inheritance, variation and evolution (T6) Flashcards
what is sexual reproduction
- involves two parents, male gamete joins w/ female gamete
- offspring show genetic variation
- use meiosis to form gametes
- occurs in most plants and animals
what is asexual reproduction
- involves one parent
- offspring are clones (genetically identical)
- cells divide by mitosis
- occurs in bacteria, fungi + some plants and animals
what are the gametes in humans
female = egg male = sperm
what are gametes
reproductive cell of an animal or plant
what are the gametes in plants
female = egg/ova male = pollen
what are the diff. types of asexual reproduction
- fission
- budding
- fragmentation
- spores
- vegetative propagation
how does fission work + e.g.
- undergoing simple cell division into 2 or more identical cells
- bacteria
how does budding work + e.g.
- fission but uneven distribution of cytoplasm
- yeast/coral/hydra
how does fragmentation work + e.g.
- body of organism breaks into smaller fragments
- flatworms/starfish/sea urchins
how do spores work + e.g.
- released from parent and germinate into new plant
- fungi/mosses/bacteria
how does vegetative propagation work + e.g.
- grow from cutting or runner of parent plant
- strawberry/potatoes/daffodils
how do malarial parasites reproduce
asexually in human host but sexually in the mosquito
what are the advantages of sexual reproduction
- produces variation in offspring
- greater degree of flexibility + adaptation to changing environment = better survival
- natural selection can be sped up by humans in selective breeding to increase food production
what are the disadvantages of sexual reproduction
- more time needed
- more complicated
- involves suitable partner/genetic exchange
what are the advantages of asexual reproduction
- faster process
- only one parent needed so do not need to find mate - saves time
- many identical offspring can be produced when conditions are favourable - opt. pop. number reached quickly
what are the disadvantages of asexual reproduction
- lack of genetic diversity, share weaknesses and pass down mutations
- changes to habitat affect all individuals
how is mitosis diff. from meiosis
- forms 2 daughter cells
- daughter cells have same number of chromosomes as the parent cell (diploid)
- daughter cell are identical to parent cell and each other
- occurs in growth and repair and asexual reproduction
how is meiosis diff. from mitosis
- forms 4 daughter cells
- daughter cells have half the number of chromosomes as parent cell (haploid)
- daughter cells are genetically diff. from each other
- only occur in formation of gametes
describe the process of meiosis
- each chromosome makes a copy of itself. the original chromosome and the copy join up in an X shape
- chromosomes and their copies line up along the middle of the cell alongside the other chromosomes of the pair
- each chromosome of the pair move to opposite ends of the cell
- cell splits to form 2 daughter cells
- the chromosomes and its copy split apart and move to opposite ends of the new cells and the cells split
- 4 daughter cells w/ half the original chromosome number are produced
what is the genome of an organism
the entire genetic material of that organism (human genome contains over 21k genes)
what are genes
small sections of chromosomes that code for different proteins
what are chromosomes made up of
molecules of DNA
what is the shape of DNA
two long strands twisted together - double helix
what is DNA
deoxyribonucleic acid
- genetic material in nucleus of a cell is composed of a chemical/polymer
what monomer is DNA made up of
repeating units called nucleotides
why is it important to understand the human genome
great importance for medicine in future:
- search for genes linked to diff. types of diseases
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past
what is each nucleotide made up of
- common sugar
- phosphate group
- base
what are the 4 diff. types of bases
- adenine
- thymine
- guanine
- cytosine
which ways do the bases bond together
adenine <=> thymine
guanine <=> cytosine
what do the order of the bases along the DNA provide
the instructions to make the amino acids that make up the proteins
how does DNA code for proteins
instructions for making new proteins are contained in bases on DNA. the sequence of bases provides the code. a set of three bases codes for a specific amino acid. small sections are joined together to make a gene which holds info to make all the amino acids in one protein
where in the cell are proteins made
ribosome
where in the cell are the instructions to make the proteins held
nucleus
what is the problem with synthesising the protein straightaway
DNA is too big to get out of the nucleus
how do cells solve the problem of DNA being too big
makes a copy of the section of DNA needed onto a molecule called messenger RNA (mRNA)
how does protein synthesis work
- DNA does not leave nucleus so protein code is transferred to ribosomes by a molecule called mRA
- in nucleus DNA double helix unzips and one strand acts acts as a template for formation of protein
- mRNA leaves nucleus and becomes engulfed by a ribosome.
