• Meiosis Cornell notes

• Meiosis animation video

• https://www.youtube.com/watch?v=rqPMp0U0HOA

• Each one of us have characteristics passed on to us from our parents

• Each characteristics we have is called a trait

• The DNA on the chromosomes are arranged in segments called genes

• Each chromosome consist of hundreds of genes

SEXUAL REPRODUCTION

Sex cells formed by meiosis

Requires 2 parents

Offspring not identical

A kind of cell division that results in gametes (sex cells) withhalf the number of chromosomes

In order to maintain the same chromosomes # from generation to generation, an organism produces gametes (sex cells) that have half the # of chromosomes

Haploid means HALF, as in the number of chromosomes,written as n

Meiosis

Gametes

Haploid

Homologous Chromosomes

* Human body cells have 46 chromosomes

* Human body cells have 23 homologous pairs

Meiosis and Fertilization

One haploid gamete combines with another haploid gamete.As a result of fertilization, the cell now will contain a total of 2n chromosomes

Fertilization

The union of an egg and a sperm

n

n 2n

Homologous chromosomes

Phases of Meiosis (2 cell divisions )

• Interphase

–Chromosomes replicate

–Chromatin condenses

Phases of Meiosis (2 Cell divisions – Meiosis I & Meiosis II)

MEIOSIS I

Prophase I

Pairing of homologous chromosomes, crossing over occurs, nuclear envelope breaks down, and spindles form

Metaphase I

Spindle fibers attach to homologous chromosomes (pairs) and line up in the middle of the cell.

Anaphase I

The fibers pull the homologous chromosomes apart. Chromosomes move toward opposite sidesof the cell.

Telophase I

During Telophase I and cytokinesis, the spindles break down, chromosomesuncoil and form two new nuclei, the cell divides (2 daughter cells)

**** The Chromosome number is reduced to half during Meiosis I forming haploid (n) daughter cells

MEIOSIS II

Prophase II

Chromosomes condense, spindle fibers form in each new cell, Spindle fibers attach to chromosomes

Metaphase II

Chromosomes line up in the middle of the cell

Anaphase II

Sister chromatids separate and move towards opposite sides of the cell

Telophase II

Cells divide, resulting in 4 haploid cells – gametes (sex cells)

MeiosisMeiosis

Parent cell – chromosome pair

Chromosomes copied

1st division - pairs split

2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

• Summary • 3 to 4 sentences of meiosis notes

15

Mitosis, Meiosis, or Neither

Number 1 - 6

17

How this sperm cell was created

18

DNA replication happens before this process.DNA replication happens before this process.

19

When the sperm actually meets the egg.

20

I’m a single celled

paramecium. Time to

reproduce!

21

DNA replication happens before this process.DNA replication happens before this process.

22

ANSWERS!

Number 1 - 6

24

How this sperm cell was created

25

DNA replication happens before this process.DNA replication happens before this process.

26

When the sperm actually meets the egg.

27

I’m a single celled

paramecium. Time to

reproduce!

28

DNA replication happens before this process.DNA replication happens before this process.

29