meiosis and sexual reproduction n n 2n review question discussion question
TRANSCRIPT
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Meiosis and Sexual Reproduction
n
n 2n
Review Question
Discussion Question
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Mitosis ReviewSingle-cell organisms (prokaryotic) carry
out Mitosis for asexual reproductionMulti-cell organisms (eukaryotics) carry
out Mitosis for growth and repairThe phases of mitosis in order are:
Prophase, Metaphase, Anaphase, and Telophase
Interphase is known as the “resting phase”
Cytokinesis occurs at the same time as telophase
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Through which process do eukaryotic cells reproduce?
Requires sex cells from two parents (male and female)
Sex cells form as a result of meiosisOffspring are usually not identicalImportant for the survival of many
species◦Process results in genetic variation of
offspring
Sexual Reproduction
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Define the following terms:
Sexual Reproduction
MeiosisGameteSomatic CellsHaploid
Textbook pg 46 - 51
• Fertilization• Zygote• Diploid• Homologous
Pairs
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New Vocabulary
Meiosis: The process that results in the formation of gametes
Gametes: Sex cells (egg in females; sperm in males); contains haploid chromosomes
Somatic Cells: All body cells except for sex cells; contain Diploid chromosomes
Haploid: another term for half; refers to the number of chromosomes; written as n◦Chromosomes found singular
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Fertilization: the union of an egg and a sperm
Zygote: Cell that forms as a result of fertilization◦Contains Diploid chromosomes (2n)
Diploid: Chromosomes found in pairs; written as 2n; Somatic Cells
Homologous Chromosomes: Similar chromosomes that are found in pairs; ½ of pair comes from mother, other ½ from father◦Human Body somatic cells contain 46
chromosomes, so 23 homologous pairs
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MeiosisTwo division of the nucleus occursSteps of each division are similar to
those of mitosisMeiosis I
◦Each chromosome is duplicated, similar to mitosis
Meiosis II◦Two cells that form as a result of Meiosis I
divide again◦Four daughter cells are produced
Video
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Meiosis
Parent cell – chromosome pair
Chromosomes copied
1st division - pairs split
2nd division – produces 4 gamete cells with ½ the original no. of chromosomes
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Meiosis IPhase Image Description
Prophase I
- Homologous chromosomes pair together - Crossing over occurs between pairs resulting in genetic variation
Metaphase I
- Spindle fibers attach to chromosomes and line up in the middle of the cell
Anaphase I - Spindle fibers pull the homologous pairs apart- Chromosomes move to opposite sides of the cell
Telophase I
(& cytokinesi
s)
-Nuclear Membrane forms-Cell splits into two new cells- Cells contain haploid chromosomes (n)
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Meiosis IIPhase Image Description
Prophase II
-new Spindle fibers form and attach to sister chromatids
Metaphase II
- Spindle fibers attach to sister chromatids and line up in the middle of the cell
Anaphase II
- Spindle fibers pull the sister chromatids apart- Chromosomes move to opposite sides of the cell
Telophase II(&
cytokinesis)
-Nuclear Membrane forms-Each cell splits into two new cells-Forms 4 haploid cells
What is the end result of Meiosis?
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End Results of MeiosisFemale Eggs are MUCH larger than
male spermEach haploid cell in males become a
gamete◦Results in 4 sperm
Only 1 of the haploid cells in females become a gamete◦Results in 1 egg and 3 polar bodies◦Polar bodies are unused and broken down
K K K K
K K K K
EggPolar Bodies Why does
only one gamete form in Females?
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How do Mitosis and Meiosis differ?
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The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in
Meiosis
Mitosis The first (and distinguishing) division of meiosis
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Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.
Explain the significant of crossing over.
Another Way Meiosis Makes Lots of Different Sex Cells
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Another Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment
Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes.
That’s a lot of diversity by this mechanism alone.
In humans, n = 23 and 223 = 6,000,0000.
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Meiosis – division error
Chromosome pair
Describe the errors that occur during each division.
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Meiosis error - fertilization
Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’.
In humans this often occurs with the 21st pair – producing a child with Downs Syndrome
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21 trisomy – Downs Syndrome
Can you see the extra 21st chromosome?