- another form of RNA called transfer RNA (tRNA) attaches itself to specific amino acids that are free in the cytoplasm
- tRNA carries amino acids onto the ribosome where they line up against the matching mRNA sequence
- amino acids are bonded together to from a protein which is then released from the ribosme
- tRNA molecules detach themselves ready to pick up more amino acids
how do proteins fold up
in a specific shape which enables them to act as enzymes, hormones or forming structures in the body such as collagen
what are mutations
changes in DNA which can result in changes to genes, when a single codon/section of chromosome/whole chromosome are altered.
what are the diff. types of mutation
- substitution > when one base is swapped, changes one amino acid at most
- addition + deletion > when a base is added or removed, affects all the following amnio acid codes
what effect do mutations have on protiens
- most do not alter the protein, or only alter it slightly so that its appearance or function is not changed
- a few mutations code for an altered protein with a different shape. a substrate may no longer bind to the enzyme’s acrive site or a structural protein may lose its strength.
what happens when a base is changed
different amino acid will be coded for so a diff. protein will be synthesised
what effects do mutations have
- some have no noticeable effect
- some have devastating effects such as genetic disorders
- some may have beneficial effects
when can mutations be particularly devastating
when they occur in the formation of gametes b/c mutation will be passed on to every cell of the offspring
what do mutagens do
exposure to mutagens can increase chance of mutations. mutagens include x-rays, ionising radiation and certain chemicals
when do mutations occur
can occur at anytime but most common when DNA is copied when a cell divides
what is the inheritance of one characteristic
monohybrid inheritance
what are characteristics controlled by
genes
what is an allele
diff. form of the same gene
what is a dominant allele
stronger gene - only one copy needed
what is a recessive allele
weaker gene - two copies needed
what is a genotype
genetic makeup of an individual regarding a particular characteristic
what is a phenotype
physical appearance of an individual regarding a particular characteristic
what is homozygous
individual w/ two identical alleles for a characteristic
what is heterozygous
individual w/ two different alleles for a characteristic
who came up with the genetic ratios
george mendel
what were mendel’s observations
- when he bred red-flowered plants w/ white - flowered plants all of the offspring produced red flowers
- inheritance of each characteristic is determined by ‘units’ passed on to descendants unchanged
why was mendel’s work so impressive
expanded knowledge of genetic inheritance before DNA had been discovered
why was mendel’s work not accepted
- did not communicate his findings well to other scientists
- published it in a not well-known scientific journal
what discovery and observations let to theory that mendel’s ‘units’ were genes
- late 19th - better microscopes and staining techniques allowed visualisation of behaviour of chromosomes
- early 20th - observed that ‘units’ behaved similarly to chromosomes
- mid 20th - structure of DNA discovered
what genetic ratios did mendel come up with
- if you cross two heterozygous individuals (Bb) the offspring will always show a 3:1 ratio
- if you cross a heterozygous individual (Bb) with a homozygous recessive (bb) the offspring will show a 1:1 ratio.
how does inheriting gender work
- controlled by the 23rd pair of chromosomes
- females have two X chromosomes in the pair whereas males have one X and one Y.
- sperm and egg have half the number of chromosomes of a normal cell
- this means the sperm can either have an X or Y
- the egg will always have an X
- this means there is a 50% chance that the baby will be a boy or a girl.
name two inherited diseases
- cystic fibrosis
- polydactyly
is cystic fibrosis caused by a dominant or recessive allele
recessive
is cystic fibrosis passed on by one or both parents
both
what are the symptoms of cystic fibrosis
- produce too much mucus - breathing problems, digestion problems, stunted growth, lung infections
is polydactyly caused by a dominant or recessive allele
dominant
is polydactyly passed on by one or both parents
one
what are the symptoms of polydactyly
extra fingers or toes - can be removed but ppl live happily w/ them
what are the options for a couple who carry a genetic disorder who want to have a child
- screening the fetus
- IVF
what advantages of embryo screening
- gives you info to help you make an educated decision on whether you want to keep the child
- allows you to plan accordingly if you keep the child
what are the disadvantages of embryonic screening
- increases the risk of miscarriage
- increases chance of termination which may be considered unethical
what is a family tree diagram
includes all members of family and indicates their sex and whether or not they have the disease
what is variation
differences in the characteristics of individuals in a population
what is nature and an example
features inherited through genes e.g. eye colour/hair colour
what is nurture and an example
differences caused by environment e.g. scars/tattoos
what features can be caused by a combination of nature (genes) and nurture (environment)
- height, flower colour, skin colour, intelligence, freckles, leaf size, weight
why is it easier to study causes of variation in plants than animals (part. humans)
easy to produce genetically identical plants and then put in diff. situations to see how env. affects appearances
who can be used to investigate variation in humans
only genetically identical humans are twins - also unethical to force humans into diff. env. and conditions
what is the main idea behind natural selection
- the better adapted an organism is to its environment or ecosystem, the more likely it is to survive
describe the process of natural selection
- variation - all living things in a species are not the same (show a wide range of phenotypes
- competition - there is not enough food or space for all of them
- survival - some individuals have features which help them to survive
- reproduction - more likely to have offspring so more of next gen. will have the feature (useful allele is passed on)
when was penicillin discovered
1928
explain how antibiotic resistance works
- has arisen and increased because of antibiotic resistance
- within a pop. there are a small number of bacteria that are resistant to antibiotics because they have undergone a mutation
- when antibiotics are taken most of the ordinary bacteria are killed but the drug resistant ones survive and divide.
