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Meiosis - 7th Grade

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by

William Begoyan

on 20 November 2016

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Transcript of Meiosis - 7th Grade

fig. 1
Meiosis
The two sex cells responsible:
sperm

egg
Sexual Reproduction:
Production of offspring as a result of combination of genetic material from two different cells.
Not cloning (mitosis).
Disadvantages of Meiosis:
Fertilization (fusing egg and sperm) can be complicated, and is not guaranteed to work.
Organisms created by sexual reproduction usually grow slower.
Advantages of Meiosis :

Genetic variation
:
No two individuals are the same.
This variation allows species to adapt to environmental traits and evolve.
Example: The flu virus does not effect every human the same way, some get very sick, while others are barely bothered by it.
Selective Breeding
:
You can breed certain desirable traits (like farmers and pet breeders have been doing for generations).
This would be impossible if everything was an identical clone.
How Meiosis Works
Goes on Page 25 in your Interactive Notebook
AVID: Why can't all our cells divide by cloning?
-Fertilization
: a process by which sperm and egg fuse together.
-After fertilization, the sperm/egg combination is called a
Zygote
.
What is sexual reproduction?
What are the two sex cells called?
What is fertilization?
List 2 advantages and 2 disadvantages of meiosis.
What is the purpose of meiosis?
What are diploid cells?
What are haploid cells?
The Simpsons family, brought to you by "Meiosis"
You can think of meiosis as a mitosis happening twice in a row, called Meiosis I and Meiosis II.
The second division is necessary to maintain the right amount of chromosomes.
At the end of Meiosis I you are left with 2 cells that have 46 chromosomes (just like mitosis).

Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Diploid
Haploid
In Meiosis II the two cells from Meiosis I divide again, resulting in 4 new cells (double that of mitosis).
Each of the four cells has 23 chromosomes, half that of a normal cell.
Cells with 46 chromosomes are called
diploid
, while cells with just 23 chromosomes are called
haploid
.
During prophase I of meiosis, homologous chromosomes will exchange bits and pieces of each other.
This process is called
crossing over
, and will make each chromosome unique, increasing diversity.
What is crossing over?
Homework
On page 24 of the ISN, research 3 examples of selective breeding, and describe how they have had an effect in our society.
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