Download - G7 Ch4.1 - Sexual Reproduction and Meiosis
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Sexual Reproduction and MeiosisChapter 4 Lesson 1
p.116-126
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Cell DivisionMitosis• Body cells
Meiosis• Sex cells
– Sperm and Egg Cells
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Meiosis• A special kind of cell division that end in four
cells with half the number of chromosomes.
• Creates sex cells (egg cells and sperm cells)
• The original cell has 46 chromosomes.
• The final four cells has 23 chromosomes each.
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Sexual Reproduction• When two parents make one offspring.
• Two different sex cells combine to form an offspring.
• An egg is a female sex cell.
• A sperm is a male sex cell.
• Fertilization is the joining of an egg and a sperm.• A fertilized egg cell is called a zygote.
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Chromosomes• Human cells have 46 chromosomes, or
23 pairs of chromosomes.
• 23 of our chromosomes come from our mom.
• 23 of our chromosomes come from our dad.
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Chromosomes• Each pair of chromosomes have the
same type of information.
• One set from mom
• One set from dad
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Mom Dad
Gene for Eye Color
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Mom Dad
Gene for Eye Color
Mom Dad
Before DNA is replicated, copied during interphase.
Duplicated Chromosomes after interphase.
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Dad
Gene for Eye Color
Homologous Pairs of chromosomes have genes for the same traits.
Mom
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Mom Dad
These are still homologous pairs. Now they are just duplicated.
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We have 23 homologous pairs.
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Sexual Reproduction
• Body cells have a full set of chromosomes in homologous pairs.
• We call these cells diploid.
• Sex cells have half the number of chromosomes.
• They do not have homologous pairs.
• We call them haploid. (half)
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• In meiosis, one diploid cell divides and makes four haploid cells.
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• When fertilization occurs, the new cell, called a zygote, will have the normal number of cells.
Diploid (2N)
Haploid (N)
Haploid (N)
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Different organisms have different numbers of chromosomes.
– How many homologous pairs does each species have?
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Stages of Meiosis
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Fig. 2.7 ©Scion Publishing Ltd
The stages of meiosis.
Meiosis is used only for the production of sperm and eggs.
It consists of two successive cell divisions, producing four daughter cells (although in oogenesis only one of these develops into a mature oocyte; the others form the polar bodies).
Meiosis has two main functions: to reduce the chromosome number in the gamete to 23, and to ensure that every gamete is genetically unique.
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Growth and Development
• After fertilization a single celled zygote is formed.
• The zygote will go through mitosis and cell division to become an organism.
MITOSIS MEIOSIS
MEIOSIS I
Prophase IChromosome
replication
Homologouschromosomepair
Chromosomereplication
2n = 6
Parent cell
Prophase
Replicated chromosome
Metaphase Metaphase I
Anaphase ITelophase I
Haploid n = 3
Daughter cells ofmeiosis I
MEIOSIS II
Daughter cells of meiosis II
nnnn
2n2n
Daughter cellsof mitosis
AnaphaseTelophase
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• Choose one color to be the maternal chromosome.
• Choose one color to be the paternal chromosome.
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• Cut a maternal and paternal chromosome to both be 5cm long.
• Then, cut a maternal and paternal chromosome to be both 8cm long.
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• Chromosome 1
• Chromosome 2
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How many chromosomes does the cell have total?
• Chromosome 1
• Chromosome 2
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Cell Division
Mitosis Meiosis