b6 inheritance, variation and evolution Flashcards
what is sexual reproduction?
where genetic information from two organisms combined to produce offspring which are genetically different to either parent
what is produced by the mother and father in sexual reproduction and how are they produced?
- gametes ( sperm and ovum in animals, and pollen and egg in plants)
- produced by meiosis
what is fertilisation?
when the egg and sperm fuse together to form a cell with the full number of chromosomes
why do offspring inherit features from both parents?
because its received a mixture of chromosomes from its mum and dad
what occurs in asexual reproduction?
theres only one parent, so theres no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. - offspring are clones
how does asexual reproduction take place?
by mitosis - an ordinary cell makes a new cell by dividing into two.
the new cell has the exact same genes as the parent cell
what organisms can produce asexually?
bacteria
some plants
some animals
how are gametes produced?
by meiosis.
1) the cell duplicates its genetic information, forming two armed chromosomes.
2) in the first division, the chromosome pairs line up in the centre of the cell and the pairs are pulled apart so each new cell only has one copy of each chromosome.
3) in the second division, the chromosomes line up again in the centre of the cell. the arms of the chromosomes are pulled apart.
what is the product of meiosis?
four gametes, each with only a single set of chromosomes in it. each of the gametes is genetically different because the chromosomes all get shuffled up during meiosis, and each gamete gets half of them at random
what does the cell produced by the gamete fusion do?
replicates itself
- after two gametes have fused during fertilisation, the resulting new cell divides by mitosis to make a copy of itself.
- mitosis repeats many times to produce lots of new cells in an embryo.
- as the embryo develops, these cells can begin to differentiate into the different types of specialised cells that make up a whole organism
advantages of sexual reproduction?
1) produces genetic variation
- this increases the chances of a species surviving if there is a stimulus. it is likely that variation will lead to some offspring being able to survive in the stimulus. they have a survival advantage.
2) natural selection
- when individuals with characteristics which make them better adapted to the environment they are more likely to breed successfully and pass the genes for characteristics more.
3) using selective breeding to speed up natural selection to allow us to produce animals with desirable characteristics. eg increasing food production by breeding animals who produce a lot of meat.
advantages of asexual reproduction?
1) only needs one parent so it is energy efficient as organisms dont have to find a mate.
2) faster that sexual reproduction.
3) many identical offspring can be produced in favourable conditions
how do malarial parasites produce sexually and asexually?
when a mosquito carrying the parasite bites to a human, the parasite can be transferred to the human.
the parasite produces sexually when its in the mosquito and sexually when its in the human host.
how and why do fungi reproduce both asexually and sexually?
- many species of fungi can reproduce both sexually and asexually.
- these species release spores which can become fungi when they land in a suitable place.
- asexually produced spores are genetically identical to the parent fungi.
- sexually produced spores introduce variation and are often produced in response to unfavourable change in environment, increasing the chance that the population will survive the change
how do plants reproduce sexually?
by producing seeds (pollen), animals and insects are attracted to their vibrant colours and transfer their pollen to other plants for fertilisation.
how do plants reproduce asexually?
- by producing ‘runners’, which are stems that grow horizontally on the surface of the soil away from the plant. at various points of the runner, a new strawberry forms plant form that is a clone to the original plant.
- some plants (eg daffodils) grow from bulbs. new bulbs can form from the main bulb and divide off. each new bulb can grow into a new identical plant.
what does DNA stand for?
deoxyribonucleic acid. its the chemical that all the genetic material in the cell is made up of
what does DNA contain and what is its importance?
contains coded information- which are all the instructions to put an organism together and make it work.
- the importance of it is that whats in ur DNA determines what inherited characteristics you have
where is DNA found and in what structure?
- found in the nucleus of animal and plant cells, in really long chromosomes which normally come in pairs.
- DNA is a polymer, it’s made up pf who strands coiled together in the shape of a double helix
what is a gene?
what does it do?
- a small section of DNA found on a chromosome.
- each gene codes for a particular sequence of amino acids which are put together to make a specific protein and only 20 amino acids are used but can make up thousands of proteins.
what does DNA also do?
determines what proteins the cell produces. this determines what type of cell it is
what is a genome?
the entire set of genetic material in an organism
why is the understanding of the human genome a really important tool for science and medicine?
1) allows scientists to identify genes in the genome that are linked to different types of disease.
2) knowing what genes are linked to inherited diseases could help us to understand them better and develop effective treatments for them.
