Meiosis

1
Meiosis

• Chapter 10, Section 2

2
Meiosis Activity

• You need one textbook for every two students and
  a sheet of paper with both your names on it.
• You will be taking notes from the screen and
  using your textbook.

3
Genes and Chromosomes

• Punnett squares help us to study a few genetic
  traits at a time
• Organisms actually have tens of thousands of
  genes that make each of us unique
• Genes are lined up on chromosomes
• One chromosome can contain a thousand genes along
  its length

4
Turn to page 265 in the textbook

• Take a sheet of paper and put both your names on
  it. With your partner, find the bold word
  meiosis. Read about meiosis and answer the
  following questions.
• 1. Does meiosis occur in liver, heart, and skin
  cells?
• 2. Why is it important for organisms to produce
  cells with HALF the number of chromosomes?

5
Diploid Haploid Cells

• Diploid a cell with two sets of chromosomes, 2n
• Haploid a cell with one set of chromosomes,
  gametes, 1n
• Meiosis forms haploid gametes required for sexual
  reproduction
• Meiosis has 2 stages
• Meiosis I
• Meiosis II

6
Turn to page 265

• Study Table 10.1 Chromosome Numbers of Common
  Organisms and answer the following questions with
  your partner. Be prepared to share your answers.
• 3. What does the n stand for in the table?
• 4. Look at the data for the leopard frog. Why is
  the number in the body cell column double the
  number in the gamete column?

7
? MEIOSIS I

• Separation of homologous pairs
• Homologous Pair in a diploid cell the 2 sets of
  chromosomes pair up

8
? 1. Prophase I

• DNA coils into chromosomes
• Nuclear envelope nucleolus break down
• Synapsis homologous chromosomes pair up into
  tetrads
• Crossing-over homologous pairs switch pieces of
  their chromatids
• Genetic Recombination maternal paternal
  genetic info get shuffled during crossing-over

9
(No Transcript)
10
Turn to page 269

• Study Figure 10.13 and answer the following
  questions. Be prepared to share your answers!
• 5. Are sister chromatids identical or different
  to each other? What about homologous pairs?
• 6. In part C, if you put the four chromosomes
  back into pairs, would they be the same as the
  original Homologous chromosomes in part A?

11
? 2. Metaphase I

• Tetrads line up in the middle of the cell
• Spindle fibers attach at the centromeres of each
  homologous chromosome

12
Homologous chromosomes line up sideby side as
tetrads
13
? 3. Anaphase I

• Each homologous chromosome moves to the opposite
  end of the cell
• Independent Assortment random separation of
  chromosomes, allows for genetic variation

14
(No Transcript)
15
? 4. Telophase I Cytokinesis I

• Two newly formed cells are haploid
• Each chromosome is still made up of two
  chromatids

16
2 Non-Identical Cells Created
17

• Humans have 46 chromosomes (23 pairs)
• 7. With your partner, discuss what would happen
  if the formation of gametes stopped after meiosis
  I. How many chromosomes would the resulting human
  end up with? Be prepared to share with the class!

18
? MEIOSIS II

• Separation of sister chromatids
• Sister Chromatids identical halves of a
  chromosome that has been duplicated

19
? 5. Prophase II

• 2 newly created cells from Meiosis I start to
  divide

20
? 6. Metaphase II

• Chromosomes line up in the center

21
? 7. Anaphase II

• Sister Chromatids separate

22
? 8. Telophase II Cytokinesis II

• 4 new cells, each with half the number of
  chromosomes of the original cell

23
Development of Gametes

• Spermatogenesis production of sperm cells
• Oogenesis production of mature egg cells

24
Turn to page 269

• Read the section titled Meiosis Provides for
  Genetic Variation and answer the following
  questions
• 8. Describe the major difference between cells
  formed by mitosis and cells formed by meiosis.
• 9. What is variability mean in meiosis and why
  is it important to us?

25
Nondisjunction

• Nondisjunction failure of homologous pairs to
  separate in Meiosis I
• If an organism survives, it may have a genetic
  disorder

26
Polyploidy

• Polyploid organisms with more than the usual
  number of chromosome sets
• Occurs frequently in plants, results in plants
  that are larger than normal