Chromosomes and Karyotypes

Question 1

What are chromosomes?

Answer 1

Structural units, made up of DNA and proteins, and carry genes in a linear sequence shared by a number of species.

Question 2

What is a gene locus?

Answer 2

Specific position of a gene on or a chromosome. Alleles are different forms of a specific gene.

Question 3

What is a karyogram?

Answer 3

• Shows images of chromosomes

- Arranged in homologus pairs of decreasing length

Question 4

What is prenatal karyotyping used for?

Answer 4

• To determine the gender

- To look for genetic abnormalities

Question 5

What is a chromosomal abnormality?

Answer 5

If a zygote is formed from a gamete that has experienced a non-disjunction event, the offspring will have extra or missing chromosomes (non-disjunction: failing to seperate correctly)

Question 6

What is a nuchal translucency scan?

Answer 6

• Non-invasive test carried out between 11 and 13 weeks pregnant, looks at the nuchal fluid behind the neck of the fetus
• A large amount of nuchal fluid is strongly correlated with downs syndrome

Question 7

What is amniocentesis?

Answer 7

• A sample of amniotic fluid is taken in a syringe (needle is guided using ultrasound)
• Amniotic fluid contains cells from the fetus which are used for karyotyping
• Carried out 16th week of pregnancy (1% miscarriage chance)

Question 8

What is chronic villus sampling?

Answer 8

• The chorion is membrane which is part of the placenta
• It contains many cells with villi and some of these are taken and cultured
• When sufficient cells have been grown, a karyotype is carried out in the 11th week of pregnancy (2% miscarriage chance)