Unit A Reproduction

Errors in meiosis can result in changes to both the gametes and
the offspring.
• When homologous chromosomes do not separate in meiosis, gametes
have either too many or too few chromosomes. Having an extra copy
of chromosome 21 causes Down syndrome.
• When sex chromosomes fail to separate
during meiosis, gametes have either an
extra sex chromosome or are missing one.
Having only one X chromosome causes
Turner syndrome. Having an extra X
chromosome causes Klinefelter syndrome.
XXY
Klinefelter
syndrome
Scientists have developed technologies that can identify potential
problems and allow humans to produce offspring successfully.
• Ultrasound uses sound waves to create
an image of the fetus. The image is used to
check that the fetus is developing properly.
• Amniocentesis tests for chromosomal
disorders by karyotyping fetal cells
found in the amniotic fluid.
• Chorionic villus sampling takes cells from the
fetal part of the placenta and uses them to create
a karyotype of the fetus.
• Fertility drugs are used to help a woman produce
more eggs, which increases the chance of conception.
• In artificial insemination, sperm from the father
is inserted into the vagina.
• In in vitro fertilization, the egg is fertilized by the
sperm outside the mother’s body and the resulting
embryo is placed in the mother’s womb.
X0
Turner
syndrome
uterus (womb), p. 113
endometrium, p. 113
cervix, p. 113
vagina, p. 113
menstruation, p. 114
flow phase, p. 114
follicular phase, p. 114
luteal phase, p. 114
embryonic development, p. 115
amniotic fluid, p. 117
labour, p. 119
differentiation, p. 120
stem cells, p. 120
karyotype, p. 123
sex-linked characteristics, p. 125
nondisjunction, p. 127
Down syndrome, p. 127
Turner syndrome, p. 128
Klinefelter syndrome, p. 128
ultrasound, p. 130
amniocentesis, p. 130
miscarriage, p. 130
surrogate mother, p.135
NEL
Chapter 4 Review 141