Download Meiosis vs Mitosis notes

6.1 Chromosomes and Meiosis
KEY CONCEPT
Gametes have half the number of chromosomes
that body cells have.
13.1 Ecologists Study Relationships
The fusion of two gametes results in offspring
that are a genetic mixture of both parents.
• Fertilization occurs when a sperm and an egg
combine.
•The new “combined” cell must contain the same
number of chromosomes as the parents.
• Sperm and egg cells need only half the usual
number of chromosomes.
6.1 Chromosomes and Meiosis
You have body cells and gametes.
• Body cells are also called somatic cells.
• Germ cells develop into gametes.
– Germ cells are located in the ovaries and testes.
Gametes are sex cells: egg and sperm.
Gametes have DNA that can be passed to offspring.
body cells
sex cells (sperm)
sex cells (egg)
6.1 Chromosomes and Meiosis
Your cells have autosomes and sex chromosomes.
•
Your body (somatic) cells have 23 pairs of
chromosomes.
– Homologous pairs of chromosomes have the
same structure.
– For each homologous pair, one chromosome
comes from each parent.
– Chromosome pairs numbers 1 – 22 are
autosomes (determine non sex-related
characteristics).
– Chromosome pair 23 are sex chromosomes
(X and Y determine gender in mammals.)
6.1 Chromosomes and Meiosis
Body cells are diploid ; gametes are haploid
Diploid (2n) cells have two copies of every chromosome.
• Body cells are diploid.
• Half the chromosomes come from each parent.
– This example shows a diploid cell with two homologous
pairs of chromosomes.
6.1 Chromosomes and Meiosis
• How many pairs of chromosomes do human body cells
have? 23
• How many individual chromosomes do human body cells
have? 46
• Which chromosomes in the previous diagram are pairs?
How can you tell? Purlpe & green; red and teal – can tell
by length
• Are the two chromosomes in a homologous pair
identical? Not identical but they match
6.1 Chromosomes and Meiosis
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– This example shows a haploid cell with two individual
chromosomes.
6.1 Chromosomes and Meiosis
• How many pairs of chromosomes do human gamete cells
have? None – no pairs in a gamete
• How many individual chromosomes do human gamete
cells have? 23
6.1 Chromosomes and Meiosis
• Chromosome number must be maintained in animals.
• Mitosis and meiosis are types of nuclear division that
make different types of cells.
• Mitosis makes two identical daughter cells.
6.1 Chromosomes and Meiosis
• The top cell in the previous diagram is in what phase of
Mitosis? prophase
• How many chromosomes are contained in the original
“mother” cell? 4
• Which cell did the original “mother” look like? Like the
daughter cells
6.1 Chromosomes and Meiosis
• Meiosis makes haploid cells from diploid cells.
– Meiosis occurs in sex cells.
– Meiosis produces gametes.
6.1 Chromosomes and Meiosis
• What did the original “mother” cell (for the previous
diagram) look like? Like the mother cell in mitosis (4
chrom – 2 long and 2 short)
• Which row in the previous diagram shows haploid cells?
Bottom row
6.1 Chromosomes and Meiosis
Mitosis / Meiosis Comparison
6.1 Chromosomes and Meiosis
• How is the division of chromosomes different between
Mitosis and Meiosis?
Mitosis – 1 division – makes 2 cells – same # chrom as mother
Mitosis – 2 divisions – makes 4 cells – half # chrom as mother
• What is the difference in function between Mitosis and
Meiosis?
Mitosis – body cells
Mitosis – reproductive cells
• Are each of the four cells in the last row of the previous
diagram unique? No – two pairs of “twins”
6.1 Chromosomes and Meiosis
•Every sperm and every egg
cell produced is genetically
unique.
•The genes contained in one egg
cell are different than any other
egg cell produced by that
organism.
•The genes contained in one
sperm cell are different than any
other sperm cell produced by that
organism
•How is that possible??
6.1 Chromosomes and Meiosis
Meiosis and Crossing Over
• How does the simulation show that each cell is unique?
– Color of each strand is different
• What is this process called?
– Crossing over
• How would this process compare with 23 sets of
chromosomes vs. 1 set?
– With 23 pairs there are billions and billions of possible
combinations
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter11/meiosis_with_crossing_over.html
6.1 Chromosomes and Meiosis
Meiosis and Crossing Over