Meiosis grade 8

Science Bio Grade8

1. Unit 7 Lesson 2 Meiosis

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2. Unit 7 Lesson 2 Meiosis
Indiana Standards
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•8.3.3 Explain that genetic information is
transmitted from parents to offspring mostly by
chromosomes.

3. Number Off!
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How do sex cells differ from body cells?
•Before sexual reproduction can take place, each
parent produces sex cells.
•Sex cells have half of the genetic information that
body cells have.
•When genetic information from two parents
combines, the offspring will have one full set of
genetic information.
Unit 7 Lesson 2 Meiosis

4. How do sex cells differ from body cells?
•In body cells, chromosomes are found in pairs of
homologous chromosomes , which have the
same structure and size.
•Homologous chromosomes carry the same genes.
However, some may be different versions of the
genes.
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Unit 7 Lesson 2 Meiosis

5. How do sex cells differ from body cells?
•One chromosome pair is made up of sex
chromosomes.
•Cells with homologous chromosomes are called
diploid.
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Unit 7 Lesson 2 Meiosis

6. Why do organisms need sex cells?
•Normal human body cells contain 46
chromosomes.
•Sex cells are also known as gametes. Gametes
have only half of the usual number of
chromosomes.
•Gametes are haploid, meaning they have one
chromosome from each homologous pair.
Gametes are made in the reproductive organs.
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Unit 7 Lesson 2 Meiosis

7. Why do organisms need sex cells?
•Sex cells are needed so that in sexual
reproduction offspring receive a total of 46
chromosomes.
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Unit 7 Lesson 2 Meiosis

8. How are sex cells made?
•Mitosis produces two new cells that contain exact
copies of the chromosomes of the parent cell.
•A different kind of cell division is needed to
produce sex cells.
•Meiosis is the type of cell division that produces
haploid sex cells such as sperm or egg cells.
•When an egg is fertilized by a sperm cell, a new
diploid cell forms.
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Unit 7 Lesson 2 Meiosis

9. One Step at a Time
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What are the stages of meiosis?
•Meiosis has two parts: meiosis I and meiosis II.
•Recall that homologous chromosomes have the
same genes but are not exact copies of each
other.
Unit 7 Lesson 2 Meiosis

10. One Step at a Time
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What are the stages of meiosis?
•Before meiosis I begins, each chromosome is
duplicated. Each half is called a chromatid.
•Chromatids are connected by centromeres.
•During meiosis I, pairs of homologous
chromosomes and sex chromosomes split apart
into two new cells.
Unit 7 Lesson 2 Meiosis

11. What are the stages of meiosis?
•In prophase I, duplicated homologous
chromosomes pair up.
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Unit 7 Lesson 2 Meiosis

12. What are the stages of meiosis?
•In metaphase I, the homologous chromosome
pairs line up in the middle of the cell.
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Unit 7 Lesson 2 Meiosis

13. What are the stages of meiosis?
•In anaphase I, the homologous chromosomes
separate from their partners and move to opposite
sides.
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Unit 7 Lesson 2 Meiosis

14. What are the stages of meiosis?
•In telophase I and cytokinesis, the nuclear
membranes re-form and the cell divides into two
cells. The chromatids are still joined.
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Unit 7 Lesson 2 Meiosis

15. What are the stages of meiosis?
•Meiosis II involves both of the new cells that
formed during meiosis I.
•The new cells divide during meiosis II.
•Meiosis II results in four haploid sex cells.
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Unit 7 Lesson 2 Meiosis

16. What are the stages of meiosis?
•In males, the four sex cells develop into sperm
cells.
•In females of some species, three cells are broken
down, and only one haploid cell becomes an egg.
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Unit 7 Lesson 2 Meiosis

17. What are the stages of meiosis?
•In prophase II, the nuclear membrane breaks
apart.
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Unit 7 Lesson 2 Meiosis

18. What are the stages of meiosis?
•In metaphase II, the chromosomes line up in the
middle of the cells.
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Unit 7 Lesson 2 Meiosis

19. What are the stages of meiosis?
•In anaphase II, the chromatids are pulled apart
and move to opposite sides.
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Unit 7 Lesson 2 Meiosis
.

20. What are the stages of meiosis?
•In telophase II and cytokinesis, the nuclear
membranes re-form and the cells divide. Each cell
is haploid.
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Unit 7 Lesson 2 Meiosis

21. How does meiosis compare to mitosis?
•Only sex cells undergo meiosis. All other cells
divide by mitosis.
•In meiosis, chromosomes are copied once, and
the nucleus divides twice.
•In mitosis, the chromosomes are copied once, and
the nucleus divides once.
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Unit 7 Lesson 2 Meiosis

22. How does meiosis compare to mitosis?
•Meiosis produces haploid cells. Mitosis produces
diploid cells.
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Unit 7 Lesson 2 Meiosis

23. Unit 7 Lesson 2 Meiosis
Down Syndrome
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•Down syndrome is a genetic disease caused by an
error during meiosis.
•The chromatids in chromosome 21 do not
separate, so one of the sex cells gets an extra
copy of chromosome 21.
•Down syndrome causes a number of health
problems and learning difficulties, but many
people with Down syndrome have fulfilling lives.