what is a chromosome
a chromosome is a long DNA molecule with part of the genetic material of an organism
where in a cell are chromosomes located?
the nucleus
how many chromosomes are there in a typical human cell?
43
26 pairs
what is the structure of DNA
DNA is a polymer made up of two strands wrapped around each other to form a double helix
what are sex chromosomes?
the 23rd pair of chromosomes
they determine whether an individual is a male or female
what sex chromosomes do females have?
xx
what sex chromosomes do males have?
xy
what is a gene?
a small section of DNA on a chromosome
each gene codes for a particular sequence of amino acids, to make a specific protein
what is the genome of an organism?
the entire genetic material of an organism
how does understanding the whole human genome help science?
it could help us understand and treat inherited disorders
it could be used in tracing human migration patterns from the past
it will allow scientists to search for genes linked to different diseases
what is an allele?
different versions of a particular gene
how many alleles of each gene does an individual have?
2
what does it mean to be homozygous for a particular gene
both alleles of that gene are identical
what does it mean to be heterozygous for a particular gene?
the two alleles of that gene are different
what is a dominant allele?
the one which is always expressed, even if there is one copy of that allele
what is a recessive allele?
the one which is only expressed if there are two copies of it
what does ‘genotype’ mean?
there are two definitions
an individual’s collection of genes
the two alleles present for a particular gene
in either case, the term genotype refers to the specific genes or alleles that an individual has
what does phenotype mean?
the characteristic an organism has as a result of their genotype (and environment)
how are most characteristics determined?
most characteristics are determined by the combination of multiple genes and the environment
what is sexual reproduction
a mode of reproduction in which new offspring are produced by the fusion of male and female gametes
during sexual reproduction in animals, which two gametes fuse together?
sperm cell and egg cell
during sexual reproduction in plants, which two gametes fuse together?
pollen and egg cell
does sexual reproduction lead to genetically identified offspring or genetically unique offspring?
genetically unique offspring
is a sperm cell haploid or diploid?
haploid because it only half the number of chromosomes = 23
what is fertilisation?
the fusion of male and female gametes
what is asexual reproduction?
a type of reproduction where new offspring are produced by a single parent
does asexual reproduction lead to genetically identified offspring or genetically unique offspring?
genetically identical offspring
what is the most common way of reproduction for
animals
fungi
plants
bacteria
sexual
asexual
most
asexual
what do we call the process by which bacteria reproduce asexually?
binary fission
does asexual reproduction in plants use mitosis or meiosis?
mitosis
what is a gamete and how many chromosomes do they have?
a sex cell
23
where does meiosis take place?
in the sex organs
the testes in males
the ovaries in females
how many cells does meiosis produce and are they genetically identical or unique?
4
genetically unique
when writing genotypes, such as AA, what does the upper-case letter mean?
it means that that allele is dominant
when writing genotypes, such as Aa, what does the lower-case letter mean?
it means that that allele is recessive
what does it mean for an individual to be homozygous dominant or recessive for a gene?
dominant → 2 dominant alleles for that gene e.g. AA HH
recessive → 2 recessive alleles for that gene e.g. aa hh
what is a family tree?
a diagram representing family relationships across multiple generations
also called a pedigree chart
wat is an inherited disease?
a condition that can be passed on genetically through the inheritance of certain alleles
what is cystic fibrosis?
an inherited disorder of cell membranes
it is a recessive condition
it causes sticky mucus to build up in the lungs and the digestive system
what does it mean for an individual to be a carrier of cystic fibrosis?
they are heterozygous and only have one cystic fibrosis allele
this means they can pass it onto their offspring, but do not have the condition themselves
what is polydactyly?
an inherited disorder in which an individual can be born w extra fingers or toes
it is a dominant condition
what is IVF?
the process by which eggs are fertilised by sperm outside the body
the embryos are then grown in a lab until they are ready to be implanted into the mother’s womb
what is embryo screening?
the process of taking a cell from an embryo and analysing its DNA for genetic abnormalities
it’s normally done during the IVF process, before the embryo is implanted into the mother’s womb
how is embryonic screening carried out?
DNA is isolated from the embryo
probe is mixed with the DNA
probe binds with DNA
UV light shows the alleles for disorders
give 2 advantages of embryo screening
reduces suffering by stopping children from being born with genetic disorders
it can save the country a lot of money as treatment for inherited disorders is very expensive
this is not an advantage but there are laws in place to stop embryo screening from being abused
give 3 disadvantages of embryo screening
screening against inherited disorders may imply that people with such disorders are undesirable - which is not fair or true
embryo screening is very expensive process and therefore is not available to all potential parents
it could be a ‘slippery slope’ - people may begin screening for less and less harmful conditions, until they start screening for things like height, gender, eye colour etc.
what is variation?
the differences in the characteristics of individuals within a population
which two factors contribute to the variation between organisms?
the genes each individual inherits
the environments each individual is exposed to
what is natural selection?
the idea that in each generation, the individuals with the most favourable characteristics are most likely to survive and reproduce, therefore passing on their genes
it is the idea that ‘nature’ is ‘selecting’ the fittest individuals
what is evolution?
