Genetics Ch.1-4

Phenotype

Phenotype

Observable Characteristic

Alleles

Alternate forms of a gene

Independent Assortment

alleles of one gene separate into gametes randomly with respect to alleles of other genes

Gamete

Reproductive cells containing only one copy of each gene

Gene

The heritable entity that determines a trait

Segregation

The separation of the two alleles of a gene into different gametes

Heterozygote

An individual with two different alleles of a gene

Dominant

The allele expressed in the phenotype of the heterozygote

F₁

Offspring of the P generation

Testcross

The cross an individual of ambiguous genotype with a homozygous recessive individual

Genotype

The alleles an individual has

Recessive

The allele that does not contribute to the phenotype of the heterozygote

Dihybrid Cross

A cross between individuals both heterozygous for two genes

Homozygote

Having two identical alleles of a given gene

Epistasis

The alleles of one gene mask the effects of alleles of another gene

Modifier Genes

Genes who alleles alter phenotypes produced by the action of other genes

Conditional lethal

A genotype that is lethal in some situations but viable in others (eg. high temp)

Permissive conditon

Environmental condition that allows conditional lethals to live

Reduced penetrance

Less than 100% of the individuals possessing a particular genotype express it in their phenotype

Complex trait

A trait produced by the interaction of alleles of multiple genes and often also the environment

Incomplete dominance

The heterozygote resembles neither homozygote

Codominance

Both parental phenotypes are expressed in the F₁ hybrids

Mutation

A heritable change in a gene

Pleiotropy

One gene affects more than one trait

Variable expressivity

Individuals with the same genotype have related phenotypes that vary in intensity

Meiosis

One diploid cell gives rise to four haploid cells

Gametes

Haploid germ cells that unite at fertilization

Karyotype

The array of chromosomes in a given cell

Mitosis

One diploid cell gives rise to two diploid cells

Interphase

The part of the cell cycle during which the chromosomes are not visible

Synapsis

Pairing of homologous chromosomes

Sex Chromsomes

X and Y

Cytokinesis

Division of the cytoplasm

Anaphase

The time during mitosis when sister chromatids seperate

Chromatid

One of the two identical halves of a replicated chromosome

Autosomes

Chromosomes that do not differ between the sexes

Centromeres

The sites of the closest connections between sister chromatids

Centrosomes

Microtubule organizing centers at the spindle points

SRY

Y-linked gene that determines maleness

Dosage compensation

Processes that equalize the dosage of X-linked gene products in the somatic cells of males and females

Sex-linked

The inheritance pattern of genes on X chromosome

Hemizygous

Describe genes present in only one copy such as those on the X in males

Pseudoautosomal regions (PAR1/2)

The tips of X and Y chromosomes

Nondisjunction

Failure of homolog separation in meiosis I or chromatid separation in meiosis II

X-Chromosome inactivation

In XX cells, most genes a random X chromosome are turned off

Klinefelter syndrome

XXY Males

Turner syndrome

XO females

Oogonia

Cells in the ovary that undergo mitosis

Oocytes

Cells in the ovary that undergo meiosis

Spermatid

Haploid cell at the end of meiosis II that will become a sperm

Spermatocytes

Cells in the testes that undergo meiosis to create spermatid

Epistatic

gene that is masking other gene

Hypostatic

gene that is being masked

Additive

Four distinct F₂ phenotypes, 9:3:3:1

Recessive Epistasis

Homozygous recessive allele of one gene masks both alleles, 9:3:4

Reciprocal recessive epistasis

When homozygous recessive of either gene masks the dominant allele of the other gene, 9:7

Dominant Epistasis 1

Dominant allele of one gene hides effects of both alleles of the other gene, 12:3:1

Redundancy

Only one Dominant allele of either two genes is necessary to produce phenotype, 15:1

Complementation

Mutations in two different genes. For example aaBB x AAbb, both have no hearing, the child will have hearing because it is heterozygous

Noncomplementation

Mutations in the same gene. For example AAbb x AAbb, both have no hearing, the child will not have hearing.

Penetrance

How many members of a population with a particular genotype, show the expected phenotype

Complete Penetrance

Mendels Studies

Incomplete Penetrance

75% percent of the people with mutant allele get the disease

Expressivity

The degree or intensity a genotype is expressed in phenotype

Modifier Genes

Alter the phenotype produced by alleles of other genes

Permissive

Range of temps that allele is functional

Restrictive

Range of temps that allele is not functional

Conditional lethal

allele is lethal under certain conditions

Discontinuous Trait

Two distinct phenotypes, smooth/wrinkled

Continuous Trait

Trait that has a variation of phenotypes, height/weight

G₁

Growing and preparation for S phase

S phase

DNA synthesis and chromosome duplication

G₂

Growth and preparation for mitosis

Reductional vs Equational Division

reductional division reduces the number of chromosomes in a cell, while equational division does not

Autosome

Chromosome not involved in sex determination

Sex Chromosome

Chromosome that determine sex of an organism