Inheritance, Variation & Evolution Flashcards
how many parents are involved in asexual reproduction?
1
how many gametes are involved in asexual reproduction?
none
what type of cell division is involved in asexual reproduction?
mitosis
what type of offspring does asexual reproduction produce?
genetically identical (clones)
what are some disadvantages of asexual reproduction?
- all offspring have the same weakness/disease due to no variation
- no adaptation or evolution
what are some advantages of asexual reproduction?
- guaranteed to reproduce
- large numbers of offspring
- no mutations
how many parents are involved in sexual reproduction?
2
how many gametes are involved in sexual reproduction?
2 - egg and sperm or ovum and pollen
what type of offspring does sexual reproduction produce?
genetically different but similar
what type of cell division is involved in sexual reproduction?
mitosis and meiosis
what are some advantages of sexual reproduction?
- can choose mates (survival of the fittest)
- variation and adaptation
- multiple offspring (some survive)
what are some disadvantages of sexual reproduction?
- mates may be scarce
- longer process
- negative mutations or diseases
describe the process of mitosis
- cell grows larger
- DNA and organelles (eg ribosomes and mitochondria) are replicated
- one set of chromosomes is pulled to each end of the cell
- nucleus divides
- cytoplasm and cell membrane split in half
- 2 new genetically identical cells formed
why do cells divide?
- growth of new tissue
- repair of damaged tissue
- asexual reproduction
describe the process of meiosis
- cell grows larger
- DNA and organelles (eg ribosomes and mitochondria) are replicated to form chromosomes that have double DNA
- (meiosis 1) 1 set of chromosomes are pulled to each end of the cell and pairs of homologous chromosomes separate leading to variation (any one of the pair can go to either side)
- nucleus divides
- (meiosis 2) chromosomes split in half, half going to each new cell
- cytoplasm and cell membrane divide to form 4 daughter cells from the original 1 cell
- all cells are different from each other
how many divisions are in mitosis?
1
how many divisions are in meiosis?
2
how many cells are produced in mitosis?
2
how many cells are produced in meiosis?
4
how many chromosomes are in the daughter cells after mitosis?
diploid - full
how many chromosomes are in the daughter cells after meiosis?
haploid - half
what is meiosis used for?
sexual reproduction - production of gametes
where does mitosis take place?
any cell
where does meiosis take place?
sex organs
what parts of a daffodil are involved in sexual reproduction?
flowers to attract pollinators (if it is warm enough)
what parts of a daffodil are involved in asexual reproduction?
produce clones of bulbs under the soil if there are no pollinators
why is it an advantage for daffodils to use both sexual and asexual reproduction?
- flowers are favoured because it introduces variation which is good for the species
- asexual reproduction gives a guarantee of reproduction in the absence of pollinators
what parts of a strawberry plant are involved in sexual reproduction?
flowers to attract pollinators (if it is warm enough)
what parts of a strawberry plant are involved in asexual reproduction?
runners producing clones (plantlets) of original parent plant
how can a strawberry producer take advantage of asexual reproduction in strawberry plants?
grow strawberries inside polytunnels to stop sexual reproduction so its faster (dont have to wait for pollinators) and no animals to eat the strawberries
describe the reproductive system of fungi
- the network of hyphae is haploid.
- 2 hyphae grow together and fuse
- from this, a spore-producing fruiting body develops.
- cells in the fruiting body undergo fertilisation and then meiosis to produce haploid spores
what are the parts of a nucleotide?
- phosphate group (circle)
- pentose (sugar - deoxyribose - pentagon)
- nitrogen-containing base (rectangle)
what type of molecule is DNA?
A polymer, made from 4 different nucleotides
what is the function of DNA?
to store coded information which can be used to make proteins
what is a gene?
a small section of DNA on a chromosome; it codes for a particular sequence of amino acids to make a particular protein
what are the complementary base pairing rules?