the process by which the inherited characteristics of a population change over time due to natural selection
in some cases, this may result in the formation of a new species
what does survival of the fittest mean?
the individuals with the most favourable characteristics are most likely to survive
what is speciation?
the evolutionary process by which populations evolve to become distinct species
what is selective breeding?
also known as artificial selection
is the process by which humans use animal or plant breeding to selectively develop characteristics by choosing which males and females will sexually reproduce and have offspring together
describe how the process of selective breeding could be used to increase the yield of tomato plants
select the two tomato plants with the highest yield from the population
breed them together
once the plants have grown and produced tomatoes, repeat the process by breeding together the ones with the highest yield
keep repeating this over multiple generations, and the average yield will increase
give examples of traits that might be selectively bred for in plants or animals
plants:
colour of flowers
drought resistance
improved yield of fruits/grains and vegetables
animals:
improved yield of meat or milk
desirable size, fur colour, level of aggression
what effect does selective breeding usually have on variation within a population?
it decreases it
what is inbreeding?
the process of mating together closely related individuals
give 3 drawbacks of inbreeding
reduces the size of the gene pool
rare inherited diseases are more likely to be expressed
the population as a whole will be more at risk of disease
what is genetic engineering/modification?
the process of modifying the genome of an organism by introducing a gene from another organism, in order to give a desired characteristic
what do we call crops that have been genetically engineered?
GM crops
how has genetic engineering played a role in the treatment of diabetes
bacterial cells have been genetically engineered to produce human insulin to treat diabetes
give 3 traits that could be altered by genetic engineering in crops?
increased yield
increased quality
resistance to disease
resistance to insects
resistance to herbicides
resistance to droughts
give 2 drawbacks of genetic engineering
if the crops breed with wild plants, they could spread the new genes into the wild and affect the wild population’s gene pool
there is a small risk that genetically modified food could negatively affect our health
describe the steps of genetic engineering (GM)
isolate the desired gene from human DNA
insert the DNA into a vector, such as a plasmid
insert the plasmid into a host bacterium
let the bacterium divide and then produce the desired protein
what is gene therapy?
the treatment of an inherited disorder by giving the patient a healthy copy of the faulty gene
what is a fossil?
fossils are the remains of organisms from millions and billions of years ago, which are found in rocks
why are fossils used as evidence for evolution?
they show how species have changed over millions of years
why are there not many fossils from the earlier organisms on earth?
early organisms were soft-bodied, so they did not fossilise well
geological activity has destroyed most fossils that formed so long ago
what are the 3 ways fossils formed?
hard body parts, such as bones and shells, which decay very slowly, are gradually replaced by minerals, forming rock-like substances
animals can leave impressions or casts, such as footprints or burrows, these became covered by layers of sediment, which eventually become rock
some parts of organisms may not decay at all, e.g. dead animals and plants could be preserved in amber, peat bogs, tar pits or ice
what does extinction mean?
when there are no remaining individuals of a species still alive
give ways a species could go extinct
rapid environmental change such as an increase in temperature
reduction in habitat, as it could reduce food and living space
high levels of hunting as individuals are directly killed
the spread of a new disease
competition
catastrophic events
what is antibiotic resistance?
the ability of bacteria to survive exposure to antibiotics
how does antibiotic resistance arise?
a population of bacteria infect somebody, and that person takes antibiotics to kill bacteria
some bacteria have a random mutation that makes them less susceptible to the antibiotic than others (or completely resistant)
the antibiotics kill all the bacteria except those that are resistant
the resistant strains of bacteria survive and now have more resources to grow and multiple
more mutations may arise, leading to greater resistance → there is now a strain of bacteria that can’t be killed by antibiotics, which we call ‘antibiotic-resistant bacteria’
give 3 reasons for the recent rise and spread of antibiotic resistance
some doctors prescribe antibiotics inappropriately, such as for non-serious or viral infections
some patients don’t complete their course of antibiotics so some bacteria survive, mutate, and develop antibiotic resistance
the agriculture industry give huge amounts of antibiotics to farm animals to help them grow more quickly
why is the spread of antibiotic resistance a problem?
if more bacteria are resistant to antibiotics, we won’t be able to treat those infections
this means more people will die of bacterial infections
who was Carl Linnaeus?
18th-century scientist who came up with the binomial system for naming organisms and the Linnean classification system for classifying living organisms
what is the binomial naming system?
every species has a binomial name, which is made up of two parts: the genus name and the species name
e.g. ^^Homo ^^sapiens
rules:
both names should be written in italics
all letters should be lowercase except for the first letter of the genus name
give 3 advantages of using a binomial naming system?
each species has a unique name → avoids confusion
allows scientists from all over the world to discuss species
shows how closely related organisms are because closely related organisms often have the same genus name
what is the Linnaeus classification system?
kingdom
phylum
class
order
family
genus
species
who was Carl Woese?
20th-century scientist who used microscopes and modern technology to develop the three-domain system to classify organisms
what are the three domains?
Archaea
Bacteria
Eukaryota → animals, plants, fungi, protists