9.10.2 Problems in Heredity: Chromosomal Aberrations

Question 1

note

Answer 1

• Review: The addition or deletion of an entire chromosome can lead to a serious genetic condition.
• An alteration in the structure of a chromosome can lead to genetic disorders.
• The possible alterations are deletion and crossover mistakes.
• Two types of crossover mistakes include duplications and inversions.
- Review: During meiosis, homologous chromosomes can exchange parts. The process takes place during crossing over (when segments break off and recombine.)
- Mistakes sometimes occur during this process. Parts of the chromosome may break off, and genetic information will be lost.
- In a deletion mutation, a portion of the chromosome is lost entirely. The disease Cri du chat is caused by a deletion of chromosome #5. The name literally translates as “cry of the cat” because of the cat-like cry of children with the disorder. Individuals with this disease are microcephalic, mentally retarded, and have a shortened lifespan.
- In a duplication mutation, a portion of the chromosome is present in extra copies. Duplications can occur from an unequal crossover event, causing one of the chromosomes to get a portion of the other one. A duplication can result in extra copies of the gene being made.
- In an inversion mutation, part of the chromosome flips
around, possibly reversing the order of the gene sequence

Question 2

What is a likely cause of a duplication mutation?

Answer 2

• An unequal crossover event

Question 3

Two types of crossover mistakes that lead to a change in the structure of a chromosome are:

Answer 3

• Duplication mutations and inversion mutations

Question 4

When part of chromosome number 5 is deleted, the resulting disorder is called:

Answer 4

• “Cri-du-Chat” syndrome

Question 5

What occurs in an inversion mutation?

Answer 5

• A section of a chromosome is flipped around.

Question 6

Which statement concerning homologous chromosomes is not true?

Answer 6

• It is not common for homologous chromosomes to trade genes.

Question 7

Which of the following are two ways that chromosome structures can be altered?

Answer 7

• Deletion mistakes and crossover mistakes

Question 8

What causes Cri du chat syndrome?

Answer 8

• A deletion mutation