A + T, C + G
what do the full lines in a diagram of DNA represent?
covalent bonds
what do the dotted lines in a diagram of DNA represent?
hydrogen bonds
describe the strength of hydrogen bonds
very weak individually (which they must be to be able to separate strands of DNA) but together they are quite strong
how many sugar phosphate backbones are in a double helix?
2
why are 3 different DNA bases needed (triplet codes)?
to make enough combinations to code for 20 different amino acids
how many base combinations are there in triplet codes?
64
what does it mean when the protein a triplet code produces is ‘stop’?
the gene is finished and protein is completed, so stops production of protein
what are some functions of protein in living things?
- collagen
- antibodies
- receptor proteins
- haemoglobin
- actin and myosin (muscle proteins)
- enzymes
describe the process of protein synthesis
- DNA strands separate as hydrogen bonds are broken, so one strand can form a template
- the DNA code of a gene is copied to form a mRNA molecule (but not exactly - there are different bases for mRNA [no T] so cells can tell DNA and mRNA apart)
- mRNA molecule leaves the nucleus through a nuclear pore and attaches to a ribosome
- ribosome moves along mRNA strand, reading bases, and tRNA (carrier molecules) bring the correct amino acids to the ribosome
- amino acids join together to form a polypeptide
- polypeptide detaches and folds into a uniquely shaped protein
what is a polypeptide?
a long chain of amino acids
what is a mutation?
a change in the sequence of bases in DNA / a gene
how are base sequences altered in mutations?
substitution, insertion, deletion, inversion
describe the effect of a change in a base sequence of DNA
- change in amino acid sequence
- change in protein structure/shape
- change in protein function
why do most mutations not alter the amino acid sequence?
- there are multiple codons for the same amino acid, so it doesn’t matter if it mutates, as we still get the right amino acid.
- not all DNA codes for proteins; some in non-coding, so if it mutates it won’t make a difference or affect proteins
how could a mutation affect the function of an enzyme?
if amino acids change in the active site, the shape will change and substrates won’t fit, so the enzyme won’t work
how does a change to gene coding cause sickle cell disease?
- change to the gene coding for haemoglobin
- haemoglobin is the wrong shape (clumped [fibrous] rather than normal [globular]) so doesn’t fit in RBC properly
- this means the RBC are stretched out of shape
- so they get can’t fit through capillaries and get stuck, lowering O2 levels
how can mutations in part of non-coding DNA cause cancer tumours?
- division of cells is usually controlled by genes
- cells grow and reproduce uncontrollably therefore are not the right shape and function and are cancerous
what is meant by n + n ⇒ 2n?
gamete + gamete ⇒ fertilised egg
what is meant by 2n ⇒ n + n?
Diploid cell undergoing meiosis to produce haploid cells.
what is meant by 2n ⇒ 2n or n ⇒ n?
2n represents diploid cells undergoing mitosis, while n represents haploid cells undergoing mitosis.
what does haploid mean?
Having a single set of unpaired chromosomes - cell’s with one copy of each chromosome - 23 chromosomes
what does diploid mean?
Having two sets of chromosomes - 46 chromosomes
what is DNA?
a polymer made of 2 strands forming a double helix; contained in structures called chromosomes
what is a chromosome?
larger structure of DNA, found in the nucleus of a eukaryotic cell
what is a human genome?
- Complete set of DNA in an organism
- complete set of genes in a cell
why is the understanding of the human genome useful?
- can recognise genetic disease early and make lifestyle changes accordingly
- can choose surgery to avoid cancers (eg breast cancers)
what are alleles?
Different forms of a gene - the 2 copies of a gene on a pair of chromosomes
what is a genotype?
Genetic makeup of an organism, representing the specific combination of alleles for a particular trait.
what is a phenotype?
Observable characteristics or features of an organism determined by its genetic makeup and environmental factors.
what is a gamete?
sex cell - 23 chromosomes
what is a recessive allele?
