Mendelian Genetics Vocabulary Flashcards (:

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Alleles

The different forms of a gene. Y and y are different alleles of the gene that determines seed color. Alleles occupy the same locus, or position, on chromosomes.

Autosomal

A locus on any chromosome but a sex chromosome. Not sex-linked.

Co-Dominant Alleles

Two different alleles at a locus are responsible for different phenotypes, and both alleles affect the phenotype of the heterozygote.

Complete Linkage

Complete linkage describes the inheritance patterns for 2 genes on the same chromosome when the observed frequency for crossover between the loci is zero.

Crossing Over

Exchange of genetic material between non-sister chromatids from homologous chromosome during prophase I of meiosis; results in new allele combinations

Dioecious

Organisms produce only one type of gamete; i.e. humans

Diploid

Cell with two of each kind of chromosome; is said to contain a diploid, or 2n, number of chromosomes

Dominant Trait

cell with two of each kind of chromosome; is said to contain a diploid, or 2n, number of chromosomes

Egg haploid female sex cell produced by meiosis
Epistasis

One gene masks the expression of a different gene for a different trait.

F1 Generation

Offspring of a cross between true breeding plants, homozygous for the trait of interest

F2 Generation

Offspring of a cross involving the F1 generation.

Fertilization

fusion of male and female gametes

Gamete

male and female sex cells, sperm and eggs

Genetic Recombination

major source of genetic variation among organisms caused by re-assortment or crossing over during meiosis

Genetics

branch of biology that studies heredity

Genotype The genetic constitution of an organism with respect to a trait.
Haploid

cell with one of each kind of chromosome; is said to contain a haploid or n, number of chromosomes.

Hemizygous

If there is only one copy of a gene for a particular trait In a diploid organism, the organism is hemizygous for the trait, and will display a recessive phenotype. X-linked genes in fly or human males are hemizygous.

Hereditary

passing on of characteristics from parents to offspring

Heterozygous

Differing alleles for a trait in an individual, such as Yy.

Homologous Chromosomes

The pair of chromosomes in a diploid individual that have the same overall genetic content. One member of each homologous pair of chromosomes in inherited from each parent.

Homozygous

Both alleles for a trait are the same in an individual. They can be homozygous dominant (YY), or homozygous recessive (yy).

Hybrid

heterozygous; usually referring to the offspring of two true-breeding (homozygous) individuals differing in the traits of interest.

Incomplete Dominance Intermediate phenotype in F1, parental phenotypes reappear in F2.
Lethal Alleles

Mutated genes that are capable of causing death.

Linkage

genes that are inherited together on the same chromosome. Three inheritance patterns are possible: non-linkage, Partial linkage, and complete linkage.

Meiosis

type of cell division where one body cell produces for gametes, each containing half the number of chromosomes in a parent’s body.

Mendel's Law of Independent Assortment

Alleles of different genes are assorted independently of one another during the formation of gametes.

Mendel's Law of Segregation

Alleles segregate from one another during the formation of gametes.

Monoecious Organisms produce both male and female gametes; i.e. garden pea.
Monohybrid Cross

Cross involving parents differing in only one trait.

Mutation

Change in the DNA sequence of a gene to some new, heritable form. Generally, but now always a recessive allele.

Non-Disjunction

failure of homologous chromosomes to separate properly during meiosis; results in gametes with too many or too few chromosomes

Non-Linkage

Non-linkage describes the inheritance patterns for 2 genes on the same chromosome, when the expected frequency for crossover between the loci is at least one.

Partial Linkage Partial linkage describes one of the inheritance patterns for 2 genes on the same chromosome, when the expected frequency for crossover between the loci is greater than zero but less than one.
Phenotype The physical appearance of an organism with respect to a trait, i.e. yellow (Y) or green (y) seeds in garden peas.
Pleiotropic

A single gene determines more than one phenotype for an organism.

Pollination

Transfer of male pollen grains to the pistil of a flower

Polyploidy

The condition in which an organism has extra sets of chromosomes

Probability

A number that describes how likely it is that an event will occur.

Punnet Square

A chart that shows the possible combinations of alleles that result from a genetic cross.

Purebred

The offspring of many generations that have the same traits.

Recessive Trait

The opposite of dominant. A trait that is preferentially masked.

Reciprocal Cross

Using male and female gametes for two different traits, alternating the source of gametes.

Sex Chromosomes

Sex determination is based on sex chromosomes

Sex-Linked

A gene coded on a sex chromosome, such as the X-chromosome linked genes of flies and man.

Sexual Reproduction

pattern of reproduction that involves the production of subsequent fusion of haploid cells.

Sperm

haploid male sex cells produced by meiosis

Test Cross

Generally a cross involving a homozygous recessive individual.

Trait characteristic that is inherited; can be either dominant or recessive
True-Breeding

Homozygous for the true-breeding trait.

Wild-Type Allele

The non-mutant form of a gene, encoding the normal genetic function. Generally, but not always a dominant allele.

Zygote

diploid cell formed when a sperm fertilizes an egg.