Meiosis Flashcards
What happens in the process of Meiosis I?
Diploid cell become haploid (reductive division)
- Homologous chromosomes become separated
Name all cells involved in spermatogenesis?
- Spermatogonium
- Primary spermatocyte
- Secondary spermatocyte
- Spermatid
- Spermatozoa
What do spermatagonium undertake to become primary spermatocytes?
Mitosis
What do primary spermatocytes undergo to become secondary spermatocytes?
Meiosis I
What do secondary spermatocytes undergo to become spermatids?
Meiosis II
What so spermatids undergo to become spermatozoa?
Spermiogenesis
What stage of meiosis are primary oocytes arrested in until puberty?
Prophase of meiosis I
After puberty what stage of meiosis are oocytes arrested in until fertilisation?
Metaphase of meiosis II
What does the term aneuploidy mean?
An abnormal chromosome number (monosomy or trisomy)
What is disomy?
2 copies of a chromosome (normal)
What is monosomy?
1 copy of chromosome
What is trisomy?
3 copies of chromosome
What is meiotic nondisjunction?
Failure of chromosome pairs to separate
When can meiotic nondisjunction occur?
Either in meiosis I or II
If meiotic nondisjunction occurs in meiosis I how many chromosomes will the daughter cells have by Meiosis II?
There will be 2 diploid daughter cells (with mixture of maternal and paternal genes) and 2 cells w/o chromosomes
Give an example of a syndrome with monosomy?
Turner syndrome (45X)
What trisomys are compatible with life?
- Trisomy 21: Down syndrome
- Trisomy 18: Edward syndrome
- Trisomy 13: Patau syndrome
What percentage of Down Syndrome is due to meiotic nondisjunction?
95%
Why is it that it is most likely that it is through the mother that NDJ errors occur?
Because meiosis I is suspended for such a long time
- Also why advanced maternal age increases the chances of trisomy
How can you differentiate between trisomy caused by NDJ in Meisosis I vs Meiosis II?
Meiosis I NDJ chromosomes will all be different
- Meiosis II NDJ - 2 chromosomes will be identical
What is uniparental disomy?
When the child has 2 copies of 1 parent’s chromosomes
What is uniparental disomy?
Child has 2 copies of 1 parent’s chromosomes
- No copies of other parent’s chromosomes
What is isodisomy?
Uniparental disomy
- 2 copies of same chromosome (meiosis II error)
What is heterodisomy?
Uniparental disomy
- Meiosis I error, chromosomes are different
What is the phenotypical features of a child affected by uniparental disomy?
Usually has a normal phenotype
- Can lead to phenotype of recessive disease
How many chromosomes do children with uniparental disomy have?
Normal number of chromosomes
- Child is ‘euploid’
What kind of chromosomes have robertsonian translocations?
Acrocentric chromosomes
- Centromere near end (short short arm)
What is robertsonian translocation?
Fusion of long arms of 2 chromosomes
What chromosomes are acrocentric (centromere near end)?
13, 14, 21, 22
What is a less common cause of down syndrome?
Robertsonian translocation
What are the most common robertsonian translocations?
- 13-14
- 14-21
What are the clinical consequences of people with a carrier robertsonian translocation?
- Many monosomy and trisomy gametes
- Frequent spontaneous abortions
- Carrier may have child with Down Syndrome (trisomy 21)
Why are those with robertsonian translocations usually have a normal phenotype?
Only lose short arms
How many chromosomes do people with a carrier robertsonian translocation have?
45 (one translocated)
How can a robertsonian translocation be diagnosed?
Karyotyping
