Patterns of Inheritance

Flashcards covering the fundamental concepts of Mendelian genetics, including laws of inheritance, cross types, and genetic variations.

Heredity

The passing of traits from one generation to the next.

Genetics

The scientific study of heredity.

Gregor Mendel

A scientist who began the field of genetics in the $1860s$ by breeding garden peas.

Character

A heritable feature that varies among individuals, such as flower color.

Trait

Each variant for a character, such as purple or white flowers; a different version of a character.

Alleles

Alternative versions of genes that account for variations in inherited characters.

Dominant Allele

The allele that determines the trait when the inherited alleles are different.

Recessive Allele

An allele that has no noticeable effect on the organism's appearance when inherited alongside a dominant allele.

Law of Segregation

The hypothesis that a sperm or egg carries only one allele for each inherited character because allele pairs segregate into different daughter cells during gamete formation.

Punnett Square

A diagram used to show the four possible combinations of alleles that could occur when gametes combine.

Heterozygous

An organism that has two different alleles for a gene, such as a $Pp$ genotype.

Locus

The specific location of a gene along a chromosome.

Dihybrid Cross

A mating of parental varieties that differ in two characters.

Law of Independent Assortment

The principle stating that each pair of alleles segregates independently of other pairs of alleles during gamete formation; the inheritance of one character has no effect on the inheritance of another.

Testcross

A mating between an individual of unknown genotype and a homozygous recessive individual used to determine the unknown genotype.

Recessive Disease

A genetic disorder where the individual must carry two recessive disease alleles to exhibit symptoms.

Carrier

A person carrying only one recessive allele for a disease who appears normal but can pass the allele to offspring.

Complete Dominance

A situation where the phenotypes of the offspring always look like one of the two parental varieties.

Incomplete Dominance

A variation where the appearance of $F_1$ hybrids falls between the phenotypes of the two parental varieties, resulting in intermediate phenotypes.

Multiple Alleles

A condition where more than two possible alleles exist in a population for a particular gene, such as the human ABO blood group.

Codominance

A phenotype where both alleles are expressed in the individual, such as the $AB$ blood group resulting from the $I^A$ and $I^B$ alleles.

Pleiotropy

A condition where one gene influences multiple characters, such as sickle-cell disease affecting red blood cell shape and organ function.

Polygenic Inheritance

The additive effects of two or more genes on a single phenotypic character, such as human skin color.