Genetics

Question 1

What are the three different types of chromosomal abnormalities

Answer 1

Numerical, structural, and mutational

Question 2

Define trisomy

Answer 2

Extra copy of chromosomes

Question 3

Define monosomy

Answer 3

Only 1 chromosome present from a pair is present in cells

Question 4

What is trisomy 21 known as

Answer 4

Down’s Syndrome

Question 5

What is trisomy 13 known as

Answer 5

Patau Syndrome

Question 6

What is trisomy 18 known as

Answer 6

Edward’s Syndrome

Question 7

What is the result of non-disjunction

Answer 7

1. Two gametes with disomy and 2 dull gametes (meiosis 1)
2. 1 gamete with disomy, 1 gamete null, and 2 gametes normal (meiosis 2)

Question 8

What are the features of Down Syndrome

Answer 8

1. Low IQ (less than 50)
2. Low muscle tone
3. Short stature
4. Flat nasal bridge
5. Protruding tongue

Question 9

What can Down syndrome cause

Answer 9

1. Alzheimer’s disease in later life
2. Higher risk of conditions e.g. epilepsy

Question 10

What increases the risk of Down’s syndrome

Answer 10

Advancing maternal age

Question 11

What are the chromosomal findings of Down’s syndrome

Answer 11

1. Trisomy 21, non-dysjunction (95%), usually maternal origin
2. Unbalanced Robertsonian translocation (4%)
3. Mosaicism

Question 12

What are the features of Patau Syndrome

Answer 12

Multiple dysmorphic features and mental retardation

Question 13

What is the complication of Patau Syndrome

Answer 13

5% die within the first month and very few survive beyond first year

Question 14

What are the chromosomal findings of Patau Syndrome

Answer 14

1. Non-dysjunction (90%), maternal origin
2. Unbalanced Robertsonian translocation (10%)

Question 15

What does Edward’s Syndrome cause

Answer 15

Severe developmental problems with most patients dying within the first year, many within the first month

Question 16

What are the features of Edward’s Syndrome

Answer 16

1. Low birth weight
2. Heart, resp, kidney, and GI conditions

Question 17

What is monosomy 45 X known as

Answer 17

Turner’s Syndrome

Question 18

What are the features of Turner’s Syndrome

Answer 18

1. May be born with swollen hands and feet due to excess fluid but will resolve
2. Neck webbing and widely spaced nipples
3. Short stature and infertile
4. Doesn’t affect intelligence or lifespan

Question 19

Who can present with Turner’s Syndrome

Answer 19

Females only

Question 20

What condition has 47, XXY

Answer 20

Klinefelter Syndrome

Question 21

Who can present with Klinefelter Syndrome

Answer 21

Men only

Question 22

What are the features of Klinefelter Syndrome

Answer 22

1. Tall stature, long limbs
2. Infertile, small testies, about 50% gynaecomastia
3. Mild learning difficulties

Question 23

What are the different types of structural abnormalities

Answer 23

1. Translocations (reciprocal and Robertsonian)
2. Deletions
3. Insertions
4. Inversions

Question 24

Describe what is balanced translocation

Answer 24

2 different chromosomes exchange large sections of information with no DNA missing or any additional DNA

Question 25

What is the outcome of reciprocal translocation

Answer 25

Meiosis can create: 1. Normal gamete (inherit the two normal gametes) which results in a normal zygote 2. Balanced gamete (inherit the two chromosomes that exhanged information) which results in a balanced carrier zygote 3. Unbalanced gamete (inherit a normal and a translocated chromosome) which results in a partial trisomy and partial monosomy

Question 26

Describe what Robertsonian translocation is

Answer 26

Involves the fusion of acrocenteric chromosomes (long Q arm which has normal coding DNA and a short P arm which has no coding DNA on it)

Question 27

What is the effect of Robertsonian translocation

Answer 27

When the two acrocentric chromosomes undergo a fusion, they finish up with a Robertsonian translocation. The two Q arms fuse to present in one chromosome and the short P arms also form a new chromosome

Question 28

What is the outcome of Robertsonian translocation

Answer 28

1. Normal gamete which results in a normal zygote 2. Balanced robertsonian translocation (only robertsonian translocation is inherited) which results in a balanced carrier 3. Unbalanced robertsonian translocation (a robertsonian translocation chromosome and a normal chromosome is inherited) which results in trisomy or monosomy (normal chromosome inherited on its own)

Question 29

Describe the structural abnormality of deletion

Answer 29

DNA gets broken down in chromosomes which is normal but becomes abnormal if it is not repaired

Question 30

Describe the structural abnormality of inversion

Answer 30

A large piece of DNA is reversed (paracentric inversion is away from the centromere and pericenteric inversion is at the centromere)