PAPER 2 combined

gamete

a sex cell that contains half the normal chromosome number

chromosome

a long dna molecule containing many genes

gene

a small section of dna on a chromosome that codes for a partiular sequence of amino acids to make a specific protein

allele

different versions of the same gene

dominant allele

this allele is always expressed even if only one copy is present. represented by a capital letter

recessive allele

an allele that is only expressed if two/both copies are present. represented by a lower case letter

homozygous

if two alleles present are the same, individuals are said to be homozygous for that trait

heterozygous

if two alleles present are different, individuals are said to be heterozygous for that trait

genotype

describes the alleles present or genetic makeup of an individual regarding a particular characteristic

phenotype

the physical appearance of an individual regarding a particular characteristic

how many parents in sexual reproduction

2, opposite sex

how many parents in asexual

1

sexual reproduction

• genetic information

• offspring

• genetic information is mixed

• variety in offspring as reproductive cells in meiosis

asexual reproduction

• genetic information

• offspring

• no mixing of genetic information

• genetically identical offspring (clones)

• only mitosis involved

where do cells divide by meiosis

reproductive organs to produce gametes

3 stages of MEIOSIS

1. copies of genetic information are made

2. cell divides TWICE to form FOUR gametes with single set of chromosomes (haploid cells)

3. all gametes are genetically different from each other (creates variation)

what happens when gametes join

• ferilisation

• normal number chromosomes restored

• cells divide by mitosis

• cells differentiate in embryo

sexual reproduction speed and energy cost

MORE energy and time needed to reproduce (find mate+ spread gametes)

asexual reproduction speed and energy cost

LESS energy and time needed to reproduce (more efficient)

variation with sexual reproduction (why is this good)

• genetic variation in offspring

• if environment changes = survival advantage

• some will survive and reproduce

variation with asexual (pros and cons)

• no genetic variation

• many identical offspring can be produced if conditions are favourable

• vulnerable if conditions change

• if 1 individual can’t survive, none can

is artificial selection possible with sexual reproduction?

• yes

• speeds up natural selection

• used by humans in selective breeding

is artificial selection possible with asexual reproduction?

NO

organisms that reproduce w sexual + asexual

• fungi (asexual by spores, sexual for variation)

• malaria (asexual in human, sexual in mosquito)

• plants (asexual = runners, strawberry plants + daffodil bulbs. sexual = seeds)

dna is a ____ made up of _______

polymer

two strands forming a double helix

DNA monomers

• nucleotide

• phosphate group + sugar backbone

• base (at, cg)

genome

the entire genetic material of an organism

studying genome allows us to

• search for genes linked to different types of diseases

• understand and treat inherited disorders

• trace human migration patterns of the past

sequence of bases form a….

code

how many bases in a codon

3

what does a codon code for

• amino acid in a protein

• order of bases controls order of amino acid

• joined to make specific protein

what carries code for sequence of amino acid

template molecule

• coded for by genes in nucleus

• goes to ribosome

amino acids assembled by

carrier molecules (bring specific amino acids to protein chain)

what happens when chain is complete

protein folds into specific shape for job (enzyme, hormorne, structural components, antibodies)

mutation

change in the DNA base sequence

occur continuously, particularly when dna replicated

few mutations code for

altered protein with different shape, affects the shape + functionality of the protein

Non coding parts of dna…..

switch genes on and off, variations will impact whether protein is made

female chromosomes

XX

male chromosomes

XY

chance of male/female

50%

polydactyly- dominant or recessive?

dominant

what is polydactyly?

having extra fingers/toes

what genotype to not have polydacyly?

homozygous recessive

cystic fibrosis- dominant or recessive?

recessive

to have CF, what genotype?

homozygous recessive

to be carrier of CF, what genotype?

heterozygous

gene therapy

replacing faulty genes

positives of embryo screening

• reduces no. of people with disease (if aborted)

• reduces healthcare costs (if aborted)

