Meiosis Chapter 11.4 Objectives Describe how homologous chromosomes are alike and how they differ...
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Transcript of Meiosis Chapter 11.4 Objectives Describe how homologous chromosomes are alike and how they differ...
Meiosis Chapter 11.4 Objectives
Describe how homologous chromosomes are alike and how they differ
Contrast haploid and diploid cells
Summarize the process of meiosis
Compare mitosis & meiosis
Explain how genetic variation occurs in offspring of populations
Your body cells have 23 pairs of chromosomes. That is ___ total chromosomes.– Chromosome pairs # 1-22
are autosomes. (=44 chromosomes)
– Pair # 23 are the Sex chromosomes, X and Y, (determine gender)
2 Groups of Chromosomes: 1. Autosomes
2. Sex chromosomes
The pairs are called Homologous Chromosomes
Diploid (2n) cells have two copies of every chromosome.
Body cells are diploid*
Half the chromosomes
come from each
parent.
Body cells have 44
autosomes & 2 sex
chromosomes
Haploid (n) cells have one copy of every chromosome (or ½ the normal amount)
–Gametes are haploid*
–Gametes have 22 autosome chromosomes and 1 sex chromosome.
–Total = 23 chromosomes
Diploid (2n) vs. Haploid (n) Cells
•Body Cells
•Contain 2 copies of each chromosome
•Total = 46 chromosomes
(44 autosomes & 2 sex)
• Reproduce through mitosis
•Sex Cells
•Contain 1 copy of each chromosome
•Total = 23 chromosomes
(22 autosomes & 1 sex)
• Reproduce through meiosis
Sexual Reproduction relies on Meiosis
Meiosis – a type of nuclear division that produces four haploid gamete cells (each with ½ the number of chromosomes as the parent cell) (humans 46 chromosomes to 23 chromosomes)
Involves germ cells which divide to form gametes (sex cells) (sperm & eggs)
Still occurs after interphase in the cell cycle
**Remember**Mitosis involves body cells, which are also called
somatic cells
Homologous Chromosomes
Body cells are diploid having two sets of chromosomes
One set comes from each parent
Homologous Chromosomes: each chromosome from the male has a corresponding chromosome from the female
Homologous Chromosomes
Homologous chromosomes pair up in meiosis
Half of the homologous chromosomes come from each parent.
Homologous pairs of chromosomes also known as “TETRADS” have the same structure (genes)
• Are pairs of chromosomes which contain a paternal and maternal copy of the same genes
How do we get genetic variation?
Crossing OverDuring Prophase 1 – when
homologous chromosomes while paired in “tetrads” swap alleles.
This creates genetic recombination.
Quick Check / Review1. Your body has what 2 types of cells?
2. Somatic Cells reproduce through ________.
3. Sex Cells reproduce through __________.
4. Cells in your body have what 2 types of chromosomes?
5. Where do pairs of homologous chromosomes come from?
Phases of MeiosisWhat events occur during each phase of
meiosis?• MEIOSIS IS DIVIDED INTO TWO PARTS…• Involves two cell divisions
MEIOSIS I: • Is preceded by a
replication of chromosomes
• Includes:• Prophase I• Metaphase I• Anaphase I• Telophase I
Meiosis is the process that separates homologous pairs of chromosomes in a diploid cell, forming a haploid gamete
MEIOSIS II:• Chromosomes do not
replicate• Includes:
• Prophase II• Metaphase II• Anaphase II• Telophase II
Meiosis results in 4 haploid gametes– Meiosis occurs in sex cells
– Involves 2 nuclear Divisions*– Meiosis produces 4 gametes* which are
haploid (n) cells.
Meiosis 1
Meiosis 2
4 haploid gametes
Parent Germ Cell46 single
46 – Sister Chromatids
23 23
2323 23 23
Note: Without an Interphase between Meiosis 1 and Meiosis 2, the DNA is not duplicated!
During interphaseHomologous Chromosomes
pair up and then move to opposite ends of the cell
Sister chromatids line up and split to opposite ends of the cell
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Prophase 2 & Metaphase 2
Anaphase 2
Telophase 2
Meiosis 1
Meiosis 2
2n
n n
n n n n
Mitosis vs. MeiosisMitosis and meiosis are types of nuclear division
that make different types of cells.
Mitosis makes more diploid (2n) cells
Meiosis occurs in sex cellsMitosis occurs in body cells
Meiosis produces gametes
(haploid (n) cells)
Crash Course - MeiosisMeiosis: Where the Sex Starts - Crash Course
Biology #13 - YouTube
Let’s play a review GAME!http://hrsbstaff.ednet.ns.ca/bfougere/Science%20Jeopardy_files/frame.htm