INHERITANCE< VARIATION< EVOLUTION Flashcards
what is dna
the chemical that genetic material in a cell is made from
what does dna contain
coded information
what 2 things does dna determine
-what inherited charecteristics you have
-what protiens a cell produces
where is dna found
in chromosomes (in the nucleus)
describe briefly structure of dna
a polymer made of two strands forming a double helix
what are chromosomes
really long strands of dna
what is a gene
a small section of dna on a chromosome
what does each gene ( small section of dna on a chromosome) do
-codes for (tells the cell to make) a particular sequence of amino acids to make a specific protien
(+tells the cells what order to put the amino acids together)
how many amino acids are used
20 amino acids used ( they make up thousands of different protiens)
dna determines what protiens a cell produces. this then determines what….
what type of cell it is
what is genome
the entire set of genetic material of that organism
scientists have worked out the complete human genome- why is understanding the human genome important in medicine and in general x3
-scientists can search for genes in the genome that link to different types of disease
-knowing which genes are linked to inherited diseases help us understand them better and help develop effective treatments
-to trace human migration patterns from the past track ancestry)
Scientists investigate genomes to track human migration patterns from the past.how x3
-humans descend from a common ancestor
-they developed tiny differences in their genome
-investigating the differences help us work out when new populations split from others and the direction they took
dna strands are….
polymers made up of lots of repeating units called nuleotides
a nucleotide consists of..
a common sugar and phosphate group with 1 of 4 different bases attached to the sugar
what do the sugar and phosphate groups in the nucleotide form
a backbone to the dna strand
what is complementary base pairing
A pairs with T
C pairs with G
what does the order of bases in a gene control
the order in which amino acids are assembled to produce a particular protien
(the order of amino acids in a protien)
a sequence of three bases in a gene codes for ……
a particular amino acid
how are protiens formed
what doesthe type of protien fromed depend on
the amino acids join together
the order of the genes bases
long strands of dna consist of ….
alternating sugar and phosphate sections, 1 of 4 bases attached to each sugar
what do the non coding parts of dna (parts that don’t code for protiens) do
switch genes on and off- control if a gene is expressed (used to make a protien)
where are protiens syntheised
protiens are synthesised according to….
(in cytoplasm), on ribosomes, according to a template
what do ribosomes use to make proteins, what is an issue with this
-ribosomes use the code in the dna
-dna cant move out the very large nucleus
-cell needs to get code from dna to ribosomes
what is used to get the code from dna to the ribosome?
how is this made
mRNA molecule
made by copying the code from dna
what does mRNA do
carries the a copy of code from DNA to the ribosome- acts as a messenger
what do carrier molecules do
bring specific amino acids to ribosomes in the correct order
what happens when a protien chain (chain of amino acids) is complete
it folds into a unique shape enables/allows the protien to do its job
three examples of protiens and what they do
enzymes- act as biological catalysts to speed up chemical reactions
hormones-carry messages around body
structural protiens- physically strong
what is a mutation of a gene
a random change in an organisms dna
how often does mutation occur
mutation occurs continuously
can sometimes occur spontaneously
the chance of a mutation is increased by…..
exposure to certain substances/types of radiation
what do mutations do
what is formed
mutations change the sequence of DNA bases in a gene
a genetic variant is formed (a different form of the gene)
what do the sequence of DNA bases code for
the sequence of amino acids that make up the protien
describe the effect of most mutations on a protien
no effect on the protien
or
alter protien slightly so appearance and function stay the same
a few mutations code for …..
an altered protien with a different shape - this would affect the protiens ability to function
give an 2 examples of when a mutation has altered the protien
an enzyme may not fit the substrate binding site because the shape of active site is changed
structural protiens lose their strength- useless at providing structure and support
what happens if there is a mutation in a non coding part of dna
the way genes are expressed are altered- cell may produce a protien its not meant to have at that time
3 ways mutations can change the dna base sequence
insertions
substitutions
deletions
what happens in insertion
new base inserted into dna base sequence where it shouldnt be
what do insertions do
have a knock on effect.
