Lecture 46

Question 1

What is euploid?

Answer 1

normal numbers of each chromosome

Question 2

What is aneuploidy? What are the two types?

Answer 2

wrong number of one chromosome

monosomy 2n-1 (missing chromosome)

trisomy 2n+1 (extra chromosome)

Question 3

What is disjunction?

Answer 3

separation. normal disjunction occurs in anaphase, where chromatids separate correctly

Question 4

What are causes of aneploidy?

Answer 4

nondisjunction

failure of chromosome separation in

mitosis: patch of aneuploid cells

meiosis I = homologs fail to separate

meiosis II = sister chromatids fail to separate

Question 5

Is monosomy or trisomy more lethal?

Answer 5

monosomy - too few proteins

Question 6

Aneuploidy is common in embryos. What fraction?

Answer 6

1/3

Question 7

Aneuploidy is rare in infants. It is only tolerated if the chromosome is:

Answer 7

small (21)
has few genes (Y)
can be inactivated (X)

Question 8

Down syndrome has what other name?

What is the genotype of a female and male with down syndrome?

How does it occur?

Answer 8

trisomy 21

47,XX,+21 or 47,XY,+21

Female oocytes arrest at prophase I until ovulation
longer arrest = higher nondisjunction risk

Question 9

What are the phenotypes of someone with down syndrome? What is the penetrance and expressivity?

Answer 9

mild to moderate intellectual disability

increased leukemia risk

complete penetrance

broad expressivity

Question 10

People with down syndrome also have heart defects in 40% of infants. What is the penetrance and expressivity?

Answer 10

40%, broad expressivity

Question 11

What is the genetic basis of intellectual disability in those with down syndrome?

Answer 11

overexpression of DYRK (21q22) (because there are 3 copies of the gene)

inhibits neuron reproduction in fetal brain

Question 12

People with DS have (blank) risk of hypertension

Answer 12

very low

Question 13

What does SHOX do and where is it located?

Answer 13

activate limb bone development in fetus (opposite of FGFR3)

located in pseudo autosomal region (top of X and Y chromosome)

Question 14

How many SHOX proteins and Barr bodies does 47,XXX have?

Answer 14

3 SHOX proteins = taller
2 Barr bodies

usually unrecognized

Question 15

How many SHOX proteins and Barr bodies does 47,XXY (Klinefelter) have?

Answer 15

1 barr body
mild health issues
3 SHOX genes = tall

Question 16

How many SHOX proteins and Barr bodies does 45,X have (turner)?

Answer 16

0 Barr bodies
1 SHOX gene = short
mild health issue