Topic 4 - Cytogenetics

Question 1

What is cytogenetics?

Answer 1

The study of the structure and function of chromosomes and their role in genetics.

Question 2

Why is chromosome number important?

Answer 2

It is species-specific and deviations often cause developmental disorders.

Question 3

Does chromosome number correlate directly with genome size?

Answer 3

No. Chromosome number and genome size are not directly comparable.

Question 4

What is a nucleosome?

Answer 4

DNA wrapped around 8 histone proteins.

Question 5

Approximately how many times does DNA wrap around histones?

Answer 5

~1.65 turns.

Question 6

What is core DNA?

Answer 6

DNA in direct contact with histones.

Question 7

What is linker DNA?

Answer 7

DNA between nucleosomes.

Question 8

What is euchromatin?

Answer 8

Loosely packed chromatin; transcriptionally active.

Question 9

What is heterochromatin?

Answer 9

Tightly packed chromatin; transcriptionally inactive.

Question 10

What are the three main structural components of a chromosome?

Answer 10

Centromere, telomeres, p and q arms.

Question 11

What is the function of the centromere?

Answer 11

Joins sister chromatids and attaches spindle fibers during cell division.

Question 12

What type of DNA is found in centromeres?

Answer 12

Satellite DNA (tandem repetitive sequences).

Question 13

What is a telomere?

Answer 13

Repetitive double-stranded DNA at chromosome ends that protects from degradation.

Question 14

What are chromosome arms called?

Answer 14

p (short) and q (long).

Question 15

What determines whether a chromosome is metacentric, submetacentric, acrocentric or telocentric?

Answer 15

Centromere position.
Metacentric: center
Submetacentric: off-center
Acrocentric: near-end
Telocentric: terminal end (not found in humans)

Question 16

How many autosomes are in humans?

Answer 16

22 pairs (44 total).

Question 17

What are sex chromosomes in humans?

Answer 17

X and Y.

Question 18

How many chromosomes are in a normal human somatic cell?

Answer 18

46.

Question 19

How many chromosomes are in a gamete?

Answer 19

23.

Question 20

What is a karyotype?

Answer 20

A photographed and arranged set of chromosomes from a dividing cell.

Question 21

How are chromosomes arranged in a karyotype?

Answer 21

By size and centromere position.

Question 22

What stain is used in standard karyotyping?

Answer 22

Giemsa stain (produces G-bands).

Question 23

What can karyotypes detect?

Answer 23

Chromosome number abnormalities and large structural changes.

Question 24

What is amniocentesis?

Answer 24

Sampling amniotic fluid (usually at 16 weeks) to obtain fetal cells.

Question 25

What is chorionic villus sampling (CVS)?

Answer 25

Sampling placental tissue (8–9 weeks) for genetic testing.

Question 26

Which prenatal test has a higher miscarriage risk, amniocentesis or CVS?

Answer 26

CVS.

Question 27

What is polyploidy?

Answer 27

Having extra full sets of chromosomes (e.g., triploidy, tetraploidy).

Question 28

What is aneuploidy?

Answer 28

Having an abnormal number of individual chromosomes.

Question 29

What causes aneuploidy?

Answer 29

Non-disjunction during meiosis.

Question 30

What is monosomy?

Answer 30

Missing one chromosome (2n−1).

Question 31

What is trisomy?

Answer 31

Having one extra chromosome (2n+1).

Question 32

Is autosomal monosomy viable?

Answer 32

No, it is lethal.

Question 33

Why does maternal age increase trisomy risk?

Answer 33

Oocytes remain arrested in meiosis for decades, increasing non-disjunction risk.

Question 34

Is at least one X chromosome required for development?

Answer 34

Yes.

Question 35

What is Turner syndrome?

Answer 35

45,X (monosomy X).

Question 36

What is Klinefelter syndrome?

Answer 36

47,XXY.

Question 37

What causes structural chromosomal abnormalities?

Answer 37

Errors in crossing-over during meiosis.

Question 38

What is a deletion?

Answer 38

Loss of chromosomal material.

Question 39

What causes Cri-du-chat syndrome?

Answer 39

Deletion of short arm of chromosome 5 (5p).

Question 40

What causes DiGeorge syndrome?

Answer 40

22q11.2 deletion.

Question 41

What is a duplication?

Answer 41

Extra copy of a chromosome segment.

Question 42

What often causes duplications?

Answer 42

Unequal crossing over.

Question 43

What is an inversion?

