Week 9 - Chromosomes

Question 1

Karyotypes can reveal numerical or structural abnormalities. What are some numerical abnormalities?

Answer 1

Aneuploidy - presence of extra individ. (Trisomy) Chromosomes or absence of individ. Chromosome (monosomy)

Polyploidy - presence of extra set of chromosomes (FATAL)

Nullisomy - lack of any chromosomes

Question 2

What are consequences of trisomy and monosomy?

Answer 2

Monosomy - too little protein produced

Trisomy - too much protein produced

Question 3

What causes aneuploidies?

Answer 3

Error at meiosis 1 and meiosis 2

At meiosis 1 chromosomes dont get separated into two different cells, called NON DISJUNCTION

Question 4

What percentage of early miscarriages involve a chromosomal abnormality?

Answer 4

60%

30% due to trisomy.. Where risk increases with maternal age

Question 5

Characteristics of turner syndrome?

Answer 5

Monosomy X 
Short stature ( average height is 4 feet 8) 
Infertility and incomplete ovarian development 
Normal intelligence and life expectancy 

1 in 5000 females ***

Treatment: hormone replacement therapy, oestrogen for sexual development

Question 6

Characteristics of Downs Syndrome

Answer 6

Trisomy 21 (96% of cases)

• characteristic appearance
• learning difficulties
• risk of congenital heart malformations
• risk of early onset Alzheimer’s disease

Question 7

Characteristics of Klinefekter syndrome

Answer 7

XXY in mals

Tall, infertile, poorly developed secondary chracteristics

Question 8

Characteristics of 47 XXX, 47 XYY?

Answer 8

47 XXX - tall, slight reduction in IQ

47 XYY - tall, slight reduction in IQ

Question 9

Why are the effects of sex chromosome abnormalities so mild?

Answer 9

Due to X CHROMOSOME INACTIVATION

• ensure balance if number if X chromosome genes
• always only 1 chromosome that is active

Question 10

What are the structural abnormalities that can occur in karyotypes?

Answer 10

Remember TRIDD.

T - translocations 
R - ring chromosomes 
I  - inversions 
D - duplications 
D - deletions

Question 11

What are karyotypes?

Answer 11

A picture of someones chromosomes, describes;

• number and shape of chromosomes
• centromere position and arm length

Recorded as-
No, of chromosomes
Identity of sex chromosomes
Anomalies

E.g. 47, XX +21 (trisomy of chromosome 21 i.e. Extra chromosome 21)

-^^^^ female with downs syndrome