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Chapter 11: Meiosis and sexual reproduction. 0. Sexual vs. Asexual Reproduction. Sexual : 2 parents Offspring are genetically different from parent – mix of traits Union of egg & sperm. Asexual : 1 parent Offspring are identical to parent Binary fission in bacteria

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Chapter 11:

Meiosis and sexual reproduction


0

Sexual vs. Asexual Reproduction

  • Sexual:

  • 2 parents

  • Offspring are genetically different from parent – mix of traits

  • Union of egg & sperm

  • Asexual:

  • 1 parent

  • Offspring are identical to parent

  • Binary fission in bacteria

  • Regeneration in worms


  • In sexual reproduction, each parent produces a reproductive cell called a gamete

    • Male gamete – sperm

    • Female gamete – egg

  • Zygote– formed when sperm fertilizes egg

  • Fertilization – process in which sperm and egg fuse together


  • Examples of asexual reproduction:

  • Fragmentation – body breaks into several pieces, each of which regrows into an adult

  • Budding – new individuals split off from existing ones

  • Parthenogenesis – a female makes a viable egg that grows into an adult without being fertilized by a male

  • Binary fission – a type of cell division used by prokaryotic cells


  • Advantage of sexual reproduction:

  • Produces offspring that are different from their parents so they have a better chance of surviving changes in the environment, diseases, etc.

  • Advantages of asexual reproduction:

  • Simple and efficient

  • No need to find a mate

  • May produce many offspring in a relatively short period of time


Somatic cells– body cells such as skin, hair, muscle, bones, or organs thatdo no participate in sexual reproduction

Germ cells– cells that are specialized for sexual reproduction, such as eggs or sperm



  • Viewing the Chromosomes

  • Karyotype - a photograph of the chromosomes in a dividing cell

    • Shows the gender of the child

    • Shows abnormalities in chromosome number or structure.

  • Humans have 23 pairs of homologous chromosomes(chromosomes with the same genes; similar in size and shape), or 46 chromosomes total.

    • You get 1 of each chromosome from mom, and 1 from dad.


  • Of the 23 pairs of chromosomes:

    • 1 pair aresex chromosomes– determine your gender; may determine other traits as well

      • Females are XX

      • Males are XY

    • 22 pairs areautosomes– all other pairs of chromosomes; do NOT determine gender


  • How is karyotyping done?

  • Cells are taken from the fetus of a pregnant woman

  • Chemicals added to the cells make them divide

  • Another chemical stops division at the midpoint

  • The stained cells are photographed and can be paired based on cross-bands, size, and shape.





  • Body cells contain the diploid(2n) number of chromosomes – contain2 chromosomes of each kind (1 from each parent)

  • Sex cells (eggs and sperm) contain only 1 chromosome of each kind – haploid(1n) number of chromosomes


  • Meiosis– form of cell division tha produces

  • daughter cells with half the number of

  • chromosomes that are in the parent

  • Produces sex cells (gametes)

    • Female gamete –egg

    • Male gamete - sperm

  • Reduces the chromosome number

    • Egg or sperm cells each have only one of each kind of chromosome

    • Diploid cells (2n)  haploid cells (1n)


Overview of meiosis

http://www.cellsalive.com/meiosis.htm



  • Meiosis I

  • Original cell produces 2 new cells

  • Splits homologous chromosomes so that each new cell has 1 chromosome from each homologous pair

  • Diploid cells (2n) create haploid cells (1n)

  • Crossing over (chromosomes exchange genetic material) can occur


  • Meiosis II

  • Each of the 2 cells made in meiosis I splits

  • 2 haploid cells divide to make 4 haploid cells

  • Chromatids of chromosomes are separated

  • Errors in meiosis can result in missing or extra chromosomes


  • Changes in Chromosome Number

  • Occurs when:

    • In meiosis I, homologous pair both go into the same daughter cell or

    • In meiosis II, the sister chromatids both go into the same gamete.

  • The result is either:

    • Trisomy(3 copies of a single chromosome)

    • Monosomy (1 copy of a single chromosome)




  • Types of chromosomal mutations:

  • Deletion – a piece of a chromosome is lost

  • Duplication – a chromosome with a repeated section attached

  • Inversion –a section of chromosome is flipped in the reverse direction

  • Translocation – a chromosome piece ends up on another non-homologous chromosome

  • Gene rearrangement – an entire gene moves to a different location on the same chromosome


  • Ex. of deletion: Williams syndrome

    • Chromosome 7 loses an end piece

    • Children have a pixie look (turned-up noses, wide mouth, small chin, large ears)

    • Poor academic skills, good verbal and musical abilities

    • Skin ages prematurely from lack of the gene that controls the production of elastin (also affects cardiovascular health).



Duplication causes inv dup 15 syndrome


  • Ex of translocation causes inv dup 15 syndrome: Alagille syndrome results from a deletion of chromosome 20 or a translocation that disrupts an allele on chromosome 20.

  • The symptoms for Alagille syndrome range from mild to severe, so people may not be aware they have the syndrome.

  • Distinctive face, abnormalities of eyes & internal organs, and severe itching.


Translocation causes inv dup 15 syndrome


  • Meiosis in males vs. females causes inv dup 15 syndrome:

  • Males:

    • Occurs in testes

    • Spermatogenesis

    • Makes 4 haploid sperm

  • Females:

    • Occurs in ovaries

    • Oogenesis

    • Makes 1 large egg & 3polar bodies(that die) – cells divide unevenly


Spermatogenesis causes inv dup 15 syndrome


Oogenesis causes inv dup 15 syndrome


Meiosis vs. Mitosis causes inv dup 15 syndrome

  • Mitosis

  • Body cells

  • Diploid cells make diploid cells

  • End result 2 cells

  • No variation in cells produced

  • Meiosis

  • Sex cells

  • Diploid cells make haploid cells

  • End result up to 4 cells

  • Cells made are different from parent


Meiosis compared to mitosis causes inv dup 15 syndrome


  • Cloning causes inv dup 15 syndrome: Produces an organism that is genetically identical to the parent

  • Steps:

    • DNA is removed from a fertilized egg

    • Fertilized egg cell is fused with cell of individual being cloned

    • Egg with new DNA is implanted into a woman

http://gslc.genetics.utah.edu/units/cloning/clickandclone/


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