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http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html. Unit 6: Meiosis. 1 asexual reproduction. In unicellular organisms such as bacteria and protists , cell division is also reproduction called binary fission. Offspring are identical to the parents.

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http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.htmlhttp://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html

1 asexual reproduction
1 asexual reproduction
  • In unicellular organisms such as bacteria and protists, cell division is also reproduction called binary fission.
  • Offspring are identical to the parents.
  • Division for unicellular organisms can happen very quickly.
2 asexual reproduction
2 asexual reproduction

Can occur in multicellular organisms.

So, if an amoeba has two chromosomes, how many chromosomes do the two daughter cells have?

By what process did they divide?

3 sexual reproduction
3 Sexual Reproduction
  • When offspring are created from the union of two cells from two different parents, often called sex cells or gametes.
  • Offspring inherit genetic material from two parents.
slide6

4

slower

able to adapt in a changing environment

genetically unique offspring

two parents

must find one another to mate

  • faster
  • take full advantage of a good environment
  • genetically identical offspring
  • only one parent
5 sexual reproduction
5 Sexual Reproduction
  • If a fruit fly has 8 chromosomes, how many chromosomes do the offspring have?
  • So, could there be 8 chromosomes in the egg and sperm cells? Why or why not?
  • So, how many chromosomes should be in each egg and sperm for a fruit fly?
  • Could the egg and sperm be created by mitosis?
  • Somehow, we have to do what to the chromosome number?
6 chromosome number
6 Chromosome Number
  • Most cells are diploid, meaning that they have two sets of chromosomes (“di” means two).
  • So if you have 46 chromosomes, how many pairs do you have?
  • If a fruit fly has 8 chromosomes, how many pairs do they have?
  • The pairs of chromosomes are called homologous pairs.
  • The diploid number is often referred to as 2N.
7 karyotypes
7 Karyotypes
  • Show the chromosome pairs for an organism.
8 cutting the chromosome in half
8 Cutting the chromosome # in half
  • For gametes, though, we want half the chromosome number, or only one chromosome from each pair.
  • This is called the haploid number and is shown as 1N or N.
  • What would the haploid number be for a fruit fly or a human?
  • What do we call the process of producing gametes are haploid?
9 meiosis
9 Meiosis
  • Occurs in two stages, Meiosis I and Meiosis II.
  • Within each stage, there is a prophase, metaphase, anaphase and telophase.
  • Meiosis I yields two daughter that have half the chromosomes.
  • Those two cells enter Meiosis two, where they divide again and sister chromatids separate, creating a total of four haploid daughter cells.
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So N =?

How many daughter cells are made by the end of Meiosis I?

How many chromosomes does each daughter cell have?

11 How many chromosomes does the cell start with?

2N = ?

How many homologous pairs?

12 meiosis goals
12 Meiosis Goals
  • For Meiosis 1 – split chromosome number in half
  • For Meiosis 2 – split sister chromatids in half
  • So what must have happened to the DNA before Meiosis occurred?
13 tetrads
13 Tetrads
  • During Prophase 1 of Meiosis 1, a tetrad is formed when the homologous pair comes together.
  • A tetrad contains four chromatids: 2 chromosomes, each with its own copy.
14 crossing over
14 Crossing Over
  • When the tetrads form, some genetic variety is created from crossing over.
  • Crossing over is done when chromatids cross over one another and the crossed sections are exchanged.
mitosis vs meiosis

Mitosis vs. Meiosis

http://www.pbs.org/wgbh/nova/miracle/divide.html