Date _________
Meiosis-Sexy Cells
Definition* Cell __________by which eggs and sperm are__________.
* The production of sex cells, which are not _________identical,
through a series of _____divisions.
What does it ensure?
Ensures that ________have the same number of ________________in
each generation.
What is it?
It is a ____________process that reduces the chromosome number by
half—from ___ to 23—to form _____and _____cells.
This is a reduction in genetic material.
Fertilization Results in:
When the sperm and egg cells join at_______________, each
contributes 23 chromosomes so the resulting ____________will have
the usual 46.
How Does Genetic Variation Happen?
Meiosis also allows genetic variation through a process of _____shuffling
while the cells are _________.
Meiosis
• TWO divisions
• ONE DNA replication
• Results
• in 4 daughter cells with only 23 chromosomes in each
First Stage:
• Interphase: Before meiosis begins, genetic material is duplicated.
• First division of meiosis
– Prophase 1: Duplicated chromatin condenses. Each chromosome
consists of two, closely associated sister chromatids. Crossing
over can occur during the latter part of this stage.
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–
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•
•
•
•
Metaphase 1: Homologous chromosomes align at the equatorial
plate.
Anaphase 1: Homologous pairs separate with sister chromatids
remaining together.
Telophase 1: Two daughter cells are formed with each
daughter containing only one chromosome of the homologous
pair.
Second division of meiosis: Gamete formation
– Prophase 2: DNA does not replicate.
– Metaphase 2: Chromosomes align at the equatorial plate.
– Anaphase 2: Centromeres divide and sister chromatids migrate
separately to each pole.
– Telophase 2: Cell division is complete. Four haploid daughter
cells are obtained.
One parent cell produces four daughter cells. Daughter cells have half
the number of chromosomes found in the original parent cell and with
crossing over, are genetically different.
Crossing Over
Where a section of one chromosome switches places with the same
section from the other chromosome of the pair.
Recombination
http://www.accessexcellence.org
Comparing Mitosis With Meiosis:
http://post.queensu.ca/
What is a zygote and how is it formed?
A zygote is a cell that is formed when a sperm fertilizes and egg.
Compare and contrast sexual and asexual reproduction.
Sexual reproduction – offspring is produced when sex cells (egg & sperm)
combine. Offspring are __________different from each other and the
parents.
Asexual reproduction – One parent produces genetically_________
offspring