Abnormalities in Sexual Reproduction (lesson four)

• Males have an X and a Y chromosome • Females have a pair of X chromosomes • All non-sex chromosomes (#s 1-22) are called autosomes

• Several factors can impact these two processes • Some of these factors would be random meiotic errors • Others would be environmental factors

It is possible that an entire chromosome can be lost or gained by cells if the homologous chromosomes fail to separate in anaphase I or II of meiosis I or II

• This would result in one daughter cell having an extra chromosome and the other having a missing chromosome • This is called non-disjunction

• In humans, this would result in gametes with 24 and 22 chromosomes, not the expected 23 • This also means that the resulting zygote would have 47 or 45 chromosomes, not the expected 46, after fertilization

Nondisjunction can be easily observed through the use of a karyotype

• Your sex chromosomes can be viewed in a karyotype, and these are a pair of chromosomes that differ between males and females • During stages of cell division, chromosomes can be stained and photographed so they can be counted and compared • A picture of chromosomes that have been arranged according to number, size, shape, or some other characteristic is called a karyotype

• Trisomy • Monosomy

• A chromosomal abnormality in which there are three homologous chromosomes in place of a homologous pair

A chromosomal abnormality in which there is a single chromosome in place of a homologous pair

Down syndrome is caused by trisomy 21, or having 3 copies of the 21st chromosome - This extra chromosome means there is an excess of genetic information - Symptoms of this disorder include a round full face, short stature, intellectual disabilities, poor immune function, etc.

In addition to karyotyping, genetic disorders can commonly be diagnosed before birth by pre-natal testing - At 8 weeks, you can collect fetal cells - Chorionic villus sampling (CVS) removes cells from the placenta for testing - Amniocentesis involves the use of a syringe to collect cells from the amniotic sac for testing

• At 15-20 weeks, you can also do multiple marking screening • This assesses hormone levels in the mother’s blood to check for markers of increased risk of genetic conditions

Causes could include: - Poor or reduced egg or sperm quality or quantity - Blocked fallopian tube of the female - Blocked epididymis or vas deferens of the male

Assistive Reproductive technologies (ARTs) can be used to increase reproductive success

• Hormone treatments are given to the woman to increase egg production • Those eggs are retrieved through a minor procedure • Fertilization occurs outside the body using a sample from the male, and the embryo is then implanted in the uterus

• This is when sperm is placed into the reproductive tract of a female through a process called intrauterine insemination • A sperm sample, which can be fresh or frozen, is washed and concentrated and inserted directly into the uterus • This technique has also been used in non-humans to help save endangered species, including pandas