Meiosis – Part B Take out a piece of paper and write for two minutes what makes you unique 

Activity 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?) 19 After Meiosis II 11

Development of Male and Female Gametes 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

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

Cell Division and Life Cycles 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)

Pollen contains male sex cells, female egg stored in flower 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. Specialized cells undergo meiosis to produce haploid spores. Spores undergo mitosis to produce mature multicellular gametophyte (also a haploid). Specialized cells develop into gametes. Cycle begins again.

The gametes are haploid and single celled 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.

Abnormal Meiosis 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

Nondisjunction Disorders 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.

Karyotype Charts 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.