exam Q's

Question 1

homeobox genes show astonishing similarity across widely different species of animals

explain why there has been very little change by mutation in these genes

Answer 1

-mutations like it would be lethal and so unlikely to survive and pass on
-mutations would make big effects/alter the body as they are very important

Question 2

what is meant by a homeobox gene

Answer 2

-regulatory gene
-activates transcription

Question 3

explain how lactase is produced in the cells of the small intestine in humans but not other body cells

Answer 3

transcription factor that is needed to switch on lactase gene is expressed in the small intestine cells

Question 4

the lactase persistence mutation leads to more transcription factors being attracted to the lactase gene during adulthood. Explain how this could lead to continued high levels of lactase production

Answer 4

-it could increase the rate at which the gene is transcribed
-this would mean more lactase mRNA gets produced so more lactase will be made compared to adults without lactase persistence mutation

Question 5

the lactase persistence mutation leads to more transcription factors being attracted to the lactase gene during adulthood. Explain how this could lead to continued high levels of lactase production

Answer 5

-it could increase the rate at which the gene is transcribed
-this would mean more lactase mRNA gets produced so more lactase will be made compared to adults without lactase persistence mutation

Question 6

suggest why the lactase persistence mutation is a beneficial mutation

Answer 6

allows adults to consume/ derive nutrients from milk/ dairy products

Question 7

give two reasons why a substitution mutation that occurs in a gene may have a neutral effect on protein function

Answer 7

-may produce a base triplet that still codes for the same amino acid
-the mutation could produce a base triplet that codes for an amino acid that’s not involved with the proteins function and crucial folding

Question 8

suggest and explain why substitution mutation that occurs in a gene is more likely to have a neutral effect on protein function than insertion or deletion

Answer 8

-indel mutations change the number of bases present in the DNA sequence
-this changes the way the base sequence is read (frameshift) so multiple triplets will be affected
-this increases the likelihood that multiple/important amino acids will change which is likely to alter the protein’s function
-substitution mutations do not change the number of bases present so fewer base triplets (and so amino acids) are likely to be affected

Question 9

explain how hox genes affect the development of body plans

Answer 9

-homeobox sequence of on hox genes code for a particular region of a protein called homeodomain
-homeodomain binds to specific site near the start of its target developmental gene and acts as a transcription factor
-it activates or represses the transcription of developmental gene and so alters production of a protein involved in the development of the body plan

Question 10

suggest and explain how the webbing between digits is removed in the developing embryo

Answer 10

-internal/ external stimulus triggers apoptosis in the cells that make up the webbing
-this causes enzymes inside the cells to break down the cell components
-causing the cell to break up into fragments which are engulfed and digested by phagocytosis

Question 11

with reference to the proteins coded for by the seed colour gene, explain why the y allele is recessive

Answer 11

protein will still be synthesised even if you only have one Y allele, wouldn’t happen if only one y allele was present

Question 12

explain how the structure of galactose allows it to be used as a respiratory substrate

Answer 12

-bonds can be broken down for respiration which have energy
- OH/H groups can H bond with water = soluble= can move within cells

Question 13

Some regions of DNA are non-coding.

Explain why.

Answer 13

introns are non-coding regions of DNA that are removed (when primary mRNA is edited)
regions are not present in mature mRNA
some regions are not translated

Question 14

Describe the difference between structural and regulatory genes

Answer 14

structural genes code for proteins that have functions within cells

regulatory genes code for proteins that help to control the expression of other genes

Question 15

explain the function of enzymes coded for by the lac operon

Answer 15

β-galactosidase digests/hydrolyses lactose to glucose and galactose

(lactose) permease increases uptake of lactose by cell