Chromosome Anomalies

Question 1

What is Mendel’s Law

Answer 1

Structure of chromosome determines inheritance

Genes inherited in blocks

Question 2

What is the difference between dark and light bands on the chromosome

Answer 2

Light bands = Replicate early. Less condensed chromatin. Protein coding genes
Dark bands = Replicate late. Condensed chromatin. Structural Proteins

Question 3

What is flourescent in situ hybridisation

Answer 3

Flourescent probes that bind to parts of chromosome with high degree of sequence similarity

Question 4

What is array

Answer 4

Can be used to hybridise RNA from tumours to determine patterns of gene expression
Does patient have more of some type of DNA

Question 5

What type of chromosomal anomaly is Down Syndrome. How is it caused?

Answer 5

Triosomy 21
3 copies of 21
Robertsonian translocation
Mosaicism

Question 6

How does 3 copies cause down syndrome

Answer 6

Gene Dosage Effect = 1.5x amount of specific gene products

Amplified developmental instability = overall effect of imbalance

Question 7

What is Edwards Syndrome

Answer 7

Triosomy 18
Multiple malformations
Clenched hands with overlapping fingers

Question 8

What is Patau Syndrome

Answer 8

Triosomy 13
Multiple malformations
Affects midline structures

Question 9

What is Klinefelter Syndrome

Answer 9

47, XXY
Poorly developed secondary sexual characteristics
Infertile

Question 10

What is Turner’s Syndrome

Answer 10

45, X
Primary Amernorrhoea
Congenital Heart Defect
Webbed Necks

Question 11

What is non-disjunction

Answer 11

Failure of chromosomes to separate during meiosis 1 or 2

Result in nullisomic (no chromosome) or disomic (2 instead of just 1)

Question 12

Why the association with maternal age

Answer 12

Lengthy interval between onset & completion of meiosis

Accumulating effect on primary oocyte, wear and tear on cell division machinery

Question 13

What are the different types of triploidy

Answer 13

YYX = Large cystic placenta. Severely growth retarded foetus
XXY = Small + Underdeveloped Placenta
XXX

Question 14

How does organism identify paternal/maternal genes

Answer 14

Some human genes behave differently depending from which parent
Small number of genes are imprinted. Some expressed in paternally inherited chromosome, others in maternally

Question 15

What is Robertsonian translocation

Answer 15

Involve only chromosome 13,14,15,21,22 (Acrocentric)
Breakage of chromosome at/close to centromere with subseqeunt fusion of their long arms-short arms
Correct number of genes but location altered
Can be balanced = normal phenotype/unbalanced = deletion/addition
Reduce number of chromosomes to 45

Question 16

What is reciprocal translocation

Answer 16

Breakage along short/long arm of 2 non-homologous chromosomes with exchange of fragments
Balanced = clinically normal
Un-balanced = harmful

Question 17

What is mosaicism

Answer 17

2 population of cells with different genetic constitutions

Can be somatic/gonadal

Question 18

What do we know about the Y chromosome

Answer 18

Apart from tip of p arm, no recombination with homologous chromosome
Sext determining region Y determines male-ness

Question 19

How does translocation affect the next generation

Answer 19

Balanced translocation carriers are at greater risk of creating gametes with an unbalanced translocation

Question 20

What is the difference between Robertsonian and reciprocal translocation

Answer 20

Robertsonian occur in the five acrocentric chromosomes (e.g., chromosomes in which the short (p) arm is so short, it is very difficult to observe) 13, 14, 15, 21, and 22. Reciprocal translocations typically occur between chromosomes 13 and 14, 13 and 21, and 21 and 22, where the long (q) arms fuse at the centomere and the short arms of each chromosome disappear