Reproduction - meiosis I and II etc Flashcards
How many chromasomes/chromatids does a cell have?
Normally - one chromatid per chromasome
During replication - two chromatids per chromosome, joined by a centromere
What does poildy mean?
The number of pairs of chromosomes in a set
What is haploid?
the normal number of chromasomes/chromatids in a set - one
What is diploid?
Two sets of chromosomes, seen in division §
Where does meiosis occur?
Only in germ cells, leads to the production of gametes (egg/sperm)
How does meiosis occur?
In two stages: Meiosis I and II
What happens in meiosis I?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase and cytokinesis
Exchange of genetic material can occur here
What happens in prophase I?
Replication to form sister chromatids
Nuclear envelop disintegrates
Chromosomes condense
Spindle fibres appear
Chiasmata occurs
What is chiasmata/crossing over?
A homologous cross over, DNA exchanging . Mediated by synaponemal complexes
What happens in prometaphase I?
Spindle fibres attach to centromeres
What happens in metaphase I?
maternal and paternal chromosmes align and assorted
What happens in anaphase I?
Homologous chromosomes are pulled as spindles retract, dividing the DNA
What happens in telophase and cytokineses?
The nuclear envelop reforms
Spindles disappear
Cell divides
What happens in prophase and prometaphase II?
Same as in the first step
What happens in metaphase II?
Chromosomes line up in single file along the equator
What happens in anaphase Ii?
Sister chromatids are pulled to opposite ends
What happens in telophase and ctyokinesis II?
similar to first but 2 non-identical haploid cells are formed rather than diploid.
What is non-disjunction/aneuploidy?
Failure to separate during meiosis
What is the result of non-disjunction/aneuploidy?
Production of zygotes with abnormal chromosome numbers
Either whole (meiosis I)
or chromatids (meiosis II)
What happens when theres abnormalities due to translocation?
Where the chomosomes break arms - reciprocal translocation
or even whole chromosomes join end to end - robertsonian translocation
