Meiosis

1. “Principle in Animal Life-II”
ZOO102
Lecture 13
“Meiosis”
By: Mr. Noor ul Akbar
Lecturer, Department of Zoology
KUST
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2. “Meiosis”
 What is Meiosis
 Stages of Meiosis
 Meiosis I
 Meiosis II
 Genetic Variations
 Mechanism of Variations
 Spermatogenesis and Oogenesis
 Features of Meiosis
 Significance of Meiosis
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Discussing Agenda
Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk

3. “Meiosis”
Lecture Outcome
After watching and listening this lecture student will know about
• Meiosis, feature and different stages of meiosis
• Genetic Variations and Mechanism of Variations
• Spermatogenesis and Oogenesis
• Significance of Meiosis
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk

4. “Meiosis”
 Meiosis is the process in which the parent cell divides twice into four daughter cells containing
half the original amount of genetic information, i.e., the daughter cells are haploid.
 The gametes are produced by meiosis.
 A single germ cell divides into four unique daughter cells.
 Daughter cells have half the number of chromosomes as parent cell, so they considered haploid
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What is Meiosis
Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk

5. “Meiosis”
Exploring Meiosis in Animal Cell
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
(Campbell, 2008)

6. “Meiosis”
Exploring Meiosis in Animal Cell
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
(Campbell, 2008)

7. “Meiosis”
Genetic Variation
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 Genetic variation
 Is the raw material for evolution by natural selection
 Natural selection results in the accumulation of genetic variations favored by the
environment

8. “Meiosis”
Mechanisms of Variation
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 Meiosis provides various mechanisms for variation by:
 Crossing over
 Independent assortment
 Random fertilization
 Mutations

9. “Meiosis”
Crossing Over
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 Crossing over produces recombinant chromosomes
 Combines DNA from each parent
 Homologous portions of two nonsister chromatids trade places
 Crossing over increases genetic variation by combining DNA from two parents
into a single chromosome

10. “Meiosis”
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Prophase I
of meiosis
Nonsister chromatids
held together
during synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Anaphase II
Daughter
cells
Recombinant chromosomes
Crossing Over
Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
https://www.slideshare.net/deskam2/13-
lecture-biol-103030-gillette-college

11. “Meiosis”
Independent Assortment
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 In independent assortment
 Each pair of chromosomes sorts its maternal and paternal homologues into
daughter cells independently of the other pairs
 There are 2n possibilities of arrangements (i.e. 8.4 million in humans)

12. “Meiosis”
Random Fertilization
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 Don’t forget random fertilization!
 Adds to genetic variation: any sperm can fuse with any ovum (unfertilized
egg)
 Each gamete has 8.4 million possible chromosome combinations
 Produces a zygote with any of about 70 trillion diploid combinations

13. “Meiosis”
Random Fertilization
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
Possibility 1 Possibility 2
Metaphase II
Daughter
cells
Combination 1 Combination 2 Combination 3 Combination 4
2n = 4 so 2n is 22 = 4 possible combinations
https://biologypost.files.wordpress.com/
2013/01/independent_assortment.jpg

14. “Meiosis”
Mutation
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 A mutation is a change that occurs in our DNA sequence, either due to mistakes
when the DNA is copied or as the result of environmental factors such as UV light
and cigarette smoke.
 Over a lifetime our DNA? can undergo changes or 'mutations?' in the sequence of
bases?, A, C, G and T.

15. “Meiosis”
Spermatogenesis and Oogenesis
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 The result of meiosis in most animals is the formation of sperm and egg cells.
Gametogenesis in testes is called spermatogenesis, and in ovaries, oogenesis.
 Spermatogenesis produces mature sperm cells.
 Oogenesis produces a mature ovum or egg.
 It differs from spermatogenesis in that only one of the four meiotic products
develops into the functional gamete. The other products of meiosis are called polar
bodies and eventually disintegrate.

16. “Meiosis”
Features of Meiosis
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 Responsible for the formation of gametes
 Activation and deactivation of the genetic information.
 Maintenance of the constant number of chromosomes.
 Reshuffling of Chromosomes.
 Genetic mutation occurs
 Crossing over produces a new combination of traits and variations.

17. “Meiosis”
Significance of Meiosis
1. Meiosis is responsible for the formation of sex cells or gametes that are responsible for sexual
reproduction.
2. It activates the genetic information for the development of sex cells and deactivates the
sporophytic information.
3. It maintains the constant number of chromosomes. This is important because the chromosome
number doubles after fertilization.
4. In this process independent assortment of maternal and paternal chromosomes takes place. Thus
the chromosomes and the traits controlled by them are reshuffled.
5. The genetic mutation occurs due to irregularities in cell division by meiosis. The mutations that
are beneficial are carried on by natural selection.
6. Crossing over produces a new combination of traits and variations.
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk

18. “Meiosis”
Significance of Meiosis
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
(Miller-Harley, 2001)

19. “Meiosis”
Review of Mitosis vs Meiosis
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
https://biologypost.files.wordpress.com/2013/01/independent_assortment.jpg

20. “Meiosis”
References
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Course: Principle in Animal Life–II ZOO102, Instructor: Mr. Noor ul Akbar, Lecturer, Department of Zoology , KUST Email: noorulakbar@kust.edu.pk
 Miller-Harley: 2001. Zoology, Fifth Edition The McGraw-Hill Companies,
 Campbell, N.A. 2002. Biology, 6th Ed. Menlo Park, California: Benjamin/Cummings Publishing Company, Inc.
 https://biologypost.files.wordpress.com/2013/01/independent_assortment.jpg
 https://www.slideshare.net/deskam2/13-lecture-biol-103030-gillette-college

21. Thank you …
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