Chromosomal Abnormalities

Question 1

What is chromatin made of?

Answer 1

DNA, non-histone proteins, RNA, histones (H2A, H2B, H3 & H4 octamer - H1 stabilises octamer)

Question 2

What are the different types of numerical chromosomal abnormalities?

Answer 2

Polyploidy, aneuploidy, monosomy and trisomy

Question 3

What are the different types of structural chromosomal abnormalities?

Answer 3

Physical changes to one or more of the chromosomes - balanced or unbalanced.

Question 4

In a karyotype how are the chromosomes aligned?

Answer 4

Largest to smallest from (1-22) with 23 at the end

Question 5

How do you write out a karyotype formula?

Answer 5

Starts with total number of chromosomes on the cell, followed by a comma, then the X chromosomes and Y chromosomes. + or - indicates an extra/missing piece e.g. 6p- means missing a segment of the p-arm on chromosome 6

Question 6

Why would you perform a karyotype?

Answer 6

Congenital abnormalities (prenatal screening, birth defects, abnormal sexual development, infertility, recurrent foetal loss), acquired abnormalities

Question 7

How would prepare cells for a karyotype?

Answer 7

Procure cells, add phytohaemagglutin, culture, add colcemid, culture, brief digestion with trypsin, Giemsa stain.

Question 8

What is the culturing time length for bone marrow?

Answer 8

0-1 day

Question 9

What is the culturing time length for blood?

Answer 9

2-3 days

Question 10

What is the culturing time length for solid tissue, amniotic fluid and chorion villus?

Answer 10

7-21 days

Question 11

When is chromatin activated?

Answer 11

When it’s acetylated

Question 12

When is chromatin inactive?

Answer 12

When it’s methylated

Question 13

What is non-disjunction?

Answer 13

Creation of a gamete with a missing chromosome or containing both homologous chromosomes i.e. failure of chromosome pairs to separate properly

Question 14

What causes aneuploidy?

Answer 14

Non-disjunction

Question 15

How can non-disjunction arise?

Answer 15

Failure of homologous chromosomes to separate in meiosis I or failure of sister chromatids to separate during meiosis II

Question 16

What are the possible autosomal trisomies in humans?

Answer 16

21, 18 & 13

Question 17

What is anaphase lag?

Answer 17

Chromosome which are left behind at cell division (due to defects in the spindle fibres)

Question 18

What are the three types of chromosomal structures in humans?

Answer 18

Meta-centric, sub-metacentric and acrocentric

Question 19

What are the types of mutations that occur in one chromosome?

Answer 19

Deletion, duplication, inversion, ring chromosome and isochromosome

Question 20

What are the types of mutations with two chromosomes?

Answer 20

Inversion, reciprocal translocation, robertsonian translocation

Question 21

Where is polyploidy common?

Answer 21

Human muscle and liver

Question 22

What is sex chromosome aneuploidy?

Answer 22

Only one X is active in human cells. Inactive forms - Barr bodies in periphery of cells

Question 23

What are the symptoms of Down syndrome?

Answer 23

Intellectual disability, congenital heart disease, haematological malignancies, hypothyroidism, infertility, eye disorders, hearing disorders

Question 24

What is the karyotype for Edwards syndrome?

Answer 24

(47,XX,+18) - modal life span of ~5-15 days

Question 25

What is the karyotype for Patau syndrome?

Answer 25

(47,XY,+13) - polydactyly. >80% die in a year

Question 26

What is the karyotype for Turner syndrome and what are the effects?

Answer 26

(45,X). Short, broad chest, low hairline, webbed neck, CNS problem, renal, infertility

Question 27

What is the karyotype for Klinefelter and what are its effects?

Answer 27

(47,XYY) - after onset of puberty gynocomastia, language/reading impairment

Question 28

What is the karyotype for Triple X and what are its effects?

Answer 28

(47,XXX). Two/three X chromosomes are activated - tall, microcephaly, delayed motor skills, speech and learning disabilities

Question 29

What is Philadelphia chromosome?

Answer 29

Chronic myelogenous leukaemia (CML) - reciprocal translocation between 9 & 22