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MEIOSISQ2 WK3 D2
Meiosis
Meiosis is the type of cell division by which germ cells (eggs and sperm) are
produced.
One parent cell produces four daughter cells.
Daughter cells have half the number of chromosomes found in the parent cell
MeiosisDuring meiosis, DNA replicates
once, but the nucleus divides twice.
There are 2 parts to Meiosis:
1. Meiosis 1
2. Meiosis 2
The 4 new daughter cells have variation of the parent DNA; this is genetic variation
Meiosis Terminology• Karyotype: Arranging of chromosomes from
largest to smallest; pairing up the homologous chromosomes
• Autosomes: All non-sex chromosomes; (#1-22 for humans)
• Sex Chromosomes: Chromosomes that determine the sex of an organism (#23 for humans)
• Set (n): # of different chromosomes. REMEMBER: Haploid = 1set, Diploid= 2 sets
Amniocentesis
Karyotype of a human• Is this person male or
female?
• How many sex chromosomes are present?
• How many autosome chromosomes are present?
• How many homologous pairs of chromosomes are present?
Background on Meiosis
• Meiosis involves 2 divisions of the nucleus– Meiosis 1 & Meiosis 2
Meiosis STARTS with HOMOLOGOUS CHROMOSOMES
Homologous Chromosomes: They are similar in shape, size & genetic content
Meiosis 1: 1st Division of Meiosis• Prophase I: Chromosomes
condense, nuclear envelope breaks, homologous chromosomes pair at ends.
• ***Cross-Over: Part of chromatid on 1 homologous chromosome exchanges with the other chromosome***
DRAW ME
THIS ISGENETIC
VARIATION
Meiosis 1: 1st Division of Meiosis• Metaphase I: Homologous chromosomes
move to center of the cell by the spindle fibers.
• Anaphase I: Homologous chromosomes separate and move to opposite poles, BUT sister chromatids stay together. A set of chromosomes moves to each pole
• Telophase I: The spindle fibers disappear, cells begin to cleave; still, two sets of chromosomes are at opposite poles
End of Meiosis I
• Once Meiosis I is complete, cytokinesis occurs and the cell splits into 2 haploid cells. These 2 cells enter Meiosis II
Meiosis I: STOP & THINK1. What is the purpose of Meiosis?
2. Describe genetic variation
3. Explain purpose of karyotyping
4. Explain cross-over
5. What major event occurs in Anaphase I ?
6. Are the daughter cells haploid or diploid? Explain
Any questionson Meiosis I
?????
Meiosis I: Video
• http://www.youtube.com/watch?v=D1_-mQS_FZ0
Meiosis II• Prophase II: A new spindle forms around the
chromosomes (no longer HOMOLOGOUS CHROMOSOMES)
• Metaphase II: Chromosomes line up at center & spindle fibers attach to centromere
• Anaphase II: Centromeres split, chromatids move to opposite poles of cell
• Telophase II: Nuclear envelope forms around each set of chromosomes & spindles retracts, cell begins cytokinesis
Result of Meiosis II• 4 HAPLOID cells form as a result of Meiosis II
• Haploid = cell containing 1 set of chromosomes
Meiosis II: 2nd division of Meiosis
Prophase II
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Metaphase II
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Telophase II
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Meiosis I & II Venn Diagram
Meiosis I Meiosis II
Meiosis Booklet 1. Everyone needs 3 sheets of blank paper
2. Fold each one hotdog style3. Cut straight up the fold
(You should have 6 long sheets, only use 5)
4. Label each square with the phases of meiosis the same as the mitosis booklet
Meiosis Review Questions 1. What type of cells are
used in Meiosis? Give examples of these cells.
2. Meiosis is used in sexual reproduction. Explain the process of “cross-over”
3. Draw homologous chromosomes going through cross-over.
4.Meiosis is divided into two parts, why?
5. Define “Haploid”
6. Compare and Contrast Meiosis to Mitosis.
In your notebook!
Mitosis & MeiosisComparison Worksheet
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
http://www.usoe.k12.ut.us/curr/science/sciber00/7th/genetics/sciber/animatin.htm
Meiosis & Genetic Variation
Q2 WK4 D2Nov. 5th, 2013