Presentation on theme: " Mistakes made during meiosis can lead to abnormal numbers of chromosomes. This occurs when a homologous pair of chromosomes fail to separate. These."— Presentation transcript:
Mistakes made during meiosis can lead to abnormal numbers of chromosomes. This occurs when a homologous pair of chromosomes fail to separate. These mistakes can occur in either meiosis I or II.
Occurs when there is nondisjunction during meiosis I. Half the gametes will carry an extra chromosome 21. A person with an extra chromosome 21 is said to have down syndrome.
Trisomy 21 affects about 1/700 children in the USA. People with down syndrome generally have a shorter lifespan, and will exhibit varying degrees of developmental delays.
Other physical characteristics include a round face, flattened nose bridge, small teeth, short stature, heart defects, and susceptibility to respiratory infections. Most people with down syndrome are also sterile, and therefore unable to have children.
The occurrence of trisomy 21 increases with the age of the mother. Women who are over 30 have a 1% chance of having a child with down syndrome. This risk increases with older mothers. Women over 35 can have genetic testing done to find out if their fetus has trisomy 21.
Occurs when there is nondisjunction in the sex cells. Klinefelter’s occurs in males who have an extra X chromosome.
Males with klinefelter’s will have smaller testes, some breast development, lanky, and poor facial hair. These males are also sterile. Therefore many men do not realize that they have an extra X chromosome until they wish to start a family of their own.
Occurs in females because of the nondisjunction of sex cells resulting in females with only one X chromosome. Women with turner syndrome have a webbed neck, poor development ovaries (sterile), short stature, broad chest, heart defects, and increased weight.
Males with XYY generally have regular fertility and regular physical characteristics.
Women who have three X chromosomes usually do not experience any physical or mental characteristics due to the disorder. In females only 1 X chromosome will be active in each cell.