Genetics Flashcards
What is DNA?
+A molecule that carries all the instructions for your characteristics.
+A carrier for genetic information
What is DNA made up of?
Nucleotides
What are DNA strands?
Polymers made up of lots of repeating units called nucleotides.
What does each nucleotide consist of?
+One sugar molecule
+One phosphate molecule
+One ‘base’
What do the sugar and phosphate molecules form?
+In the nucleotides, they form a ‘backbone’ to the DNA strands.
+The sugar and phosphate molecules alternate
What joins to each sugar?
One of four different bases joins to each sugar.
What are the four bases?
+A (adenine)
+T (thymine)
+C (cytosine)
+G (guanine)
What does a DNA molecule have?
+Two strands coiled together in the shape of a double helix (a double stranded spiral)
What does each base link with?
Each base links to a base on the opposite strand in the helix.
What do the bases ALWAYS pair up with?
+A always pairs up with T
+C always pairs up with G
This is called complementary base pairing.
What are the complementary base pairs joined together by?
Weak hydrogen bonds
What is DNA stored as?
Chromosomes which contain genes
What are chromosomes?
+Long coiled up molecules of DNA
+They’re found in the nucleus of eukaryotic cells
What is a gene?
A section of DNA on a chromosome that codes for a particular protein
What is a genome?
+All of an organism’s DNA
+The complete set of genes or genetic material present in an organism.
What do DNA molecules contain?
+A genetic code that determines which proteins are built
+Proteins determine how all the cells in the body function
What do proteins determine?
How all the cells in the body function
How are proteins made?
By reading the code in DNA
What does DNA control?
The production of proteins (protein synthesis) in a cell.
What are proteins made up of?
+Molecules called amino acids
+Each different protein has it own particular number of amino acids
What is sexual reproduction?
+Where genetic information from two organisms [male and female] is combined to produce offspring which are genetically different to either parent.
What does the father and mother produce in sexual reproduction?
+Gametes [reproductive cells].
+In animals these are sperm and egg cells
What do gametes contain?
+They are haploid so they contain half the number of chromosomes of normal cells [23]
+Normal cells with the full number of chromosomes are diploid.
What happens at fertilisation?
+A male gamete fuses with a female gamete to produce a fertilised egg [zygote].
What is a zygote?
+A fertilised egg
+The zygote ends up with the full set of chromosomes so it is diploid.
+A diploid cell resulting from the fusion of two haploid gametes
What does the zygote undergo?
Cell division by mitosis and develops into an embryo
What does the embryo inherit?
Characteristics from both parents - as it has received a mixture of chromosomes [and therefore genes] from its mum an dad
What is meiosis?
+A type of cell division that results in the production of gametes.
+In humans meiosis only happens in the reproductive organs [ovaries and testes].
What happens first in meiosis?
The cell duplicates its DNA [so there’s enough for each new cell].
+One arm of each x-shaped chromosome is an exact copy of the other arm.
What happens in the first division in meiosis?
+The chromosomes line up in pairs in the centre of the cell.
+One chromosome from each pair came from the organism’s mother and one from its father.
+The pairs are then pulled apart - each new cell only has one copy of each chromosome.
+Some of the father’s and mother’s chromosomes go into each new cell.
+Each new cell have a mixture of the mother’s and father’s chromosomes.
Why is mixing up the chromosomes [therefore genes] important in the new cells.
It creates genetic variation in the offspring.
What happens in the second division of meiosis?
+Chromosomes line up again in the centre - the arms of the chromosomes are pulled apart.
+You get four haploid daughter cells [the gametes]. +Each gamete only has a single set of chromosomes.
+The gametes are all genetically different.
What is the result of meiosis?
+Four haploid daughter cells are produced [the gametes].
+Each gamete only has a single set of chromosomes.
+The gametes are all genetically different.
What is asexual reproduction?
+Cells divide by mitosis - results in two diploid daughter cells - genetically identical to each other and to the parent cell.
What does sexual reproduction involve?
+Meiosis and the production of genetically different haploid gametes.
+This fuses to form a diploid cell at fertilisation
What are the advantages of asexual reproduction?
+It can produce lots of offspring quickly as the reproductive cycle [the time it takes to produce independent offspring] is so fast.
+Eg. bacteria such as E.coli can divide every 30mins
+This allows organisms to colonise a new area very rapidly.
+Only one parent is needed - which means organisms can reproduce whenever conditions are favourable without having to wait for a mate
+Eg. aphids reproduce asexually during summer when there is plenty of food.
