Chromosomes, Mitosis and Meiosis
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Big Question:
Chromosomes are made of both DNA and protein. A human cell contains at least 2 meters of DNA.
The DNA is packed into a tiny nucleus with the help of the proteins. Each species has a characteristic
number of chromosomes. For example, human cells contain 46 chromosomes (23 pairs), corn has 20 (10
pairs) and crayfish has 200 (100 pairs) chromosomes. The number of chromosomes is not generally
related to the complexity of the organism. Mitosis is nuclear division in which the chromosome number
stays constant. Meiosis is nuclear division in which chromosome number divides in half. Mitosis is
responsible for the production of all body cells. Meiosis is responsible for the production of sperm and
egg.
I) What are Chromosomes?
A) Chromosomes are made of both DNA and proteins. The
proteins help the DNA wrap and fit into a tiny nucleus.
B) All normal body cells are diploid. They contain two sets of
chromosomes, one set from each parent, so the number of
chromosomes is always even. All cells except sex cells are
diploid.
C) Genes are sections of the DNA molecule. They code for
proteins. There are usually two copies of every gene. The
genes line up in the same order on each chromosome in a pair.
Though simple organisms generally have relatively small
genomes, gene number is not necessarily correlated to
complexity.
D) Approximate number of genes in the DNA of each organism:
Organism Genes Organism Genes Organism
Genes
Fruit fly
14,889 Human
22,333 Chicken
16,736
Grape
30,434 E. Coli
4,149
Water flea
31,000
II) What is Mitosis?
A) Mitosis is ONE of the steps of normal cell division to create
TWO IDENTICAL daughter cells.
B) During mitosis, the chromosomes are copied ONCE and the
nucleus of the parent cell divides ONCE.
C) The nucleus of each daughter cell ends up with the EXACT
number of chromosomes as the parent cell.
III) What is Meiosis?
A) Meiosis is ONE of the steps to produce FOUR special sex
cells, sperm and egg.
B) During meiosis, the chromosomes are copied ONCE and the
nucleus divides TWICE.
C) The nucleus of each sex cell ends up with HALF the number
of chromosomes as the parent cell. All sex cells are haploid.
They contain one set of chromosomes.
D) The chromosomes change during meiosis. Each sex cell
receives chromosomes that are somewhat different than
another sex cell. That is why offspring form the same parents
are NOT identical.
Rev: 2/9/2016
Chromosomes, Mitosis and Meiosis
1.
Chromosomes are made of __________________
and _________________.
3. In a diploid cell, one set of chromosomes comes
2.
The number of chromosomes in normal body
cells is always __________________.
A) Odd
B) Even
C) 46
4.
True or False? Genes are randomly distributed
on chromosomes in a pair.
from the _________________ and the other set of
chromosomes comes from
the____________________.
5.
True or False? Simpler organisms like sea
anemones always have fewer genes than complex
organisms like whales.
6.
True or False? During mitosis, chromosomes are
copied twice.
7.
True or False? During meiosis, chromosomes are
copied twice.
8.
Before sexual reproduction can happen, each
parent must reduce its number of chromosomes
involved in sexual reproduction by
_______________.
9.
The number of chromosomes in a sex cell of a
corn plant is __________________________.
A) 10
B) 20
C) 30
10. The number of chromosomes in a body cell of a
human is ________________.
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11. Mini-Essay (10 pts) Read, Understand, and Answer: Explain the difference between meiosis and
mitosis. In your explanation, describe what happens to the chromosomes in each process and
why. Give details.
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Self:
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Honest and fair self-evaluation helps you improve.
Other:
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You are evaluating the work of the person
NOT the person.
If your handwriting is hard to read, maximum score is 5. You can type your essay and paste in the space.
Rev: 2/9/2016