Unit-06-Lessons-6-7

body cells sex cells (sperm) sex cells (egg)
6.1 Chromosomes and Meiosis
I. Types of cells in the body
A. somatic cells – body cells (muscle cells, bone cells, etc.)
a. Use mitosis to reproduce
B. gametes - germ cells (sperm and egg cells)
a. Use meiosis to reproduce
1. sperm cells – located in testes
2. egg cells – located in ovaries

6.1 Chromosomes and Meiosis
II. DNA in cells
A. Your body cells have 23 pairs of
chromosomes (46 total)
1. autosomes - (numbered 1-22) –
determine all of your traits
2. sex chromosomes – (X and Y) –
determine gender in mammals
Ex) XX = female XY = male
B. Each of the 22 pairs of autosomes are
said to be homologous (chromosomes
have the same structure)
1. One chromosome in homologous
pairs comes from each parent
C. The sex chromosomes are
nonhomologous (not matched)

6.1 Chromosomes and Meiosis
D. ploidy – refers to number of chromosomes in a cell
1. Diploid – (2n) – cells have two copies of every chromosome
a. All body cells are diploid.
b. Half the chromosomes come from each parent.

6.1 Chromosomes and Meiosis
2. Haploid – (n) – cells have one copy of every chromosome
a. Gametes are haploid.
b. Gametes have 22 autosomes and 1 sex chromosome.

6.1 Chromosomes and Meiosis

6.1 Chromosomes and Meiosis

6.1 Chromosomes and Meiosis
E. How this works for humans:
1. Chromosomes are replicated and then reduced by half the
amount through meiosis to make the gametes (sperm and egg
cells)….gametes are haploid
2. During fertilization, a haploid sperm cell fuses with a haploid
egg cell to create a diploid cell.
3. The diploid embryonic cell reproduces through mitosis.

6.2 Process of Meiosis
III. Meiosis
A. Meiosis only occurs in the gonads (testes and ovaries) for the
purpose of making gametes (sperm and egg cells).
B. Meiosis has 2 divisions: Meiosis I and Meiosis II
1. Meiosis I – sepatates homologous pairs of chromosomes (the
matched pair – one from mom and one from dad)
2. Meiosis II – separates identical sister chromatids (replicated
during interphase
homologous chromosomes
C. The goal of meiosis is to reduce the
number of chromosomes by half (creates
either 4 haploid sperm cells or 4 haploid
egg cells)
sister
chromatids
sister
chromatids

6.2 Process of Meiosis

6.2 Process of Meiosis

6.2 Process of Meiosis
D. Gametogenesis – the production of gametes
1. Gametogenesis differs between females and males.
a. Males – cytoplasm is divided evenly into 4 sperm cells
1. Flagella are added to sperm are motile (can swim).

6.2 Process of Meiosis
b. Females – divide cytoplasm unevenly between 1 egg
cell and 2 polar bodies
1. Polar bodies eventually disintegrate
2. Egg cell has enough of a food supply and organelles
to survive for a while.