What are the disadvantages of asexual reproduction?
+There is no genetic variation within the population - meaning if the environment changes and conditions become unfavourable, the whole population may be affected.
+Eg. Black Sigatoka is a disease that affects banana plants, which reproduce asexually.
+So if there is an outbreak of the disease, it’s likely that all banana plants in the population will be affected as there are none that are resistant to it.
What are the advantages of sexual reproduction?
+Creates genetic variation within the population, meaning different individuals have different characteristics.
+This means that if the environmental conditions change, it’s more likely that at least some individuals would survive the change.
+This can lead to natural selection and evolution as species become better adapted to their new environment.
What are the disadvantages of sexual reproduction?
+This takes more time and energy than asexual reproduction so organisms produce fewer offspring in their lifetime.
+Organisms need to find and attract mates, - takes time and energy.
+Eg. male bowerbirds build structures out of twigs and then dance to impress females.
+Two parents are needed for sexual reproduction. This can be an issue if individuals are isolated.
+Eg. polar bears often live alone so male polar bears may have to walk up to 100miles to find a mate.
How can DNA be extracted from fruit?
1] Mash strawberries then put them in a beaker containing a solution of detergent and salt. Mix well.
+The detergent will break down the cell membranes to release the DNA.
+The salt will make the DNA stick together.
2] Filter the mixture to get the froth and big, insoluble bits of cell out.
3] Gently add some ice-cold alcohol to the filtered mixture.
4]The DNA will start to come out of solution as it’s not soluble in cold alcohol.
+It will appear as a stringy white precipitate [a solid] that can be carefully fished out with a glass rod.
What do the amino acids do?
+They fold up to give each protein a different, specific shape - which means each protein can have a different function.
+This is why enzymes have active sites with a specific shape and so only catalyse a specific reaction.
What decides the order of amino acids in a protein?
The order of bases in a gene
What is a base triplet?
+When each amino acid is coded by a sequence of three bases in the gene.
What does each gene contain?
A different sequence of bases - which is what allows it to code for a particular protein.
What does it mean when some regions of DNA are non-coding?
+They don’t code for any amino acids
+Some can still be involved in protein synthesis
What is all of an organism’s DNA [including non-coding regions]?
The organism’s genome
How can genetic variants arise?
By mutations
What is a mutation?
+A rare random change to an organism’s DNA base sequence that can be inherited
What happens if a mutation happens in a gene?
It produces a genetic variant [a different version of the gene]
What can a genetic variant do?
+It may code for a different sequence of amino acids which may change the shape of the final protein and so its activity.
+Eg. the activity of an enzyme may increase, decrease or stop altogether.
+This could end up changing the characteristics [phenotype] of an organism.
+Eg. XDH is an enzyme. Fruit flies with normal XDH activity have red eyes. Fruit flies with no XDH activity have brown eyes because they can’t produce the red eye pigment.
Where can mutations also occur?
In non-coding regions of DNA
How many stages are there to make protein?
There are two stages:
1]Transcription
2]Translation
Where are proteins made?
In the cell cytoplasm by subcellular structures called ribosomes
Where is DNA found?
+In the cell nucleus and can’t move out of it because it’s really big.
+The cell needs to get the information from the DNA to the ribosome in the cytoplasm.
+This is done using a molecule called messenger RNA (mRNA).
What is mRNA?
+[messenger RNA]
+Like DNA, mRNA is a polymer of nucleotides - but it’s shorter and only a single strand.
+It also uses uracil (U) instead of thymine [T] a base.
What is transcription?
Where DNA is copied to make mRNA
What is RNA polymerase?
The enzyme involved in joining together RNA nucleotides to make mRNA
What is the process of transcription?
1]RNA polymerase binds to a region of non-coding DNA in front of a gene.
2]The two DNA strands unzip and the RNA polymerase moves along one of the strands of the DNA.
3]It uses the coding DNA in the gene as a template to make to mRNA.
+Base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene.
4]Once made, the mRNA molecule moves out of the nucleus and joins with a ribosome.
What is translation?
Once mRNA is bound to a ribosome, the protein can be assembled.
+The assembling of the protein
What is the process of translation?
1]Amino acids are brought to the ribosome by another RNA molecule called transfer RNA [tRNA]
2]The order in which the amino acids are brought to the ribosome matches the order of the base triplets in mRNA. Base triplets in mRNA are also known as codons.