An allele that is only expressed in the phenotype if 2 copies of that allele are present and there is not the dominant allele of that gene
what is a dominant allele?
An allele that is always expressed in the phenotype when present in the genotype whether partnered by a recessive or another like itself
define homozygous
a genotype in which the 2 alleles for the characteristic are identical - AA or aa
define heterozygous
a genotype in which the 2 alleles for the characteristic are different - Aa
define monogenic
Trait controlled by a single gene.
define polygenic
Trait controlled by two or more genes - because multiple genes are involved, traits do not follow patterns of Mendelian inheritance
what are the female sex chromosomes?
XX
what is an inherited disease?
a disease which can be passed on from parent to child through chromosomes
what are the male sex chromosomes?
XY
how can people pass on a genetic disease without suffering from it?
By being carriers of the recessive allele for the genetic disease - recessive alleles require 2 copies to be expressed so can be carriers without suffering
what are some examples of characteristics caused by environmental factors?
- scars
- tattoos
what are some examples of characteristics caused by a mixture of genetic and environmental factors?
- height
- body mass
- skin colour
- personality
what are some examples of human mutations that cause new phenotypes?
- cystic fibrosis (thicker mucus)
- haemophilia (blood doesn’t clot)
- polydactyly (extra digits)
- diabetes (insulin doesn’t form)
- huntington’s (alters brain proteins)
- eye colour (anything not brown or blue)
- hair colour (anything not dark brown)
- freckles
- lactose tolerance
- ability to roll tongue
- dis/connected earlobes
describe the process of natural selection
- there is variation within a population due to mutations
- some individuals are better adapted to their environment than others as a result of their genetic makeup
- these individuals are more likely to survive the competition with other members of that species
- these individuals reproduce and pass on their advantageous alleles to the next generation
- over many generations, the advantageous alleles are more frequent in the gene pool than the non-advantageous alleles
what are the stages of natural selection + mnemonic?
“Very Many Elephants Can See Ravenous Antelopes”
- Variation
- Mutation
- Environment
- Competition
- Survive
- Reproduction
- Alleles
describe the stages in development of antibiotic resistance
- mutations occur naturally in original population, causing variation (some bacteria have high or low antibiotic resistance)
- an antibiotic is introduced so the environment changes
- different bacteria are better adapted to this change (have higher resistance) and survive the competition with other members of its species (survival of the fittest)
- the surviving bacteria with higher resistance reproduce and pass on their resistant alleles
- over generations, these resistant alleles become more frequent in the gene pool than the non-resistant alleles
why shouldn’t doctors prescribe antibiotics for viral infections?
Antibiotics are ineffective against viruses because they target bacterial infections but they do increase the resistance of bacteria
why should patients complete their courses of antibiotics, even if they feel better?
To prevent antibiotic resistance and ensure complete eradication of the infection.
why are antibiotics used in agriculture?
to prevent infections in livestock
why should agricultural use of antibiotics be restricted?
To prevent antibiotic resistance in bacteria.
what was Lamarck’s theory?
- a characteristic which is used more and more by an organism becomes bigger and stronger and one that is not used, eventually disappears
- any feature of an organism that is improved through use is passed to its offspring
what was wrong with Lamarck’s theory?
it can’t account for all observations in nature; the theory implies that all organisms would gradually become complex and simple organisms would disappear
what was darwin’s theory?
- individual organisms within a particular species show a wide range of variation for a characteristic
- individuals with characteristics most suited to the environment are more likely to survive and breed
- the characteristics that have enabled these individuals to survive are then passed on to the next generation
why was darwin’s theory only gradually accepted?
- it challenged creationism
- there was insufficient evidence when the theory was published to convince many scientists
- mechanism of inheritance and variation wasn’t known until 50 years after the theory was published
why is darwin’s theory now widely accepted?
- fits with recent research (ie watson’s and crick’s work on the structure of DNA)
- less religious devotion
- more evidence
how does natural selection lead to speciation?
