L14- Mitosis and meiosis review

Question 1

missegregation in meiosis (non-disjunction)

Answer 1

• A third of all identified miscarriages • Infertility • Leading cause of learning disabilities

Question 2

in a metaphase spread

Answer 2

chromosomes are stained when they are actively dividing - can then be grouped according to size and shape (A-G)

Question 3

karyotyping

Answer 3

A way of organising/ numbering chromosomes in order of size and pattern

Question 4

• How are karyotypes described (separated by commas, no space)

Answer 4

o Chromosome number o Sex complement o Structural changes  E.g. 46,XY, Normal male karyotype

Question 5

describe a male with trisomy 21

Answer 5

47, XY, +21

Question 6

during proper disjunction of chromosomes

Answer 6

one chromatid goes to either pole

Question 7

mosaicism

Answer 7

Presence of two or more cell lines in an individual

Question 8

mosaicism can be

Answer 8

Throughout the body or tissue limited

Question 9

in non disjunction

Answer 9

both chromatids go to one pole-causes aneuploidy

Question 10

if mitotic nondisjunction occurs at the first post zygotic division

Answer 10

leads to non-mosaic karyotype - monosomy line usually lost unless involves X chromosome

Question 11

if mitotic nondisjunction occurs in later cell divisions

Answer 11

leads to mosaic karyotype

Question 12

degree of mosaicism

Answer 12

depends on when the nondisjunction occurs (i.e. during the first post-zygotic division or in later mitotic divisions)

Question 13

mitotic nondisjunction can occur in both

Answer 13

meiosis I and II

Question 14

the later the non-disjunction occurs in meiosis

Answer 14

the more likely you will have more normal cells

Question 15

nondisjunction in the sex chromosomes - X chromosomes

Answer 15

• Living with one X is still viable i.e. in women one X chromosome is always silenced through imprinting • Living with 3 X is viable (2 silenced)

Question 16

nondisjunction in the sex chromosomes- Y

Answer 16

XYY- though male may have more masculine traits e.g. over production of testosterone (criminal thing)

Question 17

what stage is G0

Answer 17

• Separate stage outside the cell cycle directly after M - Quiescent stage  Can be destination for the cell- e.g. nerve or cardiac cell which doesn’t need to divide anymore.  Could enter cell cycle (temporary rest) again if correct signal are there

Question 18

is random assortment or crossing over more important in eugenic variation

Answer 18

both equally important

Question 19

how many chromosomes does every human somatic cells contain in G2, just before mitosis

Answer 19

47 chromosomes (92 chromatics)

Question 20

during which phase of mitotic are the homologues chromosomes of each pair lined up

Answer 20

ever in mitosis- homologous pairs do not line up in mitosis (only in meiosis when maternal and paternal chromosomes line up)

Question 21

5. During mitosis the nucleolus disappears during prophase. - What is the nucleolus?

Answer 21

 Region of 5 diff chromosomes where ribosomal RNA genes are expressed  Heavily stained area in the nucleus

Question 22

Why is it that the nucleolus is present in the nucleus during interphase, but absent during most of mitosis?

Answer 22

 Nucleolus is absent during mitosis:  Chromosomes condense in prophase  Genes on chromosome will not be transcribed anymore  Join other chromosomes to be separated in mitosis

Question 23

How do the sex chromosomes ‘find each other’?

Answer 23

 X and X have very similar sequences  X and Y (different sequences) find each other due to having a small region of identical sequence

Question 24

7. Consider the consequences of a two crossing over events happening, one chiasma in PAR1 and one chiasma in AMELX/AMELY.

Answer 24

• Swap over between the 2 cross over events- any material between cross over will swap from non-sister chromatid to another

Question 25

describe anaphase lag

Answer 25

Anaphase lag- chromosome either stays behind or is too slow and will stay behind and become degraded- diff to nondisjunction- unequal distribution