AP Bio Unit 6

Meiosis and Genetics

Purpose of meiosis

Produce haploid gametes from diploid cells and increase genetic variation

Why cells undergo meiosis

To reduce chromosome number by half and create genetically unique gametes for sexual reproduction

Homologous chromosomes

A pair of chromosomes with the same genes, one from each parent

Sister chromatids

Identical copies of a chromosome joined at the centromere

Tetrad

Structure formed in prophase I, consisting of two homologous chromosomes

Crossing over

Exchange of genetic material between non-sister chromatids in prophase I - increase variation

Independent assortment

Random alignment of homologous pairs during metaphase I

Independent assortment

Random alignment of homologous pairs during metaphase I

Meiosis I vs Meiosis II

Meiosis I: homologous chromosomes separate

Meiosis II: sister chromatids separate

Daughter cells after meiosis

4 haploid, genetically different cells

Mitosis vs meiosis

Mitosis: growth/repair, 2 identical diploid cells

Meiosis: gametes, 4 different haploid cells

Nondisjunction

Failure of chromosomes or chromatids to separate properly during meiosis

Down syndrome

Trisomy 21

Klinefelter syndrome

Male with XXY sex chromosomes

Turner syndrome

Female with only one X chromosome

Allele

Different versions of the same gene

Law of Segregation

Allele pairs separate during gamete formation

Pleiotropy

One gene affects multiple traits

Polygenetic inheritance

Traits are controlled by multiple genes (skin color)

Codominance

White with pink spots

Incomplete dominance

Red flower and white flower make pink flower