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Meiosis – Part B Meiosis – Part B

Meiosis – Part B - PowerPoint Presentation

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Uploaded On 2016-10-25

Meiosis – Part B - PPT Presentation

Take out a piece of paper and write for two minutes what makes you unique Human Cat Shrimp Bean Before Meiosis Chromosome number haploid or diploid 46 Number of pairs of homologous ID: 480374

cells meiosis gametes chromosome meiosis cells chromosome gametes chromosomes haploid number diploid zygote mitosis sperm homologous produce female egg

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Slide1

Meiosis – Part B

Take out a piece of paper and write for two minutes what makes you unique

Slide2

Human

Cat

ShrimpBeanBefore MeiosisChromosome number (haploid or diploid?46???Number of pairs of homologous chromosomes23?127?After Meiosis IChromosome number (haploid or diploid?)2319??After Meiosis IIChromosome number (haploid or diploid?)23??11Number of pairs of homologous chromosomes0???

ActivitySlide3

Gametogenesis – formation of female or male sex cells

Female cytoplasm does not divide equally after each nuclear division – the

OOTID receives most of cytoplasmSperm cells have equal division of cytoplasmDevelopment of Male and Female GametesSlide4

Sperm are streamlined for movement, Egg cells use nutrients and organelles within cytoplasm to fuel future divisions

Spermatocytes (Diploid) – give rise to sperm cells – are capable of mitosis before meiosis ever begins

Males can produce 1 billion sperm a day!Females are born with ~ 2 million primary oocytes. Oocytes have already entered meiosis I but remain suspended until prophase I until puberty. Meiosis is resumed in one oocyte once a monthSlide5

Asexual reproduction = offspring through mitosis

Bacteria and Yeast – daughter cells with the same chromosome number as parent cell

Sexual reproduction = chromosome number changes through meiosis (gametes – half the chromosome number as the somatic cells) and fertilization (zygote – two gametes joining where chromosome number is restored to that of somatic cells)Cell Division and Life CyclesSlide6

Pollen contains male sex cells, female egg stored in flower. Gametes contain a haploid

chromosome. Diploid zygote is formed after fertilization. Undergoes mitosis to

produce seeds. Further mitosis produces mature plant called sporophyte. Specializedcells undergo meiosis to produce haploid spores. Spores undergo mitosis to producemature multicellular gametophyte (also a haploid). Specialized cells develop into gametes. Cycle begins again.Slide7

The gametes are haploid and single celled. Gametes fuse and form a diploid zygote.

Zygote undergoes mitosis to form multicellular diploid adult body. Specialized cells

undergo meiosis to produce gametes. Animals do not undergo mitosis to form multicellular gametophyte. Haploid gametes unite, fertilize and cycle begins again.Slide8

Nondisjunction – two homologous chromosomes fail to separate during meiosis or mitosis. One daughter cell has too many chromosomes and the other too few. Any cell can be affected, but most dramatic is in sex cells during meiosis.

Polyploidy – more than two complete chromosome sets. Three chromosome sets –

tripoloidy; four chromosome sets – tetraploidy.Diploid egg cell fertilized by a haploid sperm = 3n cellIn humans, nondisjunction produces gametes with 22-24 chromosomes.If gamete of 24 chromosomes, and joins with normal gamete will have zygote with 47 chromosomes. Zygote will have three chromosomes in place of normal pair TrisomyIf gamete of 22 chromosomes joins with normal gamete will have zygote with 45 chromosomes. Will have only one of the chromosomes rather than homologous pair. MonosomyAbnormal MeiosisSlide9

Trisomic

Conditions – Down Syndrome (trisomy 21)

Monosomic Conditions – Turner Syndrome Female with single x chromosome. both homologous pairs moved to the same pole during meiosis I. Egg with no X chromosome is fertilized with sperm – 45 chromosome zygote.Nondisjunction in sperm or egg – child inherits 2 X chromosomes and single Y. Male at birth but at puberty begins producing high levels of female sex hormones.Nondisjunction DisordersSlide10
Slide11

Detecting results of abnormal meiosis.

Mix small sample of tissue with solution that stimulates mitotic division. Another solution is added to stop division at metaphase.

Karyotype Charts