3) used in tracing human migration
what are DNA strands made up of?
polymers made up of lots of repeating units called nucleotides.
at does each nucleotide consist of?
a sugar, a phosphate group and one ‘base’
what is the structure of
- the sugar and phosphate groups in the nucleotides form a ‘backbone’ to the DNA strand.
- the sugar and phosphate groups alternate. one of 4 different bases- A, T, C, G- joins each sugar.
- each base links to a base on the opposite strand in the helix:
A-T C-G
what decides the order of amino acids in a protein?
the order of the bases
what is each amino acid coded by?
a sequence of 3 bases in a gene
what do amino acids join together to make?
various proteins depending on the order of the gene’s bases
what do some parts of DNA that dont code for proteins do?
some of these non-coding parts switch the genes on and off, so they control whether or not the gene is expressed
where are proteins made?
in the cell cytoplasm on ribosomes
how are proteins made?
ribosomes use the code in DNA which is transported by mRNA from the nucleus to the ribosome
how is mRNA made?
by copying the code from the DNA
why must mRNA be used to carry the code in DNA from the nucleus to the ribosome?
because the DNA is found in the nucleus and cant move out of it because it’s rlly big
what happens to a chain of amino acid which allows it to perform the tasks its meant to?
it folds into unique shapes when its being assembled
what are some examples of proteins?
1) ENZYMES- biological catalysts
2) HORMONES- carry messages around the body
3) STRUCTURAL PROTEINS- are physically strong and strengthens parts of the body (eg collagen strengthens ligaments)
what is cystic fibrosis and what is it caused by?
1) a genetic disorder of the cell membranes. it results in the body producing a lot of thick, sticky mucus.
2) it is caused by a recessive allele ‘f’
what is polydactyly and what is it caused by?
1) a genetic disorder where a baby is born with extra fingers or toes and it is not life threatening.
2) it is caused by a dominant allele ‘D’
what are the advantages of embryonic screening?
1) it will help to stop people suffering as doctors can screen out for diseases.
2) treating disorders costs the government and tax payers a lot of money.
3) there are laws to stop it going too far. at the moment parents cannot even select the sex of their baby.
what are the disadvantages of embryonic screening?
1) it implies that people with genetic problems are ‘undesirable’ and could increase prejudice.
2) designer babies
3) screening is expensive
how many pairs of chromosomes are in every human body cell?
what are the 23rd pair labelled as?
1) 23 pairs
2) xx and xy which determine your sex
what is the percentage charge that a sperm cell gets an x and y chromosome?
50% for both
what are genetic differences called?
variation
what are the two types of variation called?
1) genetic variation
2) environmental variation
how does genetic variation work?
1) an organisms characteristics are determined by the genes inherited by the parents
2) during sexual reproduction where the genes in the father gamete and mother gamete fuse together.
3) as no two organisms who were produced sexually are identical, this means that they have genetic variation.
how does environmental variation work?
1) different environments for animals and plants live in causes different adaptations for the plant to better suit that environment.
2) also, the environment itself could cause the variation, for example having a suntan because you’re at a sunny beach for a while
how are most characteristics due to genes and the environment?
for example, an animal or plant may have a gene to grow very tall, however it is the environment that they live in which determine whether this gene can play out as a phenotype . (eg: how much food it gets)
how can mutations introduce variation?
1) a mutation is a change to the sequences of bases in DNA.
2) mutations can lead to changes in the protein that a gene codes for.
- most mutations have no effect on phenotype.
- some have a small influence on phenotype.
- some mutations can determine a phenotype.
3) if the environment changes and the new phenotype makes an individual better suited to the new environment, it can become common throughout the species by natural selection.
what is the theory of evolution?
that all of todays species have evolved from simple life forms that firs started to develop over 3 billion years ago
what is evolution?
a change in the inherited characteristics of a population over time through a process called ‘natural selection’. which may result in a new species
how did Darwin conclude with the theory of evolution?
1) he knew that organisms within a species had genetic variation. he knew that organisms have to compete for limited resources in an ecosystem.
2) therefore those with the most suitable characteristics for the environment would be more successful competitors and more likely to survive (survival of the fittest).
3) organisms which were less likely to survive and pass on their genes.
4) so overtime, beneficial characteristics become more common in the population and the species changes- they evolve.
what is speciation?
when a new species is created
what is a factor of speciation?
they cant interbreed with other species to produce fertile offspring
what is extinction?
when no individuals of a species remain
what are the factors of extinction?
