Lecture 12

Question 1

Causes of Aneuploidy

Answer 1

• Deletion of centromere during mitosis and meiosis
• Robertsonian translocation
• Nondisjunction during meiosis and mitosis

Question 2

Nullisomy

Answer 2

Loss of both members of a homologous pair of chromosomes (2n-2)

Question 3

Monosomy

Answer 3

Loss of a single chromosome (2n-1)

Question 4

Trisomy

Answer 4

Gain of a single chromosome (2n+1)

Question 5

Tetrasomy

Answer 5

Gain of 2 homologous chromosomes (2n+2)

Question 6

Trisomy 21 (Primary Down Syndrome) and Familial Down Syndrome

Answer 6

Primary down syndrome is the result of 75% random nondisjunction in egg formation (occurs in about 1/900 with a maternal age of 30 and 1/90 with a maternal age of 41); familial down syndrome is the result of Robertsonian translocation between chromosomes 14 and 21 (part of 21 ends up on 14)

Question 7

Trisomy 18

Answer 7

Edward syndrome; occurs in about 1/8,000 live births

Question 8

Trisomy 13

Answer 8

Patau syndrome; occurs in about 1/15,000 live births

Question 9

Trisomy 8

Answer 9

1/25,000 - 1/50,000 live births

Question 10

Klinefelter Syndrome

Answer 10

Condition that occurs in males as a result of an extra X chromosome; most common symptom is infertility; affects about 1/500-1,000 newborn males

Question 11

Autopolyploidy

Answer 11

Means from a single species; can arise through nondisjunction in mitosis or meiosis

Question 12

Allopolyploidy

Answer 12

Means from two or more species; most arise from hybridization between 2 species followed by chromosome doubling

Question 13

Significance of Polyploidy

Answer 13

• Increase in cell size
• Larger plant attributes
• Evolution: may give rise to new species

Question 14

What are fragile sites?

Answer 14

Chromosomal regions susceptible to breakage under certain conditions

Question 15

Fragile X Syndrome

Answer 15

Considered to be an X-linked dominant condition with variable expressivity and reduced penetrance; however, due to X-inactivation in females and genetic anticipation, the inheritance of FXS does NOT follow standard X-linked dominant inheritance; females with full mutations have a milder phenotype than males as a result of variability in X-inactivation

Question 16

Common Fragile Sites

Answer 16

Heritable, nonrandomly distributed loci on human chromosomes that exhibit an increased frequency of chromosomal breakage under conditions of replicative stress; preferential targets for high genomic instability from the earliest stages of human cancer development, and increased chromosome instability at these loci has been observed following replicative stress in a subset of human genetic diseases