NCA Flashcards
What happens in G1?
→Cell makes a variety of proteins needed for DNA replication and grow
What happens in S-phase?
→chromosomes are replicated so that each chromosome now consists of two sister, identical chromatids
What happens in G2-phase?
→synthesis of proteins especially microtubules
→finish growing in size
What is metaphase?
→chromosomes condense
→become distinguishable
→they align in the centre of the dividing cell.
What type of chromosomes are used for karyotyping?
→Metaphase chromosomes
What are the two purposes of meiosis?
→produces (haploid) gametes with 23 chromosomes
→introduces variation in the resulting cells through independent assortment and recombination
What is the difference in cells produced from meiosis in males and females?
→In males= production of four haploid sperm cells.
→In females, only one of the four haploid cells produced forms the egg,
→the other three products of meiosis form the polar bodies
What is the synaptonemal complex?
→a lattice of proteins between the homologous chromosomes
→supports crossing ovver
Describe the formation of the synaptonemal complex
→first forms at specific locations →then spreads to cover the entire length of the chromosomes
What is synapsis?
→tight pairing of the homologous chromosomes
What happens in synapsis?
→the genes on the chromatids of the homologous chromosomes are aligned precisely with each other
What allows the X and Y chromosomes to pair up during prophase I even though they are not homologous?
→a small region of homology
→A partial synaptonemal complex
What is crossing over?
→reciprocal breaking and re-joining of the homologous chromosomes
What is the result of crossing over?
→exchange of chromosomal segments and new allele combinations
What happens in meiosis I?
→Align as 23 bivalents
→Allows for chiasma formation (i.e. recombination)
→Pulls apart homologues from one another
→Daughter cells have 23 chromosomes (each with 2 chromatids)
What happens in meiosis II?
→Align as independent chromosomes
→Sister chromatids pulled apart
→Daughter cells have 23 chromosomes (each of 1 chromatid)
What is the difference between the chromosomes in meiosis I and II?
→meiosis I has daughter cells have 23 chromosomes each with 2 chromatids
→meiosis II has daughter cells have 23 chromosomes (each of 1 chromatid)
What are metacentric chromosomes? Give examples
→p & q arms even length
→1-3, 16-18
What are submetacentric chromosomes? Give examples
→p arm shorter than q
→4-12, 19-20, X
What are the acrocentric chromosomes?
→Long q, small p
→p contains no unique DNA
→13-15, 21-22, Y
How are numerical chromosomal changes detected?
→karyotyping
→FISH
→QF-PCR
→NGS
How are structural chromosomal changes detected?
→karyotyping
→FISH
→array CGH
What is polyploid?
→multiple of the haploid number (e.g. 4n=92)
What is aneuploid?
→chromosome number which is not an exact multiple of haploid number - due to extra or missing chromosome(s)
What us non-disjunction?
→failure of chromosomes/chromatids to separate correctly at anaphase
→ can happen in meiosis I and II
What is the primary mechanism of aneuploidy?
→non-disjunction
Give examples of autosomal aneuploidies
→Trisomy 13 (Patau’s, 2 in 10,000 births)
→Trisomy 18 (Edward’s, 3 in 10,000)
→Trisomy 21 (Down’s, 15 in 10,000)
Give examples of sex chromosomes aneuploidies
→Turner’s (45,X) (1 in 5000 female births)
→Triple X syndrome (47,XXX) (1 in 1000 female births)
→Klinefelter’s (47,XXY) (1 in 1000 male births)
What can sex chromosome aneuploidies affect?
→fertility
What can happen as a result of mitotic non-disjunction?
→majority of cells 2n, some 2n+1 = mosaic
What happens if non-disjunction happens in gametes?
→all cells are affected
What happens to monosomic cells in mitosis?
→they die
What is mosaicism?
→presence of two or more genetically different cell lines derived from a single zygote
→thought to be less severe
What is trisomy rescue?
→cell recognises wrong number of cells and throws out a chromosome randomly
→may only end up with only maternal or paternal copies of the cells
What is partial trisomy and monosomy?
→microdeletion/duplication syndromes
→Lacking parts of a chromosome or acquired parts of chromosome
