L15: Numerical Chromosomal Abnormalities 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)
