Human Genome & Chromosomes

Question 1

Define aneuploidy

Answer 1

aneuploidy= Abnormal chromosome number

Question 2

Define polyploidy

Answer 2

polyploidy = gain of one or more haploid chromosome

Question 3

Define disomy

Answer 3

Disomy is 2 copies of a chromosome

Question 4

Define triploid

Answer 4

Triploid = 3 haploid sets

Question 5

Define tetraploid

Answer 5

Tetraploid= 4 haploid sets

Question 6

Define monosomy

Answer 6

Monosomy= 1 copy of a chromosome

Question 7

Define trisomy

Answer 7

Trisomy= 3 copies of a chromosome

Question 8

Define tetrasomy

Answer 8

Tetrasomy = 4 copies of a chromosome

Question 9

what is the generic name given to a condition in which we have an incorrect number of chromosomes

Answer 9

aneuploidy

Question 10

Identify some aneuploidy conditions

Answer 10

Down syndrome (trisomy 21)
Edwards syndrome (trisomy 18)
Patau syndrome (trisomy 13)
Klinefelter syndrome (males with extra X chromosome)
Turner syndrome (females with missing X chromosome/ partially missing X chromosome)

Question 11

How many chromosomes does an individual with Down syndrome have and what do we call this/ what does it mean

Answer 11

Individual with Down syndrome has 47 chromosomes
They have an extra copy of chromosome 21
This is known as trisomy 21 (they have 3 chromosome 21’s)

Question 12

What percentage of down syndrome babies miscarry/ still born

Answer 12

~30%

Question 13

In Down syndrome individuals there’s a 70% chance of early onset Alzheimers disease, why do we think this is

Answer 13

Presence of amyloid precursor protein (amyloid beta) on chromosome 21

Question 14

Describe the 3 different types of Down Syndrome

Answer 14

1) 95%= chromosomes don’t split apart/ non-disjunction so DS individual has 3 separate copies of chromosome 21

2) 4%= have extra copy of chromosome 21 because of ROBERTSONIAN TRANSLOCATION( extra copy of chromosome 21 on chromosome 14, one of chromosome 14 loses its short arm and that’s replaced by chromosome 21)

3) 1%= have MOSAICISM with mixture of normal + trisomy 21 cell lineages, individuals usually have milder features (occurs postzygotically)

Question 15

Define postzygotically

Answer 15

After fertilisation

Question 16

Why do individuals with mosaicism (form of Down Syndrome) have milder features ?

Answer 16

Because of the presence of the normal cells (mixed with trisomy 21)

Question 17

What is the correlation between maternal age and trisomies

Answer 17

Trisomies are associated with an increase in maternal age (on graph after 25 risk increases)

Question 18

What does a triploid abnormality in baby mean

Answer 18

69 chromosomes = most embryos miscarry

Question 19

In which 2 autosomal aneuploidy syndromes do babies die in first few weeks of life

Answer 19

Edwards syndrome (trisomy 18)
Patau syndrome (trisomy 13)

If baby does survive (very rare) = severe intellectual and physical disability

Question 20

Edwards syndrome

Answer 20

•Trisomy 18
•1 in 3000 births
•multiple malformations (heart, kidneys)
•clenched hands w overlapping fingers

Question 21

Patau syndrome

Answer 21

•trisomy 13
•1 in 5000 births
• multiple malformations affecting midline structures I.e. incomplete lobation of brain, cleft lip, congenital heart disease

Question 22

Identify the type of mutation in which a part of a chromosome breaks off and attaches to a different chromosome

Answer 22

Translocation

Question 23

What is the Down syndrome nuchal fold test

Answer 23

The nuchal translucency test measures the nuchal fold thickness. This is an area of tissue at the back of an unborn baby’s neck. Measuring this thickness helps assess the risk for Down syndrome and other genetic problems in the baby (thicker = Down syndrome) major advantage non-invasive!