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Worksheet on chromosomal non-disjunction, Exercises of Biology

Typology: Exercises

2020/2021

Uploaded on 04/20/2021

ehaab
ehaab 🇺🇸

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Worksheet on non-disjunction:
(a) Fill in the cells below showing the NORMAL process of meiosis of the male’s sex chromosomes
(The large black chromosome is the X and the smaller red one is the Y). DO NOT show crossing over.
½ of the gametes will have the X chromsome and ½ of the gametes will have a Y chromosome.
Remember we are only showing the sex chromosomes, and there would be 22 other chromosomes in
each of the gametes.
(b) Fill in the cells below showing the process of meiosis of the male’s sex chromosomes with non-
disjunction occurring during meiosis I. DO NOT show crossing over.
prior to meiosis
prior to meiosis
sister chromatids split
but two end up in both
cells does not split
The black chromosome is
representing the large X
chromosomes, and the red
represents the Y-
chromosome
homologous pairs split
sister chromatids split
homologous pair does not
split normally the X and Y
chromosomes stay together
with the first split – they are
still duplicated.
no sex
chromosomes go
to this cell – due to
nondisjunction
pf2

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Worksheet on non-disjunction: (a) Fill in the cells below showing the NORMAL process of meiosis of the male’s sex chromosomes (The large black chromosome is the X and the smaller red one is the Y). DO NOT show crossing over. ½ of the gametes will have the X chromsome and ½ of the gametes will have a Y chromosome. Remember we are only showing the sex chromosomes, and there would be 22 other chromosomes in each of the gametes. (b) Fill in the cells below showing the process of meiosis of the male’s sex chromosomes with non- disjunction occurring during meiosis I. DO NOT show crossing over. prior to meiosis prior to meiosis sister chromatids split but two end up in both cells does not split The black chromosome is representing the large X chromosomes, and the red represents the Y- chromosome homologous pairs split sister chromatids split homologous pair does not split normally the X and Y chromosomes stay together with the first split – they are still duplicated. no sex chromosomes go to this cell – due to nondisjunction

What are the possible abnormal gametes the male can produce with non-disjunction occurring in Meiosis I? All gametes are abnormal – ½ will have an extra chromosome – having BOTH AN X and Y chromosome, and ½ will have NO SEX CHROMSOMES – shown as a blank cell. Could this man father a Tuner syndrome (XO) child? Could this man father a Klenfelter’s syndrome child (XXY)? Yes to the Turner’s syndrome, and yes to the Klenfelter’s syndrome (contributing an abnormal XY gamete). (c) Fill in the cells below showing the process of meiosis of the male’s sex chromosomes with non- disjunction occurring during meiosis II. DO NOT show crossing over. What are the possible abnormal gametes the male can produce with non-disjunction occurring in Meiosis II? ½ abnormal gametes -- XX and O (no sex chromosome) – ½ normal gametes – only one Y chromosome. Could this man father a Tuner syndrome (XO) child? Could this man father a Klenfelter’s syndrome child (XXY)? Yes to the Turner’s Syndrome, donating a gamete with no sex chromosome. Yes to the XXY individual IF THE non-disjunction occurred in the mother (this male could contribute a normal Y gamete) – but if the egg was normal, than no this man (with non-disjunction in meiosis II) could not have fathered the child, since none of his gametes would be XY (and the Y has to come from the male). prior to meiosis homologous pair splits normally sister chromatids do not split – both go to one cell and neither sister chromatid to the other normal splitting of these sister chromatids