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MEIOSIS Chapter 11-4

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MEIOSIS Chapter 11-4. Warm Up Chapter11-4. What does diploid mean? What does haploid mean? How many chromosomes does mitosis produce in a cell? How many chromosomes does meiosis produce in a cell? What are homologous chromosomes?. Warm Up Chapter 10 and 11-4.

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MEIOSIS

Chapter 11-4

slide2

Warm Up

Chapter11-4

  • What does diploid mean?
  • What does haploid mean?
  • How many chromosomes does mitosis produce in a cell?
  • How many chromosomes does meiosis produce in a cell?
  • What are homologous chromosomes?
slide3

Warm Up

Chapter 10 and 11-4

  • How many chromosomes do humans have?
  • What does Meiosis do so that each cell does not have 92 chromosomes during fertilization?
  • Mitosis produces what kind of cells?
  • Meiosis produces what kind of cells?
  • How many cells does Mitosis produce?
  • How many cells does Meiosis produce?
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Meiosis cuts down the number of chromosomes in our cells to 23, so they can come together and create a cell with 46 chromosomes

  • -Meiosis creates variance - 23 chromosomes from mom, 23 chromosomes from dad
  • - Creates variants through reproduction
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1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).

a. This is a good idea if you’re going to combine two cells to make a new organism. B. This trick is accomplished by halving chromosome number.

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2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives.

a. This makes for a lot of genetic diversity. This trick is accomplished through and crossing-over.

b. Genetic diversity is important for the evolution of populations and species.

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The purpose of MITOSIS is to produce twoIDENTICAL(diploid) cells.

The purpose of MEIOSIS is to produce fourASSORTED and DIFFERENT(haploid)cells.

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Mieosis vs. Mitosis Animation 1:00

Mitosis/Meiosis Quiz

Meiosis/Mitosis side by side PPT

Dr. Thinkwell. Meiosis I and II 5:15

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Cornell Notes…

  • Meiosis and Mitosis
  • Mitosis goes through PMAT once.
  • Meiosis goes through PMAT twice.
  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
  • Cytokinesis
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II
  • Cytokinesis

MEIOSIS I

MEIOSIS II

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Mieosis vs. Mitosis Animation 1:00

Mitosis/Meiosis Quiz

Meiosis/Mitosis side by side PPT

Dr. Thinkwell. Meiosis I and II 5:15

Thinkwell.Spermatogenesis 2.3

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Cornell Notes…

  • Meiosis and Mitosis
  • During Prophase I, Meiosis undergoes “Crossing Over” between the paired chromatids.
  • Mitosis has NO crossing over.
  • Prophase I has crossing over between the chromatids resulting in the chromosomes of the offspring being DIFFERENT than either parent.
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The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis

The first (and distinguishing) division of meiosis

Mitosis

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End

P6

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The process of Meiosis

  • 2 Parts to Meiosis… Meiosis I and Meiosis II
  • Meiosis I is very similar to Mitosis
  • Interphase I – same as mitosis – the cell is growing – DNA replicates tetrads (4 sets of chromosomes)
  • Prophase I – chromosome pair together to make homologous pairs
  • Metaphase I – tetrads(4) stack and form in the middle (crossing over occurs) allows for more diversity
  • Anaphase I – homologous chromosome go to each side – they don’t separate they form dyads (2)
  • 5. Telophase I – nuclear membranes form – cytokinesis
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Meiosis II – going straight from Telophase I

6. Prophase II – diploid cells now – (2n) – each

cell has same amount as the parent cell

7. Metaphase II – similar to mitosis – line up in

the middle (centromeres on midline)

8. Anaphase II – chromosomes separate

9. Telophase II – nucleus forms and cytokinesis

results in 4 haploid cells (n).

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End

P5

P7

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Understanding Chromosomes

  • Somatic Cells ( Normal Human Body cells)
  • = 46 chromosomes (23 sets)
  • Diploid = 2 n
  • 2. Gametes (sex cells – sperm and egg) = 23 Chromosomes with one set
  • Haploid – 1n - not paired
  • 3. Ploidy – the number of chromosomes in a single cell.
  • some diseases happen when there is a different #
  • (Down’s syndrome has 47 chromosomes)
  • Down’s syndrome has 3 chromosomes for chromosome #21.
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Keys to Understanding Meiosis

1. Chromosomes are paired.

2. Chromosomes carry genes.

3. The gene forms on a pair of chromosomes may be homologous or non-homologous

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Spermatogenesis

Men are busy – meiosis produces roughly 250,000,000 sperm per day.

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Oogenesis –

Women are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime.

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What Meiosis is About

Meiosis allows the creation of unique

individuals through sexual reproduction.

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End

P3

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We are all unique – 1 chromosome from mom and one from dad

we are half like our parents, which are half like their parents, which are half like their parents and so on … That creates diversity! – We are 1/2 our parents, 1/4 like our grandparents, 1/8 of our great grandparents  go back so many years – that’s how different we all are from each other.

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Meiosis I – Prior to Meiosis I, each chromosome is replicated to form a tetrad = X X

Name ________

Date_________

Phase

Metaphase I

Spinal fibers attach to entire chromosome

Phase Prophase I

Each chromosome pairs with its corresponding chromosomes “homologous” to form a tetrad.

\

Phase

Crossing Over

Exchange portions of chromatids

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Y chromosome

X chromosome

Boy or Girl? The Y Chromosome “Decides”

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One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment

Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes.

In humans, n = 23 and 223≈ 8,000,0000.

That’s a lot of diversity by this mechanism alone.

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Crossing over

Meiosis Following a Single Chromosome Pair

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