Chromosomes & Meiosis

Section 6-1
“Chromosomes
& Meiosis”
Write everything that is
underlined
6.1 Chromosomes and Meiosis
One of Biology’s Essential Questions:
At the end of this unit you will need to be able to
answer this question …
The Big Question: WHY ARE ALL
HUMANS DIFFERENT?????
…Look around the room- no one is
exactly like you
…Your siblings are not exactly like you
(unless you have an identical twin)
…There is an amazing process that
makes us all different … meiosis
6.1 Chromosomes and Meiosis
KEY CONCEPT:
Gametes have half the number of
chromosomes that body cells have
6.1 Chromosomes and Meiosis
Fill out this chart for reference as we move along in our
notes 
Term
Somatic Cell
Gamete
Homologous
Chromosome
Autosome
Sex Chromosome
Sexual Reproduction
Fertilization
Diploid
Haploid
Meisois
Definition
6.1 Chromosomes and Meiosis
A. Body cells and gametes
1. Body cells are also called somatic cells
2. Gametes are sex cells: egg and sperm
– Gametes have DNA that can be passed to
offspring
(Psst…Fill out your vocabulary chart…)
body cells
sex cells (sperm)
sex cells (egg)
6.1 Chromosomes and Meiosis
Take a Vote!!!!
Is a skin cell a somatic cell or a gamete?
-Somatic
Is an egg a somatic cell or a gamete?
-Gamete
What is a liver cell considered- somatic or gamete?
-Somatic
What is another type of somatic cell?
-Sperm Cell
6.1 Chromosomes and Meiosis
B. Autosomes and sex chromosomes
1. Your body cells have 23
pairs of chromosomes
2. The first 22 pairs of
chromosomes are
autosomes
3. Sex chromosomes (X
and Y) determine what
gender you will be (male
or female)
6.1 Chromosomes and Meiosis
4. Homologous pairs
of chromosomes
have genes for the
same traits
5. For each
homologous pair,
one chromosome
comes from each
parent
6.1 Chromosomes and Meiosis
Think-Pair-Share (2 min.)
• Do you believe that homologous chromosomes are
identical to each other?
• Why or why not???
6.1 Chromosomes and Meiosis
C. Diploid and Haploid
1.Diploid (2n) cells have two
copies of every chromosome
– Body cells are diploid
– Half the chromosomes come
from each parent
6.1 Chromosomes and Meiosis
2. Haploid (n) cells have one copy of
every chromosome
–Gametes (sex cells) are haploid
–Gametes have 22 autosomes and 1
sex chromosome
6.1 Chromosomes and Meiosis
Quick Thinking!
• You can write, draw, diagram, or write a quick song
for your answer…
• Why is it so important that gametes are
haploid cells? What would happen if, for
some reason, it occurred that one
wasn’t?
6.1 Chromosomes and Meiosis
D. Fertilization: When the egg and
sperm cell unite
1. 2 haploid cells unite to form a cell
(zygote) that once again has the
diploid number of chromosomes
– Chromosome number must be
maintained in animals
– Many plants have more than two
copies of each chromosome
2. A zygote grows to be a human
6.1 Chromosomes and Meiosis
REMEMBER THIS
• Mitosis and meiosis are types of
nuclear division that make different
types of cells
• Mitosis makes more identical
diploid cells
6.1 Chromosomes and Meiosis
• Meiosis makes haploid cells from diploid
cells and:
– occurs in sex cells
– produces gametes
6.1 Chromosomes and Meiosis
Compare and Contrast MITOSIS and
MEIOSIS on a separate sheet of paper
based on what you already know about
both. Turn in at the end of the period
before you walk out the door.
Mitosis
Meiosis
Differences go HERE
Differences go HERE
Things they have in
common go HERE
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