AP BIO Ch 14 & 15

(Mendel & The Gene Idea) & (The Chromosomal Basis of Inheritance)

Character

An observable heritable feature that could vary in individuals

Trait

Variant of a character

True-Breeding

Organisms that produce offspring of the same variety over many generations of self-pollination

Hybridization

The mating/crossing of 2 true-breeding varieties

P Generation

True-breeding (homozygous) parents

F1 Generation

The first hybrid generation form the P cross

F2 Generation

The offspring that results from interbreeding/self-pollinating the F1 generation

Dominant

An allele that is fully expressed in a heterozygote

Recessive

An allele whose phenotypic effect isn’t seen in a heterozygote

Allele

Alternative versions of a gene that might produce different phenotypic effects

Gene

Homozygous

To have identical alleles for a gene

Homozygote

An organism that has identical alleles for a gene: AA/aa

Heterozygous

To have 2 different alleles for a gene

Heterozygote

An organism that has 2 different alleles for a gene: Aa

Phenotype

The observable physical traits of an organism that are determined by the genetic makeup

Genotype

The genetic makeup of an organism

Testcross

Breeding an organism of unknown genotype with a homozygous recessive organism to figure out what the unknown genotype is

Monohybrid

Heterozygous for 1 thing—a result of completely dominant X completely recessive. So—AA X aa = monohybrid child—Aa

Dihybrid

Heterozygous for 2 different things—a result of completely dominant X completely recessive. So—AABB X aabb = dihybrid child—AaBb.

Law of Segregation

2 alleles in a pair segregate into different gametes during gamete formation. So an egg/sperm cell gets only one of the two alleles that are present in a diploid cell of the organism.

Law of Independent Assortment

Each pair of alleles segregates independently of the other during gamete formation—applies when the genes for two characters are located on different pairs of homologous chromosomes/far enough apart on the same chromosome that they don’t affect each other as much

Complete Dominance

When the phenotypes of the heterozygote and the homozygote dominant are the exact same

Incomplete Dominance

The phenotype of heterozygotes is an intermediate between the phenotypes of the homozygous individuals — Like red + white = pink

Codominance

2 alleles will both affect the phenotype in separate distinguishable ways—example: red + white = red AND white

Pleiotropy

One gene affecting multiple different things

Epistasis

The phenotypic expression of a gene at one locus alters that of another gene at a second locus

Quantitative Characters

Heritable features that vary continuously

Polygenic Inheritance

2 or more genes affect one single phenotypic character

Multifactorial

Phenotypic character that is influenced by multiple genes and environmental factors—example: hydrangeas

Pedigree

A family tree diagram that shows heritable characters over generations. Square—male, Circle—female, Solid—affected

Carriers

Someone who is heterozygous for a genetic condition. Phenotypically normal but capable of passing on the condition.

Aminocentesis

Technique for prenatal diagnosis. Amniotic fluid is taken from the uterus and the fetal cells in it are analyzed to detect genetic/congenital defects in the fetus.

Chorionic Villus Sampling (CVS)

Technique for prenatal diagnosis. Basically you get a sample of the tissue from the placenta to detect genetic/congenital defects in the fetus

Chromosome Theory of Inheritance

Genes have specific loci (sites) along chromosomes & the chromosomes undergo segregation and independent assortment.

Wild Type

Phenotype most commonly observed in nature.

Sex-Linked Genes

Gene located on either sex chromosome (most are on the X chromosome though)

X-Linked Genes

Gene located on the X-chromosome—distinctive pattern of inheritance.

Barr Body

A dense object lying along the inside of the nuclear envelope—contains highly condensed & inactivated X chromosome

Linked Genes

Genes that are located near each other on a chromosome and tend to be inherited together

Genetic Recombination

Term for the production of offspring with combinations of traits that differ from the parents

Parental Types

Offspring with a phenotype that matches one of the true breeding parents

Recombinants

Offspring whose phenotype is different than the true breeding parental generation

Crossing Over

Exchange of genetic material between nonsister chromatids during prophase 1 of meiosis

Genetic Map

A list of genes/genetic markers on a chromosome

Linkage Map

A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes

Map Units

A unit of measurement of the distance between genes. One map unit = 1% recombination frequency.

Nondisjunction

An error during mitosis or meiosis where a pair of homologous chromosomes/sister chromatids don’t separate from each other

Aneuploidy

A chromosomal defect where you have too many chromosomes or not enough

Monosomic

A diploid cell that has only one copy of a chromosome instead of 2

Trisomic

A diploid cell that has three copies of a chromosome instead of 2

Polyploidy

A chromosomal alteration in which the organism has more than two complete sets of chromosomes—accident in cell division.

Deletion

A deletion removes a chromosomal segment.

Duplication

A duplication repeats a segment

Inversion

An inversion reverses a segment within a chromosome. (Switchy switchy)

Translocation

Moves a segment from one chromosome to a non-homologous chromosome. Non-homologous chromosome exchange fragments. (Swapy swapy)

Genomic Imprinting

A phenomenon in which expression of an allele in the offspring depends on whether the allele is inherited from the mother or the father.