CHROMOSOME ABNORMALITIES Flashcards
How do deletion and duplication abnormalities occur?
- Unequal crossing over
- misalignment between homologous chromosomes
How does trisomy 21 occur?
Nondisjunction - The chromosome doesn’t separate into two during meiosis II. One daughter cell has trisomy and the other has monosomy
Can survive this chromosome abnormality
What are the 3 non sex chromosome related survivable chromosome abnormalities?
- Down syndrome - trisomy 21
- Edward’s syndrome - Trisomy 18
- Patau syndrome - trisomy 13
What are the sex chromosome related abnormalities?
- Turners syndrome - 45, X
- Kleinfelter’s syndrome - 47, XXY
cause of aneuploidy?
Meiotic nondisjunction related to maternal age - eggs wear and tear as women get older
Translocation chromosome abnormality?
Fragments of one chromosome move to another chromosome. Not harmful if fragments move but aren’t lost. Harmful when the genetic material is lost or goes to another chromosome giving it extra info (monosomy and trisomy).
Robertsonian translocation?
Centromere is found at the top of chromosome and so either has no short arm or very small short arm. It fuses with another chromosome e.g 14 and 21. No genetic info is lost, just moved. Not harmful for individual but can be for child. Short arm is lost
Probability of recurrence of robertsonian translocation
- Theoretically there is a high probability that there will be offspring with Down syndrome
- In reality, less Down syndrome liveborns than expected
How to view chromosomes by producing a karyotype
- Karyotype - take a sample of someones blood with dividing cells. Stop the cell division and photograph the chromosomes and then view chromosomes under a microscope - this is the karyotype
What is Mosaicism?
When there are two populations of cells with different genetic constitutions usually as a result of an error in mitosis. The egg and sperm are normal
