Numerical chromosomal abnormalities Flashcards
What is the difference between mitosis and meiosis?
Mitosis = cell division where somatic cells are produced
Meiosis = cell division process where gametes are produced
What is non-disjunction?
failure of the sister chromatids/homologous chromosomes to segregate properly in meiosis/mitosis
What is a karyotype?
= humans have 23 pairs of chromosomes
- 22 pairs autosomes, 1 pair sex chromosomes XX or XY
- Can be
- Metacentric - p&q arms even length
- Submetacentric - p arm shorter than q
- Acrocentric - long q, small p
- P contains no unique DNA
What is haploid, diploid and polyploid?
Haploid = one set of chromosomes, n = 23 in a normal gamete
Diploid = cell contains 2 sets of chromosomes 2n = 46, normal in human
Polyploid = multiple of the haploid number, 4n=92
What is meiotic non-disjunction?
= when there’s been an error in segregation of chromosomes
- Error in meiosis 1 - 2 pair of chromatids goes into the one cell rather than 2
- Error in meiosis 2 - sister chromatids go into 3/4 gametes
What is recombination?
Happens in meiosis 1 where there is a physcial change of material between homologous material
- During metaphase (in meiosis 1) - homoeologous chromosomes align with each other and form a bivalent
- Stuck together by the synaptonemal complex
- Exchange genetic material (recombine)
What is crossing over?
= breaking and re-joining of the homologous chromosomes in meiosis
- Creates new recombination chromosomes with new allele combinations
What happens within meiosis 1?
- align as 23 bivalents
- allows for chiasma formation (recombination)
- pulls apart homologues from one another
- daughter cells have 23 chromosomes (each with 2 chromatids)
What happens within meiosis 2?
- align as independent chromosomes
- sister chromatids pulled apart
- daughter cells have 23 chromosomes (each of 1 chromatid)
- daughter cells are genetically unique
What are some examples of autosomal aneuplodidies and sex chromosome aneuploidies?
Autosomal aneuploidies
- Trisomy 13 - Patau’s
- Trisomy 18 - Edward’s
- Trisomy 21 - Down’s
Sex chromosome aneuploidies
- Turner’s - 45,X
- Triple X syndrome
- Klinefelter’s (47,XXY)
- 47, XYY
How does non-disjunction happen in meiosis 1?
How does non-disjunction happen in meiosis 2?
How does non-disjunction happen in mitosis?
What is mosacicism?
= presence of two or more genetically different cell lines derived from a single zygote
- a cell will have a missing chromosome
What is the relationship of being trisomic and becoming mosaic?
Cell recognise it has wrong number of chromosomes and will throw out a random chromosome to get to the correct number
