Principles of Inheritance and Variation

Vocabulary flashcards covering the principles of inheritance and variation, Mendelian genetics, chromosomal theory, and genetic disorders based on the lecture transcript.

Genetics

The branch of science that deals with the study of heredity and inherited variations.

Heredity

The transmission of traits from one generation to next generation.

Inheritance

The process in which the characteristics of parents are transferred to the offsprings.

Variations

The differences among the members of species and offsprings of the same parents, which help organisms adapt to changing environments.

Gene

The units of inheritance; an inherited factor that determines a biological character of an organism.

Alleles

The two alternative forms of the same gene.

Homozygous

A condition where both the alleles representing a character are similar, such as "$TT$" or "$tt$".

Heterozygous

A condition where both the alleles representing a character are dissimilar, such as "$Tt$".

Phenotype

The external observable characters of an organism.

Genotype

The internal genetic constitution of an organism.

Dominant allele

The allele which expresses itself in the presence of its contrasting allele.

Recessive allele

The allele which fails to express itself in the presence of its contrasting dominant allele.

Monohybrid cross

A cross in which the inheritance of one gene or one pair of contrasting characters is studied.

Dihybrid cross

A cross in which the inheritance of two genes or two pairs of contrasting characters are studied.

First Filial generation ($F_1$ generation)

The first generation of hybrids formed by a cross between two pure parents.

Second Filial generation ($F_2$ generation)

The progeny or offsprings produced by a cross between $F_1$ plants.

Gregor Johann Mendel

Scientist known as the Father of Genetics who proposed the rules of inheritance.

Pisum sativum

The scientific name of the Garden Pea plant selected by Mendel for breeding experiments.

Law of Dominance

A Mendelian law stating that characters are controlled by factors occurring in pairs, where one member dominates the other in a dissimilar pair.

Law of Segregation

Also called the Law of Purity of Gametes, it states that alleles do not blend but separate during gamete formation so each gamete receives only one allele.

Law of Independent Assortment

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

Test Cross

A cross between an $F_1$ individual and the recessive parent, used to determine the genotype of an individual.

Incomplete Dominance

A phenomenon where neither allele is fully dominant, resulting in an intermediate hybrid phenotype, such as pink flowers in Snapdragon.

Co-dominance

A phenomenon in which both alleles are able to express themselves completely and independently when present together, as in ABO blood groups.

Gene I

The gene that controls ABO blood groups in humans, which has three alleles: $I^A$, $I^B$, and $i$.

Multiple Alleles

The presence of more than two alleles governing the same character within a population, such as the alleles for human blood groups.

Pleiotropy

A phenomenon where a single gene exhibits multiple phenotypic effects, such as the gene causing Phenylketonuria.

Polygenic Inheritance

Traits controlled by three or more genes where the phenotype reflects the additive contribution of each allele, such as human skin colour.

Chromosomal Theory of Inheritance

Theory proposed by Walter Sutton and Theodore Boveri in $1902$ noting that chromosome behavior is parallel to the behavior of genes.

Drosophila melanogaster

The fruit fly organism used by Thomas Hunt Morgan to study sex-linked genes, linkage, and recombination.

Linkage

The physical association or linkage of two genes present on a single chromosome.

Recombination

The generation of non-parental gene combinations during reproduction.

Alfred Sturtevant

A student of Morgan who used recombination frequency between gene pairs to map their positions on the chromosome.

Haplodiploid Sex Determination

The mechanism in honey bees where fertilized eggs develop into females ($2n=32$) and unfertilized eggs develop into males (drones, $n=16$) via parthenogenesis.

Male Heterogamety

A system where males produce two different types of gametes (e.g., $XO$ in grasshoppers or $XY$ in humans).

Female Heterogamety

A system where females produce two different types of gametes, seen in birds ($ZZ-ZW$ system).

Mutation

A phenomenon resulting in the alteration of DNA sequences, leading to changes in genotype and phenotype.

Point Mutation

A mutation arising from a change in a single base pair of DNA, as seen in Sickle Cell Anaemia.

Mutagens

Physical, chemical, or biological factors (such as UV rays, nicotine, or viruses) that induce mutations.

Pedigree Analysis

The analysis and representation of a particular trait across several generations of a human family tree.

Haemophilia

A sex-linked recessive disorder where a protein cascade needed for blood clotting is affected, resulting in non-stop bleeding.

Sickle-Cell Anaemia

An autosome-linked recessive trait caused by the substitution of Glutamic acid by Valine at the sixth position of the beta globin chain.

Phenylketonuria

An inborn error of metabolism where the lack of the enzyme phenylalanine hydroxylase leads to mental retardation and pigment reduction.

Thalassemia

An autosome-linked quantitative blood disease resulting in a reduced rate of synthesis of alpha or beta globin chains in haemoglobin.

Aneuploidy

The gain or loss of individual chromosomes due to failure of chromatid segregation during cell division.

Polyploidy

An increase in a whole set of chromosomes, often seen in plants, resulting from a failure of cytokinesis after telophase.

Down's Syndrome

A genetic disorder caused by the trisomy of chromosome $21$, leading to short stature and mental retardation.

Klinefelter’s Syndrome

A genetic disorder in males caused by an extra X-chromosome ($47, XXY$), leading to masculine development with expressed feminine features.

Turner’s Syndrome

A genetic disorder in females caused by the absence of one X chromosome ($45, XO$), resulting in sterility and underdeveloped ovaries.