Genetics: Meiosis and Karyotypes Flashcards
Meiosis: Parent _______ cells divide into daughter ______ cells with _______ the number of chromosmes
Parent dipoid cells divide into daughter haploid cells with half the number of chromosomes
What happens before meiosis?
Interphase: DNA replication, chromosomes form two chromatids.
What happens in Prophase I?
Chromosomes condense.
Synapsis: Homologous pairs form. Then, chromatids of the homologous pairs cross over, exchanging DNA. The genetic info is now recombinant (genetic variation)
What happens in Metaphase I?
Spindle fibres direct the homologous chromosomes to line up along the centre of the cell. The are assorted randomly on either side of the equatorial plate (genetic variation)
What happens in Anaphase I?
Homologous chromosomes are moved to opposite ends of the cell (centromere doesn’t split)
What happens in Telophase I?
Nuclear membrane forms around the chromosomes at each end of the cell. Division occurs.
What happens between meiosis I and II? What DOESN’T happen?
Cytokinesis: cytoplasm divides.
DNA replication does not occur.
What happens in Prophase II?
Chromosomes condense.
Nuclear membrane dissolves.
Spindle fibres form.
What happens in Metaphase II?
Spindle fibres align chromosomes along centre of the cell.
What happens in Anaphase II?
Sister chromatids separate, moved to opposite poles. They become separate, single chromosomes.
What happens in Telophase II?
New nuclear membranes form.
Division occurs.
Chromosomes decondense.
What happens after meiosis II?
Cytokinesis (cytoplasm divides)
How many chromosomes do normal gametes contain?
23
How many chromosomes do normal human cells contain?
46
What disorder is trisomy 21?
Down