change the way the groups of three bases are read, changing the amino acids they code for
what happens in deletions
random base deleted from dna base sequence
what happens in substitutions
random base changed to different base
describe what mutations do and the effect they have
change the sequence of bases in DNA
this affects the amino acid sequence
and therefore the protien coded for
why might the function of a protien be affected by gene mutation
4 points
-mutations change the dna base sequence
-this can change the amino acids that the bases code for
-this can change the shape of the protien the amino acids make up
-this can affect its function
describe the process of mRNA carrying code to the ribosomes
7 points
protiens are made on ribosomes
ribosomes use the code in the dna to make protiens
dna cant move out of the big nucleus
mRNA is made by copying the code from DNA
it carries the code from dna to ribosomes
the correct amino acids are brought to the ribosomes in correct order by carrier molecules
what is sexual reproduction
genetic info from 2 organisms is combined
produce offspring that are genetically different
4 examples of gametes
sperm and egg
pollen and egg cells in flowering plants
what process are gemetes made from
meiosis
how many chromosomes do human gametes have
23
(instead of having 2 of each chromosome, they have 1)
sexual reproduction involves-
the fusion of male and female gametes
why is there variation in offspring with sexual reproduction
because there is a mixing of genetic info
(offspring recieves mixture of chromosomes from mom and dad)
asexual reproduction involves-
one parent and no fusion of gametes, no mixing of genetic info
in asexual reproduction, there is only one parent, this means that offspring are….
genetically identical to parent, clones
what process is involved in asexual reproduction
mitosis
in a sexual reproduction, the new cell is a clone because
the new cell has exactly the same genetic information (genes) as parent cell
eg 3 organisms that reproduce asexually
bacteria,
some plants
some animals
once the two gametes fuse during fertilisation to form a new cell, what does this cell do x3
divides by mitosis to make a copy of itself,
mitosis repeats many times to produce new cells in an embryo
embryo develops and cells differentiates into specialised cells
why do cells divide by mitosis
to make gametes with 1/2 the original no. of chromosomes so that when gametes fuse, the offspring gets the right amount of chromosomes
how many cell divisions happen in meiosis
2
where does meiosis happen in humans
only in reproductive organs
3 steps of cell division to form gametes
- copies of the genetic information are made
- the cell divides twice to form four gametes, each with a single set of
chromosomes - all gametes are genetically different from each other
process of meiosis-
spec says knowledge is not required
6 pints
genetic info doubled, chromsomes arrange into pairs.
first division- chromosomes line up in centre of cell
pairs pulled apart, each cell has one copy of each chromosome
second division- chromosomes line up in centre of cell
arms of chromosomes pulled apart - 4 gametes formed
advantage of sexual reproduction
-how can natural selection be sped up
produces variation in offspring
if environment changes, variation gives a survival advantage by natural selection
natural selection can be sped up by humans in selective breeding to increase food production
why is variation in offspring from sexual reproduction an advantage
explain 3 points
variation increases the chance of a species surviving a change in environment.
change in environment could kill some individuals
due to variation, some offspring will be able to survive
what does variation give some individuals in a species
survival advantage
describe how variation gives a species survival advantage by natural selection
individuals with a survival advantage are more likely to successfully breed
they pass on genes for the characteristic.
this is known as natural selection
how can natural selection be sped up by selective breeding to increase food production
individuals with desired characterisitcs are bred so offspring have these aswell. we can increase food production by breeding animals that produce alot of meat.
advantages of asexual reproduction
x4
- only one parent needed
- more time and energy efficient as do not need to find a mate
- faster than sexual reproduction
- many identical offspring can be produced when conditions are favourable
three organisms that reproduce asexually and sexually.
describe this for each
malarial parasite-
asexually in human host
sexually when in mosquito
fungi- release spores- become new fungi when they land
spores can be produced asexually/ sexually
asexually produced spores are identical to parent
sexually produced spores introduce variation-
a response to unfavourable change in environment, increase chance that population will survive
plants-
produce seeds sexually
asexually by runners eg strawberry plants/ bulb division eg daffodils.
