topic 6 - inheritance, variation and evolution Flashcards
what is sexual reproduction?
- sexual reproduction involved the fusion of male and female gametes:
-> sperm and egg cells in animals
-> pollen and egg cells in flowering plants - in sexual reproduction, there is mixing of genetic information which leads to variety in the offspring. The formation of gametes involves meiosis.
what is asexual reproduction?
- asexual reproduction involves only one parent and no fusion of gametes
- there is no mixing of genetic information
- this leads to genetically identical offspring (clones)
- only mitosis is involved
what is fertilisation?
fertilisation is the fusion of the nucleus of a male gamete with the nucleus of a female gamete
where does meiosis take place in humans?
- meiosis only takes place in reproductive organs
- in humans that is the: testes in males and the ovaries in females
how are gametes formed?
cells in reproductive organs divide by meiosis to form gametes
what are the stages of meiosis?
- all of the chromosomes are copied
- the cell now divides into two
- now, both of these cells divide one more time forming the gametes
- in the gametes, the chromosomes are now single, not paired
- each of these four gametes is genetically different from each other with different alleles
describe fertilisation and its resulting outcome
- gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis
- as the embryo develops, cells differentiate
what happens after fertilisation
- the new cell divides by mitosis, producing a clump of identical cells - an embryo
- as the embryo develops, the cells differentiate forming different cell types
- in animals, these include nerve cells and muscle cells
what are advantages of sexual reproduction?
- sexual reproduction produces variation in the offspring. this means that some of the offspring may survive if there is a change in environment -> sexual reproduction gives a species survival advantage by natural selection
what are the disadvantages of sexual reproduction?
- two parents are required. this makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles
- more time and energy is required so fewer offspring are produced
what are the advantages of asexual reproduction?
- 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
what are the disadvantages of asexual reproduction?
- risky because all the offspring are genetically identical, there is a risk they could all die if conditions become unfavourable
what are examples of organisms that reproduce by both methods of reproduction?
- malarial parasites reproduce asexually in the human host, but sexually in the mosquito
- many fungi reproduce asexually by spores but also reproduce sexually to give variation
- many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils
where do malarial parasites reproduce sexually?
mosquitoes
what conditions causes malarial parasites to reproduce sexually?
low temperatures
where do malarial parasites reproduce asexually?
liver and red blood cells in humans
where are chromosomes located?
chromosomes are found in the nucleus of cells
what do chromosomes contain?
the molecule DNA
what does DNA determine?
our inherited features
what is DNA?
- DNA is a polymer made up of repeating units called nucleotides.
- The polymer is made up of 2 strands that is twisted into a double helix
what is a gene?
a gene is a small section of DNA that codes for a particular sequence of amino acids, to make a specific protein
what is a genome?
- the genome of an organism is the entire genetic material of that organism
what are the benefits of understanding the entire human genome?
- understanding the human genome will help us to search for genes that are linked to a disease e.g genes that increase the risk of developing cancer or Alzheimer’s disease
- understanding the human genome will help us to understand and treat inherited disorders e.g. cystic fibrosis
- we can use the human genome to trace human migration patterns from the past - this helps people to discover their ancestry
where is the DNA located?
DNA is contained in chromosomes in the nucleus
what does a nucleotide consist of?
a phosphate group attached to a sugar molecule that is joined to a base
what never changes in a nucleotide in DNA?
- in DNA, the phosphate group and sugar molecule never change
how many different nucleotides make up DNA?
4
what are the four bases?
A, C, G, T
which bases pair up together?
A-T
C-G
what are proteins?
polymers of amino acids
what is protein synthesis?
the formation of a protein from a gene
how many different amino acids are there in humans?
twenty
what does the specific order of amino acids determine?
- the specific order of amino acids determines the shape of the protein
what does the shape of the protein determine?
the shape of the protein determines its function
how does a gene code for a protein?
- a sequence of three bases in a gene forms a triplet
- each triplet codes for an amino acid
- the order of amino acids determines the structure and function of protein formed
what occurs during transcription?
- in this stage, the base sequence of the gene is copied into a complementary template molecule
- scientists call this template messenger RNA or mRNA for short
- mRNA is a single stranded molecule
- the mRNA now passes out of the nucleus and into the cytoplasm
what occurs during translation?
- in this stage, the mRNA molecule attaches to a ribosome
- amino acids are now brought to the ribosome on carrier molecules
- these carrier molecules are called transfer RNA or tRNA for short
- the ribosome now reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order
- once the protein chain is complete, it now folds into its unique shape
what does the base sequence of a gene determine?
- the base sequence of a gene determines the amino acid sequence of a protein
what is a mutation?
- a change in the base sequence of DNA
- mutations occur continuously
what are the effects of mutation?
- most do not alter the protein, or only alter it slightly so that its appearance or function is not changed
- if a mutation does not change the amino acid sequence, there is no effect on protein structure or function
what happens if a mutation changes the shape of a structural protein?
- it may lose its strength
what are non-coding parts of DNA?
