Post on 29-Dec-2015
transcript
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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https://www.youtube.com/results?search_query=meiosis+square+dance