Runners in strawberry plants- stems grow on soil surface, away from plant. At points, identical strawberry plant form
Bulbs- new bulbs form from main one and divide off. new bulb grow into identical plant
Ordinary human body cells contain 23 pairs of chromosomes.
22 pairs control characteristics only, the 23rd pair…..
contains the genes that determine sex
23rd pair labelled XX or XY
how is it determined if your male/ female
what are the chances of being male/ female
male have x chromosome and y chromsome
female have x chromosome and x chrmosome
50% chance
what is genotype
what is an allele
what is a gene
what is a chromosome
what is phenotype
genotype-what alleles you have- eg Tt
allele- alternative version of a gene
gene- short section of dna found on a chromosome which contains instructions to make a protien
chromosome- long molecule of dna that contains many genes
phenotype-the characterisitcs you have eg brown eyes
what is a gamete
what is homozygous
what is hetrozygous
what is a dominant allele
what is a recessive allele
gamete- a sex cell eg egg/ sperm
homozygous- organism has 2 alleles for a particular gene that are the same
hetrozygous- organism has 2 alleles for particular gene that are different
dominant-the allele for the characteristic thats shown even if there are two different alleles present for that characteristic
recessive- an allele whose characteristics only appear in organism if there are 2 copies present
some characteristics are controlled by single gene eg …… and ……….
However most characteristics are controlled by ………..
fur colour in mice
red green colour blindness in humans
several genes interacting
what do your alleles do
work at MOLECUlAR level to determine your phenotype- what characteristics you have
2 inherited genetic disorders
briefly say what they do
what allele causes them
Polydactyly (having extra fingers or toes) is caused by a dominant
allele.
* Cystic fibrosis (a disorder of cell membranes) is caused by a
recessive allele.
what happens in cystic fibrosis
how many people does it affect
how dangerous is polydactyly
how can it be inherited
-cystic fibrosis affects 1 in 25 ppl
thick sticky mucus gets stuck in air passages and pancreas
polydactyly
-not life threatening
- can be inherited if only one parent has an allele for it (the allele is dominant)
describe how embryonic screening is used to detect genetic disorders. 2 points
in IVF, embryos are fertilised in a lab, then implanted into mother.
-remove a cell from each embryo + analyse its genes to detect inherited genetic disorders
-can take dna from an embryo in the womb + then test for disorders
what are the decisions embryonic can lead to x2
reasons for embryonic screening x3
reasons against embryonic screening x3
-embryos produced by IVF with ‘ bad’ alleles can be destroyed
-could terminate pregnancy if embryo already in womb.
for:
help stop ppl suffering
treating disorders costly for government and tax payers
laws stop it going too far ( eg cant select sex of baby unless for health reasons)
AGAINST:
increase prejudice- imply ppl with disorders are undesirable
may reach point where everyone screens embryos to pick most desirable one
expensive
what did mendel do (peas)
mid-19th century Mendel carried out breeding experiments
on pea plants.
he did 2 crosses for height in pea plants
mendels 3 important conclusions
-inheritance of characteristic in plants determined by hereditary units
-hereditary units passed onto descendants unchanged - one unit from each parent
-hereditary units are recessive or dominant- if individual has a dominant and recessive unit - the dominant characterisitic will be expressed
why the importance of Mendel’s discovery was not
recognised until after his death.
late 19th century
early 20th century
mid 20th century
scientists didn’t have knowledge to understand his findings
later scientific work by scientists led to gene theory being developed
late 19 th century- behaviour of chromosomes during cell division observed
early 20th century- realised chromosomes and mendels ‘ units’ behaved similarly.- idea that ‘ units’ located on chromosomes
‘units’ now called genes
mid 20th century- structure of DNA determined + found out how genes worked
2 types of variation within a species
give examples of characterisitcs determined ONLY by genes
genetic/ environmental
eye colour, blood group, inherited disorders
Differences in the characteristics of individuals in a population is called
variation and may be due to differences in:
x3
- the genes they have inherited (genetic causes)
- the conditions in which they have developed (environmental causes)
- a combination of genes and the environment.
why do plants + animals have characteristics similiar to their parents
2 points
characteristics determined by the genes inherited from parents. Genes passed on in gametes from which offspring develop
what is genome
give an example of how the genome and its
interaction with the environment influence the development of the
phenotype of an organism
all of the genetic material in an organism
-the maximum height an animal can grow is determined by its genes.