- with the continued overuse of antibiotics the ordinary bacteria are knocked out wile the drug resistant ones continue to multiply. eventually the antibiotic resistant bacteria become dominant
what contributes to the increase of antibiotic resistance
- overuse of antibiotics
- people not completing the full course of antibiotics
- use of antibiotics in food chain
- use of broad spectrum antibiotics
- lack of hygiene in hospitals and care homes
what is selective breeding
humans select and breed plants and animals for desired characteristics
what features can selective breeding be used to increase
- disease resistance in food crops
- animals that produce more meat + milk
- domestic dogs + farm animals w/ a gentle nature
- large brightly coloured flowers
what are the limitations of selective breeding
- reduces number of alleles in a pop. bc only individuals w/ chosen alleles allowed to breed => due to lack of variation, if conditions change none of organisms can cope so pop. dies out
- can lead to inbreeding, reduces variation in a pop., animals more prone to certain diseases and inherited defects.
what is inbreeding
breeding animals/plants together w/ too close a genetic makeup - too closely related
describe the process of selective breeding
- living things in a species are not all the same
- some individuals have features that are more desirable to humans
- humans choose the individuals w/ the features they want
- these are the plants and animals that are allowed to breed
- they pass their genes onto their offspring
- more of the next generation have the chosen feature
- if people keep choosing the same feature then even more of the next gen. will have it
how can you clone plants artificially
- cuttings
- tissue culture
what is cutting
older but simple method use by gardeners to produce many identical new plants from a parent plant
what is a tissue culture
taking a small tissue sample from a plant then using hormones and nutrients to form a big mass pf identical plant cells, which can each be stimulated to grow into a new plant.
what are the pros and cons of tissue cultures
pros:
- allows you to produce 1000s of plants from one tiny piece of tissue
cons:
- more expensive
- more complex than cuttings
what’s the advantages of cloning
quicker and cheaper than growing them from seeds and we can be sure the good characteristics will be passed on
what are embryo transplants
splitting apart cells from a developing animal embryo before they become specialised then transplanting the identical embryos into host mothers
what are the advantages of embryo transplants
valuable cows w/ good characteristics can have many offspring within a short amount of time
explain the process of adult cell cloning
- The nucleus is removed from an unfertilised egg cell.
- The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell.
- An electric shock stimulates the egg cell to divide to form an embryo.
- These embryo cells contain the same genetic information as the adult skin cell.
- When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.
what is genetic engineering
using special enzymes from bacteria to cut out specific genes from DNA of one organism. these genes can then be inserted into the DNA of a diff. organism using a vector such as bacteria or virus.
