Meiosis – Part B

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 chromosomes

23 ? 127 ?

After Meiosis I

Chromosome number (haploid or diploid?)

23 19 ? ?

After Meiosis II

Chromosome number (haploid or diploid?)

23 ? ? 11

Number of pairs of homologous chromosomes

0 ? ? ?

Activity

Gametogenesis –

formation of female or male sex cells

Female cytoplasm does not divide equally after each nuclear division – the OOTID receives most of cytoplasm

Sperm cells have equal division of cytoplasm

Development of Male and Female Gametes

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 month

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 Cycles

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

The gametes are haploid and single celled. Gametes fuse and form a diploid zygote.Zygote undergoes mitosis to form multicellular diploid adult body. Specialized cellsundergo meiosis to produce gametes. Animals do not undergo mitosis to form multicellular gametophyte. Haploid gametes unite, fertilize and cycle begins again.

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 cell In 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 Trisomy

If 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. Monosomy

Abnormal Meiosis

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 Disorders

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