W1 L1

Question 1

where is most of the DNA found in the cell ?

Answer 1

95% in the nucleus the rest is in the mitochondria (mitochopndirial dna from mother)

Question 2

How many hydrogen bond do each of the DNA complementary base pairs create ?

Answer 2

A=t. 2
G=-C. 3

Question 3

Describe the structure of dna unravelled to condemned

Answer 3

DNA - double helix
The double helix is wrapped around a group of histones= nucleosome
These nucleosomes coil again into a supercoil
Supercoil again into chromosomes

Question 4

How many chromosomes does the genome have ? Pairs ?

Answer 4

46 chromosomes
22 pairs

Question 5

Describe the structure of a chromosome

Answer 5

Kp- short arm (p= petite )
Kq- long arm
Centrosome connecting the two
End of chromosomes telomeres - shorten with age

Question 6

How can chromosomes been prepared for analysis ?

Answer 6

They can be stained

Giemsa: G banding, Quinacrine: Q banding)
G banding gives ~ 400-500 bands/haploid human chromosome set
Each band ~6-8 Mbp

Question 7

What are the phase stein the cell cycle ?

Answer 7

interphase
(G0
G1
S
G2)
Mitosis -
Prophase
Pro-metaphase
Metaphase
Anaphase
Telophase

Question 8

In s-phase of interphase what’s happens to the cell

Answer 8

DNA replication
Centrosome replication

Question 9

In prophase of mitosis what happens in the cell

Answer 9

Chromatin condensed into chromosomes

Centrosomes nucleate microtubles
+ move to opposite poles of the nucleus

Question 10

What are the steps of mitosis in prometaphase

Answer 10

Nuclear membrane breaks down
Microtubules invade nuclear space
Chromatids attach to microtubules

Question 11

What are the steps of mitosis - metaphase

Answer 11

Chromosomes line up along equatorial plane

Question 12

what are the steps of mitosis - anaphase

Answer 12

Sister chromatids separate…
…and are pushed to opposite poles of the cell

Question 13

what are the steps of mitosis - telophase

Answer 13

Nuclear membranes reform
Chromosomes unfold into chromatin
Cytokinesis begins

Question 14

what are the steps of mitosis - telophase

Answer 14

Nuclear membranes reform
Chromosomes unfold into chromatin
Cytokinesis begins

Question 15

which drug that interrupts mitosis causes a halo like ring of genetic information in a histological image ?

what phase does this interrupt ?

Answer 15

colchicine- like drugs

interrupts anaphase

Question 16

where does meiosis take place ?

Answer 16

Only in gametes

Question 17

how many cell divisions in mitosis / meiosis ?

Answer 17

mitosis- 1
meiosis -2

Question 18

describe how meiosis causes genetic variety

Answer 18

crossing over in prophase 1

Question 19

describe sperm production
-cell origin
-when it happens
-no. of divisions
-types of cells produces

Answer 19

Primordial germ cells → lots of mitoses →Spermatogonia
Meiotic divisions commence at puberty
The cytoplasm divides evenly
After meiosis II four equal gametes

Question 20

describe egg production
-origin
-time span
-types of cells produced
-stages of meiosis that it takes place at (under what conditions )

Answer 20

-Primordial germ cell → 30 mitoses → oogonia/ova
-1Oogonia/ova enter prophase of meiosis I by 8th month of intrauterine life
-2Process suspended
-3Cells enter ovulation 10-50 years later
-Cytoplasm divides unequally – 1 egg and 3 polar bodies (that apoptose)
-Meiosis I is completed at ovulation
-Meiosis II only completed if fertilisation occurs

Question 21

what is Non-disjunction

Answer 21

Failure of chromosome pairs to separate in Meiosis I or sister chromatids to separate properly in meiosis II

Question 22

what is Non-disjunction

Answer 22

Failure of chromosome pairs to separate in Meiosis I or sister chromatids to separate properly in meiosis II

Question 23

describe down syndrome + karyotype

Answer 23

Most cases result from regular trisomy 21
47,XX/XY,+21

Question 24

what is Gonadal mosaicism?

what factors increase the chance of this ?

how are the parents effected?

examples

what inheritance patters are common with this

Answer 24

when precursor germline cells are a mixture of two or more genetically different cell lines One cell line is normal, the other mutated

increases with age

parents are not effected but fetus may have genetic disease

conditions, including osteogenesis imperfecta and Duchenne muscular dystrophy

most commonly autosomal dominant and X-linked