Bellringer Mon, 12/7

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Bellringer Mon, 12/7

• What is mitosis?
• What are the phases of mitosis again?
• How many cells do we get after mitosis?
• Quickly draw a chromosome!
• Look up and tell me what is meiosis!
• Use your books! 5 MINS today!
• REMINDERS HW 14 due Fri, Progress Reports
• Grades this Wed,LAB FEE anytime!!!

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1 Minute
Times Up!
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3 Minutes
30 Seconds
2 Minutes
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Meiosis
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Reminders, Review and Something New

• Chromosomes condensed chromatin (DNA)
• Made up of 2 sister chromatids held together in
  by the centromere
• Genes- sections of a chromosome responsible for
  one trait (eye color, height, etc)

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• Again, how many chromosomes do we have?
• 23 (Maternal) 23 (Paternal) Total 46

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What is MEIOSIS? Cell division that results in 4
daughter cells with half as many chromosomes as
the parent cells!
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Meiosis
Parent cell chromosome pair
Chromosomes copied
1st division - pairs split
2nd division produces 4 gamete cells with ½ the
original no. of chromosomes
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What cells go through meiosis?
only gametes or sex cells. And we
get males-sperm and females-eggs
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Why do we need meiosis?

• To reduce the number of chromosomes in 1/2 in
  gametes (sex cells)!
• Why 1/2 the chromosomes in gametes?
• the male and female gametes need to provide ½ the
  chromosomes each so the offspring has one
  complete set (1/2 from mom and 1/2 from dad)!

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Meiosis PMAT I and II
Parent cell
Meiosis I First division
Meiosis II Second division
4 daughter cells
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Meiosis I Prophase I homologous pairs (and
copies) synapse (pair up). Crossing over
occurs! Metaphase I homologous chromosomes
align in the middle of the cell!
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What are homologous chromosomes?

• paired chromosomes with genes for the same trait
  aligned

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Anaphase I homologous chromosomes move to
opposite ends Telophase I 2 nuclei form,
original cell finishes to divide
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Meiosis II No INTERPHASE or DNA copied between I
and II Prophase II chromosomes condense again
and start to move toward the center Metaphase II
chromosomes line up in the center of cells
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Anaphase II sister chromatids separate to
opposite poles Telophase II two nuclei form
for each of the cells Cytokinesis happens like
in mitosis! 4 daughter cells with half the amount
of chromosomes formed!
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Results after meiosis 4 Sex cells (gametes)
that are haploid (n) - half as many chromosomes
as parent cell (2n)
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n
n number of chromosomes from each parent

• Gametes (sex cells)- haploid

2n

• Body cells diploid

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Diploid vs. Haploid
Organism Gamete (n) Body Cell (2n)
Humans 23 46
Mosquito 3 6
Toad 11 22
Potato 24 48
Dog 39 78
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Stages of Meiosis Meiosis I and Meiosis II
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What next? Fertilization
Egg (n) Sperm (n) Zygote (2n)
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ZygotegtEmbryogtFetus
A fertilized egg with diploid set of
chromosomes. After fertilization, the zygote
divides by mitosis and becomes an embryo. Later
, the embryo becomes a fetus
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Mitosis vs. Meiosis
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2 Key Differences Between Mitosis and Meiosis 1.
Look at the Way Chromosomes Pair and Align
Meiosis
Mitosis
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2. Crossing-Over
Chromosomes exchange genetic material between
homologous pairs!