Understanding Sexual Reproduction

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Understanding Sexual Reproduction

• Science 9

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Sexual Reproduction

• The word "homologous" comes from the Greek word
  "homologos,"
• It means agreeing.
• How do the chromosomes in a homologous pair
  "agree" with each other?

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Mitosis and Asexual Reproduction

• When a body cell, such as a skin cell, undergoes
  mitosis and cell division, two new identical skin
  cells are produced.
• One parent divides mitotically to produce two
  identical offspring.
• Another process is responsible for producing
  unique or non-identical individuals.

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• This process is called
• Sexual Reproduction

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Sexual Reproduction

• Your body has specialized organs that make
  specialized cells, or gametes, for sexual
  reproduction.
• These gametes from two parents combine during a
  process called fertilization to form a new cell,
  or zygote.
• This zygote is the first body cell of a new
  organism.

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Sexual Reproduction

• Where do gametes come fro?
• How are they different from body cells?
• Why are gametes necessary for sexual reproduction?

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Sexual Reproduction

• Your 46 chromosomes could be arranged into 23
  pairs of chromosomes that resemble each other in
  size and shape.
• Matching" pairs of chromosomes are known as
  homologous pairs.
• You receive one member of each pair from your
  mother, the other from your father.

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Sexual Reproduction

• Chromosomes in a human body 46
• Human Body cells are called diploid.
• di double
• The human diploid number is ___
• (hint 2 X number of pairs)
• Human gametes are called haploid because they
  have half the number of cells that normal cells
  have.
• ha half

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Sexual Reproduction

• Number of Chromosomes16
• Number of homologous pairs ?
• Diploid Number ?
• Haploid Number ?

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Sexual Reproduction

• The body cells of every typical organism in a
  species have the same number of chromosomes in
  each cell.
• This is the diploid number
• This number stays the same from one generation to
  the next.
• The gametes of the same species have the haploid
  number.

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Sexual Reproduction

• In order for the human chromosome number to
  remain at 46, gametes must have one-half the
  number of chromosomes of normal body cells.
• Only haploid gametes can combine during
  fertilization to form a diploid zygote.
• Only a diploid zygote can function as the
  offspring's first body cell

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Meiosis

• Mitosis ensures that chromosome number does not
  change.
• The process that ensures each gamete contains
  only one-half set of chromosomes is called
  meiosis.
• In meiosis each gamete has a different
  combination of the chromosomes that were present
  before meiosis.
• Offspring have the potential to be different from
  parents.

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Meiosis I
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Meiosis II
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Meiosis

• Why are some of the chromosomes in the new nuclei
  not identical to the originals?
• During the early part of meiosis, double-stranded
  chromosomes come together.
• Crossing over occurs

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Meiosis

• Sexually reproducing animals produce gametes in
  reproductive organs called gonads.
• Male gonads are called testes and female gonads
  are called ovaries.

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Meiosis

• Sexually reproducing animals produce gametes in
  reproductive organs called gonads.
• Male gonads are called testes and female gonads
  are called ovaries.

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Meiosis

• During the process of fertilization, gametes come
  together to produce a zygote,
• Zygote then starts to divide through mitosis to
  develop all the cells of a new organism.

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Meiosis

• Meiosis occurs continuously in the testes of
  human males once their gonads are sexually
  mature.
• In females, meiosis begins in the ovaries before
  birth, then stops until the age of about 12 to 15.

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Meiosis
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