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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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