aneuploidy

Question 1

aneuploidy

Answer 1

diploid genome which lacks a chromosome or has an extra chromosome

Question 2

how is aneuploidy different from polyploidy

Answer 2

organism gains or is missing a single chromosome whereas in polyploidy all sets are affected

Question 3

trisomies

Answer 3

2N+1
- diploid for all chromosomes but +1 chromosome for one of the homologous groups
- some result in aborted embryo

Question 4

monosomies

Answer 4

2N-1
- diploid for all chromosomes but -1 for one of the homologous groups

Question 5

when is it a possibility for trisomies or monosomies to be viable

Answer 5

when they are sex chromosomes

Question 6

cause of aneuploidy

Answer 6

meitotic or meiosis non disjunction

Question 7

aneuploidy from nondisjunction in meiosis I

Answer 7

• all gametes are wrong
• homologous pairs do not disjoin
• final zygotes are 2 trisomies and 2 monosomies
• all monosomies are aborted except sex chromosomes

Question 8

aneuploidy from nondisjunction in meiosis II

Answer 8

• half the gametes are wrong
• sister chromatids will not disjoin
• final zygotes are 1 trisomie, 1 monosomie and 2 normal diploids
• if happens to one cell usually doesn’t happen to the other - low frequency event

Question 9

autosomal trisomies that are seen as live births

Answer 9

trisomy 21 (down syndrome)
trisomy 13 (Patau syndrome)
trisomy 18 (Edwards syndrome)
- only those with trisomy 21 can live into adulthood

Question 10

down syndrome karyotype

Answer 10

• chromosome 21 is one of the smallest chromosomes
• most trisomy can be tolerated because it is the smallest amount of extra genes - still bad but the least bad

Question 11

Aneuploidy in sex chromosomes

Answer 11

• trisomy and monosomy can be tolerated
• comes from X inactivation

Question 12

XO - turner syndrome

Answer 12

• female with a single X
• can be caused by the mom or dad
• 2n - 1

Question 13

XXY - klein felter syndrome

Answer 13

• male with an extra X
• 1 barr body
• mom could give XX or day could give XY
• if from dad, nondisjunction in meiosis I
• some female hormones are heightened

Question 14

XXX - triple X syndrome

Answer 14

• female with an extra X
• mom gives XX
• 2 barr bodies

Question 15

XYY - double Y males

Answer 15

• male with an extra Y
• gets YY from dad, nondisjunction in meiosis II
• most common phenotype = very tall (due to extra hormones)

Question 16

why are older mothers more likely to give birth to down syndrome children

Answer 16

frequency of trisomies increases due to prophase arrest
- in the human female fetus meiosis begins and arrests, germ cells remain in an arrested prophase I until ovulation
- stalled gametes are constantly exchanging genetic material through recombination which causes them to break apart from mitotic spindle

Question 17

prophase arrest

Answer 17

problems with pairing of homologous chromosomes

Question 18

correlation between trisomies and maternal age

Answer 18

• bivalents with crossovers near the ends of chromosomes are fragile and increasingly unstable over time
• if the bivalent dissociates, non-disjunction of the homologues occur

Question 19

cohesion

Answer 19

non-disjunction between sister chromatids

Question 20

what sorts of chemicals can cause non-disjunction

Answer 20

colchicine and Bisphenol A

Question 21

causes of down syndrome

Answer 21

• 96% due to meiotic nondisjunction
• of these, 80% from oogenesis in the mother and 20% from spermatogenesis in the father
• in males due to random chance, in females due to prolonged prophase I

Question 22

deletions / deficiency in chromosome segment

Answer 22

• missing part of the chromosome
• could be due to mistakes in how they are copied

Question 23

duplication in chromosome segment

Answer 23

• an extra part of the chromosome
• hyperploidy

Question 24

hyperploidy and hypoploidy

Answer 24

hypoploidy: less genetic material
hyperploidy: more genetic material

Question 25

Hypoploidy example: cri-du-chat syndrome

Answer 25

• missing the tip of one chromosome 5, due to mistake in DNA replication
• grow into adulthood with developmental disorder