Meiosis and Chromosome Abnormalities Flashcards
What is the process of Meiosis? (PMAT-PMAT)
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
- Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2
Description of the first PMAT
- Almost same as mitosis
- Non-sister chromatids touch at points called chiasmata
- Crossing over and recombination occurs
- This results in variation
Description of second PMAT
- Similar to first but DNA is not copied or crossed over
- Results in 4 haploid cells
How many sperm cells are formed per meiotic cycle?
4
How long does the meiotic cycle to produce the 4 sperm cells take?
60 days
Why do more mutations occur in spermatogenesis than oogenesis?
Sperm undergo far more divisions that ova so there is a greater mutation chance
What does each meiotic division of an ova produce?
- 1 ovum
- 3 polar bodies
What do these polar bodies become later in life?
Ova
When does spermatogenesis begin?
Puberty
When does oogenesis begin?
Early embryonic life
What does non disjunction mean?
- Sister chromatids don’t split during meiosis
- Results in both of them being present in one gamete
What is caused by trisomy 21?
Down’s Syndrome
What are some common characteristics of down syndrome?
- Facial characteristic
- IQ less than 50
What % of down syndrome, Patau syndrome and Edward’s syndrome is caused by non disjunction
90%
What is caused by trisomy 13?
Patau Syndrome
Common features of Patau syndrome?
- Dysmorphic features
- Death in first year of life
What is caused by trisomy 18?
Edward’s Syndrome
What usually happens to people with Edward’s syndrome
Death within the first month of life
What condition is characterised by a single X chromosome (monosomy X)?
Turner syndrome
What are common characteristics of turner syndrome?
- Short stature
- Infertile
- Neck webbing
- Widely spaced nipples
- Normal intelligence and lifespan
What percentage of zygotes normally terminate at conception when monosomy X is present?
97%
What condition is caused by trisomy XXY?
Klinefelter Syndrome
What are common characteristics of Klinefelter syndrome?
- Tall stature
- Infertile
- Small testes
- 50% develop breasts
- Mild learning difficulties
What is the development of breasts called?
Gynaecomastia
