Meiosis and Gametes 1
Chapter 11 Sexual Reproduction and Meiosis
Rev Question
Meiosis and Gametes 2
When and where does meiosis occur in humans?
Why is meiosis necessary?
“reductive division”
Meiosis and Gametes 3
What are the stages of Meiosis?
Meiosis I vs Meiosis II
Prophase I
Metaphase I
Anaphase I
Telophase I
McGraw-Hill Meiosis
Meiosis unique features
Meiosis and Gametes 4
How does Prophase I differ from Prophase of Mitosis?
1) Bivalents form -- “synapsis”
-- homologous chromosome pairs
2) Crossing over occurs-- exchange of DNA segments-- “chiasmata”
During Metaphase 1,bivalents are aligned at equatornot individual chromosomes
Question
Meiosis and Gametes 5
During Meiosis I parental homologous chromosomes are independently sorted to daughter cells
Chromosome reduction occurs during Meiosis I
Interkinesis
What happens during Meiosis II?
Chromosome reduction ---- sister chromatids separate
Gametes produced
McGraw-Hill sorting
Question
Meiosis and Gametes 6
Comparison of Meiosis and Mitosis
Metaphase looks differentfor each process
2N=4Question
Question
Meiosis and Gametes 7
Homework assignment:10 points: due next class
For a cell where 2N=6, draw a series of diagrams showing the chromosomes moving through the stages of meiosis.
In one of the diagram clearly label:-- a pair of homologous chromosomes-- a bivalent
Label all stages
Make diagrams large, clear and neat
Also answer the following questions:For an organism with a chromosome number of 2n = 56:
A. How many pairs of homologous chromosomes does each normal body cell possess? ___B. How many chromosomes does each cell possess after mitosis? ____C. How many pairs of sister chromatids are present at the beginning of meiosis? ___D. How many bivalents will form during prophase-I? ____E. How many chromosomes does each cell possess after meiosis? ___
Drawings must be neatly done and chromosomes drawn with
adequate detail. Chromosomes, bivalents and spindle fibers
must be recognizable as these structures.
Meiosis and Gametes 8
Why does meiosis in females yieldonly 1 viable gamete?
Why does spermatogenesis in males assure 50:50 ratio of males to females?
Sex of the sperm determines sex of the offspring
Meiosis and Gametes 9
How can errors during meiosis causeCongenital birth disorders?
Non-disjunction of chromosomes
e.g., Down’s syndrome
What is karyotyping?
“trisomy 21”-- an example of “aneuploidy”
Many effects-- reduced intellectual development-- heart and kidney defects
-- often fatal-- early onset Alzheimer's
Meiosis and Gametes 10
How does meiosis create genetic diversity?
1) crossing over
2) random assortment of chromosomes
and later …
3) random pairing of gametes