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Sex
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Male sex is determined by presence of Y
chromosome. Strictly speaking by the fragment with testis-determine
factors. Lack of that region (for example there is no Y chromosome)
leads to developing ovaries from undifferentiated embryo’s
gonads and determines female sex.
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woman
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According to Mendel’s laws chromosomes
are segregated to gametes independently. Half of spermatozoons
produced by a man have X chromosome, the other half have Y
chromosome. For women each gamete contain X chromosome. Mother
delivers one of her X chromosomes to her children. Daughters
inherit X chromosome from father, sons Y chromosome.
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man
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| parents |
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sex
chromosomes |
| gametes |
| children |
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sex chromosomes |
In each female’s cell one of the X
chromosomes is inactivated. Consequently amount of products encoded
by genes from X chromosome is similar for both men and women. This
process is random. Some cells switch off father’s X
chromosome, some mother’s one. This causes differences in
expression of abnormal genes for women carriers. Inactivated
chromosome is highly condensed and visible during interphase as
so-called Barr body.
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