1) the environment changes too quickly
2) a new predator kills them all
3) a new disease kills them all
4) they cant compete with other new species for food
5) a catastrophic event happens and kills them all
what is selective breeding?
when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.
why are organisms selectively bred?
1) to develop features that are useful or attractive, eg:
- animals produce more meat or milk
- plants with disease resistance
- decorative plants with big or unusual flowers
- tender domestic dogs
what is the basic process involved with selective breeding?
1) from your existing stock, select those who have the desired characteristics.
2) breed them together
3) select the best of the offspring, and breed them together
4) continue this process over several generations, and the desired trait gets stronger and stronger.
5) eventually, ALL the offspring will have this desired characteristic
what can selective breeding be used for in agriculture?
to improve yields. eg a farmer could breed vows and bulls with the best characteristics for producting meat
what is the main drawback of selective breeding?
1) a reduction in the gene pool- the number of different alleles in a population.
2) this is because the farmer keeps breeding from the ‘best’ animals or plants which are closely related. (inbreeding)
3) this can cause health problems because theres a higher chance of the animal inheriting harmful genetic defects when the gene pool is limited.
4) also the lack of genetic variation can be a serious problem if a new disease appears, if one of them is killed then it is likely that all of them will also be killed
what is genetic engineering?
the process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
why have plants been genetically engineered?
to be resistant to specific diseases or to produce better fruits
why have bacterial cells been genetically engineered?
to produce useful substances such as human insulin to treat diabetes
what are the main steps in the process of genetic engineering?
1) a useful gene is isolated from one organism’s genome using enzymes and is inserted into a vector.
2) the vector is usually a virus or a bacterial plasmid.
3) the vector is used to insert the gene into the required cell.
this is all done at an early stage of an organisms development so that it can develop the desired features
what are GM crops?
crops that have had their genes modified to improve the size and quality of their fruit or make them resistant to disease, insects and herbicides
what are the concerns about GM crops?
- effects on the populations of wild flowers and insects.
- some people feel that the effects of eating GM crops on human health have not been fully explored
advantages of GM crops?
1) increases yield
2) GM crops can be engineered to contain nutrients that are missing from people who live in developing nations.
3) GM crops are already being grown in some places, often without problems
disadvantages of GM crops?
1) they can affect the number of wild flowers (and so the population of insects that live around the crops)- reducing biodiversity.
2) some are not convinced that they are safe as we do not fully understand the effects of eating them.
3) transplanted genes may get out into the natural environment . eg: herbicide resistance gene may be picked up by weeds
what is tissue culture?
using a small group of cells from a part of a new plant to grow identically new plants.
- this is important in preserving rare plant species or commercially in nurseries.
- they grow very quickly, in little space and can be grown all year
what are cuttings?
when gardeners take cuttings from good parent plants, and then plant them in moist conditions to produce genetically identical clones.
- these can be produced quickly and cheaply.
- this is an older, simpler method than cuttings
how can you make animal clones using embryo transplants?
1) sperm cells are taken from a prize bull and egg cells are taken from a prize cow.
2) the embryo that develops is then split many times to form clones BEFORE any cells are specialised.
3) ]the cloned embryos are implanted into lots of other cows where they grow into baby calves.
how can you use adult cell cloning to make a clone?
1) the nucleus of an unfertilised egg is removed.
2) the nucleus from an adult body cell, such as a skin cell, is inserted into the egg.
3) an electric shock stimulates the egg divide to form a normal embryo.
4) when the embryo is a ball of cells, it is implanted in a womb and it grows into a genetically identical copy of the original body cell.
what are the issues of cloning?
1) reduced gene pool, meaning fewer alleles in a population.
2) cloned animals may not be as healthy as other animals.
3) the possibility of human clones. failure= disabled children
advantages of cloning?
1) could lead to a greater understanding of the development of the embryo and ageing.
2) could be used to preserve endangered species.
what are fossils?
the remains of organisms millions of years ago, which are found in rocks
what is one method of fossil forming (from gradual replacement by minerals) ??
1) things like teeth and bones dont decay easily and can last a long time when buried.
2) they’re eventually replaced with minerals as they decay, forming a rock-like substance shaped like the original artefact.
3) the surrounding sediments also turn into rocks, but they remain distinct inside the rock
what is another method of fossil forming (from casts and impressions) ??
1) sometimes, fossils are formed when an organism is buried in clay.
2) the clay later hardens around it and the organism decays, leaving the cast itself.
