10.1 Meiosis 2014
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Transcript of 10.1 Meiosis 2014
1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?
Interest Grabber
1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?
Interest Grabber
46 chromosomes
2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?
Interest Grabber
2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?
Interest Grabber
46 + 46 = 92; a developing embryo would not survive if it contained 92 chromosomes.
3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?
Interest Grabber
3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?
Interest Grabber
Sperm and egg should each have 23 chromosomes.
ASEXUAL REPRODUCTION
Bacteria reproduce using binary fission
Budding and regeneration are used by plants and animals to reproduce asexually (mitosis)
DISVANTAGES OF ASEXUAL REPRODUCTION
• All offspring are alike
• Species cannot adapt and change
• One disease can wipe out whole population
SEXUAL REPRODUCTION
Combines the genetic material from two parents (sperm and egg) so offspring are genetically different.
ADVANTAGES OF SEXUAL REPRODUCTION
• Allows for variation in population
• Individuals can be different
• Provides foundation for EVOLUTION
• Allow species to adapt to changes in their
environment
EGG + SPERM
If egg and sperm had same number of chromosomes as other body cells . . .
…baby would have too many chromosomes!
DIPLOID & HAPLOIDMost cells have 2 copies of each chromosome
(one from mom; one from dad)These cells are diploid (2n) and are called:
Body cells (aka somatic cells) are diploid (2n)
HOMOLOGOUSCHROMOSOMES
HOMOLOGOUS CHROMOSOMES• Same size• Same shape• Carry genes for the same
trait• But are NOT identical! (Don’t have to have the
SAME CHOICES)
DIPLOID & HAPLOID
• Some cells have only one copy of each chromosome.
• These cells are haploid (1n)• All sperm and egg cells are haploid
MITOSIS
• Makes 2 cells genetically identical to parent cell and to each other
• Makes 2n cells• Makes somatic (body) cells• Used by organisms to:
– increase size of organism, – repair injuries, – replace worn out cells
MEIOSIS
• Makes 4 cells genetically different from parent cell & from each other
• Makes 1n cells• Makes germ cells or
gametes (sperm & egg)• Used for sexual
reproduction
WHAT MAKES MEIOSIS DIFFERENT ?
1. Synapsis and Crossing over during (PROPHASE I)
1. Segregation and Independent Assortment during (ANAPHASE I)
3. Skip Interphase II (NO Synthesis) CELL DIVIDES TWICE, BUT…
ONLY COPIES DNA ONCE
Homologous chromosomes pair up during Prophase I = Synapsis
This group of FOUR (4)chromatids is called aTetrad.
WHAT MAKES MEIOSIS DIFFERENT? #1
WHAT MAKES MEIOSIS DIFFERENT? #1
Exchange of DNA betweenhomologous pairs = crossing overduring Prophase I
Allows for shufflingof genetic material
CROSSING
OVER
• Allows for rearranging of DNA in different combinations
• After crossing over, chromatid arms are not identical anymore
WHAT MAKES MEIOSIS DIFFERENT? #1
Separation of homologous chromosomes during ANAPHASE I
• Segregation• Independent Assortment
Separates gene choices and allows shuffling of genetic material
WHAT MAKES MEIOSIS DIFFERENT? #2
INDEPENDENT ASSORTMENT at ANAPHASE I
Lots of different combinations are possible!This is why you don’t look exactly like your brothers and sisters even though you share the same parents!
WHAT MAKES MEIOSIS DIFFERENT? #2
WHAT MAKES MEIOSIS DIFFERENT recap so far:
• Crossing over, independent assortment and segregation are all ways MEIOSIS results in genetic recombination
• So daughter cells are different from parents and from each other
Skip INTERPHASE II (No Synthesis)CELL DIVIDES TWICE, BUT … …ONLY COPIES ITS DNA ONCE
G1 G2S P M A T C
G1
MITOSIS:
MEIOSIS:
S G2 P M A T CP M A T C
( I )
( II )
WHAT MAKES MEIOSIS DIFFERENT? #3
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II