• expensive to have babies with disease

• informed choice about abortion

• prepare financially + emotionally

negatives of embryo screening

• possible damage/risk to embryo

• possible harm/risk to mother

• screening expensive

• right to life

• ethical/moral/religious desicions about abortion

motor neurone

cns → effector

synapse

• physical gap between 2 neurones

• electronic impulse converted to chemical neurotransmitter

• diffuses across and binds to next neurone

  • slows down

stimulus

a change in environment

receptor

detects stimulus and converts info to impulse

effector

muscle/gland = contract/secrete hormone

response

response to stimulus

reflex arc

REACTION = AUTOMATIC/INVOLUNTARY

• protects person from damage

• doesn’t go to brain

• stimulus → receptor →sensory neurone → relay neurone → motor neurone → effector → response

order of nervous system

stimulus → receptor →sensory neurone → CNS→ motor neurone → effector → response

relay neurones in brain

neurone differentiation

fatty myelin sheath - insulation

long - dendrons/dendrites

cerebellum

muscle movement/coordination

cerebral cortex

consciousness, intelligence, memory and language

medulla

unconcious activity - breathing + heartbeat

hypothalmus

temperature regulation

location of cerebral cortex, medulla and cerebellum

3 ways to study brain

• mri scans (magnetic resonance imaging) - detailed picture

• electrically stimulating brain - sees what part of brain controls what

• studying patients with brain damage

why is studying brain risky

brain is complex and delicate

can lead to damage

eye in dim light

• pupil dilates

• circular muscles relax

• radial muscles contract

• more light enters eye

what is the eye

a sense organ containing receptors sensitive to light intensity + colour

what is accomodation

changing the shape of the lens to focus on near or distant objects

optic nerve

• sensory neurones that send impulses to brain

• transmits visual information from eye to brain as electrical impulses

retina

• contains light sensitive cells that send neural impulses to the brain when stimulated by light.

• thin layer of tissue that lines the back of the eye

focusing on distant objects

• ciliary muscles relax = larger diameter

• suspensory ligaments pulled tight

• lens pulled thinner = slightly refracts/less convergent

• Light focused on retina

focusing on near objects

• ciliary muscles contract = smaller diameter

• suspensory ligament loosen

• lens = thick, strongly refracts/more convergent

• light focused on retina

blind spot

• unaware of this - brain fills gap

  • point where the optic nerve leaves the eye - no retina

eye in bright light

• pupil constrics

• circular muscles contract

• radial muscles relax

• less light enters eye

pupil

• hole through which light enters the eye

• controls the amount of light that enters the eye

ciliary muscles

• controls the shape of the lens

• contract and relax to change the shape of the lens

• allows accomodation

sclera

• white outer layer

• tough + strong so the eyeball is not easily damaged

myopia

short sightedness

• close = clear

• distant = blurred

• light focused in front of retina = blurry

• concave lens

hyperopia

long sightedness

• distant = clear

• close = blurry

• light focused behind retina = blurry

• convex lens

cornea

• transparent part of sclera at from of eyeball

• lets into eye

• curved surface refracts light rays, focused on retina

iris

• circular + radial muscles that contract and relax to change the size of the pupil

• controls size of puil

• controls amount of light reaching retina

suspensory ligament

• holds lens in place

• attach the lens to ciliary muscles (helps accomodation)

corrective technology

• spectacles/contact lenses

• laser eye surgery (aters shape of cornea)

• replacement lens

lens

• clear disc held in place by suspensory ligament + ciliary muscles

• fine tunes the focusing of light rays, changing their direction to produce a clear image on retina

a - suspensory ligament

b - cornea

c - iris

d - pupil

e - sclera

f - lens

g - optic nerve

h - ciliary muscle

i - retina

3 reasons for differences

• genetics causes

• environmental causes

• combination of both causes

what is variation due to

mutation

how do mutations effect phenotype

• most have no effect

• some influence

• very few change

evolution is

• the change in inherited characteristics of a populaiton over time.

• this is through natural selection, which can eventually form new species

when did simpler life forms first develop

more than three billion years ago

a species is

a group of organisms with similar characteristics which can reproduce to produce fertile offspring

which 2 scientists proposed theory of evolution by natural selection

charles darwin, alfred russel wallace

charles darwin famous for work on

finches in galapogos islands

wallace famous for research on

warning colouration and speciation

4 steps of natural selection

1. genetic variation in a characteristic in a species due to a random mutation

2. those with characteristic best suited to the environment are more likely to survive and reproduce

3. pass on beneficial alleles for that characteristic to their offspring

4. the frequency of the beneficial allele increases in the population over time.

3 reasons why natural selection was not accepted initially

• strong religious beliefs

• insufficient evidence (no microscopes)

• mechanism of inheritence not known till 50 yrs later

lamarck’s theory

inheritance of acquired characteristics over a life time,

if an individual needs to adapt it will, and pass on to offspring

4 main steps for speciation

1. isolation

2. mutation

3. natural selection

4. speciation

isolation is…

geographical/physical barrier that seperated population