Pea plants for 7 years ($1856-1863$).

Monohybrid Cross Phenotypic Ratio

The $3:1$ ratio of traits (e.g., Tall to Dwarf) observed in the F2 generation of a cross involving one gene.

Monohybrid Cross Genotypic Ratio

The $1:2:1$ ratio ($TT:Tt:tt$) observed in the F2 generation of a cross involving one gene.

Reginald C. Punnett

The British Geneticist who developed the Punnett square to visualize all possible genetic combinations.

Test Cross

A cross of a progeny with the recessive parent only to determine the unknown genotype of the progeny.

Law of Dominance

Mendel's First Law suggesting that in a heterozygous condition, only one factor (dominant) will express itself.

Law of Segregation

Mendel's Second Law, also called the "Law of purity of gametes," stating factors segregate during gamete formation so a gamete carries only one factor.

Incomplete Dominance

A condition where neither allele is fully dominant, resulting in an intermediate phenotype like the pink flowers in Snapdragon ($Antirrhinium$).

Co-dominance

A condition where both alleles of a gene are expressed together in a hybrid, such as ABO blood grouping in humans.

Multiple Allelism

When more than two alleles govern the same character at a population level, such as the three alleles ($I^A$, $I^B$, and $i$) for ABO blood group.

Polygenic Inheritance

The inheritance of traits controlled by three or more genes, such as human skin colour or height, where the environment also plays a role.

Pleiotropy

A condition where a single gene controls multiple phenotypic expressions, such as the mutation causing Phenylketonuria.

Dihybrid Cross Phenotypic Ratio

The $9:3:3:1$ ratio observed in the F2 generation when Mendel crossed plants differing in seed shape and seed colour.

Law of Independent Assortment

States that when two pairs of traits are combined in a hybrid, the segregation of one pair of characters is independent of the other pair.

Chromosomal Theory of Inheritance

Proposed by Sutton & Boveri in $1902$, suggesting chromosomes are the vehicles of heredity that carry genes to the next generation.

T.H. Morgan

Known as the "flyman of genetics," he worked on $Drosophila\,melanogaster$ to prove the chromosomal theory of inheritance.

Linkage

The physical association of two or more genes on a chromosome; linked genes do not assort independently.

Recombination

The generation of non-parental gene combinations, which increases as the distance between genes on a chromosome increases.

Alfred Sturtevant

A scientist who used recombination frequency to map the position of genes on chromosomes, creating genetic maps.

Henking

In $1891$, he studied spermatogenesis in insects and observed a special structure he called the "X-body," later identified as the X-chromosome.

Haplo-diploid sex determination

Mechanism in Honey Bees where males (Drones) are haploid ($n=16$) and females (Queens and Workers) are diploid ($2n=32$).

Point Mutation

A mutation resulting from a change in a single base pair of DNA, exemplified by Sickle cell anemia.