B3 - Genetics Flashcards
What is
sexual reproduction?
where genetic information from two organisms is combined to produce offspring which are genetically different to either parent
What are
gametes?
the reproductive cells that are produced by the mother and father in sexual reproduction
these are haploid - they contain half the number of chromosones of normal cells
What occurs during
fertilisation?
a male gamete fuses with a female gemate to produced a fertilised egg, also known as a zygote
What is
meiosis?
a type of cell division which doesn’t produce identical cells
(in humans, this only happens in the reproductive organs)
Describe the process of
meiosis.
(6 steps)
- The cell duplicates its DNA.
- In the first division, the chromosones line up in pairs in the centre of the cell - one chromosone in each pair came from the organism’s mother and one came from its father.
- The pairs are then pulled apart, so each new cell only has one copy of each chromosone - some of the father’s chromosones and some of the mother’s chromosones go into each new cell.
- In the second division the chromosones line up again in the centre of the cell.
- The arms of the chromatids are pulled apart.
- Four haploid daughter cells - called gametes are produced.
Each gamete only has a single set of chromosones. The gametes are all genetically different.
What are some advantages of
asexual reproduction?
(2, explained)
- can produce lots of offspring very quickly because the reproductive cycle is so fast - so organisms can colonise a new area very rapidly
- only one parent is needed - so organisms can reproduce whenever conditions are favourable, without having to wait for a mate
What is an advantage of
sexual reproduction?
Sexual reproduction creates genetic variation within the population, meaning that different individuals have different characteristics.
This means that if the environmental conditions change, it’s more likely that at least some individuals in the population will have the characteristics to survive the change.
Over time, this can lead to natural selection and evolution.
What is the disadvantage of
asexual reproduction?
There’s no genetic variation between offspring in the population.
So, if the environment changes and conditions become unfavourable, the whole population may be affected.
What are some disadvantages to
sexual reproduction?
(2)
- it takes more time and energy than asexual reproduction, so organisms produce fewer offspring in their lifetime
- it requires two parents, which can become a problem if individuals are isolated
What are
DNA strands?
polymers made up of lots of repeating units called nucleotides
What do
nucleotides consist of?
a sugar and a phospohate group - forming the ‘backbone’ of DNA strands - and a ‘base’
What are the
four bases that make up nucleotides?
(and join to each sugar) and what are the complementary pairs of these?
adenine, thymine, cytosine and guanine
A + T, C + G
What does a
DNA molecule consist of?
two DNA strands coiled together in the shape of a double helix
each base links to another base on the opposite strand in the helix
How are the
complementary base pairs joined together?
weak hydrogen bonds
What are
chromosones?
and where are they found?
long, coiled up molecules of DNA
they’re found in the nucleus of eukaryotic cells
Define
gene.
a section of DNA on a chromosone that codes for a particular protein
What is a
genome?
all of an organism’s DNA
Describe an experiment to
extract DNA from fruit cells.
(5 steps)
- Mash some strawberries and then put them in a beaker containg 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.
- Filter the mixture to get the froth and big, insoluble bits of cell out.
- Gently add some ice-cold alcohol to the filtered mixture.
- The DNA will start to come out of solution as it is not soluble in cold alcohol. It will appear as a stringy white precipitate that can be carefully fished out with a glass rod.
What do
DNA do?
control the production of proteins in a cell
this process is called protein synthesis
Define
gene.
a section of DNA that codes for a particular protein
What are
proteins made of?
chains of molecules called amino acids
Define
base triplet.
the sequence of three bases that code for each amino acid in the gene
What is a
non-coding region of DNA?
a region of DNA that doesn’t code for any amino acids
Define
mutation.
a rare, random change to an organism’s DNA base sequence that can be inherited
Where are
proteins made?
in the cell cytoplasm by subcellular structures called ribosomes
What is
messenger RNA (mRNA)?
and how is this different to DNA?
a polymer of nucleotides
it is shorter than DNA and only a single strand
it also uses uracil (U) instead of thymine (T) as a base
What is
RNA polymerase?
the enzyme involved in joining together RNA nucleotides to make mRNA
Why is
transcription necessary for making proteins?
DNA found in the cell nucleus can’t move out of it because it is really big, however, the cell still needs to get the information from the DNA to the ribosome in the cytoplasm.
What are the
two stages of protein synthesis?
- Transcription
- Translation
Describe the process of
transcription.
(4 steps)
- RNA polymerase binds to a region of non-coding DNA in front of a gene.
- The two DNA strands unzip and the RNA polymerase moves along one of the strands of the DNA.
- It uses the coding DNA in the gene as a template to make the mRNA. (Base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene.)
