Download Unit 1 Biology

Review…
1) What type of cell division produces body
cells?
Mitosis
Review…
2) Where are chromosomes found?
Nucleus
Review…
3) What chromosomes determine if someone is
a girl?
XX
Review…
4) How many pairs of chromosomes do humans
have?
23
Review…
5) What are the phases of mitosis in order?
Prophase, metaphase,
anaphase, telophase
Cell division Meiosis
Keywords: Meiosis, gametes, genetic variation,
crossing over, bivalent, homologous, random
orientation
What are we learning?
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What is meiosis?
Why is meiosis important?
How are sex cells made?
How are mitosis and meiosis the
same/different?
Body (somatic) cell
Sex cell (gamete)
(Eggs and sperm)
Meiosis
• A type of cell division
for sex cells in the
body. Sex cells are
also called gametes
• Sex cells only have 23
chromosomes in
humans!
Why do gametes only have 23
chromosomes??
Fertilisation restores the number of
chromosomes!
Meiosis
• What is the term used to describe a pair of
chromosomes?
• Where does meiosis take place?
• What does meiosis produce?
How does meiosis
give rise to variation?
• Crossing over between
homologous
chromosomes during
prophase I
How does meiosis give rise to variation?
• Random assortment (shuffling) of chromosomes
during metaphase I and II
Fertilisation also gives rise to
variation?
• We say that gametes show genetic variation
because no two gametes have the exact
genetic information.
We cannot predict which sperm will fertilise the
egg. It is like a lottery!
Genetic Variation
• What is genetic variation?
• What are some sources of genetic variation?
Mitosis vs. Meiosis in humans
Mitosis
Meiosis
• Asexual reproduction (bacteria,
yeast, plants)
• Growth and development
• Repair
• Produce gametes with half
the number of
chromosomes
• Produces genetic variation
In which type of cell
does it occur?
Body/Somatic cells
Sex cells/gametes
# of chromosomes in
parent cell
46
46
# of divisions
1
2
# of daughter cells
made
2
4
# of chromosomes in
daughter cell
46
23
Is daughter cell
identical to parent cell?
Yes
No – all are unique!
Functions?