lecture 5- human genetic programme

Question 1

what is heterochromia

Answer 1

usually one blue and one brown eye

Question 2

what kind of gene is responsible for causing heterochromia

Answer 2

dominant gene

Question 3

what is coloboma or iris

Answer 3

abnormal development of iris

Question 4

which disease is characterised by myopia and astigmatism?

Answer 4

coloboma of iris

Question 5

what is cryptophthalmos and which gene is it caused by? state all symptoms/signs. Any treatments?

Answer 5

developmental abnormality caused by a recessive gene

Looks like child lacking an eye but cornea and eyelid fail to develop properly. Skin of forehead is growing down to cover developing eye behind it. Surgery required to correct they defect.

Question 6

what happens in:
G1- phase
S- phase
G2- phase

Answer 6

G1- cell growth
S- DNA synthesis
G2- growth phase before mitosis

Question 7

Describe prophase

Answer 7

Threadlike chromosomes appear, each thread is doubled and called a chromatid.
Takes 3-4hrs

Question 8

Describe metaphase

Answer 8

nuclear membrane disappears

chromatids located at centre of cell

chromatids become attached to spindle by centromeres

Question 9

describe anaphase

Answer 9

centromere splits

sister chromatids separate , move along spindle fibres to opposite ends of cells

Question 10

describe telophase

Answer 10

new nuclear membrane forms around chromatids

cell completes cell division

two cells produced with identical genetic constitution

Question 11

what is linker DNA?

Answer 11

very long molecule of DNA has nucleosomes as “beads” on it

Question 12

where can mitosis be seen?

Answer 12

in cells of the lens

Question 13

where does cell division take place in the eye

Answer 13

at the equator of the lens

Question 14

as mitosis takes place in the eye, what happens to the new cells that produce?

Answer 14

new cells elongate to form fibres

Question 15

what can senile changes in lens nucleus cause in elderly?

Answer 15

senile cataract

Question 16

where are old les fibres found in a lens of eye

Answer 16

centre of lens- form central nuclear core

Question 17

why can we not see the chromosome during cell division?

Answer 17

the chromosome is contracted

Question 18

what enables contraction of chromosomes to occur

Answer 18

histones

Question 19

“beads on a string” means?

Answer 19

non dividing state of chromosome
nucleosomes are the beads
linker dna is the string

Question 20

what can u see in a nucleosome?

Answer 20

histones in the centre and dna molecule is wrapped around it, the histone 1 is on the outside to give structure support

Question 21

where can u find histone 1?

Answer 21

on the outside of the histones in a nucleosome

Question 22

what happens to chromosomes as cells prepare for cell division?

Answer 22

chromosomes coil up prior to cell division

Question 23

how does a chromosome achieve its characteristic banded appearance?

Answer 23

variation in density of coiling leads to light and dark areas

light areas are less coiled

the banding pattern is unique to each chromosome

Question 24

what are the 4 types of gene sequences?

Answer 24

• long, unique (70%) 5000-10000, 1 copy
• moderately repetitive (20%) 130-300, 1000 copies
• mobile elements (?) 10,000- unknown copies
• short, repetitive (6-10%) 7 -million copies