AP Bio chapter 5

Meiosis

Meiosis

Cell division in sexually reproducing organisms that forms gametes Consists of two rounds of cell division but only one round of DNA replication Results in four cells with haploid chromosome number

Homologous chromosomes

Paired chromosomes. the same size, shape, and carry genes for the same traits

Diploid

Complete set of paired chromosomes

found in somatic (body) cells

2n

Haploid

1 chromosome from each homologous pair

found in reproductive cells

1n

Autosomes

All other chromosomes except sex chromosomes

Sex chromosomes

Determines gender Male= XY Female= XX

Gamete

Reproductive cell Contains haploid # of chromosomes Generated during meiosis

Somatic cell

Body cell Contains diploid # of chromosomes Generated during mitosis

Crossing over

Exchange of genetic material between homologous chromosomes

Zygote

Diploid cell produced by the union of haploid gametes (egg and sperm) during fertilization

True-breeding

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

P generation

True-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived. "p" stands for parental

F1 generation

Hybrid (heterozygous) offspring arising from a parental (P generation) cross

Hybrid

Heterozygous

Allele

Different versions of a gene Ex: A or a

Genotype

Genetic makeup of an individual

Phenotype

Physical traits

Heterozygous

Having different alleles for a gene Ex: Aa

Homozygous

Having identical alleles for a gene Ex: AA or aa

Law of Segregation

Two alleles for a trait separate (segregate) during gamete formation and end up in different gametes

Law of Independent Assortment

Each pair of alleles segregates independently of each other pair of alleles during gamete formation Traits are independent and require own Punnett square

Testcross

Crossing an organism with recessive individual

Monohybrid cross

A cross between two organisms that are heterozygous resulting in 3:1 ratio of dominant to recessive phenotypes

Dihybrid cross

A cross between two organisms that are heterozygous for TWO traits resulting in a 9:3:3:1 ratio

Polygenic

Traits that involve multiple genes Ex: eye, skin, and hair color

Multiple allele traits

Traits that have more than two alleles contributing to phenotype Ex: blood type

Sex-linked traits

A gene located on either sex chromosome Most sex-linked genes are on the X chromosome

Wild-type

Phenotype that most commonly observed in natural populations

Recombinants

Offspring with non-parental phenotypes (new combinations of traits) due to crossing over between linked genes

Recombination frequency

Divide total number of recombinants (non-parental phenotypes) by the total number of offspring

Linked genes

Genes located close enough together on a chromosome that they tend to be inherited together

Linkage map

A genetic map of a chromosome based on recombination frequencies

Map units

Distances between genes. one map unit represents a 1% recombination frequency

Nondisjunction

The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during meiosis

Pedigree

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