Genetics basics

Question 1

incomplete dominance

Answer 1

when a dominant allele does not completely mask the effects of a recessive allele and the resulting physical appearance shows a blending of both alleles

(ie. white and red flowers producing pink flowers)

Question 2

codominance

Answer 2

both alleles are dominant and are expressed equally in the phenotype

(ie. AB blood type - A and B alleles are codominant)

Question 3

autosome

Answer 3

any chromosome that is not a sex chromosome

Question 4

name for pair of human chromosomes (XX) or (XY)

Answer 4

allosomes

Question 5

epistasis

Answer 5

when one gene depends on another gene to be expressed

Question 6

locus

Answer 6

position on a chromosome where a particular allele is found

Question 7

monohybrid inheritance

Answer 7

inheritance of characteristics controlled by a single gene

normal GCSE punnett squares

Question 8

X-linked and Y-linked

Answer 8

genes on the X chromosome

genes on the Y chromosome

Question 9

sex-linked characteristic

Answer 9

when the allele that codes for the characteristic is on the X or Y chromosome

Question 10

gene pool

Answer 10

complete range of alleles present in a population

Question 11

genetic disorder

Answer 11

disorder caused by an abnormal gene or chromosome

Question 12

dihybrid inheritance

Answer 12

inheritance of two different characteristics simultaneously

4x4 punnett square

Question 13

autosomal linkage

Answer 13

genes located on the same chromosome (but cannot be sex chromosomes)

Question 14

Hardy-Weinberg equation

Answer 14

mathematical model which can be used to predict the allele frequencies within a population.

Question 15

Fault to Hardy-Weinberg equation

Answer 15

It assumes that there will be no change in the allele frequency between generations within a population (e.g. no deaths, births or migration), so it is not perfectly accurate.

Question 16

aneuploidy

Answer 16

abnormal number of chromosomes present in the cell (for example a human having 47 rather than 46)

Question 17

cause of Down’s syndrome

Answer 17

inherited 3 copies of chromosome 21 rather than 2

Question 18

in punnett squares what goes along the top and what goes along the side?

Answer 18

XX along top (then below the alleles)

XY along side (then to right the alleles

THEN do the matching up or whatever

Question 19

What are telomeres ?

Answer 19

A form of junk DNA

Repeats of the same six base pairs, TTAGGG that stretch for around 10 000 base pairs on the end of each of our chromosomes

Question 20

How do telomeres allow the chromosome to be replicated properly during cell division?

Answer 20

Every time a cell carries out DNA replication the chromosomes are shortened by about 25-200 bases.

However because the ends are protected by telomeres the only part of the chromosome that is lost is the telomeres so the actual DNA is left u damaged.

Without telomeres important DNA would be lost every time a cell divides and so eventually the whole genome would be lost.

Question 21

As we age, telomeres shorten. What factors can be attributed to this?

Answer 21

1) the end replication problem accounts for the loss of about 20 base pairs during cell division
2) oxidative stress accounts for the loss of 50-100 base pairs per cell division (amount of oxidative stress thought to be affected by lifestyle eg. Smoking)

Question 22

What is the end replication hypothesis?

X

Answer 22

The ends of linear DNA cannot be replicated completely during lagging strand DNA synthesis.

Question 23

What happens when a telomere becomes too short?

Answer 23

It reaches a ‘critical length’ and can no longer be replicated. The critical length triggers cell apoptosis.

Question 24

How is telomere length maintained?

Answer 24

Telomerase is an enzyme that adds TTAGGG sequences to the end air the chromosome.

Telomerase is found in low concentrations in somatic cells. Because these cells don’t regularly use telomerase they age and this leads to a reduction in normal function.

Telomerase is found in high levels in egg and sperm cells and stem cells. In these cells telomere length is maintained after DNA replication so cells do not show signs of ageing.

Question 25

Evidence that telomeres could be related to ageing? (Mice)

Answer 25

Murine models lacking the enzyme telomerase were found to show signs of premature ageing

Question 26

Telomeres and ageing cause correlation

Answer 26

Not sure whether shortened telomeres CAUSE ageing

Or whether shortened telomeres is as a result of ageing

Question 27

What could telomeres be a good predictor of?

Also talk about babies

Answer 27

Newborn babies have telomeres ranging from 8k-13k base pairs. This declines by 20-40 base pairs per year.

Telomere length could be a good predictor of life span

Question 28

How could telomeres be used in medicine?

Mass produce

Answer 28

Human cells cultured in the lab have been observed to stop dividing when telomerase is inactivated because the length of the telomere isn’t maintained after each cell division. When telomerase is activated again, cells continue dividing.

If telomerase can be used to help cells live forever it may be possible to mass produce cells for transplantations

Question 29

What did the egg and sperm nice experiments tell us about gametes?

Answer 29

If an egg nucleus and a sperm nucleus are inserted into an empty egg which has lost its own nucleus, a life mouse is generated.

If two egg nuclei or two sperm nuclei are used the resulting embers failed to develop properly.

This demonstrates that gametes contribute other information in addition to the genetic code. - epigenetics

Question 30

What do the epigenetics modifications on gametes mean happens?

Answer 30

Certain regions of DNA carry epigenetic modifications that indicate if the gamete is from mother or father, this is known as the parent of origin affect.

The epigenetic modifications control the expression of specific genes So that in each matching pair one will be turned off and one will be turned on.

Imprinting - because genes have been imprinted with information about their origin