3]Part of the tRNA’s structure is called an anticodon - it is complementary to the codon for the amino acid.
+The pairing of the codon and anticodon makes sure that the amino acids are brought to the ribosome in the correct order.
+The amino acids are joined together by the ribosome
What are codons?
Base triplets in mRNA
What is an anti-codon?
Part of the tRNA’s structure
+It is complementary to the codon for the amino acid
What does the pairing of the codon and anti codon mean?
+This makes sure that the amino acids are brought to the ribosome in the correct order.
What are the amino acids joined together by?
They are joined together by the ribosome. This makes a polypeptide.
What does Non-coding DNA affect?
The binding of RNA polymerase
What happens if a mutation occurs in the region of non-coding DNA?
+It could affect the ability of RNA polymerase binding to it.
+It might make binding easier, or more difficult
What will be affected when how well RNA polymerase can bind to non-coding region of DNA?
+This will affect how much mRNA is transcribed and therefore how much protein is produced.
+Depending on the function of the protein, the phenotype of the organism may be affected by how much of it is made.
What can genetic variants in non-coding regions still affect?
+The phenotype of an organism - even if they don’t code for proteins themselves.
Who was Gregor Mendel?
He was an Austrian Monk who trained in mathematics and natural history.
+On his garden plot at the monastery in the mid 19th century, Mendel noted how characteristics in plants were passed on from one generation to the next.
+Results of his research were published in 1866 and eventually became the foundation of modern genetics
Give an example of one of Mendel’s experiments
+Mendel crossed two pea plants of different heights - one tall, one dwarf.
+The offspring produced all tall pea plants
+Then he bred two of the tall offspring. The result was that 3 offspring were produced for every one dwarf offspring overall.
+There was a 3:1 ratio for tall-dwarf plants
What had Mendel shown in his experiment?
+The height characteristic in pea plants was determined by separately inherited “hereditary units” passed on from each parent.
+The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants [T] was dominant over the unit for dwarf plants t.
What were the three important conclusions Mendel reached?
+Characteristics in plants are determined by “hereditary units”
+Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
+Hereditary units can be dominant or recessive - if an individual has both units for characteristics the dominant characteristic will always be expressed.
Why did it take a while for people to understand his work?
+At the time, scientists didn’t have the background knowledge to properly understand Mendel’s findings - they didn’t know about genes, DNA and chromosomes.
+His “hereditary units were genes
+It wasn’t until after his death people realised how significant his work was and that the mechanism of inheritance could be fully explained.
What is an allele?
+Different forms of the same gene
+Alleles determine what characteristics you have [phenotype].
+Different combination of alleles give rise to different phenotypes.
What is the phenotype?
Physical appearance of an organism
What is the genotype?
The set of genes [alleles] that an organism possesses
+It’s specific combination of alleles for a given gene
What is homozygous?
When two alleles [gene types] are identical
What is heterozygous?
When the two alleles are different.
What is dominant?
+The allele which controls the characteristic when ever it is present
What is recessive?
+The allele whose characteristics only show up when it is present on both chromosomes.
What is monohybrid inheritance?
The inheritance of a single characteristic
What is a monohybrid cross used for?
To show how recessive and dominant traits for a single characteristic are inherited
How many matched pairs of chromosomes are there in every human body cell.
23 matched pairs
+The 23rd is labelled either XX OR XY
What chromosomes do males have?
+Males have an X and a Y chromosome [XY]
+The Y chromosome causes male characteristics
What chromosomes do females have?
+Females have two X chromosomes [XX]
+The XX combination causes female characteristics
What does sex determination in humans depend on?
Whether the sperm that fertilises the egg carries an X or Y chromosome
Which sex chromosome is smaller?
+The Y chromosome is smaller than the X chromosome and carries fewer genes
+So most genes on the sex chromosomes are only carried on the X chromosome
Why do men often have only one allele for sex linked genes?
Because men only have one X chromosome
What results in men having only one allele?
+The characteristic for the allele is shown even if it is recessive
+This makes men more likely than women to show recessive characteristics for genes that are sex linked
What are sex-linked genetic disorders?
Disorders caused by faulty alleles located on sex chromosomes
What doesn’t the Y chromosome have?
An allele for any phenotype so it is just represented by Y
What is haemophillia?
+A sex-linked disorder where the blod doesn’t clot properly.
+It is caused by a faulty allele carried on the X-chromosome
What are the four potential blood types in humans?