3) eg: things like an animals burrow, a plants roots or a footprint.
what is another way of fossil forming?
(preservation in places where no decay happens) ??
1) in amber and tar pits where there is no oxygen or moisture, so no decay microbes can survive.
2) in glaciers where its too cold for the decay microbes to work.
3) peat bogs are too acidic for decay microbes
why is it difficult to understand how life first came into being?
many early forms of life were soft bodied, which means that there have been very few traces of life left behind and those that were, were destroyed due to geological activity
how can isolation and natural selection lead to speciation?
1) isolation can happen due to a physical barrier.
2) conditions on either side of the barrier will be slightly different.
3) because the environment is different on both sides, different characteristics will become more common in each population due to natural selection.
4) eventually individuals from the different populations will have changed so much that they wont be able to breed with one another.
5) they have become separate species.
what was the work of wallace in speciation?
- he was a pioneer of the theory of speciation.
- his observations greatly contributed to how we understand speciation today.
- during his career he independently came up with the idea of natural selection.
- he then published his work on the subject with darwin.
- this then prompted darwin to publish ‘on the origin of species’.
what evidence did he provide to prove his theory of natural selection?
he realised that warning colours are used on some species like butterflies to deter predators.
- this was an example of a beneficial characteristic.
- that had evolved by natural selection
what did mendel do on his garden plot at the monastery in the mid 19th century?
noted how characteristics in plants were passed on from one generation to the next.
- the results of his research were published in 1866 and eventually became the foundation of modern genetics
mendel’s two crosses for height in pea plants
CROSS 1-
parents: one tall, one short
offspring: all 4 tall
two pea plants from the 1st set of offspring are crossed
CROSS 2:
parents: both tall
offspring: 4 tall except from one
what were mendel’s 3 important conclusions about heredity in plants?
1) characteristics in plants are determined by ‘hereditary units’
2) hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
3) hereditary units can either be dominant or recessive- if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed
what were mendel’s 3 important conclusions about heredity in plants?
1) characteristics in plants are determined by ‘hereditary units’
2) hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
3) hereditary units can either be dominant or recessive- if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed
why was it difficult to understand mendel’s work?
- they didnt have the background knowledge to properly understand his findings- they had no idea about genes, DNA and chromosomes
it wasnt until AFTER his death that ppl realised how significant his findings were
how has mendel’s work contribute to the understanding of genes that we have today?
1) in the late 1800s, a scientist became familiar with chromosomes and they were able to observe how they behaved during cell division.
2) in the early 20th century, scientists realised that there were similarities in how mendel’s ‘units’ and chromosomes work.
- based on this, it was proposed that the ‘units’ were found on chromosomes. but now we know them as genes.
3) in 1953, the structure was determined. this allowed scientists to go on and find out exactly how genes work
what is classification?
organising living organisms into groups
how were organisms traditionally classified?
(linnaean system)
according to a system proposed in the 1700s by linnaeus, which groups things based on their characteristics and the structures that make them up
under the linnaean system, how were kingdoms subdivided?
phylum
class
order
family
genus
species
how did scientists put forward new models of classification?
- development of the knowledge of biochemical processes taking place inside of organisms
- improved microscopes, which helped us to find out more abt the internal structures of organisms
what is the first domain in the three-domain system?
1) archaea- organisms in this domain are primitive bacteria. they’re often found in extreme places eg hot springs and salt lakes
what is the second domain in the three- domain system?
2) bacteria- this domain contains true bacteria. although they often look similar to archaea, there are a lot of bimedical differences between them
what is the third domain in the three- domain system?
3) eukaryota- this domain includes a broad range of organisms including fungi, plants, animals and protists
how was the three- domain system developed?
- using new evidence from new chemical analysis techniques, eg RNA sequence analysis.
- woese found that in some cases, species thought to be closely related in the traditional classification systems are in fact not as closely related as first thought
how are organisms names?
according to the binomial system.
- in the system, each organism is given its own two part latin name
how is the name of an organism determined in the binomial system?
1) first part refers to the genus that the organism belongs to.
- this gives you info on the ancestry
2) second part refers to the species.
what to evolutionary trees show?
evolutionary relationships
- how scientists believe different species are related to one another.
- common ancestors relationships between species (the more recent the common ancestor, the more closely related they are so the more characteristics they’re likely to share.
how do scientists analyse data for living organisms to work out evolutionary relationships?
they use current classification data
how do scientists use data for extinct species to work out evolutionary relationships?
they use information from the fossil record
