Week 6- Chromosomal Abnormality

Question 1

How is DNA formed into chromosomes?

Answer 1

It is wrapped around histone proteins to form nucleosomes and these coil to form chromatin fibers which condense to form a chromosome

Question 2

What are G dark bands on chromosomes?

Answer 2

Areas of the chromosome that are darker, tightly bound and DNA poor. G light bands are the opposite of this (loosely bound, light and DNA rich)

Question 3

What are the p and q arms of chromosomes?

Answer 3

P= short arm
Q= long arm

Question 4

How is a normal karyotype written?

Answer 4

46, XX

Question 5

How is a karyotype with a translocation written?

Answer 5

46, XX, t(5;10), (q 13.4; q 11.2)

t= translocation
second bracket= location of the translocation

Question 6

How is a karyotype with a deletion written?

Answer 6

46, XX, del (5), (q 21, q 23)

Question 7

How is a karyotype with monosomy written?

Answer 7

46, XX, -7

Loss of chromosome 7

Question 8

How is a karyotype with trisomy written?

Answer 8

47, XX +8

Gain or whole chromosome

Question 9

What is a haploinsufficient gene?

Answer 9

Needs to be present on both chromosomes to be expressed

Question 10

What is an imprinted gene?

Answer 10

A gene present only on maternal or paternal not both

Question 11

What is the aim of mitosis?

Answer 11

To create genetically identical daughter cells for growth and repair or to replace exhausted cells (2n goes to 2n)

Question 12

What is the aim of meiosis?

Answer 12

To achieve reduction from diploid to haploid so there can genetic variation (2n goes to n)

Question 13

What 2 processes does meiosis achieve?

Answer 13

Random assortment of homologues

Genetic recombination

Question 14

What is the main risk of the maternal age effect?

Answer 14

Non disjunction at meiosis

At meiosis 1: 2 gametes have trisomy, 2 have monosomy
At meiosis 2: 2 gametes are normal, 1 has trisomy, 1 has monosomy

Question 15

Why may cells in female meiosis be more vulnerable than cells in male meiosis?

Answer 15

Female meiosis is paused in utero till puberty

Question 16

What syndrome arises due to trisomy 13?

Answer 16

Patau’s

Question 17

What syndrome arises due to trisomy 18?

Answer 17

Edward’s

Question 18

What syndrome arises due to trisomy 21?

Answer 18

Down’s

Question 19

Which trisomy most often causes miscarriage?

Answer 19

16

Question 20

What is quantitative fluorescence PCR? What are the different results and what do they indicate

Answer 20

When polymorphisms are amplified and quantified (everyone has different ones)

A= uninformative
B= 1:1 (normal)
C= 1:1:1 (trisomy at meiosis I)
D= 1:2 (trisomy at meiosis II)

Question 21

What are some risks associated with the paternal age effect?

Answer 21

Inversions, deletions, translocation

Question 22

What is usually more tolerated out or trisomy and monosomy?

Answer 22

Trisomy

Question 23

What are observable features in those with William’s syndrome?

Answer 23

Very social personality, long philtrum, arched eyebrows, short+upturned nose

Question 24

What is array comparative genome hybridization used for and how is it carried out?

Answer 24

It is a genome wide scan for genetic imbalance carried out by hybridizing DNA after labeling it w colors, then a computer array analyzing colors that overlap to identify imbalances

Question 25

What is next generation sequencing?

Answer 25

When a reference genome is lined up to someone’s genome to compare them and look for mutation etc

Question 26

Why may there be vulnerability in male meiosis?

Answer 26

There is no menopausal limit

Question 27

What makes a disease rare?

Answer 27

Affects 1 in 2000 or less