Reproduction and Cell Division

Meiosis takes place in the testes and ovaries – Produces sperm cells – Produces egg cells Two haploid gametes unite! – Forms a diploid zygote Body cells Gamete-producing cells

Formation of sex cells during meiosis is called gametogenesis Female eggs go through oogenesis Whereas males go through spermatogenesis Although both processes produce four cells, the end results are quite different

Oogenesis The cytoplasm does not divide equally after each nuclear division One daughter cell, ootid, receives most of the cytoplasm Polar bodies die and the nutrients is absorbed only one ovum is produced from meiosis

Spermatogenesis A spermatocyte divide through meiosis to produce equal size sperm cells Much less cytoplasm than egg cells Sperm cells are meant to travel and cannot carry excess weight Males can produce one billion sperm cells every day

Female babies have approximately two million primary oocytes in their ovaries oocytes remain during reproductive years and only will be released Primary oocytes have entered meiosis I but remain in prophase I until first menstrual cycle

Sex Chromosomes After several observations on fruit flies it was found that one chromosome differed in males and females Females: two rod-shaped chromosomes – XX Males: one rod-shaped chromosome and a smaller hook-shaped chromosome – XY Called sex chromosomes Other chromosomes= autosomes

X and Y Chromosomes

Non-disjunction 61X8 61X8

Normal Meiosis In Anaphase I, homologous chromosomes split up and each one goes to a pole. In Anaphase II, the chromosome break in two and each chromatid goes to a pole.

Abnormal Meiosis I During Anaphase I, if the chromosomes do not split properly, cell will enter meiosis II with 2 extra chromosomes

Abnormal Meiosis II During anaphase II, if one of the chromosomes do not split properly, one cell will be left with a 1 chromosome, and the other with 3 chromosomes

Non-Disjunction Produces: gametes with 22 chromosomes – Produces chromosomes with 24 If 24 chromosomes combines with 23 – How many chromosomes will the zygote have? If 22 chromosomes combines with 23 – How many chromosomes will the zygote have?

24 Chromosomes If 24 chromosomes combine with 23 chromosomes – 47 chromosomes – 3 chromosomes in place of normal pair Called trisomy Trisomy 21/Down Syndrome Trisomy 13

22 Chromosomes If 22 chromosomes combine with 23 chromosomes – 45 chromosomes – 1 chromosomes in place of normal pair Called monosomy

Down Syndrome 3 copies of chromosome number 21 Round, full face Short height Large forehead Learning disabilities Heart defects Shortened life expectancy

Turner’s Syndrome Monosomic disorder Produces female with single X chromosome 45 chromosomes in zygote Characteristics: – Short and thick necks – Tend to not develop sexually – Normal life expectancy and intelligence

Klinefelter Syndrome Inheriting two XX and Y Male at birth Produces female hormones with maturity Sterile

Karyotyping exercise! ctivities/karyotyping/karyotyping.html