Answer 43

A chromosome segment flipped 180°

Question 44

What is a pericentric inversion?

Answer 44

Involves the centromere.

Question 45

What is a paracentric inversion?

Answer 45

Does not include the centromere.

Question 46

What is a reciprocal translocation?

Answer 46

Exchange between two non-homologous chromosomes.

Question 47

What is a Robertsonian translocation?

Answer 47

Fusion of two acrocentric chromosomes.

Question 48

Can someone with a Robertsonian translocation have 44 chromosomes?

Answer 48

Yes, and still have a normal phenotype.

Question 49

How does FISH work?

Answer 49

A fluorescent DNA probe binds to a complementary target sequence.

Question 50

What is FISH used for?

Answer 50

Detecting specific DNA sequences on chromosomes.

Question 51

What disorders can FISH detect?

Answer 51

Trisomies, deletions (e.g., DiGeorge), chromosomal rearrangements.

Question 52

Why is FISH faster than karyotyping?

Answer 52

It targets specific sequences rather than analyzing entire chromosome sets.

Question 53

What is non-disjunction?

Answer 53

Failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate properly during cell division.

Question 54

What happens to gametes after non-disjunction in meiosis I?

Answer 54

All 4 gametes abnormal 2 with n+1 2 with n−1

Question 55

What happens to gametes after non-disjunction in meiosis II?

Answer 55

2 normal gametes 1 n+1 1 n−1

Question 56

How does non-disjunction lead to trisomy?

Answer 56

An n+1 gamete fertilized by a normal gamete → 2n+1 (trisomy).

Question 57

How does non-disjunction lead to monosomy?

Answer 57

An n−1 gamete fertilized by a normal gamete → 2n−1 (monosomy).

Question 58

Why is paternal age less associated with aneuploidy? | parental = father

Answer 58

Spermatogenesis is continuous and does not remain arrested for decades.

Question 59

Why can some aneuploidies survive?

Answer 59

Some chromosomes (e.g., 21) contain fewer essential genes.

Question 60

What is the key structural difference between reciprocal and Robertsonian translocations?

Answer 60

Reciprocal Exchange between two non-homologous chromosomes No loss of DNA (usually balanced) Chromosome number remains 46 Robertsonian Fusion of two acrocentric chromosomes Short arms may be lost Chromosome number can be 44

Question 61

Why can a Robertsonian carrier have 44 chromosomes but be normal?

Answer 61

Genetic material is still present — just rearranged.

Question 62

Why do translocation carriers have increased miscarriage risk?

Answer 62

They can produce unbalanced gametes during meiosis.

Question 63

How do chromosomes differ in interphase vs M phase?

Answer 63

Interphase DNA is euchromatin Not individually visible Transcription active Functional state M Phase DNA fully condensed (heterochromatin) Visible sister chromatids Transcription mostly halted Division state

Question 64

Why must chromosomes condense during M phase?

Answer 64

To prevent tangling and ensure accurate segregation.

Question 65

What are the 4 basic steps of FISH?

Answer 65

Denature DNA. Add fluorescent probe. Hybridization to complementary sequence. Visualize under fluorescence microscope.

Question 66

Why can’t red blood cells be used for karyotyping?

Answer 66

Mature RBCs lack a nucleus → no chromosomes.

Question 67

Why are lymphocytes used for karyotypes?

Answer 67

They contain nuclei and can be stimulated to divide.

Question 68

Why can monosomy X (Turner syndrome) survive?

Answer 68

X-inactivation normally silences one X chromosome in females, reducing dosage imbalance.

Question 69

Why is chromosome 21 trisomy compatible with life?

Answer 69

Chromosome 21 has relatively fewer genes compared to other autosomes.

Question 69

What is gene dosage imbalance?

Answer 69

Abnormal number of gene copies leading to overexpression or underexpression.

Question 70

What are histones?

Answer 70

Proteins that wrap around DNA

Question 71

number of autosomes in a gamete | *You only have one type of gamete based off your gender

Answer 71

22

Question 72

Number of autosomes in a somatic cell | *Diploid (2n) since you get chromosomes from each parent

Answer 72

44

Question 73

Total number of chromsomes in a gamete

Answer 73

23

Question 74

Total number of chromosomes in a somatic cell

Answer 74

46

Question 75

What is chromatin?

Answer 75

Coiled and compacted mass of DNA

Question 76

What are Cen Proteins?

Answer 76

A group of essential proteins for the structure and function of centromere