AP Biology Unit 5 - Heredity

Genes

DNA segments that serve as the key functional units in hereditary transmission.

Gametes

reproductive cells

sexual reproduction

A reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents

somatic cells

any cell of a living organism other than the reproductive cells.

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

homologous chromosomes (homologs)

in a diploid organism, chromosomes that are similar in size, shape, and gene content

Autosomes

Chromosomes that are not directly involved in determining the sex of an individual.

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms

Fertilization

Process in sexual reproduction in which male and female reproductive cells join to form a new cell

Zygote

a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

Diploid (2n)

two copies of each chromosome

Haploid (1n)

one copy of each chromosome

daughter cells

the cells that result from a cell division

Meiosis 1

separates homologous chromosomes

Meiosis 2

sister chromatids separate

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis.

Tetrad

structure containing 4 chromatids that forms during meiosis

law of independent assortment

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

random fertilization

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

P generation

Parental generation, the first two individuals that mate in a genetic cross

F1 generation (first filial generation)

offspring of the P generation

F2 generation (second filial generation)

offspring of the F1 generation

Alleles

different versions of a gene

Dominant

An allele that is always expressed

Recessive

trait of an organism that can be masked by the dominant form of a trait

Homozygous

An organism that has two identical alleles for a trait

Heterozygous

An organism that has two different alleles for a trait

Phenotype

physical characteristics of an organism

Genotype

An organism's genetic makeup, or allele combinations.

test cross

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

monohybrid cross

A cross between individuals that involves one pair of contrasting traits

dihybrid cross

Cross or mating between organisms involving two pairs of contrasting traits

rule of addition

A rule stating that the probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different ways.

rule of multiplication

A rule stating that the probability of a compound event is the product of the separate probabilities of the independent events.

Codominance

A condition in which both alleles for a gene are fully expressed

incomplete dominance

Situation in which one allele is not completely dominant over another allele

multiple alleles

three or more forms of a gene that code for a single trait

Pleiotropy

The ability of a single gene to have multiple effects.

polygenic inheritance

combined effect of two or more genes on a single character

Pedigree

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

Sex-linked (X-linked)

An inheritance pattern in which traits are controlled by genes located on the X chromosome. Traits are more common in males.

X inactivation

one of two X chromosomes is randomly inactivated and remains coiled as a Barr body

linked genes

Genes located on the same chromosome that tend to be inherited together in genetic crosses.

map unit

A unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency.

Nondisjunction

Error in meiosis in which homologous chromosomes fail to separate.

Aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

Trisomy

3 copies of a chromosome instead of 2

Monosomy

Chromosomal abnormality consisting of the absence of one chromosome from the normal diploid number

Polyploidy

condition in which an organism has extra sets of chromosomes

Deletion

A change to a chromosome in which a fragment of the chromosome is removed.

Duplication

change to a chromosome in which part of the chromosome is repeated

Inversion

A condition in which a section of a chromosome is reversed in direction

Translocation

The process in which a segment of a chromosome breaks off and attaches to another chromosome.

Non-nuclear DNA

mitochondria and chloroplasts contain small amounts of DNA separate from the nucleus