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SEXUAL REPRODUCTION

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Variation. Result of sexual reproduction = differences between members of a population ... of haploid gametes causes variation. Benefits from variation ... – PowerPoint PPT presentation

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Title: SEXUAL REPRODUCTION


1
SEXUAL REPRODUCTION
  • Genetic information of one parent is combined
    with that of the other parent to produce
    genetically distinct offspring
  • All body cells in humans have 46 (23) pair of
    chromosomes Sex cells have only 23 chromosomes

2
of Chromosomes
  • DIPLOID (2n) almost all of the somatic (body)
    cells are diploid which means that they have a
    complete set of chromosomes
  • HAPLOID (n) sex cells (sperm and eggs) are
    haploid which means that they have only half the
    number of chromosomes of a somatic cell.

3
Meiosis
  • Process by which haploid cells are created
  • During meiosis, there are two cell divisions
    rather than just one and the resulting offspring
    cells are haploid rather than diploid
  • This maintains a stable number of chromosomes
    from generation to generation, so that there
    arent too many chromosomes

4
Mitosis Meiosis
  • In organs that reproduce sexually, there may be
    both haploid (sex cells) and diploid (body cells)
    in their body at some point in development
  • Sexual Reproduction haploid (egg) haploid
    (sperm) diploid (offspring)
  • Once the offspring develops, the body cells
    continue to divide by mitosis so that the
    organism can grow.

5
How it works
  • Homologous Pairs chromosome pairs that are
    exactly alike in size, location of centromere and
    the banding pattern when seen through a
    microscope (also alike in the gene sequence)
  • One pair of chromosomes in humans is NOT
    homologous the ones that code for sex (male) is
    not

6
The numbers game
  • In humans
  • Mitosis yields two daughter cells with exactly
    the same chromosomes as the parent cell
  • Meiosis yields FOUR daughter cells with ½ the
    chromosomes as the parent cell
  • Sperm results in 4 viable daughter cells
  • Eggs result in a single egg cell and 3 polar
    bodies which die off

7
Meiosis
  • Steps 1-5 are identical to mitosis, IPMAT occurs
  • In meiosis, following Telophase I, the
    chromosomes remain visible, spindle fibers
    reappear and the whole process starts again in
    tandem
  • The result is 4 cells with ½ the genetic material
    rather than 2 cells with the full complement of
    genetic material

8
Mitosis vs. Meiosis
  • Offspring cells have exactly the same of
    chromosomes as parent. (diploid)
  • Offspring are genetically identical to parent
    cell.
  • Single cell division
  • Offspring cells have half the of chromosomes as
    parent. (haploid)
  • Offspring are genetically similar to parent cells
  • Double cell division, only one interphase

9
Variation
  • Result of sexual reproduction
  • differences between members of a population
  • Results, in part, from the recombination of DNA
    that occurs during meiosis and fertilization
  • Random separation of homologous pairs and random
    recombination of haploid gametes causes variation

10
Benefits from variation
  • Because each parent gives an equal number of
    chromosomes, any genetic disorder may not express
    because the other parent doesnt have it.
  • If an organism is faced with outside
    environmental pressure, recombining genetic
    material can allow for slight mutations that
    allow the species to survive.
  • EX. Snowshoe hares and Moths in England

11
assignment
  • Do the Think About It Lab Zone activity on p. 115
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