-whether it grows that tall depends on its environment eg how much food.
describe the effect of mutations on an individuals phenotype for most cases to very few cases
what will happen if a new phenotype caused by a mutation suits an environmental change
most mutations have no effect
some influence phenotype
very few determine phenotype
very rarely, mutation will lead to new phenotype
If the new phenotype is suited to an environmental change it
can lead to a relatively rapid change in the species. (new phenotype becomes common amongst the species quickly due to natural selection)
what is evolution -2 points
what is the theory of evolution (by natural selection)
change in inherited characteristics of a population over time
through process of natural selection- may result in formation of a new species.
all species of living things evolved from simple life forms that first developed more than three billion years ago.
when can it be said that two populations of one species have formed 2 different species
populations become so different in phenotype
that they can no longer interbreed to produce fertile offspring, they are two different species
how did darwin come up with his theory of evolution
5 points
used OBSERVATIONS he made on a ROUND THE WORLD trip + EXPERIMENTS + DISCUSSIONS + new KNOWLEDGE of FOSSILS & GEOLOGY
5 steps that explain the theory of evolution
starts from variation
ends at species evolves
organisms in species show wide variation for a characteristic + have to compete for recources
Individuals with characteristics most suited to the environment-more likely to survive + breed successfully -(survival of the fittest)
The characteristics that enabled these individuals to survive are passed on to next generation.
less well adapted organisms, less likely to survive, less likely to pass on genes
beneficial characteristics become more common and species changes, evolves
The theory of evolution by natural selection was only gradually accepted because: x4
- theory challenged idea that God made all animals and plants living on Earth
- insufficient evidence at the time the theory was published to convince many scientists
- mechanism of inheritance and variation not known til 50 years after the theory was published.
• darwin couldn’t explain why these useful characteristics appeared / how they were passed on
explain why variations in phenotype occur-(not environmentally)
phenotype controlled by genes.
-variations in phenotype occur because of Genetic variants produced by mutations (change to sequence of bases in DNA)
5 reasons for extinction
environment- changes too quickly
new predator -kills them all
new disease- kills them all
cant compete- with another species for food
catastrophic event -kill them all (volcanic event, collision with asteroid)
what was the book darwin published + when
what was (Jean Baptiste) Lamark’s theory on evolution- 3 points
why was lamarks theory rejected
on the origin of species- 1859
-changes that occur in an organism during its lifetime can be inherited.
-If characteristic used alot, it becomes more developed.
-Offspring inherits acquired characteristic.
(rabbit ran alot. its legs got longer. it’s offspring would be born with longer legs)
experiments X support his hypothesis
what is the ‘evidence’ for evolution and how this supports the theory
x3
discovery of genetics-
explained how organisms born with useful characteristics can pass them on by genes
fossils-
look at fossils of different ages ( fossil record) see how changes in organisms developed slowly over time
bacteria-
can evolve to become resistant to antibiotics- supports theory of evolution by natural selection
define selective breeding.
organisms are selectively bred to develop what type of features x2
then give examples x4
process of breeding plants and animals for particular genetic characteristics.
usefulness, appearance
- Disease resistance in food crops.
* Animals which produce more meat or milk.
* Domestic dogs with a gentle nature.
