Chromosome Abnormalities, Mutations and Analysis Flashcards Preview

Principles of Disease > Chromosome Abnormalities, Mutations and Analysis > Flashcards

Flashcards in Chromosome Abnormalities, Mutations and Analysis Deck (55)
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1

What type of chromosome abnormalities can occur

Numerical
Structural
Mutational

2

What percentage of first trimester miscarriages are due to chromosomal abnormalities

50%

3

What is the main type of chromosomal abnormalities causing first trimester miscarriages

Trisomy

4

What type of abnormality and syndrome does 47, XX+21

Downs syndrome
Means there are 47 chromosomes with the extra chromosome 21

5

How can chromosomal abnormalities arise

From non-disjunction which can occur in meiosis 1 or 2

6

Give examples of autosomal aneuploidy syndromes

Trisomy 21 (Down syndrome)
Trisomy 13 (Patau syndrome)
Trisomy 18 (Edwards syndome)

7

Give examples of sex chromosome aneuploidy syndromes

45, X (Turner syndrome)
47, XXY (Klinefelter syndrome)

8

What is the incidence of trisomy 21

1 in 650 to 1 in 700 (increases with advancing maternal age)

9

Describe the features of trisomy 21

Characteristic facial dysmorphologies
IQ less than 50
Average life expectancy (50-60 years)
Alzheimer’s disease in later life

10

What is the incidence of trisomy 13

1 in 5000

11

Describe the features of trisomy 13 (Patau syndrome)

Multiple dysmorphic features and mental retardation
About 5% die within first month, very few survive beyond first year

12

What is the incidence of trisomy 18

1 in 3000

13

Describe the features of trisomy 18 (Edwards syndrome)

Severe developmental problems
Most patients die within first year, many within first month

14

Describe the features of 45, X (Turner syndrome)

Females of short stature and infertile
Neck webbing and widely spaced nipples
Intelligence and lifespan is normal

15

Describe the features of 47, XXY (Klinefelter syndrome)

Tall stature, long limbs
Male but infertile, small testes, about 50% gynaecomastia
Mild learning difficulties

16

What is gynaecomastia

Abnormal development of breast tissue in male

17

What type of structural abnormalites can occur in chromosomes

Balanced or unbalanced rearrangements
Translocations
Deletions
Insertions
Inversions

18

What type of translocations can occur

Reciprocal
Robertsonian

19

What is a reciprocal translocation

Involves breaks in two chromosomes with the formation of two new derivative chromosomes

20

What is a robertsonian translocation

The fusion of two acrocentric chromosomes (the short arms are lost)
The two chromosomes are fused but no genetic information is lost: other translocations occur but do not lead to a viable fetus

21

What are the outcomes for reciprocal translocation carriers

Partial trisomy and partial monosomy
Partial monosomy and partial trisomy

22

How can an unbalanced translocation occur

From the combination of a normal set of chromosomes which a set of balanced translocation chromosomes

23

What can the robertsonian translocation carriers produce

Trisomy 14
Monosomy 14
Monosomy 21
Trisomy 21

24

What occurs in chromosomal deletions

A break in the chromosome causes genetic material to be deleted

25

What occurs in a paracentric inversion

A break in the chromosome causes DNA to be inverted (switched upside down)

26

What type of inversions are there

Paracentric inversion
Pericentric inversion

These are balanced rearrangements

27

What occurs in a pericentric inversion

A break in the chromosome which includes the centromere causes DNA to be inverted with the centromere (switched upside down)

28

What kind of genetic mutations can occur

Germline
Somatic - in early development or later

29

What types of genetic mutations can occur

Non-coding - typically has no effect
Coding

30

What type of coding mutations are there

Silent – synonymous e.g. CGA (Arg) to CGC (Arg)
Missense e.g. CGA (Arg) to GGA (Gly)
Nonsense e.g. CGA (Arg) to TGA (Stop)
Frameshift – deletion / insertion e.g. CGA (Arg) to CCGA (Pro, then out-of-frame)