Lecture 22: Polyploidy and Human Chromosomal Abnormalities

Question 1

What is aneuploidy?

Answer 1

• Loss or gain of one or a few chromosomes

Question 2

What is polyploidy?

Answer 2

• Posession of multipls sets of chromosomes

Question 3

A tetraploid is….

Answer 3

• 4n = 12

Question 4

Karpechenko created a polyploid by…

Answer 4

• Hybridizing raphanus (2n = 18) and brassica (2n = 18)

- Everything was able to line up properly in meiosis because there were homologous chromosomes

Question 5

Macaroni wheat (2n = 28 chromosomes) + bread wheat (2n = 42 chromosomes) would results in a ______ chromosome F1 hybrid. Why?

Answer 5

• 35

- Because 14 + 21 = 35

Question 6

Cabbage has 2n = 18 chromosomes and turnip has 2n = 20. Oil-seed rape is a polyploid derived from these two Brassica species and is fully fertile. How many
chromosomes would you expect oil-seed rape to have? Why?

Answer 6

• 38

- Each chromosome must have a pair, it’s polyploid and fertile

Question 7

Why don’t bananas have seeds?

Answer 7

• Consequence of being triploids

Question 8

Some chromosomal aberrations:

Answer 8

• Deletion removes a chromosomal segment
• Duplication repeats a segment
• Inversion reverses a segment within a chromosome
• Translocation, a piece of chromosome gets attached to another chromosome
• Sometimes a bit of it is cut off and stuck on another piece of chromosome that already has a bit cut off

Question 9

What can deletion of tip of short arm of chromosome 5 do?

Answer 9

• Lejeune syndrome Cri du chat
• Microcephaly
• Mental retardation
• Eyes widely separated
• Make noise like cat crying

Question 10

What can deletion in chromosome 7 do? Only have half the DNA in chromosome 7.

Answer 10

• Williams-Beuren Syndrome
• Unusually cheerful demeanor
• Ease with strangers
• Cardiovascular problems

Question 11

Inversions don’t usually cause problems but can affect meiosis…(sperm)

Answer 11

• Instead of lining up, a loop usually forms
• If things do end up lining up and crossing over, deletion and duplication may occur
• Fertility effects

Question 12

What is the philadelphia chromosome?

Answer 12

• Normal (1) chromosome becomes elongated and Normal (2) chromosome receives abi gene in bcr gene
• t(9;22)
• 95% of patients with chronic myeloid leukemia

Question 13

Duchene muscular dystrophy in a t(X;21) female

Answer 13

• Some part of X has been translocated to 21

- Because of the way translocation acts with X inactivation

Question 14

Familial Down Syndrome from t(14;21)

Answer 14

• Robertsonian translocation
• Two long arms of chromosome 21 and 14 fuse
• Can be passed on

Question 15

Individuals with familial Down syndrome have which of

the following karyotypes?

Answer 15

• 46 chromosomes; translocation of 21.