lecture 5- human genetic programme Flashcards
what is heterochromia
usually one blue and one brown eye
what kind of gene is responsible for causing heterochromia
dominant gene
what is coloboma or iris
abnormal development of iris
which disease is characterised by myopia and astigmatism?
coloboma of iris
what is cryptophthalmos and which gene is it caused by? state all symptoms/signs. Any treatments?
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.
what happens in:
G1- phase
S- phase
G2- phase
G1- cell growth
S- DNA synthesis
G2- growth phase before mitosis
Describe prophase
Threadlike chromosomes appear, each thread is doubled and called a chromatid.
Takes 3-4hrs
Describe metaphase
nuclear membrane disappears
chromatids located at centre of cell
chromatids become attached to spindle by centromeres
describe anaphase
centromere splits
sister chromatids separate , move along spindle fibres to opposite ends of cells
describe telophase
new nuclear membrane forms around chromatids
cell completes cell division
two cells produced with identical genetic constitution
what is linker DNA?
very long molecule of DNA has nucleosomes as “beads” on it
where can mitosis be seen?
in cells of the lens
where does cell division take place in the eye
at the equator of the lens
as mitosis takes place in the eye, what happens to the new cells that produce?
new cells elongate to form fibres
what can senile changes in lens nucleus cause in elderly?
senile cataract
where are old les fibres found in a lens of eye
centre of lens- form central nuclear core
why can we not see the chromosome during cell division?
the chromosome is contracted
what enables contraction of chromosomes to occur
histones
“beads on a string” means?
non dividing state of chromosome
nucleosomes are the beads
linker dna is the string
what can u see in a nucleosome?
histones in the centre and dna molecule is wrapped around it, the histone 1 is on the outside to give structure support
where can u find histone 1?
on the outside of the histones in a nucleosome
what happens to chromosomes as cells prepare for cell division?
chromosomes coil up prior to cell division
how does a chromosome achieve its characteristic banded appearance?
variation in density of coiling leads to light and dark areas
light areas are less coiled
the banding pattern is unique to each chromosome
what are the 4 types of gene sequences?
- 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
