4. genetics

what is an ecosystem?

community of living organisms in a particular area

what is species richness?

no. of different species in a community

what is a community?

a group of interacting populations of different species living in the same place at the same time

what is a population?

a group of individuals of the same species living and interbreeding in the same area

what is the index of diversity?

index giving the relationship between the no. of species in a community and the no. of individuals in each species

what is a species?

organisms that can breed to produce fertile offspring

what is a habitat?

the environment in which an organism/population of organisms usually live(s)

what is a gene pool?

all of the alleles of all of the genes in a population

what is genetic diversity?

when a population has a large difference in alleles in a gene pool

what is a niche?

the role a species plays w/in an ecosystem

what is biodiversity?

the variety of living organisms in an area

give 6 ways in which intensive farming causes a decrease in biodiversity:

• monocultures

• converting woodland and hedgerows into fields

• filling in ponds, draining marshes and overgrazing of land

• removing weeds w/ herbicides

• using pesticides to kill crop pests

• using inorganic fertilisers

how does the use of monocultures decrease biodiversity?

• deplete nutrients from soil

• decrease diversity of plants/species which. depend on a biodiverse ecosystem for food/habitat

how does converting woodland and hedgerows into fields decrease biodiversity?

• decreases no. of trees and other species

• destroys habitats relied on by many species

how does filling in ponds/draining marshes/over-grazing land decrease biodiversity?

directly destroys habitats and reduces species diversity

how does removing weeds w/ herbicides decrease biodiversity?

may harm other species or those that depend on target species

how does using pesticides to kill crop pests?

may harm other species or those that depend on target species

how does using inorganic fertilisers decrease biodiversity?

may run off into water courses, causing issues for aquatic species

how can we balance conservation and agriculture?

• maintaining hedgerows

• reducing pesticide/herbicide use

• using organic fertilisers

• using crop rotation

give 7 effects of climate change on biodiversity:

• hanges in temp/rainfall may negatively affect species adapted to specific climates

• changed conditions make certain areas more/less habitable

• suitable habitats for some species may expand/contract

• climate change may influence species distribution/migration

• warmer → tropical diseases more likely to spread

• rising sea levels → more flooding in low lying land

why are bumblebees disappearing and why is this significant? 🐝

• intensive farming and pesticide use are causing a bumblebee decline

• sig as bumblebees are vital pollinators of arable crops which allows price of fruit and crops to remain low

• bumblebees require a high diversity of plants so farmers must maintain this to maintain the bumblebee population

give an example of the balance between conservation and farming:

balancing pesticide use:

• pesticides decrease pollination by bees which will decrease crop yield/profit

• however using pesticides kills pest species which will increase crop yield/profit

what does an index of diversity describe? what is the formula?

describes relationship between no. of species in a community and the no. of individuals in each species

what is a nucleosome?

eukaryotic DNA wrapped around histone proteins

what is the function of the protruding tails of histone proteins?

determine how tightly DNA is packaged

what is a haploid cell?

cell w/ 1 set of chromosomes (23)

what is a diploid cell?

cell w/ 2 sets of chromosomes/chromosomes in pairs (46)

what is a chromosome?

linear DNA molecule tightly associated w/ and so wrapped around histone proteins

what is chromatin?

non linear DNA molecule loosely associated w/ histone proteins

what is a gene?

sequence of bases that codes for one polypeptide/functional RNA

what is an allele?

different variation of a gene

what makes chromosomes homologous?

same length and order

(can still be homologous even if alleles!)

why is DNA enclosed in the nucleolus (rather than just freely floating in the nucleus)?

• very big - needs to be more compact

• difficult to find genes to code/replicate DNA

• histones scaffold DNA into place

how many amino acids can make up the polypeptides in the human body?

20

how many bases code for 1 amino acid? what is this called?

3 bases code for 1 amino acid - codon

give 3 key features of the genetic code:

• degenerate

• universal

• non-overlapping

what does it mean for the genetic code to be degenerate?

some amino acids are coded for by multiple codons

what does it mean for the genetic code to be universal?

genetic code is the same for humans as in other organisms (all species use same 4 bases)

what does it mean for the genetic code to be non-overlapping?

bases are only read 1x

what is an intron?

a section of non-coding DNA/RNA

what is an exon?

a section of coding DNA/RNA

what is the genome?

compete set of genes in a cell

what is the proteome?

full range of proteins coded for by the cell’s DNA/genome

how did Watson, Crick and Franklin’s discovery of DNA’s molecular structure serve to explain how DNA replicates?

the complementary bases allow for DNA strands to be predicted as complementary pairs of bases are always the same

describe the process of semi conservative replication:

name the enzymes involved in semi conservative DNA replication:

• DNA helicase

• DNA polymerase

• DNA ligase

what is the function of DNA helicase?

