BiologyChapter 10, Section 1

Meiosis

Main Idea: Meiosis produces haploid gametes.Essential Questions:

How does reduction in chromosome number occur during meiosis? What are the stages of meiosis? What is the importance of meiosis in providing genetic variation?

I. IntroductionA. There are no two individuals that are ____________________ to each

other.B. Genetic ____________________ – a variety of traits in organismsC. Trait – Characteristics (hair color, height, or eye color)

1. ____________________ in your genetic code, DNAD. Genes – DNA ____________________ that control the production of a

____________________.II. Chromosomes and Chromosome Number

A. Humans have ___________________ chromosomes.1. Each parent contributes 23 chromosomes, resulting in 23

pairs of ____________________.B. Homologous Chromosomes – Chromosomes that make up a

____________________. One chromosome from each parent.C. Haploid and Diploid Cells

1. Gametes – sex cells that have ____________________ the number of chromosomes

2. Haploid Cell – A cell with n ____________________ of chromosomes.

3. Fertilization – The process by which one haploid gamete ____________________ with another haploid gamete.

4. Diploid Cell – A cell with 2n number of ____________________.III. Overview of Meiosis

A. Meiosis – A type of cell ____________________ that reduces the number of chromosomes. (____________________ division)

1. Meiosis will ____________________ cells that have n number of chromosomes.

2. Meiosis starts with ____________________ cells which then divide and create haploid cells.

IV. Meiosis IA. Interphase:

1. Chromosomes ____________________2. ____________________ condenses

B. Prophase I:1. ____________________ of homologous chromosomes occurs,

each chromosome consists of two ____________________.2. ____________________ move to opposite poles, spindle fibers

form and ____________________ to sister chromatids at centromere.

3. The nuclear ____________________ breaks down. 4. Synapsis forms between the ____________________ of

homologous chromosomes.i. Chromosomes are ____________________ bound together.

5. Crossing over produces ____________________ of genetic information. (Figure 10.4)

C. Metaphase: Meiosis I vs Mitosis1. Chromosome centromeres ____________________ to spindle

fibers.2. Homologous ____________________ line up at the equator.3. Mitosis vs. Meiosis

i. Mitosis: sister ____________________ line up at the cell’s equator

ii. Meiosis: homologous chromosomes line up at the cell’s ____________________

D. Anaphase I1. Homologous chromosomes ____________________ and move to

opposite ____________________ of the cell.2. Chromosome number is ____________________ from 2n to n

when the homologous chromosomes separate.i. (Watch the Amoeba sister video on the website on

demystifying chromosome reduction.)E. Telophase I

1. The ____________________ break down.2. Chromosomes ____________________ and form two nuclei.3. The cell ____________________.

V. Meiosis IIA. Meiosis is only ____________________ completed at the end of meiosis

I.

1. Meiosis II will ____________________ to divide the chromosomes to ____________________ haploid cells.

B. Prophase II1. Chromosomes ____________________.2. Spindles form in each ____________________ cell.3. Spindle fibers ____________________ to chromosomes.

C. Metaphase II1. ____________________ of chromosomes line up

____________________ at the equator of each cell.2. Difference between Mitosis and Meiosis:

i. Mitosis: a diploid number of chromosomes ____________________ up at the equator

ii. Meiosis: a haploid number of ____________________ line up at the equator

D. Anaphase II1. ____________________ split.2. Sister chromatids separate and move to ____________________

poles.E. Telophase II

1. Chromosomes ____________________ the poles.2. Four nuclei ____________________ around chromosomes.3. ____________________ break down.4. ____________________ divide.

VI. ProductA. Four cells have formed.B. Each nucleus ____________________ a haploid number of

chromosomes.