- Once made, the mRNA molecule moves out of the nucleus and joins with a ribosome.
What is a
codon?
a base triplet of mRNA
What is an
anticodon?
the complementary tRNA to the codon
Describe the process of
translation.
(4 steps)
- Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA).
- The tRNA anticodons bind to their complementary codons, making sure that the amino acids are brought to the ribosome in the correct order.
- The amino acids are joined together by the ribosome to make a polypeptide (protein).
- The amino acid chains fold up to give each protein a different, specific shape.
How can a
mutation in the non-coding region of DNA affect the production of the protein?
(3 points)
- Before any transcription can happen, RNA polymerase has to bind to a region of non-coding DNA in front of a gene.
- If a mutation happens in this region of DNA, then it could affect the ability of the polymerase to bind to it. This might make it easier to bind to, or more difficult.
- How well RNA polymerase binds to this region of DNA will affect how much mRNA is transcribed - therefore how much protein is produced
What were the
three important conclusions about heredity in plants that Gregor Mendel came to?
- 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 recesive.
Why wasn’t the
importance of Mendel’s work recognised straight away?
At the time, scientists didn’t have the background knowledge to properly understand Mendel’s findings - they didn’t know about genes, DNA or chromosones.
Define
allele.
a different version of the same gene
When is an organism
homozygous?
(for a trait)
when it has two alleles for a particular gene that are the same
When is an organism
heterozygous?
(for a trait)
when it has two different alleles for a particular gene that are different
Define
genotype.
the combination of alleles you have
Define
phenotype.
the characteristics you have
(based on your genotype)
How many
chromosone pairs does each human body cell have?
23
matched pairs
What human chromosone determines
gender?
the 23rd pair
these are labelled XX or XY
Y chromosone causes male characteristics
the XX combination allows for female characteristics to develop
Define
sex-linked genetic disorder.
a disorder causes by a faulty allele located on sex chromosones
Why are
men more likely to have sex-linked genetic disorders?
(3 steps)
- The Y chromosone is smaller than the X chromosone and carries fewer genes. So, most genes on the sex chromosones are only carried on the X chromosone.
- Males only have one X chromosone, so only have one allele for sex-linked genes.
- This means that the characteristic of this allele is shown, even if it is recessive.
What are
codominant alleles?
alleles where one isn’t dominant over the other one
Describe how
alleles determine blood group.
(4 steps)
- Humans have four potential blood types - O, A, B and AB.
- The gene for blood type in humans has three different alleles - IO, IA, IB.
- IA and IB are codominant with eachother, so an individual with genotype IAIB will have the blood type AB.
- IO is recessive so you only get blood type O when you have two of the recessive alleles.
How is there
genetic variation within a species?
(2 ways)
- new alleles arising through mutations
- sexual reproduction resulting in alleles being combined in lots of different ways in offspring
What are the
environmental variations in a phenotype?
the characteristics that organisms acquire during their lifetimes
(their acquired characteristics)
What are
neutral mutations?
mutations that don’t have any effect on the phenotype of an organism
What are some general
medical applications of the genome project’s research?
(3)
- prediction and prevention of diseases
- testing and treatment for inherited disorders
- new and better medicines
How can the
genome project’s research predict and prevent diseases?
(3 points)
- Many common diseases are caused by the interaction of different genes (as well as lifestyle factors)
- If doctors knew what genes redisposed people to what diseases, we could all get individually tailored advice on the best diet and lifestyle to avoid our likely problems
- Doctors could also check us regularly to ensure early treatment if we do develop the diseases we’re susceptible to
How can the
genome project’s research test and treat for inherited disorders?
(3 points)
- inherited disorders are caused by the presence of one or more faulty genes 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 such an allele has been identified, people can be tested for it
this may make it possible to develop better treatments or even develop a cure for the disease
How can the
genome project’s research help to create new and better medicines?
(4 points)
- the research has highlighted some common genetic variations between people - some variations affect how our individual bodies will react to certain diseases and to the possible treatments for them
- this knowledge can be used to design new drugs that are specifcally tailored to people with a particular genetic variation
- the knowledge can also determine how well an existing drug will work for an individual
- also, 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 some
drawbacks of the medical applications of the genome project?
(3 points, briefly explained)
- Increased stress - if someone knew that they’re susceptible to a certain disease, they may panic every time they get a symptom (even if they never get the disease).
- Gene-ism - people with genetic problems could come under pressure to not have children.
- Discrimination - life insurance could be harder and more expensive to get if you have any genetic likelihood of serious disease. Also, employers may discriminate against people who are genetically likely to get a disease.