* Large or unusual flowers.
process of selective breeding
x4
choose parents with desired characteristic from mixed population.
breed them together
select the best offspring and breed them together
continue this process over many generations till all offspring show desired characteristic
first examples of humans using selective breeding x2 thousands of years ago
made edible crops from wild plants
domesticated animals
main problem of selective breeding 3 points
reduces the gene pool- number of different alleles in population- due to inbreeding.
inbreeding causes health problems
not much variation so new disease that can kill one can probably kill all
2 main problems in selective breeding
explain them
-less disease resistant alleles
- inbreeding can cause genetic defects
reduces gene pool- reduces number of different alleles.
less chance resistant alleles present in population (disease that can kill one likely can kill all)
farmer keeps breeding from ‘the best’ which are all related- inbreeding. health problems as animal likely to inherit genetic defect when gene pool limited
define genetic engineering
process of modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
3 main steps in genetic engineering
when must genes be transferred to cells of animals, plants, microorganisms
1- useful gene isolated from an organisms genome using enzymes and inserted into a vector
2- vector is a virus/ bacteria plasmid depending on type of organism gene is being transferred to
3- vector introduced to target organism and useful gene inserted into its cells
early stage in development so they develop with the characteristics(eg early embryo)
4 uses of genetic engineering
bacteria genetically modified - produce human insulin- treat diabetes
GM crops have modified genes - improve size and quality of fruits- or make them disease, insect, herbicide resistant
sheep genetically engineered- produce things like drugs in milk to treat human diseases
gene therapy- research into using genetic modification to overcome inherited disorders. (caused by faulty gene) working genes inserted into person with disease
why is genetic engineering controversial
can treat diseases, increase food production/efficiency
long term effects of changing organisms could create problems that pass to next generation
pros -2
cons -3
of growing gm crops
- characteristics increase yield so more food
-engineered to contain nutrients lacking in developing countries
(-grown in some places , often without problems) - reduce farmland biodiversity- affect no. of wild flowers + insects living near crops
-effects of eating gm crops on human health not understood - transplanted genes may get out into natural environment eg- herbicide resistance picked up by weeds- superweeds
what is tissue culture-
positives 3-
why is it used-
small group of plant cells put into growth medium with hormones. They grow into new clone plants.
made quick, little space, all year
preserve rare plants/ used by plant nurseries to produce stock quickly
what are cuttings
what type of method is this-
positives-
where are the cuttings kept till ready to be planted
gardeners plant cuttings- section of plant with new bud on- from parent plant. genetically identical/ clones produced
older, simpler method
quick, cheap
cuttings kept in moist conditions
what are embryo transplants used for-
describe the process- 4 steps
why is this useful
a con-
animal clones
-sperm and egg cell taken from best animals.
-egg cell artificially fertilised
-split apart cells from developing embryo before they become specialised
-these cloned embryos implanted into host mothers- babys born are all clones
many ideal offspring produced yearly
we start with sperm and egg, cant be certain offspring will have the characteristic you want
what are the main steps in adult cell cloning x5
pro of using this method
-nucleus removed from unfertilised egg cell
-nucleus from adult body cell eg skin cell, inserted into ‘empty’ egg cell
-electric shock stimulates egg cell to divide to form an embryo
-embryo cells contain genetic info identical to adult cell eg skin cell.
- when embryo is ball of cells, implanted into womb of adult female to develop - grows into clone of animal whose cell was used
will be a complete clone of adult whose cell is used- know the characteristics of the clone
positives of cloningx2
- studying clones helps understanding of embryo development, ageing, age related disorders
-preserve endangered species
issues of cloning x3
reduced gene pool- less different alleles in population- may not be a resistant allele- new disease can wipe out all
cloned animals might not be healthy
(eg dolly the sheep has arthiritis ( occurs in older sheep))
worry that humans cloned in future-
many unsuccesful attempts mean severely disabled children before a success.
what are fossils
name the three ways they are formed
remains of organisms from millions of years ago which are found in rocks.
when parts of organisms slowly replaced by minerals while decaying
as preserved traces of organisms from casts and impressions
from parts of organisms that haven’t decayed because 1 or more conditions needed are absent
describe how fossils are made from casts and impressions. -
what can leave casts -
organism buried in soft material eg clay.
clay hardens , organism decays.
a cast of organism is left.
something eg- footprints pressed into materials when soft. leaves impression when it hardens
organisms, animals burrows, plants root/rootlet traces- casts
describe how fossils are made when parts of the organism are replaced by minerals as they decay
teeth, bones, shell don’t easily decay, last a long time when buried.
