alleles and inheritance Flashcards
state –> alleles are different versions of the same gene
what determines what characteristics we develop
the genes you develop control what characteristics you develop
state –> some charactaristics are controlled by a single gene. however most charecacteristics are controlled by several genes interacting
how many copies of each gene do we have
two copies of each gene, one from each parent
state –> the version of the characteristic that appears is caused by the dominant allele. The other allele is said to be recessive. The characteristic is caused by recessive allele only appears if both alleles are recessive
codominant alleles
some characteristics are caused by codominant alleles. neither
genetic diagrams letters are used to represent genes
- in diagrams diagrams, letters are used to represent genes. dominant alleles are always shown with a capital letter. recessive alleles with a small letter
- if you are homozygous for a trait you have two alleles the same for that particular gene
- if you are heterozygous for a trait you have two different alleles for that particular gene
- your genotype is the alleles that you have. your phenotype is the characteristics the alleles produce.
state –> there are 23 matched pairs of chromosomes in every human body cell.
what is the 23rd pair labelled as
XX or XY
what does XX or XY tell you
whether you turn out female or male
what do males have
an X and Y chromosome. (the Y chromosome causes male characteristics
what do females have
females have two X chromosomes. XX
The XX combination causes female characteristics
why are animals all bound to be slightly different
because their genes are slightly different
what is most variation caused by
a mixture of genetic and environmental factors
how can the environment have a large effect on human growth before someone is born
a baby’s weight at brith can be affected by the mother’s diet. and another having a poor diet whilst you are growing up can stunt your growth
state –> environmental variation in plants is much greater
what are plants strongly affected by
- sunlight
- moisture level
- temperature
- the mineral content of soil
theory of evolution
life began as simple organisms from which more complex organisms evolved ( rather than just popping into existence)
how long does the whole process of evolution take
it takes place gradually over millions of years
what does natural selection mean
the ‘ survival of the fittest’
darwins theory
- darwin knew that organisms in a species show variation in their characteristics
- darwin also knew that the resources that organisms need to survive are limited and individuals have to compete for these resources to survive
- darwin concluded that the organisms with the most suitable characteristics for the environment would be more successful competitors and so would have a better chance of survival 0 this is known as survival of the fittest
- the successful organisms will then have an increased chance of breeding and passed on their genes
- this means that a greater proportion of individuals in the next generation will have the better alleles and so the characteristics, that help survival
- over many generations, the characteristic that increases survival becomes more common in the population, making the species become better and better able to survive. the ‘best’ features are naturally selected and the species becomes more and more adapted to its environment
who came up with the theory of evolution by natural selection
charles darwin
state –> the best genes for a particular environment tend to survive
the individuals who are less suited to an environment…
are less likely to survive than those that are better suited and so have less chance to pass their alleles on
what are variations caused by
by the environment itself. variations in a species can have either environmental or genetic causes, but only the genetic ones are passed on to the next generation and influence the evolution of the species.
state –> mutations are changes to the genetic code
what is a mutation
is a rare, random change in an organism’s DNA that can be inherited
what do mutations do
change the sequence of the DNA bases in a gene which produces a genetic variant. As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for
what is a genetic variant
different form of the gene
state –> enzymes are proteins which need an active site with a very specific shape to be able to work properly. a mutation in the gene that codes for an enzyme could lead to a change in the shape of an enzyme’s active site - altering its function. a mutation could also stop the production of the enzyme altogether
what can mutations lead to
a different phenotype, increasing variation
when can mutations happen
they can happen spontaneously - when a chromosome doesnt quite copy itself properly
the chance of mutation is increased by exposing yourself to:
ionising radiation eg: X-rays, gamma rays or ultraviolet rays
chemicals called mutagens eg: chemicals in tobacco
no effect, small effect, significant effect - mutations
- most mutations have no effect. if mutation occurs in unimportant region of the DNA or if mutated codon still codes for same amino acid, the protein’s structure and function will be unaffected. A mutation will also have no effect if it occurs in a recessive allele
- some mutations have a small effect on the phenotype. This happens when the change in amino acid only has a slight effect on the protein’s structure and function - so the individual’s characteristics are only altered very slightly
- very rarely, a mutation will have a significant effect on phenotype. for example it might result in a very different protein which can no longer carry out its function. These mutations can be harmful ( such as those which lead to cancer ) or beneficial (giving a survival advantage eg: antibiotic resistance in bacteria)
how can bacteria evolve and become antibiotic resistant
- bacteria can sometimes develop random mutations in their DNA. These can lead to changes in a bacterium’s characteristics. Sometimes, they mean that a bacterium is less effected by a particular antibiotic.
- for the bacterium this ability to resist antibiotics is a big advantage. its better able to survive, eve in a host who is being treated to get rid of the infection, so it lives for longer and reproduces many more times
- this leads to the alleles for resistance being passed on lots of offspring - its just natural selection. This is how it spreads and becomes more common in a population of bacteria over time.
This is a problem for people who become infected with these bacteria, because they cannot easily get rid of them with antibiotics. Sometimes, drug companies can come up with a new antibiotic that is effective, but ‘superbugs’ that are resistant to most known antibiotics (eg: MRSA) are becoming more common)
state –> bacteria can evolve and become antibiotic resistant
