Abnormal Meiosis (4)

Question 1

What does abnormal meiosis result in?

Answer 1

Abnormal meiosis results in chromosome abnormalities and it can take place in several different ways.

Question 2

What is chromosome disjunction and explain the effect?

Answer 2

Chromosome non-disjunction when chromosomes fail to separate occurs correctly during meiosis.

If this occurs in the sex chromosomes (X and Y), fertilization involving one of these abnormal gametes will result in a zygote with either an extra or a missing chromosome - a condition known as aneuploidy. Affected individuals have physical and mental characteristics called syndromes.

Question 3

In both cases, the ____ of the event is chromosome non-disjunction and the ____ are the various syndromes. Remember that the cause is the producer of an effect, while an effect is produced by a cause.

Answer 3

cause

effects

Question 4

What is Klinefelter’s syndrome?

Answer 4

Klinefelter’s syndrome is aneuploidy. It occurs in males when a boy is born with an extra copy of the X chromosome (XXY). This occurs when the sex chromosomes in the egg (or very rarely the sperm) split unevenly.

Question 5

Many men with Klinefelter’s syndrome do not have obvious symptoms and in others, their male sexual development and fertility may be interfered with, e.g. they may have: (5)

Answer 5

• sparse body hair
• enlarged breasts
• small testicles and penis
• not very deep voices.
• They usually cannot father children.

Question 6

What is Down’s Syndrome?

Answer 6

Down syndrome is another example of aneuploidy that occurs in children who are born with an extra (third) copy of chromosome number 21 in their cells, i.e. (2n + 1) - a condition known as trisomy.

Question 7

How does this come about? (4)

Answer 7

• During oogenesis (meiosis in the production of an egg), the two number 21 chromosomes do not separate properly during anaphase 1; both go into one daughter cell instead of one into each of the two daughter cells formed. It is apparently rare for males to be the cause of Down syndrome.
• This results in an egg with two number 21 chromosomes instead of one.
• If this egg is fertilized, the zygote will have three number 21 chromosomes (one from the father and two from the mother) and a total of 47 chromosomes in each cell instead of 46.
• As the new embryo develops by mitosis, all the cells will have 47 chromosomes.

Question 8

What are Down syndrome characteristics? (6)

Answer 8

• Children have varying degrees of mental retardation. The severity of symptoms differs widely from person to person.
• They have distinctive flattened facial features with slightly slanting eyes due to folds of skin at the corner of the eyes.
• Other physical features include short stubby fingers and toes with the big toes widely spaced from the second toe, a largish head and ears that may develop differently.
• These problems are often accompanied by heart defects and other health problems.
• Despite their many problems, Down syndrome sufferers tend to have a happy, loving nature.
• Although some of the health problems caused by Down syndrome, such as heart defects, there may be no cure. be treated through surgery and medication, there is no cure.

Question 9

Down syndrome is a relatively common birth defect, affecting about 1 in 900 births. The chances of having a baby with Down syndrome increase with the age of the mother; a 35-year-old woman has a 1 in 350 chance, whereas a woman of 45 has a 1 in 30 chance. With age, the chromosomes seem to have more difficulty in separating. This is known as the ___ ___ effect.

Answer 9

maternal age

Question 10

Do children with genetic abnormalities have problems?

Answer 10

Children with Down and other syndromes tend to grow and develop more slowly than other children. In many countries, since the early 1960s, Down syndrome children attend mainstream schools and not special institutions. Some may need special classes to help them in areas where they have more trouble learning. Despite this change in attitude towards educating people with genetic abnormalities, they still need support. Because they are different from other people, they often encounter patronizing attitudes and discrimination in the wider community. It is important, therefore, that parents work with teachers and others to come up with a plan to help each child learn and to live a normal, integrated, carefree life.

Question 11

A new test, taken early in pregnancy, combines a blood test with an ultrasound examination. This can pinpoint many fetuses with Down syndrome ___ weeks after conception and it, therefore, allows expectant women more time to decide whether to undergo the risky follow-up testing needed to confirm the diagnosis or to abort the fetus. In the follow-up process, the fetal cells can be extracted from the amniotic fluid by ____. The ____ of these cells can then be determined.

Answer 11

11
amniocentesis
karyotype

Question 12

Define amniocentesis.

Answer 12

A process whereby a small sample of fluid is removed from the amniotic cavity in the uterus.

Question 13

What is a karyotype?

Answer 13

A set of chromosomes in a cell is called a karyotype. It shows the number, size and shape of the chromosomes during metaphase of mitosis.

Question 14

In the human karyotype that follows, non-sex chromosomes, _____, of a similar size are grouped together and placed in groups A to G according to their length. The sex chromosomes, ____(X - female; Y - male) are placed separately.

Answer 14

autosomes

gonosomes

Question 15

Why are karyotypes used? (2)

Answer 15

• Whether a cell comes from a male or a female

- Abnormal chromosomes