Lecture 18

Question 1

what is a balanced translocation?

Answer 1

all genetic material is present but in the wrong place

Question 2

phenotype of balanced translocation

Answer 2

as long as haplosufficient genes are unaffected, won’t see effects but may be infertile

Question 3

what is a translocation heterozygote?

Answer 3

2 normal chromosomes, 2 translocated chromosomes

Question 4

what are the names of the 2 segregation patterns that occur in a translocation heterozygote?

Answer 4

1. adjacent
2. alternate

Question 5

what is the result of the adjacent segregation pattern?

Answer 5

both products are non-viable with deletions and duplication
- 1 has normal chr #1 and translocated chr #2
- 1 has normal chr #2 and translocated chr #1

Question 6

what is the result of the alternate segregation pattern?

Answer 6

both products are viable and balanced
- 1 has both normal chr
- 1 has both translocated chr

Question 7

which proportion of gametes are made from the adjacent vs alternate segregation patterns? and what does this indicate about the overall gametes?

Answer 7

equal proportions of each pattern –> half the gametes are non-functional

Question 8

how are somatic cells affected by balanced translocations in heterozygote?

Answer 8

unaffected –> don’t need homologous pair for mitosis

Question 9

what is a consequence of balanced translocations?

Answer 9

robertsonian translocations

Question 10

what type of chromosomes are affected by robertsonian translocations?

Answer 10

acrocentric chromosomes –> centromere close to the end

Question 11

phenotype of people with robertsonian translocation

Answer 11

normal phenotype

Question 12

describe the chromosomes produced from robertsonian translocation

Answer 12

start with 2 sets of 2 chromosomes

end up with one of each normal chromosome, a fusion chromosome, and a small fusion product that is lost

Question 13

what are 2 conclusions from the observation that robertsonian translocations cause no detectable somatic symptoms?

Answer 13

1. breakpoints did not disrupt haploinsufficient genes
2. lost region does not include haploinsufficient genes

Question 14

what can robertsonian translocation lead to?

Answer 14

parent with robertsonian translocation mating with normal person –> inheritance of trisomy 21 (down’s syndrome)

Question 15

how many possible gametes are produced from the robertsonian translocation?

Answer 15

6

Question 16

what happens when a normal gamete mates with a gamete with chr 21 and translocated chr?

Answer 16

will have 2x chr 21, 1 translocated chr, and 1 chr 14

TRISOMY 21

Question 17

what happens when a normal gamete mates with a gamete with 1 translocated chr?

Answer 17

will have 1x chr 21, 1x chr 14, and 1x translocated chr

become a translocation carrier –> viable

Question 18

what happens when a normal gamete mates with a normal gamete?

Answer 18

2 of each chr 21 and chr 14 –> normal

Question 19

what happens when a normal gamete mates with a gamete with 1x chr 21 or 1x chr 14

Answer 19

end up with 1x chr 21 and 2x chr 14 OR 1x chr 14 and 2x chr 21

both are lethal

Question 20

what happens when a normal gamete mates with a gamete with chr 14 and translocated chr?

Answer 20

end up with 1x chr 21, 1x translocation chr, and 2x chr 14

TRISOMY 14 –> lethal