Lecture 18 Flashcards
what is a balanced translocation?
all genetic material is present but in the wrong place
phenotype of balanced translocation
as long as haplosufficient genes are unaffected, won’t see effects but may be infertile
what is a translocation heterozygote?
2 normal chromosomes, 2 translocated chromosomes
what are the names of the 2 segregation patterns that occur in a translocation heterozygote?
- adjacent
- alternate
what is the result of the adjacent segregation pattern?
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
what is the result of the alternate segregation pattern?
both products are viable and balanced
- 1 has both normal chr
- 1 has both translocated chr
which proportion of gametes are made from the adjacent vs alternate segregation patterns? and what does this indicate about the overall gametes?
equal proportions of each pattern –> half the gametes are non-functional
how are somatic cells affected by balanced translocations in heterozygote?
unaffected –> don’t need homologous pair for mitosis
what is a consequence of balanced translocations?
robertsonian translocations
what type of chromosomes are affected by robertsonian translocations?
acrocentric chromosomes –> centromere close to the end
phenotype of people with robertsonian translocation
normal phenotype
describe the chromosomes produced from robertsonian translocation
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
what are 2 conclusions from the observation that robertsonian translocations cause no detectable somatic symptoms?
- breakpoints did not disrupt haploinsufficient genes
- lost region does not include haploinsufficient genes
what can robertsonian translocation lead to?
parent with robertsonian translocation mating with normal person –> inheritance of trisomy 21 (down’s syndrome)
how many possible gametes are produced from the robertsonian translocation?
6
what happens when a normal gamete mates with a gamete with chr 21 and translocated chr?
will have 2x chr 21, 1 translocated chr, and 1 chr 14
TRISOMY 21
what happens when a normal gamete mates with a gamete with 1 translocated chr?
will have 1x chr 21, 1x chr 14, and 1x translocated chr
become a translocation carrier –> viable
what happens when a normal gamete mates with a normal gamete?
2 of each chr 21 and chr 14 –> normal
what happens when a normal gamete mates with a gamete with 1x chr 21 or 1x chr 14
end up with 1x chr 21 and 2x chr 14 OR 1x chr 14 and 2x chr 21
both are lethal
what happens when a normal gamete mates with a gamete with chr 14 and translocated chr?
end up with 1x chr 21, 1x translocation chr, and 2x chr 14
TRISOMY 14 –> lethal
