9.10.1 Problems in Heredity

Question 1

problems in heredity

Answer 1

• In humans, chromosomal errors can occur during gamete formation. The term aneuploidy describes a deviation from the
normal chromosomal number.
• In most cases, embryos that have an abnormal chromosome number are not viable and do not continue to develop.
• Some forms of aneuploidy are not lethal, but cause serious disorders. Three examples are:
· Down trisomy 21
· Klinefelter syndrome
· Turner’s syndrome
- The term aneuploidy describes the situation in which
chromosomes are present in extra copies or are deficient in number. In trisomy, a chromosome is present in three copies instead of the two copies present in the normal cell. The situation occurs as a result of nondisjunction, the failure of homologous chromosomes to separate during meiosis. When
this failure occurs, a gamete may receive two copies of a particular chromosome instead of one. When the gamete pairs with a normal gamete, the zygote will have three copies of the chromosome.

Question 2

karyotyping

Answer 2

• a technique involving the preparation of an
  individual’s metaphase I chromosomes to determine their number and characteristics.
• The karyotype on the left belongs to an individual that is trisomic for chromosome 21, a situation called
  Down trisomy 21. Down syndrome most commonly occurs because of a nondisjunction event and is linked to maternal age. Some characteristics of the syndrome include mental retardation, short stature, and characteristic facial features.
• Klinefelter syndrome occurs as a result of nondisjunction of the X chromosome, resulting in an XXY genotype. Individuals with Klinefelter syndrome have underdeveloped and nonfunctioning male sex organs. They also have feminine body characteristics.

Question 3

monsomy

Answer 3

• an individual gets only one copy of a chromosome instead of the normal two. An example is Turner’s syndrome, which occurs because of a nondisjunction
  of the X chromosome. Individuals are XO and are considered to be females. Their primary and secondary sex characteristics fail to develop normally, and individuals with Turner’s are usually sterile.

Question 4

polyploidy

Answer 4

• the organism receives more than two complete
  sets of chromosomes. The situation produces viable
  individuals in plants and is considered to play a major role in their speciation.

Question 5

Typically, humans receive _________ autosomes from each parent.

Answer 5

• 22

Question 6

Which of the following statement regarding nondisjunction is correct?

Answer 6

• It occurs when chromosomes fail to separate during meiosis.

Question 7

A primary sex cell experiences one nondisjunction during meiosis I. If the normal diploid number is 46, how many chromosomes are present in one of the defective gametes?

Answer 7

• 22

Question 8

In which organism / group of organisms does polyploidy occur most frequently?

Answer 8

• Plants

Question 9

What is a picture of metaphase I chromosomes prepared in order to examine their number and condition called?

Answer 9

• A karyotype

Question 10

A species of rye grass that normally has 80 chromosomes per cell becomes tetraploid. How many chromosomes will the gametes of the new plant contain?

Answer 10

• 80

Question 11

Nondisjunction may cause all of the following conditions except:

Answer 11

• Hemophilia