Mendelism: Basic Principles of Inheritance

This set of vocabulary flashcards covers the fundamental principles of Mendelian and non-Mendelian genetics, inheritance patterns, and key terminology from Dr. Alessandro Siani's lecture.

Phenotype

An observable characteristic or trait, such as blue eyes.

Genotype

The genetic makeup of a particular trait, referring to the genes that code for a characteristic.

F1 Generation

The first filial generation, consisting of offspring produced by crossing two true-breeding homozygous strains.

F2 Generation

The second filial generation, consisting of offspring resulting from the self-fertilization of $F_1$ heterozygous plants.

Alleles

Different versions or alternative forms of the same gene.

Mendel’s 1st Law: Principle of Segregation

The principle stating that two alleles for a gene separate during gamete formation and are rejoined at random during fertilisation.

Homozygous

An individual having two identical alleles for a particular gene (e.g., $PP$ or $pp$).

Heterozygous

An individual having two different alleles for a particular gene (e.g., $Pp$).

Testcross

A technique to identify the genotype of an individual showing a dominant phenotype by crossing it with a homozygous recessive ($pp$) individual.

Mendel’s 2nd Law: Principle of Independent Assortment

The law stating that the alleles of each gene assort independently, meaning the segregation of different allele pairs is independent.

Incomplete dominance

A pattern of inheritance where the homozygous dominant and heterozygous phenotypes are not identical, often resulting in an intermediate phenotype like pink flowers.

Codominance

A genetic scenario where both alleles are expressed at the same time, such as in the ABO blood groups.

Polygenic Inheritance

An inheritance pattern involving more than one gene, which results in continuous variation or quantitative traits like human height.

Pleiotropy

A condition where a single gene controls two or more seemingly unrelated phenotypic traits, such as in cystic fibrosis or sickle cell anemia.

Autosomes

Chromosomes numbered 1-22 that are not involved in determining the sex of an organism.

X-linked recessive disorder

A genetic condition, such as hemophilia, that affects more males than females because it is encoded on the X chromosome.

Mitochondrial inheritance

A type of inheritance applying to genes in mitochondrial DNA, where fathers normally do not pass the traits to their children.

True-breeding

Strains that produce offspring identical to themselves for a specific trait over many generations.

Mendelian Ratio (Monohybrid)

The $3:1$ phenotypic ratio observed in the $F_2$ generation, which corresponds to a genotypic ratio of $1:2:1$ ($1$ homozygous dominant, $2$ heterozygotes, $1$ homozygous recessive).

Dihybrid Phenotypic Ratio

The $9:3:3:1$ ratio observed in the $F_2$ generation of a cross between two double heterozygous individuals ($RrYy \times RrYy$).