Lecture 15

Question 1

Define aneuploidy

Answer 1

An abnormal number of a particular chromosome

Question 2

How does Down syndrome trisomy 21 occur?

Answer 2

It comes from an individual getting 3 copies of chromosome 21

Question 3

What can the frequency of Down syndrome depend on?

Answer 3

The mothers ages

Question 4

What is nondisjunction?

Answer 4

Failure of chromosomes to seperate properly during meiosis

Question 5

What happens to the gametes when there is non disjunction during meiosis I?

Answer 5

N+1, N+1, N-1, N-1.

Question 6

What happens to the gametes when there is nondisjunction during meiosis II?

Answer 6

N+1, N-1, N, N

Question 7

What is Klinefelter syndrome?

Answer 7

XXY genotype

Phenotypically male but with female features

Question 8

What is turners syndrome?

Answer 8

When there is only one X chromosome and nothing else.

Phenotypically female

Question 9

What does the phenotype of an individual with Turner syndrome depend on?

Answer 9

Whether the X chromosome came from Mum or Dad

Question 10

Define polyploidy

Answer 10

Possession of multiple sets of chromosomes

Question 11

How do organisms become polyploid?

Answer 11

It occurs when a rare mitotic or meiotic catastrophe causes the formation of gametes that have complete set of duplicate chromosomes.

Question 12

What is deletion? (Chromosomes)

Answer 12

Where a chromosomal segment is removed

Question 13

What is duplication? (Chromosomes)

Answer 13

When a segment is repeated

Question 14

What is inversion? (Chromosomes)

Answer 14

When a segment is reversed

Question 15

What is translocation? (Chromosomes)

Answer 15

When a segment from one chromosome is moved to a nonhomologous chromosome

Question 16

What is lejeune syndrome (cri du chat)?

Answer 16

Lejuene syndrome occurs when there is a deletion of the short arm of chromosome 5. 
Effects: 
Severe intellectual syndrome 
Can’t speak properly 
Die as children

Question 17

What is the result of meiosis in a human inversion heterozygote?

Answer 17

Shortened arm on one chromosome and lengthened arm of other chromosome.
Reduced fertility but not completely sterile

Question 18

What do 95% of patients with chronic myeloid leukaemia have?

Answer 18

Philadelphia translocation t(9;22)

Question 19

What does Philadelphia translocation cause?

Answer 19

TK over-expression because the gene can’t be regulated.

Treatable with gleevac in 90% cases

Question 20

What is robertsonian translocation?

Answer 20

Centric fusion

Question 21

What is familial Down syndrome?

Answer 21

Occurs from t(14;21), Down syndrome that runs in families