what can genetic engineering be used to produce
human insulin
how is genetic engineering used to make insulin
gene for insulin production is cut out of the DNA of a human cell and inserted into a bacteria. bacteria multiply and produce human insulin which can be used to treat diabetes
what’s the advantage of using genetic engineering instead of pig insulin to treat diabetes
- scientists can quickly and easily make enough insulin to treat all the people with diabetes
- insulin is suitable for vegetarians
- no risk of transmitting diseases
explain the process of using genetic engineering to produce insulin
- gene cut out of of human insulin gene w/ restriction enzyme
- plasmid cut open w/ restriction enzyme
- ligase enzyme sticks insulin gene into plasmid
- plasmid put into bacterium
- bacteria with insulin gene grown in fermenter
- insulin is separated off and purified,
why is resistance to weedkillers useful + example
- weeds can be sprayed w/o killing the plant - more quicker/cheaper/less brainpower
> soya beans
why is resistance to pests useful + example
- pests do not kill the plants so there is a bigger yield
- fewer chemicals are needed so reduces risk of killing useful insects or chemicals entering food chain
> corn, cotton, tomatoes
why is slower ripening useful + example
- delays ripening so longer shelf-life
- fruits can be ripened on the plants before being picked which enables them to have more flavour
> tomatoes, melon
why is adding vitamins useful + example
- contains vitamins and oils that have positive effects
> vitamin A needed for growth and protection against infections - fish oils help human brain development
> provides enough vitamin to children in developing countries
e.g. golden rice, corn
what are the advantages in medicine of genetic technologies
- allow us to make human proteins needed to treat disease e.g. insulin produced in large quantities
- using GM mice in developing cures to human diseases
what are the advantages in agriculture of genetic technologies
- improved growth rates in plants and animals
- crops can be designed to grow well in poor conditions or be resistant to diseases
- crop plants can include essential nutrients needed in the human diet
what are the concerns regarding genetic technologies
- we are not completely sure what the long-term effects could be
- some people are worried about the effect of eating GM food on health
- genes from GM organisms might spread into the wider environment
- fears that it would lead to human engineering
what is the theory of evolution
gradual change of an organism over time. idea suggests that one type of organism, called the ancestor, might change over many generations into one or more diff. species
what did Charles Darwin come up
the idea of evolution being caused by natural selection
why did many people not believe in darwin’s ideas
- disagreed w/ religious idea of creation
- little evidence at the time that species evolve from each other
- scientists had not yet discovered genes so could not explain how features were passed on
how did Darwin develop his ideas of evolution
by studying diff. species of finch he found on the Galapagos islands
how did Darwin use his findings to explain his idea of evolution
each finch species had a diff. beak shape, drain said that all of the species had evolved from one ancestral finch species and changed as they became adapted to diff. food sources
where did Darwin publish his findings
in his book ‘on the origin of species” in 1859
who was jean-baptiste lamarck
created the idea that the ways organisms live affected the features of their body
who was Alfred Wallace
came up w/ similar ideas to Darwin but did not have as much research to back them up. his essay on evolution in 1858 prompted Darwin to write his book the following year
what did Wallace’s findings help find
his ideas on geographic isolation acted as the starting point of speciation
what is a species
group of organisms that can interbreed and produce fertile offspring
what is speciation
the formation of a new species
describe the process of speciation
- isolation - pop. becomes separated or isolated by some kind of barrier so they can no longer interbreed
- genetic variation. in each pop. there will be variation between individuals and diff. mutations will occur in the separated pop.
- natural selection - the conditions will be slightly diff. on each side of the barrier so each separated group will evolve differently
- speciation - the two sub-pop. have changed so much that they can longer interbreed and produce fertile offspring sp have formed two separate species
where does the evidence for evolution come from
- fossils
- DNA
what are fossils
remains of organisms from millions of years ago preserved in rocks
what are the diff. ways fossils can be formed
- hard parts of organisms which are replaced by minerals as they decay
- when organisms do not decay b/c one or more of the conditions needed for decay are absent (warmth, moisture or oxygen)
- when traces of organisms (footprints etc.) are preserved
how are fossils formed in rocks from the hard parts of organisms
- animals die
- soft parts may get eaten or decay
- the hard parts get buried by layers of mud and sand and are replaced by minerals
- mud and sand then turns into rocks and parts that have not decayed are preserved as fossils
why is there not a complete fossil record
- many of the earliest life forms were soft-bodied so they left little fossil trace
- most organisms that died did not become fossilised - conditions needed were rare
- many fossils have not been found yet
- early fossils may have been destroyed by geological activity
what can we learn from fossils
how much or little diff. organisms have changed as life developed on earth
what is extinction
permanent loss of all members of a species
what are the causes of extinction
- new disease
- climate change
- catastrophic events
- loss of habitat
- introduction of a new predator
- competition between species
what killed the dinosaurs
most accepted theory: asteroid collision
- impact would have caused dust in the atmosphere that made it almost dark everywhere, plants struggled to survive and temp. dropped
what are the 2 diff. types of classification
- grouping by characteristics and features - not commonly used
- Linnaean - grouping based on evolutionary relationships, shared features inherited from their ancestors, arranged into a hierarchy - commonly used
what is the order of the classification hierarchy
- kingdom
- phylum
- class
- order
- family
- genus
- species
what is the binomial name made up
genus and species/ last two boxes
why is the binomial name in latin
universal - scientists around the world can use it
who developed the three domain system
carl woese
what are the three domains
archaea, bacteria, eukaryotes
what are archea
primitive forms of bacteria including extremophiles
what are bacteria
true bacteria and cynobacteria
what are eukaryotes
cells that contain a nucleus
what is the phylum usually broken up into
vertebrates and invertebrates