- mutations occur in the population of the common ancestor, producing lots of variation
- at some point, one population was split in two, by a geographical barrier
- the two populations then lived in two different habitats, with different conditions
- within each environment, different adaptations caused by variation suit the new environment
- animals well-suited to the new environment survive the competition (survival of the fittest), reproduce and pass on their advantageous alleles
- over generations, these advantageous alleles become more frequent in the gene pool than the disadvantageous ones
- the populations will continue to evolve until the 2 populations are genetically different and can’t interbreed to produce fertile offspring and have become 2 different species
what is speciation?
The formation of new and distinct species in the course of evolution.
what are 3 ways fossils can be formed?
- no decay due to lack of one or more conditions necessary for decay (oxygen, water/moisture, warmth)
- when parts of the animal are replaced by minerals as they decay
- as preserved traces (footprints, faeces, burrows, rootlet traces)
why are there very few remains of soft-bodied early life forms?
they don’t fossilize properly due to their lack of hard parts/bones - if they don’t have bones then they can’t be replaced by mineral deposits
why are there gaps in the fossil record?
Due to the incomplete preservation of organisms (if conditions for decay occur, then the dead animal won’t fossilise) and the rarity of fossilization.
what is the fossil record?
A historical sequence of life indicated by fossils found in layers of the Earth’s crust.
how do fossils provide evidence for the theory of evolution?
By showing the gradual changes in organisms over time, indicating common ancestry and adaptation to different environments.
what is extinction?
The complete disappearance of a species from Earth - when there are no remaining individuals of a species still alive
what can extinction be caused by?
- Environmental changes (eg woolly mammoths)
- natural disasters
- human activities (eg hunting, habitat destruction)
- competition from other species
- a lack of mutation and variation causing an inability to adapt, reproduce and survive
what are the 3 domains of living animals?
- bacteria
- archaea
- eukaryota
who devised the 3-domain system?
Carl Woese
what is a species?
a group of organisms with similar characteristics that can interbreed to produce fertile offspring
Horses and donkeys are different species; explain why.
- horses and donkeys can interbreed as their chromosomes (64 and 62) are similar enough to produce offspring
- however that offspring is not fertile as its chromosomes (63) can’t be halved so can’t produce viable sperm and egg cells
the Linnaean classification system is hierarchical; what does this mean?
larger groups are split into smaller groups, each containing fewer numbers of organisms and no overlap between groups
what are the parts of the Linnaean classification system?
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
what evidence is used to determine evolutionary relationships?
- DNA and genes
- evidence of internal structures (seen using more advanced microscopes)
- understanding of biochemical processes
- fossil evidence
what is selective breeding?
the process whereby humans breed plants and animals for particular genetic characteristics and create varieties/breeds which have characteristics we value
what are some examples of characteristics selected for in selective breeding?
- animals for more milk/meat
- disease resistance
- large or unusual flowers
- domestic dogs with a gentle nature
what are the stages in selective breeding?
- decide what desirable characteristics are required in the organism
- choose parents with the required characteristics
- breed parents and let offspring mature
- select, from the offspring produced, those with the desirable characteristics
- breed selected offspring together
- repeat over many generations
what are some advantages of selective breeding?
- can produce an organism with qualities that are useful
- customers get the products they want
- farmers increase profits
what are some disadvantages of selective breeding?
- can take multiple generations
- desired characteristics aren’t guaranteed
- inbreeding can cause characteristics that cause mutations to be passed on
- can create a population with very few alleles: genes get lost, less variation - higher chance of extinction if environment changes
- may all be susceptible to disease - higher risk
summarise the process of tissue culture cloning
a few plant cells are put in growth medium with hormones and grow into new plants - clones of the parent
what are some advantages of tissue culture cloning?
- plants can be made very quickly
- can be done in very little space
- can be grown all year
- used to preserve rare plants and to produce lots of plants quickly by plant nurseries
what are some disadvantages of tissue culture cloning?
