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2 major groups of Cells
1. Somatic Cells
• Body cells
• Diploid = 2n
– two copies of each chromosome (1 from mom
and 1 from dad)
2. Gametes
– Sex cells
– Haploid = 1n or n
• one copy of each chromosome
– Ova or eggs in females (x)
– Spermatozoa or sperm in males (x or y)
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2 Types of Chromosomes in Cells
• Sex Chromosomes
• chromosomes that determine the gender of an
organism
• Humans have 2 = X and Y
• Autosomes
– All of the other chromosomes in an organism
– Humans have 22 pairs
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Sex Chromosomes and Autosomes
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Meiosis
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Formation of gametes
Division of 1 diploid cell into 4 haploid cells
DNA is copied once but divided twice
Two rounds of division = Meiosis I and Meiosis II
Each round has 4 stages
• Prophase, Metaphase, Anaphase, Telophase
• Creates unique gene combinations
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Meiosis I
• prophase I, metaphase I, anaphase I, telophase I
• Crossing-over
• portions of homologous chromosomes exchange
genetic material
• occurs during prophase I
• results in genetic “recombination”
• Genetic Linkage
• Genes located close together tend to be inherited
together
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Stages of Meiosis I
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Meiosis II
• prophase II, metaphase II, anaphase II, telophase II
• Four new haploid cells result
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Stages of Meiosis II
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Comparing Meiosis and Mitosis
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Development of Gametes
• Spermatogenesis
• is the process by which sperm cells are produced
• 1 diploid cell produces 4 haploid sperm cells
• Oogenesis
• is the process that produces mature egg cells
• 1 diploid cell produces 1 haploid egg cell and 3
polar bodies that die off
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Meiosis in Male and Female Animals
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Sexual Reproduction
• the formation of offspring through meiosis and the
union of a sperm and an egg
• Offspring produced by sexual reproduction are
genetically different from the parents
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