+A
+B
+O
+AB
What are the three different alleles for the gene for blood type?
+I^O
+I^A
+I^B
What is codominance?
Two dominant alleles expressing themselves
Which two blood alleles are codominant with each other?
+I^A and I^B
+This means that when an individual has both of these alleles [genotype I^A I^B], they’ll have the blood type AB
+One allele isn’t dominant over the other
Which blood allele is recessive?
+I^O
+So when you get I^O with eg. I^A [genotype I^A I^O], then you only see the effect of I^A - giving blood type A
+You only get blood type O when you have two recessive alleles [I^O i^O]
What is variation?
+Difference between cells, individual organisms, or groups of organisms of any species
+They can be genetic [genotypic variation] or environmental [phenotypic variation]
How is genetic variation within a species caused?
+By organisms having different alleles [versions of genes] - which can lead to differences in phenotype [the characteristics an organism displays]
How else can genetic variation be caused?
+By new alleles arising through mutations
+Sexual reproduction also causes genetic variation since it results in alleles being combined in many different ways in offspring.
+Environmental [eg plant grown in sun would grow luscious and green whereas if grown in darkness it would grow tall and spindly and leaves would turn yellow]
What are acquired characteristics?
+Environmental variations in phenotype
+They’re characteristics that organisms acquire [get] during their lifetimes
How is variation in phenotype determined?
+By a mixture of genetic and environmental factors
+Eg. the maximum height a plant or animal could grow is determined by genes but whether it actually grows that tall depends on its environment [eg. how much food it gets]
What are the possible effects of a mutation?
+Most mutations don’t have a big effect on the phenotype of an organism - most mutations don’t have any effect [they are neutral]
+Some mutations have a small effect on the phenotype -they can alter an individual’s characteristics but only slightly. [Eg a mutation can give a hamster long hair instead of short hair]
+Very rarely a single mutation will have a big effect on the phenotype. Eg. it might result in the production of a protein that is so different that it can no longer can carry out its function
+This is what happens in cystic fibrosis - a mutation causes a protein that controls the movement of salt and water into and out of the cells to stop working properly.
_This leads to the production of thick sticky mucus in the lungs and digestive system -makes it difficult to breathe and digest food.
How can new phenotypes be produced?
New combinations of alleles may interact with each other
What was the human genome project?
+Where thousands of scientists from all over the world collaborated to find every single human gene.
What happened during the human genome project?
+It officially started in 1990 and a complete map of the human genome including the locations of around 20,500 genes was completed in 2003
What has the human genome project helped to identify?
+About 1800 genes related to disease, which has huge potential benefits for medicine.
What are the medical applications for the project’s research?
+Prediction and prevention of diseases
+Testing and treatment for inherited disorders
+New and better medicines
How can the HGP predict and prevent diseases?
+Many common diseases are caused by the interaction of different genes as well as lifestyle factors
+If doctors knew what genes predispose people to what diseases, we could all get individually tailored advice on the best diet and lifestyle to avoid problems.
+Doctors could also check us regularly to ensure early treatment if we do develop diseases we’re susceptible to.
How can the HGP test and treat inherited disorders?
+Inherited disorders are caused by the presence of one or more faulty alleles in a person’s genome
+Scientists are now able to identify the genes and alleles that are suspected of causing an inherited disorder much more quickly.
+Once an allele that causes an inherited disorder has been identified, people can be tested for it and it may be possible to develop better treatments or even a cure for the disease
How can the HGP lead to the development of new and better medicines?
+Genome research highlighted some common genetic variations between people. Some variations affect how our bodies will react to certain diseases and to the possible treatments for them
+Scientists can use this knowledge to design new drugs that are specifically tailored to people with a particular genetic variation. - They can also determine how well an existing drug will work for someone. - Tests can already identify whether or not someone with breast cancer will respond to a particular drug, and what dosage is most appropriate for certain drugs in different patients.
+Knowing how a disease affects us on a molecular level should make it possible to design more effective treatments with fewer side effects.
What are the drawbacks for the project’s research?
+Increased stress - if someone knew from an early age that they’re susceptible to a nasty brain disease they could panic every time they get a headache [even if they never get the disease]
+Gene-ism people with genetic problems could come under pressure not to have children
+Discrimination by employers and insurers - life insurance could be very expensive and unaffordable if someone has any likelihood of a serious genetic disease. Employers may discriminate against people who are genetically likely to get a disease.