As they decay, they are eventually replaced by minerals. (rock like substance formed)
(surrounding sediment also becomes rock - fossil is distinct- someone digs it up)
3 places where fossils made from preservation in places because 1+ conditions needed are absent.
why cant decay happen-
in Amber / Tar pits-
no Oxygen or moisture - Decay Microbes can’t survive.
in Glaciers- too cold for Decay Microbes to work
Peat bogs- too acidic fir decay microbes
what do fossils help us learn
why are scientists uncertain about how life began
1 main reason + 2 reasons for this
how much/ little organisms have evolved/changed over time
hypotheses cannot be supported/ disproved due to lack of valid evidence.
FOSSIL RECORD INCOMPLETE
-many early life forms were soft bodied and decayed completely- left very few traces behind.
-fossils may have been destroyed by geological activity- movement of tectonic plates
describe what speciation is and when it is said to occur
what is a species
name the 2 things that cause speciation
speciation is the development of a new species.
It has occured when populations of the same species are so different they cant successfully breed to produce fertile offspring
species is group of similar organisms that can reproduce to produce fertile offspring
isolation
natural selection
what is isolation in speciation.
how can isolation happen
how does it lead to speciation
3 points
isolation- populations of a species are separated
can happen due to physical barrier-
floods / earthquakes geographically isolate individuals from main population
-conditions abit different on either side - (eg climate)
-different characteristics more common in each population due to natural selection
-eventually individuals from different populations change and cant interbreed to produce fertile offspring- two groups now seperate species.
why do populations that are separated show genetic variation
there is a range of alleles
because better adapted individuals more likely to survive and breed
the useful alleles passed on to next generation
( traits useful in one place may not be in another)
2 people who thought up the theory of evolution independantly
who was pioneer for speciation theory-
what was his best known work-
what did he do-
why has our understanding of speciation developed-
-mates Darwin, Wallace
-published writings together. This prompted Darwin to publish On The Origin Of Species - 1859
- wallace
- work on ‘waning colours’ and speciation most famous
- worldwide travel to get evolution evidence
- due to more evidence over time
how do bacteria evolve to become antibiotic resistant and spread-
5 points
-what do drug companies do to stop the spread of new resistant strains and why is this not effective
- give an example
-bacteria can develop random DNA mutation.
-This leads to antibiotic resistant strains because gene for resistance becomes common.
- bacteria evolve quickly due to rapid reproduction
-They live longer, survive, reproduce- size of resistant population increases.
-Resistant strain spreads because ppl aren’t immune and no effective treatment
= new effective antibiotics made but superbugs are becoming more common
= eg MRSA is a superbug- resistant to most antibiotics
how to prevent antibiotic resistance x3
- antibiotics X be prescribed inappropriately/ overused
non serious/ viral infections
-patients complete full course so all bacteria killed.
none survive + mutate to be resistant.
-restrict agricultural use of antibiotics
-why are antibiotics used in agriculture/ farming
- why is it an issue
why can companies not keep up with demand for new effective antibiotics
x3
-given to animals to prevent illness + speed up growth.
-resistant strains can develop + then pass to humans by consumption/ contamination
-rate of development is SLOW
-COSTLY
-unlikely to KEEP UP with NEW RESISTANT strains (and the demand for new drugs)
-what was the traditional classification system called.
-how did it work. explain
-how are all organisms named
Linnaean system
- groups living things based on chraracteristics and structure
- kingdom
-phylum
-class
-order
-family
-genus
-species
-organisms named by binomial system- genus + species
why did classification systems change-
what did it change to and who made it-
what did he discover-
how does this system work, explain.
-knowledge of biochemical processes and internal structures developed due to improved microscopes
-3 domain system- Woese.
– some species not as closely related as we thought
- using evidence from chemical analysis, splits organisms into 3 domains:
Archaea- primitive bacteria- live in extreme conditions
Bacteria- true bacteria,
Eukaryota-includes protists, fungi, plants, animals
-then split into Kingdom, Phylum, Class…. ect
describe binomial system and a positive
two part (latin) name
-genus- gives info about ancestry
-species
-used world wide to avoid confusion ( species is known by the same name regardless of country)
