MEIOSIS

Meiosis

Sexual Reproduction (two parents)

https://www.youtube.com/watch?v=qCLmR9-YY7o

What is the advantage of sexual reproduction?

Genetic Variation

3 things that contribute to genetic variation

Independent assortmentCrossing OverRandom Fertilization

These two processes occur during meiosis

Why Meiosis?Meiosis - cell division that halves the # of

chromosomes when forming sex cells such as gametes or spores

How does Meiosis Occur?

Independent Assortment

Random arrangement of pairs of chromosomes

What is crossing over?

*Exchange of genetic material between homologous chromosomes

*Occurs during prophase I of meiosis.

Crossing Over

Crossing Over

Is there anything that can wrong during meiosis?

Yes!It is called nondisjunction.

– Chromosomes don’t separate properly and some gametes end up with too many or not enough chromosomes.

What happens if nondisjunction occurs?

The gamete will die or result in conditions known as trisomy or monosomy.

Trisomy - a person has more than 2 copies of the same chromosome.

Monosomy – a person only has one copy of a chromosome.

How can you tell that?

Take a picture of the chromosomes!This is known as a karyotype.

Normal Female Karyotype

Normal Male Karyotype

Abnormal Karyotype-Trisomy #21

Down’s Syndrome

Abnormal Karyotype – Monosomy of the X chromosome

Turner’s Syndrome

Meiosis in males

Called spermatogenesis

Occurs in the testes

Results in 4 viable gametes called sperm

Meiosis in females

Called oogenesisOccurs in the ovariesResults in 1 viable gamete called the ovum

(egg) and 3 polar bodies (these will die).– Why does only one gamete survive? The one

egg will need a rich storehouse of nutrients to nourish the young organism that develops when the ovum is fertilized.

Meiosis Review

1. Is the beginning parent cell diploid or haploid (2n or n)? Diploid

2. Are the resulting daughter cells diploid or haploid (2n or n)? Haploid

More Meiosis Review

3. How many daughter cells are produced? 4

4.Are the resulting daughter cells different

from the parent cell? yes

More Meiosis Review

5. Are the resulting daughter cells different from each other? yes

7. How many chromosomes are in a human daughter cell? 23

6. How many chromosomes are in a human parent cell? 46

More Meiosis Review

8. What types of cells are produced by meiosis?

Let’s reviewMitosis & Meiosis

Mitosis vs. Meiosis  

   Event Mitosis Meiosis

Produces 4 cells

Produces 2 cells

New cells identical

New cells different

New cells have the same number of chromosomes as parent

New cells have fewer chromosomes than parent

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Mitosis vs. Meiosis  

  

Event Mitosis Meiosis

Beginning cells diploid (2n)

Beginning cells haploid (n)

Ending cells diploid (2n)

Ending cells haploid (n)

Produces egg and sperm

Produces body cells (autosomes)

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