WJEC A-Level Biology Unit 4 Variation, Inheritance and Applications overview quiz quiz

Follicle-stimulating hormone (FSH)

Progesterone

Luteinising hormone (LH)

Oestrogen

It triggers ovulation by surging sharply at the middle of the cycle

It stimulates the primary follicle to develop and mature in the ovary

It causes menstruation directly by stimulating the breakdown of the lining

It maintains the thickened uterus lining ready for implantation

3 to 1

1 to 1

9 to 3 to 3 to 1

1 to 2 to 1

Males have two X chromosomes, so they inherit two copies of the allele

Males have only one X chromosome, so a single recessive allele is expressed

The recessive allele somehow becomes fully dominant in males but not in females

Females are physically unable to carry the allele on either X chromosome

One allele completely masks the other in the heterozygote phenotype

The heterozygote shows an intermediate blend halfway between the two alleles

Both alleles are fully expressed in the heterozygote

Neither of the two alleles is expressed at all in the heterozygote

Organisms deliberately choose to mutate the useful alleles that they need to survive

All of the alleles in the population increase in frequency equally over the generations

The favourable alleles gradually disappear from the population while the harmful ones spread instead

A selection pressure favours individuals with advantageous alleles, increasing their frequency

So both have complementary sticky ends that can pair and be joined

To cut the plasmid into much smaller pieces so it fits inside the cell

To destroy the marker gene so transformed cells cannot be identified

To speed up transcription of the inserted gene once it is in the host

Restriction enzyme

DNA ligase

DNA helicase

DNA polymerase

To make proteins by translating the gene directly

To cut the DNA at specific recognition sequences

To amplify DNA, making many copies

To join separate genes into bacterial plasmids

They provide the chemical energy needed to drive the myosin power stroke

They break the cross-bridges directly so the myosin head detaches from actin

They lengthen the actin filaments so the sarcomere can shorten during a twitch

They bind troponin, moving tropomyosin to expose the binding sites on actin

It binds the myosin head to detach it and is hydrolysed to re-cock it for the next cycle

It binds directly to the actin filament in order to start off the contraction of the whole muscle

It exposes the myosin binding sites on actin by moving the tropomyosin aside

It lengthens the sarcomere by sliding the filaments apart from one another

To make the joint mechanically stronger and far more resistant to dislocation

Because muscles can only pull, so one moves the joint one way and its partner moves it back

Because one muscle of the pair actively pulls the joint while the other one actively pushes it back

To reduce the total amount of energy needed to move the joint in both directions