Chapter 3.3 Meiosis

Question 1

1 diploid nucleus divides by meiosis to produce what

Answer 1

4 haploid nuclei

Question 2

gametes

Answer 2

sperm and egg cells

Question 3

Crossing over

Answer 3

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.

Question 4

Metaphase I

Answer 4

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

Question 5

Prophase I

Answer 5

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

Question 6

Anaphase I

Answer 6

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

Question 7

Telophase I

Answer 7

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

Question 8

Prophase II

Answer 8

1- DNA condenses into visible chromosomes again

2- New meiotic spindle fibres are produced

Question 9

Metaphase II

Answer 9

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

Question 10

Anaphase II

Answer 10

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

Question 11

Telophase II

Answer 11

1- Chromosomes unwind their strands of DNA

2- Nuclear envelopes form around each of the four haploid cells, preparing them for cytokinesis

Question 12

Non-disjunction

Answer 12

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

Question 13

epidemiological studies

Answer 13

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

Question 14

amniocentesis

Answer 14

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

Question 15

Removing cells from the chorionic villus

Answer 15

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

Question 16

Two ways of extracting an unborn baby’s cells

Answer 16

amniocentesis and removing cells from the chorionic villus