Chromosomal abnormalities

Question 1

How is nondisjunction related to chromosomal variation

Answer 1

chromosomes failing to disjoin at meiosis 1 or 2 causes chromosomal variation

Question 2

Describe trisomy for sex chromosomes vs autosomes

Answer 2

Autosomes trisomy are often lethal

Question 3

Describe Down syndrome

Answer 3

results from trisomy of chromosome 21, usually a result of nondisjunction of the maternal chromosome 21 during meiosis, increased incidence with increasing maternal age

Question 4

What is familial Down syndrome

Answer 4

translocation of chromosome 21 instead of non disjunction

Question 5

Describe Patau syndrome and Edwards syndrome

Answer 5

Patau- trisomy 13
Edwards - trisomy 18

Both are usually lethal in infancy

Question 6

Describe autopolyploidy and allopolyploidy

Answer 6

auto - addition of one or more sets of chromosomes identical to the haploid component of same species

allo - combination of chromosome sets from different species as a consequence of interspecific matings, create sterile hybrid

Question 7

What is an intercalary deletion?

Answer 7

Deletion from the interior of the chromosome

Question 8

What is cri-du-chat

Answer 8

Results from a segmental deletion of a small terminal portion of the short arm of chromosome 5

Question 9

What causes duplication

Answer 9

unequal crossing over during meiosis or through a replication error prior to meiosis

Question 10

What is inversion?

Answer 10

Rearrangement of the linear gene sequence rather than the loss of genetic information, requires two breaks in the chromosome and subsequent reinsertion of the inverted segment

Question 11

Describe paracentric vs pericentric inversion

Answer 11

paracentric doesn’t change relatively lengths of two arms of chromosome, results in dicentric and acentric centromere

pericentric changes relative length of chromosome arms, includes centromere, duplication and deletion arise from inversion

Question 12

What is reciprocal translocation

Answer 12

involves the exchange of segments between two non homologous chromosomes

Question 13

What are the two segregation patterns for translocation

Answer 13

Alternate - leads to normal and balanced gamete

Adjacent - leads to gametes containing duplications and deficiencies

Question 14

What is a robertsonian translocation?

Answer 14

Involves breaks at the extreme ends of the short arms of two non homologous Afrocentric chromosomes
ex. familial Down syndrome

Question 15

Describe fragile sites

Answer 15

more susceptible to chromosome breakage

fragile x syndrome - most common form of inherited intellectual disability.