Submit your karyotype activity sheet. Feedback distributer: Sabrina 4.2 Meiosis Submit your karyotype activity sheet. Feedback distributer: Sabrina

4.2.6 Methods of karyotyping: Amniocentesis Insert a needle into uterus and extract 10 mL of amniotic fluid (liquid that bathes the fetus) Biochemical test of the fluid to identify certain chromosomal defects Some tests require that cells be cultured (several weeks) before they can be tested Performed 14th – 16th week of pregnancy

4.2.6 Methods of karyotyping: Choronic villus sampling (CBS) Chorionic villi = Microscopic, finger-like projections which surrounds developing baby. Eventually forms placenta Insert narrow tube through the cervix into the uterus and take out fetal tissue Cells of chorionic villus are rapidly multiplying, therefore tests can be carried out immediately (give results in less than 24 hours) Performed as early as 8th – 10th week of pregnancy

Chromosomes in us Humans have diploid cells Diploid (2n) = two sets of each chromosome (2n = 46, where n is 23) Haploid (n) = one set of each chromosome Arranged in pairs known as homologous chromosomes = chromosomes pairs that are of the same length and staining pattern and possess genes for the same characters at the same length

Terms – refresher Chromatid = one of two copies of DNA Sister chromatids = two identical copies of DNA Centromere = region on chromosome that joins sister chromatids Spindle fiber = microtubules that move chromosomes during cell division Centriole = microtubule organizing center

The paradox Human beings have 46 chromosomes in each cell. Your mom has 46 chromosomes in each cell. Your dad has 46 chromosomes in each cell. But you do not have 92 chromosomes in your cell. WHY?

4.2.3 Meiosis: Reduction division from diploid to haploid cells Paring of homologous chromosomes Two divisions Meiosis I: homologous chromosomes split Meiosis II: sister chromatids split 3. Product: Four haploid (n) cells

Meiosis I Prophase I: Metaphase I: Anaphase I: Telophase I: chromosomes condense spindle forms pairing of homologous chromosomes Metaphase I: homologous chromosomes line up at equator Anaphase I: Spindle attach to chromosomes and pull homologous chromosomes to separate poles Telophase I: Chromosomes arrive at opposite poles of cell Spindle disappears Q. Is the cell a diploid/haploid at this stage?

Meiosis II Prophase II: Metaphase I: Anaphase I: Telophase I: chromosomes condense spindle forms Metaphase I: individual chromosomes line up at equator Anaphase I: Spindle attach to chromatids and pull sister chromatids to separate poles Telophase I: Chromatids arrive at opposite poles of cell Spindle disappears

Meiosis versus Mitosis

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Mitosis versus Meiosis Purpose of mitosis = growth, tissue repair, asexual reproduction

Crossing over: Prophase I Non-sister chromatid from each homologous pair intertwine, reciprocal exchange genetic info

Significance: produce 4 haploid cells, each with new combination of alleles! (i.e. increases genetic variation) We didn’t do this with our activity – 4 stacks (2 different combinations)

4.2.4 Down syndrome Chromosomes move to pole as a pair instead of singly Thus, egg or sperm contain an extra copy of chromosome 21, and fertilized egg has 3 copies of chromosome 21 Occurs in meisos I or II