• unzips DNA helix by breaking H bonds

• DNA unwinds and separates into 2 strands

what is the function of DNA polymerase?

• free nucleotides that have been activated are attracted to their complementary bases and joined together

• this forms a phosphodiester bond

why does DNA polymerase only work in the 5’ - 3’ direction?

• DNA strands antiparallel

• DNA polymerase active site is specific and only complementary to 5’ endshape of 5’ end different to shape of 3’ end

describe and explain an experiment that shows evidence for semi-conservative replication:

• grew bacteria on a medium containing ¹⁴N for multiple generations before transferring bacteria to a medium containing ¹⁵N for a single generation

• extracted and centrifuged DNA

• if conservative: original DNA would only contain ¹⁵N and settle at bottom of tube, new DNA would only contain ¹⁴N and settle at top of tube

• if semi-conservative: all DNA would contain both ¹⁵N and ¹⁴N and so all would settle in middle of tube

• one band formed in middle of tube → each DNA molecule contained a mixture of the heavier and lighter N isotopes

• (if left to continue, ratio of ¹⁵N:¹⁴N would go from 1:1 to 3:1 to 7:1 etc.)

what is the function of mRNA?

messenger RNA - transfers genetic info between nucleus and ribosomes

what is the function of rRNA?

ribosomal RNA - acts as a component of ribosomes

what is the function of tRNA?

transfer RNA - needed to bring amino acids to the ribosomes

what is pre-mRNA?

• long, single stranded molecule of RNA transcribed by a gene

• contains introns

what is splicing? why is it important?

• process of removing introns from pre-mRNA to form mRNA

• this means than the mRNA is shorter so it can leave the nucleus through the nuclear pores and reach the ribosomes

describe the process of transcription:

• RNA polymerase binds to and moves along DNA double helix, separating DNA strands by breaking H bonds between strands

• non-coding strand acts as template

• RNA nucleotides join to complementary bases by RNA polymerase

• RNA polymerase catalyses formation of phosphodiester bonds between adjacent RNA nucleotides

• ends when RNA polymerase reaches a stop codon, detaches from DNA and terminates transcription

• mRNA displaced by DNA molecules becoming rejoined

• mRNA is spliced and leaves through nuclear pore

what is tRNA?

single strand of RNA that carries a specific amino acid to the ribosome

describe the process of translation:

• mRNA strand leaves nucleus via nuclear pore and is w/in cytoplasm

• ribosome attaches to mRNA strand

• tRNA molecule attaches to mRNA strand at anticodon, which is complementary to the codon

• 2nd tRNA molecule binds

• anticodon complementary to codon

• 3rd tRNA molecule binds and peptide bond formed between 1st and 2nd amino acid, facilitated by ribosome

• 1st tRNA molecule moves away and ribosome moves along

• repeats until stop codon reached, causing translation to terminate → polypeptide chain

what is the anticodon?

the part of the tRNA complementary to the codon

what is the function of the sections of dsRNA in the tRNA molecule?

to form the shape of the tRNA molecule

what are the products of meiosis?

4 genetically different haploid cells

name the 2 ways genetically different daughter cells occur in meiosis:

• independent segregation

• crossing over

describe the process of meiosis i:

meiosis i:

• chromosomes replicate

• chromosomes condense and homologous pairs join together

• nuclear envelope breaks down and spindle fibres form

• chromosomes are attaches to spindle fibres at the centromere and line up in pairs randomly along the equator of the cell → independent segregation

• crossing over - homologous chromosomes exchange parts with each other

• homologous chromosomes pulled to opposite poles of cell by spindle fibres

• cytoplasm divides, forming 2 daughter cells

• chromosomes decondense

describe the process of meiosis ii:

• nuclear envelope reforms and chromosomes recondense

• in each cell, spindle fibres attach to centromere of chromosomes and pull sister chromatids apart to opposite poles of the cell

• chromosomes recondense

• cytoplasm /es and nuclear envelopes form around 4 genetically different haploid daughter cells

what is independent segregation?

random alignment of homologous pairs along the equator of the cell

what is crossing over?

non sister chromatids exchanging alleles by sections of chromatids being broken off, exchanged and rejoined

what is the formula used to calculate the number of different possible combinations of chromosomes following meiosis (w/o crossing over)?

