Genetics4.2 & 10.1 Meiosis
   Diploid – two sets of each chromosome present  ◦ In humans, where can you find diploid cells? Haploid – one set of ea...
   Homologous chromosomes are the    chromosomes that are the same size and    show the same banding pattern. They    con...
Summary of Meiosis: ◦ Meiosis occurs after interphase ◦ (replication has occurred). ◦ There are 2 divisions of the nucleus...
 Crossing over (i.e. recombination or  synapsis) allows for genetic variability Only happens in meiosis (prophase I) Fo...
Crossing over
Gametes have genetic variability through  ◦ Crossing over during prophase I  ◦ Independent Assortment- Random orientation ...
Non-Disjunction   Non-disjunction occurs when the    centromeres do not uncouple which leads    to one nucleus with a mis...
   A karyotype is an image of a set of    chromosomes that is taken during    metaphase. The chromosomes are lined    up ...
   Karyotyping is performed using cells    located by chorionic villus sampling or    amniocentesis. This allows pre-nata...
   Karyotyping can be used to screen people    for genetic diseases.   This allows for:    ◦ The probability of a couple...
Early detection of a genetic disease in a fetus   also allows… ◦ Treatment to begin early for the genetic   disease ◦ Pare...
   Risks of side effects from karyotyping    (e.g. abortion of the fetus).   Who should make the decisions about    kary...
   What is the gender? Has non-disjunction    occurred?Analyze this karyotype:
Analyze this karyotype:
4.2 & 10.1 meiosis
4.2 & 10.1 meiosis
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4.2 & 10.1 meiosis

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4.2 & 10.1 meiosis

  1. 1. Genetics4.2 & 10.1 Meiosis
  2. 2.  Diploid – two sets of each chromosome present ◦ In humans, where can you find diploid cells? Haploid – one set of each chromosome present ◦ In humans, where can you find haploid cells? Meiosis is a reduction division. This means that a diploid nucleus is divided into 4 haploid nuclei. These become the nuclei for gametes (egg and sperm cells).Meiosis
  3. 3.  Homologous chromosomes are the chromosomes that are the same size and show the same banding pattern. They contain the same set of genes but their alleles are not identical.Homologous chromosome
  4. 4. Summary of Meiosis: ◦ Meiosis occurs after interphase ◦ (replication has occurred). ◦ There are 2 divisions of the nucleus (each with prophase, metaphase, anaphase, telophase, cytokinesis). ◦ The homologous chromosomes are paired in prophase 1. ◦ The result of the process is four haploid cells. ◦ Meiosis and sexual reproduction help to ensure genetic variety.Meiosis
  5. 5.  Crossing over (i.e. recombination or synapsis) allows for genetic variability Only happens in meiosis (prophase I) Forms a chiasmata between non-sister chromatids on homologous chromosomes. 1. Homologous chromosomes pair loosely along their lengths 2. Homologues align with each other gene by gene. 3. Homologous portions of 2 non-sister chromatids trade places (2-3 per chromosome pair for humans) 4. Locations where these genetic exchanges have occurred are visible as chiasmata.Crossing Over
  6. 6. Crossing over
  7. 7. Gametes have genetic variability through ◦ Crossing over during prophase I ◦ Independent Assortment- Random orientation during metaphase IMore genetic variability comes with random fertilization of gametes. Egg x Sperm (223 combinations of chromosomes) x (223 combinations of chromosomes) 223 x 223 diploid combinations1 in 70 trillion chance for the same genes- not even considering crossing over.Genetic Variability
  8. 8. Non-Disjunction Non-disjunction occurs when the centromeres do not uncouple which leads to one nucleus with a missing chromosome and one nucleus with an extra chromosome. This is what causes genetic disorders like Down Syndrome (trisomy 21)
  9. 9.  A karyotype is an image of a set of chromosomes that is taken during metaphase. The chromosomes are lined up in homologous pairs based on size and structure.Karyotyping
  10. 10.  Karyotyping is performed using cells located by chorionic villus sampling or amniocentesis. This allows pre-natal (before birth) diagnosis of chromosome abnormalities.Karyotyping
  11. 11.  Karyotyping can be used to screen people for genetic diseases. This allows for: ◦ The probability of a couple having a child with genetic disease can be determined beforehand. ◦ Fewer children to be born with genetic diseases because fetuses can be aborted or people carrying the diseases can avoid reproduction. Therefore there can be; ◦ Less cost for long-term health care ◦ Less frequency of harmful alleles in the gene poolGenetic Screening UsingKaryotyping
  12. 12. Early detection of a genetic disease in a fetus also allows… ◦ Treatment to begin early for the genetic disease ◦ Parents of affected children can be prepared psychologically for the arrival of their baby.Genetic Screening UsingKaryotyping
  13. 13.  Risks of side effects from karyotyping (e.g. abortion of the fetus). Who should make the decisions about karyotyping and abortion? Should national governments interfere with personal freedom to abort fetuses that have genetic disease? Should abortion based on gender be allowed? How could it be stopped?Questions about Karyotyping
  14. 14.  What is the gender? Has non-disjunction occurred?Analyze this karyotype:
  15. 15. Analyze this karyotype:

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