Lecture 1

Question 1

What is cytogenetics?

Answer 1

Cytogenetics is the study of chromosomes and their structure and inheritance.

Question 2

What is constitutional cytogenetic abnormality?

Answer 2

Constitutional cytogenetic abnormality refers to genetic make-up present at birth, found in every cell of the body, and can be inherited or passed on.

Question 3

What is acquired cytogenetic abnormality?

Answer 3

Acquired cytogenetic abnormality usually occurs after birth, is not inherited, and is usually limited to a particular cell type.

Question 4

What is karyotype?

Answer 4

Karyotype is the chromosomal complement of an individual or a species, including number, form, and size of the chromosomes.

Question 5

What is chromosome banding?

Answer 5

Chromosome banding is a technique that allows identification of individual chromosomes by treating them with trypsin and Giemsa, which shows dark and pale bands.

Question 6

What do pale bands on chromosomes indicate?

Answer 6

Pale bands on chromosomes indicate that the chromosomes are GC rich, early replicating, and gene rich.

Question 7

What do dark bands on chromosomes indicate?

Answer 7

Dark bands on chromosomes indicate that the chromosomes are AT rich, late replicating, and gene poor.

Question 8

What is FISH?

Answer 8

FISH (Fluorescence in situ hybridization) is a method for visualizing specific locations on a chromosome.

Question 9

What are fluorescent DNA probes?

Answer 9

Fluorescent DNA probes are short sequences of single-stranded DNA that are complementary to the DNA sequences being labeled and examined in FISH.

Question 10

What is chromosome painting?

Answer 10

Chromosome painting is a FISH-based technique that uses whole chromosome probes to detect differences in chromosomes based on color instead of banding patterns.

Question 11

What is comparative genome hybridization- CGH?

Answer 11

CGH (Comparative Genome Hybridization) is a technique that identifies ranges that are amplified or lost in tumor samples by labeling reference DNA as red and tumor DNA as green.

Question 12

What is ploidy?

Answer 12

Ploidy is the number of homologous sets of chromosomes in a cell

Question 13

What is euploidy?

Answer 13

Euploidy is having an integral multiple of the monoploid number of chromosomes.

Question 14

What is aneuploidy?

Answer 14

Aneuploidy is the state of not having euploidy at the level of the chromosome, such as having a pair that doesn’t match the others.

Question 15

What is trisomy?

Answer 15

Trisomy is a condition in which one gamete with two copies of a chromosome fuses with a normal gamete, resulting in three copies of a particular chromosome.

Question 16

What is monosomy?

Answer 16

Monosomy is a condition in which one gamete is missing a chromosome and fuses with a normal gamete, resulting in the lack of a chromosome.

Question 17

What is Down syndrome?

Answer 17

Down syndrome is a genetic disorder caused by trisomy of all or a critical portion of chromosome 21, resulting in 47,XX+21 or 47,XY+21.

Question 18

What is the main cause of Down Syndrome and how does it relate to age?

Answer 18

About 80% of Down Syndrome cases are due to meiosis 1 errors, while 5% are caused by non-disjunction in fathers and another 5% are due to mitosis. The risk of having a baby with Down Syndrome increases with age.

Question 19

What is non-homologous end joining?

Answer 19

Non-homologous end joining is a repair mechanism where cells join two broken ends or add telomeres to the ends.

Question 20

What causes chromosome breaks?

Answer 20

Chromosome breaks can be caused by DNA damage (such as chemicals or radiation) or errors in recombination.

Question 21

What are acentric and dicentric joining?

Answer 21

Acentric joining causes the loss of a centromere, while dicentric joining causes the presence of two centromeres.

Question 22

What is Cat-cry Syndrome, and what are its symptoms?

Answer 22

Cat-cry Syndrome is a human deletion syndrome caused by a loss of part of 5p. Symptoms include severe developmental and mental retardation, microcephaly, round face, wide-spread eyes, small chin, and most die in childhood.

Question 23

How is Cat-cry Syndrome typically acquired?

Answer 23

Cat-cry Syndrome is mostly not inherited but rather happens by sporadic deletion during sperm/egg generation or in early fetal development.

Question 24

What are the genes associated with deletions in Cat-cry Syndrome?

Answer 24

Deletions in Cat-cry Syndrome are associated with SEMAF and CTNND2 genes.

Question 25

What is inversion, and what is the most common type seen in humans?

Answer 25

Inversion is a chromosomal rearrangement where a segment of a chromosome is reversed. The most common type of inversion seen in humans is on chromosome 9 (46,X,Y).

Question 26

What are pericentric and paracentric inversions, and how do they differ?

Answer 26

Pericentric inversions occur from a crossing of centromeres, resulting in a copy that has lost some DNA and another with duplicated DNA. Paracentric inversions occur in two different ways: one gamete is normal and one has two centromeres, which causes a problem with fertilization, or one gamete is normal and one has no centromeres, which terminates immediately.

Question 27

What is reciprocal/balanced translocation, and when does it affect phenotype?

Answer 27

Reciprocal/balanced translocation is a chromosomal rearrangement where two chromosomes exchange segments. It usually has no effect on phenotype unless the break occurs within a gene or interferes with gene expression or heterochromatin or the break affects X chromosome inactivation.

Question 28

What is Robertsonian translocation/centric fusion, and what are the consequences of this chromosomal rearrangement?

Answer 28

Robertsonian translocation/centric fusion involves the fusion of two acrocentric chromosomes following a break in the short arms. This results in a chromosome with two very long arms and two centromeres close in proximity and one with no centromere (lost). The p arm is usually lost, but this usually doesn’t cause clinical complications as they consist of rDNA arrays.