Genetics and Inheritance Vocab

Alleles

Different forms of the same gene

Dominant

An allele that is always expressed (G)

Recessive

An allele that is masked when a dominant allele is present (g). Only expresses itself when homozygous recessive

Genotype

the letter combination or genetic makeup of an organism

Phenotype

physical characteristics of an organism

Homozygous

An organism that has two identical alleles for a trait (GG or gg)

Heterozygous

An organism that has two different alleles for a trait (Gg)

Probability

likelihood that a particular event will occur

Punnett Square

a tool used to predict the possible outcomes of a genetic cross

Monohybrid cross

A cross between individuals that involves one pair of contrasting traits (GG x gg)

Dihybrid cross

A cross between two individuals, concentrating on two definable traits (GGrr x ggRr)

Law of Independent Assortment

the law that states that genes separate independently of one another in meiosis

What is the phenotypic ratio of the F2 generation?

3:1

What is the genotypic ratio of the F2 generation?

1:2:1

Pedigree

A chart or "family tree" that tracks which members of a family have a particular trait

Incomplete dominance

When one allele is not completely dominant over another, the heterozygote has a phenotype between the homozygotes.

Complete dominance

The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

Codominance

A condition in which both alleles for a gene are fully expressed (mixture expression)

Multiple Alleles

three or more alleles of the same gene (blood type)

Sex chromosomes

Chromosomes that determine the sex of an individual (X and Y). XX = female and XY = male

Sex-linked inheritance

Inheritance of a genetic trait located on the sex chromosomes

Polygenic inheritance

occurs when multiple genes determine the phenotype of a trait (skin color)

Random fertilization

source of genetic variation caused by the unlimited number of possible sperm & egg combinations

True-breeding

Organisms that, when reproducing, create offspring of all the same variety.

Locus

Location of a gene on a chromosome

Test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

F1 generation (Mendel)

PP x pp

F2 generation (Mendel)

Pp x Pp

FOIL

First, Outer, Inner, Last

What is the phenotypic ratio of a dihybrid cross?

9:3:3:1

Pleiotrophy

A single gene that affects more than one trait

Epistatsis

a gene at one locus alters the phenotypic expression of a gene at a second locus

Dominant trait (pedigree)

is present and can disappear

Recessive trait (pedigree)

hides and can appear suddenly

X-linked recessive

carried by females and affects males

Mode of inheritance

the pattern in which a genetic disease is inherited through generations