- non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed
what are alleles?
different versions of the same gene
what is a dominant allele?
a version of a gene where only one copy is needed for it to be expressed
what is a recessive allele?
a version of a gene where two copies are needed for it to be expressed
what is meant when an organism is homozygous?
when an organism has two copies of the same allele
what is meant when an organism is heterozygous?
when an organism has two different versions of the same gene
what is the genotype?
the genes present for a trait
what is the phenotype?
the visible characteristic
how are dominant alleles represented in a punnett squares?
they are represented using uppercase letters
how are recessive alleles represented in a punnett square?
they use the lowercase version of the same letter as the dominant allele
what is the problem with single gene crosses?
most characteristics are controlled by multiple alleles rather than just one
what is an inherited disorder?
a disorder caused by the inheritance of certain alleles
what are two examples of inherited disorders?
- polydactyly = caused by a dominant allele
- cystic fibrosis = caused by a recessive allele
how are embryos screened for inherited disorders?
- during IVF, one cell is removed and tested for disorder-causing alleles
- if the cell doesn’t have any indicator alleles, then the originating embryo is implanted into the uterus
what are the ethical issues concerning embryo screening?
- it could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority
- the destruction of embryos with inherited disorders is seen by some as murder as these would go on to become human beings
what are causes of variation in the characteristics of individuals?
- the genes they have inherited
- the conditions in which they have developed
- a combination of genes and the environment
what is genetic variation?
- variations in the genotypes of organisms of the same species due to the presence of different alleles
- creates differences in phenotypes
what creates genetic variation in a species?
- spontaneous mutations
- sexual reproductions
what are three types of gene mutation?
- insertion
- deletion
- substitution
how may a gene mutation affect an organism’s phenotype?
- neutral mutation does not change the sequence of amino acids. Protein structure and function same. no effect on phenotype
- mutation may cause a minor change in an organism’s phenotype
- mutation may completely change the sequence of amino acids. this may result in a non functional protein -> severe changes to phenotype
what is the impact of a new phenotype caused by a mutation being suited to an environmental change?
there will be a rapid change in the species
what is the theory of evolution?
- the theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago
how many different species of animals and plants on the Earth?
9 million
what is evolution?
evolution is the change in the inherited characteristics of a population over time through a process of natural selection
outline the theory of natural selection (6)
- genetic variation exists due to spontaneous mutations
- selection pressures exist
- random mutation gives an organism a selective advantage
- organism is better adapted to the environment and survives
- organism reproduces, passing on its beneficial alleles
- frequency of advantageous alleles increase
how do two populations become different species?
- when their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring
what is selective breeding?
the process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
outline the main steps involved in selective breeding
- take a mixed population and select desired characteristics
- we then breed this together
- sexual reproduction produces variation in the offspring
- select the male and female offspring of the desired characteristic and breed these together
- continue doing this over many generations until all the offspring contain desired characteristic
what is the problem with selective breeding?
- if we breed together closely related animals or plants, then we can get inbreeding
what can inbreeding cause?
- inbreeding can cause some breeds to be prone to disease or inherited defects
what are the main advantages of selective breeding?
- crops produce a higher yield of grain
- cows produce a greater supply of milk
- plants produce larger fruit
- domesticated animals
what are examples of characteristics selected for in selective breeding?
- disease resistance in crops
- higher milk or meat production in animals
- gentle nature in domestic dogs
- large flowers
what is genetic engineering?
a process which involves modifiying the genome of an organism by introducing a gene from another organism to give a desired characteristic
what are examples of uses for genetically modified plants?
- disease resistance
- produce larger fruits
what is a use for genetically modified bacteria cells?
to produce human insulin to treat diabetes
what are the benefits of genetic engineering?
- increased crop yields for growing population
- useful in medicine
- GM crops produce scarce resources
what are the risks of genetic engineering?
- long-term effects of consumption of GM crops unknown
- negative environmental impacts
- late-onset health problems in GM animals
- GM seeds are expensive
what is the name for crops that have had their genes modified?
genetically modified crops (GM)
what is gene therapy?
gene therapy involves inserting copies of a normal allele into the chromosomes of an individual who carries the faulty cystic fibrosis allele
what are the main steps in genetic engineering?
- identify the gene that you want to transfer
- use enzymes to isolate this gene
- transfer the gene into a vector, usually a bacterial plasmid or a virus
-this 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 desired characteristics
what is tissue culture?
using small groups of cells from part of a plant to grow identical new plants
- this is important for preserving rare plant species or commerically in nurseries
what are cuttings?
- an older, but simple, method used by gardeners to produce many identical new plants from a parent plant
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 steps for 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 was Charles darwin’s theory on evolution by natural selection?
- 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 to breed successfully
- the characteristics that have enabled these individuals to survive are then passed onto the next generation
where did Darwin publish his ideas?
in ‘On the Origin of Species’ in 1859
why was Darwin’s theory of evolution by natural selection only gradually accepted?
- the theory challenged the idea that God made all the animals and plants that live on Earth
- there was insufficient evidence at the time the theory was published to convince many scientists
- the mechanism of inheritance and variation was not known until 50 years after the theory was published
how can fossils give evidence for evolution?
- older fossils simpler
suggest how the insects came to be preserved in the amber
- engulfed by resin
- prevented decay
