Chromosome Disorders

Question 1

What is nondisjunction in meiosis?

Answer 1

The failure of homologous chromosomes or sister chromatids to separate properly during cell division - can occur in meiosis I or II, and gives rise to aneuploidies - e.g. trisomy 21 (Down’s syndrome)

Question 2

What is a Robertsonian translocation?

Answer 2

• A rare form of chromosomal rearrangement, usually involving the acrocentric chromosomes.
• Chromosomes break at their centromeres and the long arms fuse together to form one long chromosome.

Question 3

What is a reciprocal translocation?

Answer 3

• Exchange of material between non-homologous chromosomes
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Question 4

Describe the different forms of mosaicism.

Answer 4

• Germline mosaicism
• Somatic mosaicism

Question 5

What is non-invasive prenatal testing (NIPT)?

Answer 5

• Release of foetal DNA into maternal plasma
• Extraction and analysis of foetal DNA
• Screening for genetic markers

Question 6

Describe the use of preimplantation genetic diagnosis.

Answer 6

• Essentially a type of IVF
• Embryo tested for genetic defects before implantation by taking a biopsy
• Only healthy embryos implanted