genetics Flashcards
meiosis
a type of cell division that produces 4 haploid genetically non-identical gametes/daughter cells
describe the process of meiosis
- chromosomes duplicate so that there is enough for each new cell
- FIRST DIVISION:
- similar chromosomes pair up
- one chromosome in each pair comes from the father and one from the mother
- pairs are pulled apart so each new cell has a copy of one chromosome (a mixture of the mother’s and father’s) - this is important for GENETIC VARIATION
- there are now two cells
- SECOND DIVISION:
- chromosomes line up in the centre of the cells and arms are pulled apart
- each cell divides into two to form 4 genetically non identical daughter cells
sexual reproduction
where genetic information from two organisms is combined to produce offspring which are genetically different from either parent
gamete
haploid sex cells
fertilisation
when a male gamete haploid cell fuses with a female gamete haploid cell to produce a fertilised egg cell/diploid zygote
what happens after fertilisation
the zygote uses mitosis to develop into an embryo
the embryo has characteristics from both parents as it has received a mixture of chromosomes from both mother and father
asexual reproduction
a type of reproduction not involving fertilisation but by mitosis
what are two advantages of sexual reproduction
+ created genetic variation within a population so individuals are more likely to be able to adapt and survive if the environment changes
+ genetic variation can lead to natural selection and evolution so a species becomes better adapted to its environment
what are two disadvantages of sexual reproduction
- two parents are needed which can be a problem if individuals are isolated
- takes more time and energy so fewer offspring are produced in a lifetime
what are two advantages of asexual reproduction
+ can produce lots of offspring quickly so organisms can colonise an area very quickly
+ only one parent is needed so organisms can reproduce when conditions are favourable without having to wait for a mate
what is one disadvantage of asexual reproduction
there is no genetic variation so if an environment changes unfavourably, the whole population may suffer
dna structure
a polymer made of lots of repeating nucleotides forming two strands coiled together in a double helix held together by weak hydrogen bonds
the backbone of a dna strand is made form alternating sugar and phosphate molecules
nucleotide
an organic molecules consisting of one sugar molecule, one phosphate molecule and one base
what are the base pairs
adenine and thymine
cytosine and guanine
chromosomes
long coiled up molecules of DNA
gene
a section of DNA that codes for a particular protein
how would you extract dna from a fruit
1) mash fruit and place in a beaker containing detergent and salt - mix well
- detergent breaks down cell membranes
- salt makes dna stick together
2) filter mixture to remove froth and insoluble parts
3) add ice cold ethanol to mixture
4) a stringy white precipitate will start to form as dna is insoluble in cold ethanol, collect with a glass rod
what is the role of dna in protein synthesis
controls protein synthesis in a cell
- a section of dna coding for a particular protein is a gene
the order of bases controls the order of amino acids
each amino acids is coded for by 3 bases (triplet) which are joined together to form the protein
protein
a chain of amino acids
each protein has its own number and order of this
what are the two stages of protein synthesis
transcription
THEN
translation
what happens in transcription (4)
1) RNA polymerase binds to a region of non-coding DNA in front of a gene
2) 2 dna strands unzip and RNA polymerase moves along one of the strips of DNA
3) the coding DNA is used to make a template to make the mRNA (base pairing ensures the mRNA is complementary)
4) once ready, the mRNA leaves the nucleus through the nuclear membrane and joins with a ribosome
what happens in translation (5)
1) amino acids are brought to the ribosome by tRNA (transfer RNA)
2) the order in which amino acids are brought to the ribosome matches the order of codons in mRNA
3) the tRNA has an anticodon which is complementary to the codon for the amino acid, this pairing makes such amino acids are in the right order
4) amino acids are connected to the ribosome to form the polypeptide/protein
5) the protein folds up to its unique shape
mutation
a rare, random change to an organism’s DNA base sequence that can be inherited
effects of a mutation on coding DNA
affects phenotype by altering the amino acid sequence which may change the shape of the final protein and therefore affect its activity (increasing, decreasing or stopping altogether)
effects of a mutation on noncoding DNA
affects phenotype by altering the amino acid sequence influencing binding of RNA polymerase and altering quantity of protein produced
allele
a different version of a gene
we have two alleles for each gene (one on each chromosome)
homozygous
when an organism has two alleles for a particular gene that are the same
heterozygous
when an organism has differing alleles for a gene
genotype
the combination of alleles you have
phenotype
the physical characteristics of an organism
monohybrid inheritance
the inheritance of a characteristic controlled by a single gene
family pedigree
a family tree of genetic disorders
sex linked genetic disorder
disorder caused by faulty alleles located on sex chromosomes
why are men more likely to have sex linked recessive disorders
the y chromosome is smaller
men only have one of the bigger X chromosomes
so they often only have one allele for a certain characteristic making them more likely to exhibit sex-linked recessive characteristics
codominant
when together, one allele isn’t dominant over the other
blood type allele I^A and I^B are what
codominant
why is colour blindness more common in men
colour blindness is a sex linked disorder, caused by a faulty allele on the X chromosome
women need two copies of the recessive allele to be colour blind whereas men only need one copy
what did mendel observe
he observed patterns of inheritance
- finding that certain traits were dominant over other
what were mendel’s conclusions
characteristics in plants are determines by ‘hereditary units’
these units are passed on unchanged, one from each parents
the units can be dominant or recessive
if an individual inherits both then the dominant trait will be expressed
variation
differences within a species
environmental variation
variation caused by the conditions in which organisms live
environmental variations in phenotype are ACQUIRED CHARACTERISTICS
genetic variation
variation in features as a result of mutation or sexual reproduction
sexual reproduction causes genetic variation as alleles are being combined in lots of different ways
most variation in phenotype is due to….
a mixture of genetic and environmental factors
background on the human genome project
started in 1990, finished 2003
20500 genes and their locations mapped
now scientists are trying to find out what every gene does - so far 1800 genes have be identified as disease-related
what are 3 medical applications of the human genome project
prediction + prevention of diseases
testing and treatment for inherited diseases
new and better medicines
how can the hgp be used in terms of prediction and prevention of diseases
lots of common diseases are caused by the interaction of certain genes
if a doctor knows what genes make us susceptible to certain diseases, we could all have tailored advice for how to avoid our likely problems
we could have regular check-ups to receive early treatment if we do develop the disease
how could the hgp be used in terms of testing and treatment for inherited diseases
inherited diseases are caused by the presence of one or more faulty genes in a genome
we can easily identify these genes now, and once identified people can be tested for a disease and better treatments/cures developed
how could the hgp be used in terms of new and better medicines
some genetic variations affect how our individual bodies will react to particular diseases and treatments
with this knowledge we can design personalised drugs to treat people with specific genetic variations
tests help us to identify if a cancer patient will respond to a drug or what dosage will be best for them
what are 3 potential drawbacks of the hgp
- increased stress if aware of future illness
- people with genetic problems feel pressure to not have children
- discrimination from employers/ insurers if aware of illness