- need some specialist equipment
- has to be done in sterile environment
summarise the process of plant cutting cloning
take cuttings from good parent plants and put them in soil with auxins (to encourage root growth) to produce genetically identical copies of the parent plant
what are some advantages of plant cutting cloning?
- plants can be produced quickly
- plants can be produced cheaply
- simple
what is a disadvantage of plant cutting cloning?
small scale
describe the process of adult cell cloning
- remove nucleus from unfertilised egg cell
- remove nucleus from an adult body cell
- insert nucleus from adult body cell into empty unfertilised egg cell
- stimulate egg cell with an electric shock, to make it divide
- when the embryo is a ball of cells, implant into womb of an adult female
- it will grow into a clone of the original adult body cell
what is an advantage of adult cell cloning?
guaranteed characteristics
what is a disadvantage of adult cell cloning?
reduced lifespan of offspring
describe the process of embryo transplant cloning
- sperm cells taken from best male animal and egg cells from best female
- sperm is used to artificially fertilise an egg cell
- the embryo is split many times to form clones, before any cells become specialised
- cloned embryos can be implanted into lots of other cows and grow into baby calves which will wall be genetically identical to each other
what are some advantages of embryo transplant cloning?
- hundreds of ‘ideal’ offspring can be produced every year
- guaranteed characteristics
- produces true young animals
what is a disadvantage of embryo transplant cloning?
reduced variation leads to health problems
what are 3 main issues surrounding cloning?
- produces a reduced gene pool; if a population are all closely related and a new disease appears, they could all be wiped out, as there may be no allele in the population giving resistance to it
- cloned animals might not be as healthy as normal ones
- some people worry that humans might be cloned in the future - eugenics and failed attempts causing sever disabilities
what does a ‘reduced gene pool’ mean?
fewer different alleles in a population
what are the 2 main positives surrounding cloning?
- studying animal clones could lead to better understanding of the development of the embryo, ageing, and age-related disorders
- could help preserve endangered species
what are some characteristics that may be considered desirable in genetic engineering of crops?
drought-, disease-, and pest-resistant, fast-growing, high yield, strong stem, golden rice has added vitamin A
what are some characteristics that may be considered desirable in genetic engineering of bacterial cells?
bacterial cells used to produce insulin
what are some characteristics that may be considered desirable in genetic engineering of humans?
potential treatment for genetic disorders
what are the stages of genetic engineering?
- enzymes are used to isolate the required gene
- the same enzyme is used to cut open a plasmid or virus (the vector) and the gene is inserted into it
- the vector is used to insert the gene into the required cells
- genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with required characteristics
what are the stages of genetic engineering to make bacteria produce insulin?
- plasmid from bacterium is cut by an enzyme
- the human gene for insulin production is isolated by the same enzyme
- insulin production gene inserted into plasmid
- the engineered plasmid is inserted into a new bacterium
- the bacterium undergoes binary fission, divides, and begins producing insulin
why is the same enzyme used to isolate the gene and cut the plasmid in genetic engineering?
it creates complimentary shapes in them both so they can bind using complimentary base pairing
what are the advantages of using GM crops?
- higher yields increases food value which could help an expanding population
- animals and plants grow faster
- crops can grow in dry, hot, cold, or flooded areas which could help manage the effects of global warming on agriculture
- crops can produce their own pesticide, be resistant to herbicide or contain specific nutrients
what are the disadvantages of using GM crops?
- people aren’t sure of the long-term effects of eating GM food on human health
- pesticide-producing crops may result in insects developing resistance to pesticides
- genes from GM crops or animals could spread to species in the wild
what are the advantages of using GM to overcome inherited disorders in humans?
can mass produce human proteins like insulin
what are the disadvantages of using GM to overcome inherited disorders in humans?
people worry this may lead to the manipulation of human genes to make ‘designer children’
