L39 Chromosomes

Question 1

what are the stages of cell division and what happens in each stage?

Answer 1

G1 - celllular comtents excluding the chromosomes are duplicated

S - 46 chromosomes are duplicated

G2 - cell double checks the duplicated chromosomes for errors or repairs

Mitosis

Cytokinesis

Question 2

what are the stages of mitosis and what happens in each phase?

Answer 2

Interphase - G1, S and G2

Prophase - chomatin condenses into chromosomes

Metaphase - Nuclear envelope disappears, chromosomes align at the equatorial plate

Anaphase - sister chromatids separate, centromeres divide

Telophase - chromatin expants, cytoplasm divides

Question 3

how many chromosomes in a gamete and in a diploid cell?

Answer 3

gamete - 23

diploid - 46

Question 4

what is the function of meiosis?

Answer 4

used only for the production of sperm and eggs
reduction division to 23 chromosomes per gamete
ensures that every gamete is genetically unique

Question 5

how does meiosis ensure each gamete is genetically unique?

Answer 5

crossing-over and independent segregation of chromosomes

Question 6

what is the mechanism of meiosis?

Answer 6

each homologue (“chromosome”) replicates to give two sister chromatids

the maternal and paternal homologues pair together

exchange of material between non-sister chromatids by crossing-over (recombination)
chiasma (visible cytologically) are the physical manifestations of crossing-over

Question 7

what are the stages of meiosis?

Answer 7

MEIOSIS I
prophase 1
metaphase 1
anaphase 1

MEIOSIS II
prophase 2
metaphase 2
anaphase 2
telophase

Question 8

how many of the daughter cells develop into a mature oocyte in oogenesis?

Answer 8

one out of four. the others form polar bodies

Question 9

how does gene re-assortment by crossing over occur?

Answer 9

during meiosis I, a homologous pair of choromosomes (II) duplicate to produce two sister chromatids (II II)

crossing over of one sister chromatid with another sister chromatid (not from the same pair) is recombination

Question 10

what is the structure of chromosomes?

Answer 10

DNA double helix wrapped around histones makes chromatin. the chromatin is lade up of packed nucleosomes. it is condensed to make an entire metaphase chromosome

Question 11

what is bright field G-banding?

Answer 11

trypsin digestion of chromosomes followed by DNA staining with Giemsa

G bands stain darkly with Giemsa

Question 12

what is the anatomy of metaphase chromosomes?

Answer 12

has a long arm (q for queue) and a short arm (p for petit)

light bands:
replicate early in S phase
less condensed chromatin
transcriptionally active gene and GC-rich

Dark (G) bands:
replicate late
contain condensed chromatin
AT-rich

centromeres at the centre of the chromosomes, where both arms meet - joins sister chromatids, essential for chromosome segregation at cell division. some are chromosome specific

telomeres on either end of the chromosome - DNA and protein cap ensures replication of the tip tethers to nuclear membrane

Question 13

what else do chromosomes contain?

Answer 13

RNA, histone proteins, non-histone proteins as packaging

Question 14

when are chromosomes most condensed?

Answer 14

during metaphase they are condensed and visible

Question 15

how may chromosomal anomalies be classified?

Answer 15

numerica, usually due to de novo error in meiosis:

• aneuploidy (monosomy, trisomy)
• polyploidy (triploidy)

structureal usually by de novo error in meiosis but cannot be inherited

• translocations (reciprocal or robertsonian (centric fusion)
• deletions
• duplications
• inversions

different cell lines - occurs post-zygotically during mitosis)
- mosaicism

Question 16

how is the normal karyotype described?

Answer 16

46XX or 46XY

anything other than this describes as a chromosomal anomalie

Question 17

in early miscarriages, 60% had chromosomal abnormalities. which are most common?

Answer 17

trisomy (47 chr - one extra) = 30%

45, X (45 chr - one missing) = 10%

triploidy (69 chr - three sets) = 10%

tetraploidy (92 chr - four sets) = 5%

other chromosomal anomalies eg structural anomalies = 5%

Question 18

what are the most common autosomal numerical anomalies in liveborn?

Answer 18

down syndrome (trisomy 21:47,XX,+21)

edwards syndrome (trisomy 18:47,XX,+18)

patau syndrome (trisomy 13:47,XX,+13)

Question 19

whttps://www.brainscape.com/hat are the most common sex chromosome numerical abnormalities in liveborn?

Answer 19

turner syndrome 45,X

klinefelter syndrome 47,XXY

Question 20

what is the most common general chromosomal abnormality?

Answer 20

triploidy (69 chr)

Question 21

how many spermatozoa form from one spermatogonium and how long does the process take?

Answer 21

4 spermatozoa from one spermatogonium, every 16 days from puberty

Question 22

what are the cell divisions required to produce a human sperm?

Answer 22

SLIDE 29