Errors in Meiosis & X Inactivation Flashcards
What is the scientific name for down syndrome and what is this an example of?
Trisomy 21. Aneuploidy.
What is aneuploidy?
Abnormal number of a particular chromosome.
What is nondisjunction?
Failure of chromosomes to separate properly during meiosis. Can happen during either Meiosis 1 or 2 and each of these have different effects.
What type of nondisjunction do 95% of Down syndrome babies have?
Two maternal chromosome 21, occurring in Meiosis 2.
What does nondisjunction look like in Meiosis 1 vs Meiosis 2?
Meiosis 1: Two cells with 2 chromosome 21’s and two cells with no chromosomes.
Meiosis 2: Two cells with 1 chromosome 21 (normal cells), one cell with no chromosomes and one cell with two maternal chromosomes.
What is Klinefelter syndrome?
Trisomy in the sex chromosomes resulting in XXY. The individual is assigned a male at birth but they have some female phenotypes.
What is Turner syndrome?
Aneuploidy with XO. The individual has only one sex chromosome, and it is an X chromosome. They are usually assigned female at birth.
- Where the X came from (maternal or paternal) has an effect on their mental impairment and social skills.
- Defining feature is a fold of skin near their neck.
What is polyploidy?
Possession of multiple sets of chromosomes. It is a result of meiotic error and self fertilisation.
Offspring with this karyotype may be viable and fertile because when this individual produces gametes, all of the chromosomes have something to line up with appropriately.
What did Kerpechenco do in 1928?
Created a polyploid 4n raddage.
This came from a raddish and a cabbage and resulted in two types of offspring:
- A sterile hybrid with 18 chromosomes
- A fertile allopolyploid with 36 chromosomes.
What is an allopolyploid?
An individual that is a hybrid of two different species and that possesses more than two sets of chromosomes.
Why are commercial bananas seedless?
We make them so they are sterile because we don’t want to eat the big seeds. They are triploid (three sets of 11 chromosomes).
Things with odd numbers are usually sterile because during meiosis they cannot arrange properly.
What are the four other types of chromosomal aberrations?
Deletion:
- The removal of a chromosomal segment
Inversion:
- An inversion reverses a segment within chromosome
Duplication:
- A duplication repeats a segment
Translocation:
- A translocation moves a segment from one chromosome to a non-homologous chromosome.
What is Lejeune syndrome?
Deletion of tip of short arm of chromosome 5.
Individuals with this have severe mental impairment and make distressed cat noises. They usually don’t live past childhood.
What is the result of meiosis in a human inversion heterozygote?
The individual will probably have reduced fertility because the homologs can’t line up properly and you end up with strange loops. When crossing over occurs you get big deletions and insertions so the recombinants have too many or too few genes.
What is Philadelphia Translocation?
Reciprocal translocation between chromosomes 9 and 22.
The overexpression of this gene results in chronic myeloid leukaemia in 95% of patients.
We can now treat this with Gleevec and it works in 90% of cases.
