Chapter 3.3 Meiosis Flashcards Preview

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Flashcards in Chapter 3.3 Meiosis Deck (16):

1 diploid nucleus divides by meiosis to produce what

4 haploid nuclei



sperm and egg cells


Crossing over

exchange of genetic material between non-sister chromatids in a process called crossing over. This happens when sections of two homologous chromatids break at the same point, twist around each other and then each connects to the other's initial position.


Metaphase I

1- homologous pairs of chromosomes line up along the center of the cell by random orientation
2- the nuclear membrane disintegrates


Prophase I

1- chromosomes become visible as the DNA becomes more compact
2- homologous chromosomes are attracted to each other and pair up: one from father, one from mother
3- crossing over occurs
4- spindle fibres made from microtubules form


Anaphase I

1- Spindle fibres from the poles attach to chromosomes and pull them to opposite poles of the cell


Telophase I

1- spindles and spindle fibres disintegrate
2- usually the chromosomes uncoil and new nuclear membranes form
3- many plants do not have a telophase I stage


Prophase II

1- DNA condenses into visible chromosomes again
2- New meiotic spindle fibres are produced


Metaphase II

1- Nuclear membranes disintegrate
2- the individual chromosomes line up along the equator of each cell in no special order, called random orientation
3- Spindle fibres from opposite poles attach to each of the sister chromatids at the centromeres


Anaphase II

1- centromeres of each chromosome split, releasing each sister chromatid as an individual chromosome
2- the spindle fibres pull individual chromatids to opposite ends of the cell
3- Because of random orientation, the chromatids could be pulled towards either of the newly forming daughter cells
4- in animal cells, cell membranes pinch off in the middle, whereas in plant cells new cell plates form to demarcate the 4 cells


Telophase II

1- Chromosomes unwind their strands of DNA
2- Nuclear envelopes form around each of the four haploid cells, preparing them for cytokinesis



21st pair of homologous chromosomes fails to separate during anaphase I.


epidemiological studies

look at trends in populations, often examining thousands of cases. study for down syndrome



involves using a hypodermic needle to extract some of the amniotic fluid around the developing baby in order to extract an unborn baby's cells


Removing cells from the chorionic villus

Cells are obtained by chorionic villus sampling, which involves obtaining a tissue sample from the placenta's finger-like projections into the uterus wall


Two ways of extracting an unborn baby's cells

amniocentesis and removing cells from the chorionic villus