2ⁿ

give and explain 4 processes which result in an increase in genetic diversity w/in a species:

• mutations

• independent segregation of homologous chromosomes

• crossing over between homologous chromosomes

• random fertilisation of gametes

  • all produce new allele combinations

describe the process of crossing over and explain how it increases genetic diversity:

• homologous pairs of chromosomes associate/form a bivalent

• chiasmata form

• = length of non sister chromatids/alleles are exchanged

• producing new allele combinations

describe and explain the appearance of cell X:

• chromosome formed of 2 chromatids

• DNA replication has occurred

• sister chromatids held together by the centromere

describe what has happened during division 1:

• chromosomes in homologous pair

• one of each/haploid number into daughter cells

give 5 processes which result in an increase in genetic variation w/in a species:

• mutations

• independent segregation of homologous chromosomes

• crossing over between homologous chromosomes

• random fertilisation of gametes

  • all produce new allele combinations

what is a gene mutation?

a change in the base sequence of chromosomes

why may not all base substitutions cause a change in the encoded sequence of amino acids?

the genetic code is degenerate - more than one codon may code for the same amino acid

what is a mutagenic agent?

• a factor that increases the rate of mutations

• e.g. UV light, ionising radiation

what is a frameshift mutation?

where an insertion/deletion mutation changes the triplets in a DNA sequence as the sequence shifts right/left (respectively) by one base

what is a point mutation?

a mutation where a single nucleotide is altered

how may gene mutations occur?

spontaneously, if DNA is misread during DNA replication

what are the 5 types of gene mutation?

• substitution

• deletion

• insertion

• duplication

• inversion

what effect may gene mutations have?

• change amino acid sequence coded for by gene

• → different polypeptide

• → potentially different tertiary structure

• → potentially changing organism’s phenotype

• (if enzyme, potentially different active site shape, preventing E-S complex forming)

what is a substitution gene mutation?

one or more nucleotides substituted for another in a DNA base sequence

what is a deletion gene mutation?

one or more nucleotides deleted from a DNA base sequence

what is an insertion gene mutation?

one or more nucleotides inserted into a DNA base sequence

what is a duplication gene mutation?

one or more nucleotides in a DNA base sequence are duplicated

what is an inversion gene mutation?

a group of nucleotides in a DNA base sequence separate and rettach in the same position but in the reverse order

what is a chromosomal mutation?

change in the structure/number of chromosomes in a cell

what causes chromosomal mutations?

errors in cell division

what are the 7 types of chromosomal mutation?

• deletion

• insertion

• duplication

• inversion

• translocation

• non disjunction

what is a translocation mutation?

a portion of one chromosome switches places w/ another non homologous chromosome

what is a non disjunction mutation?

• in meiosis, the chromosomes are not separated properly/all chromosomes stay in one cell

• chromatids go to different poles

what is polyploidy?

a cell having 3 or more sets of chromosome (e.g. triploid/tetraploid cells)

describe the process of natural selection:

• a population has a gene pool w/ a wide variety of alleles

• random mutation may introduce new alleles, increasing variation

• some alleles may make individuals better adapted to the environment (sometimes due to an environmental pressure)

• better adapted individuals are more likely to survive and reproduce (differential reproduction)

• individuals that reproduce pass on their advantageous alleles to the next generation (heredity)

• over many generations, advantageous alleles increase in frequency

what are the 4 main principles of natural selection?

• variation

• environmental pressure

• differential reproduction

• heredity

what does natural selection result in?

species being better adapted to their environment

what are the 3 types of adaptation?

• anatomical

• physiological

• behavioural

what are anatomical adaptations? provide an example:

• structural features of an organism’s body that increase its chance of survival

• e.g. whale blubber → keep warm

what are physiological adaptations? give an example:

• processes inside an organism’s body that increase its chance of survival

• e.g. brown bears hibernating over winter → conserves energy

what are behavioural adaptations? provide an example:

• ways in which an organism acts that increase its chance of survival and reproduction

• e.g. possums ‘playing dead’ → evades attack from predators

what is a genetic bottleneck?

• an event which causes a large reduction in population

• this reduces no. of different alleles in gene pool and so reduces genetic diversity

• survivors reproduce and a larger population is created from a few individuals

what is the founder effect?

• type of genetic bottleneck

• a few organisms from a pop start a new colony

• this means there are only a small no. of different alleles in the initial gene pool

• freq of allele in new colony may be different to original colony