New B5 Flashcards
Give definitions for:
-gamete
-chromosome
-gene
-allele/variant
-dominant allele
-recessive allele
-homozygous
-heterozygous
-genotype
-phenotype
-gamete: an organism’s reproductive cell (egg/sperm), which has half the number of chromosomes (23)
-chromosome: a structure found in the nucleus which is made up of a long strand of DNA
-gene: a short section of DNA that codes for a protein, and therefore contribute to a characteristic
-allele/variant: the different forms of a gene - humans have 2 alleles for each gene as they inherit one from each parent
-dominant allele: only 1 of the 2 alleles is needed for it to be expressed and for the corresponding phenotype to be observed
-recessive allele: 2 copies are needed for it to be expressed and for the corresponding phenotype to be observed
-homozygous: when both inherited alleles are the same (2 dominant or 2 recessive)
-heterozygous: when one of the inherited alleles is dominant and the other is recessive
-genotype: the combination of alleles an individual has
-phenotype: the physical characteristics that are observed in an individual
Describe the genome and how it contributes to genetic variation
-the genome is the entire genetic material of an organism
-its genetic material and its interaction with the environment influences the development of an organism’s phenotype
-this can be with continuous variation (e.g. height) or discontinuous variation (e.g. eye colour)
-all alleles are caused by a mutation, which normally has no effect on the phenotype, as most DNA is non-coding and therefore doesn’t cause a change in proteins
-however, some may have a small influence on phenotype and very few can completely change phenotype if they are in coding regions
Describe how genetic variants may influence phenotype in coding DNA and non-coding DNA
-if the mutation occurs in a coding region of DNA, then it can alter the activity of the protein that the altered area of DNA is meant to code for
-this can occur by changing the protein structure, such as the shape of active site of enzymes, so substrates no longer fit into them
-if the mutation is in a non-coding region of DNA, it can still affect how genes are expressed by stopping transcription of mRNA in the protein synthesis process
Explain some advantages and disadvantages of asexual and sexual reproduction in a range of organisms
Advantages of sexual reproduction:
-produces variation in offspring, so even when there is an environmental change, it is likely that an organism in the species will have a characteristic that will help them survive (called a survival advantage).
-a disease is less likely to affect all the individuals of a species if there is variation
-allows us to use selective breeding
Disadvantages of sexual reproduction:
-requires 2 parents, so may take a while to find a mate
-fewer offspring produced, as reproduction is slower
Advantages of asexual reproduction:
-only one parent is needed, so organisms don’t need to find a mate which means it’s a quicker process
-population can increase rapidly, as lots of identical offspring can be produced
Disadvantages of asexual reproduction:
-harsh changes to environment may lead to extinction of the species, as there is no variation between individuals
-species may only be suited to one habitat, as there is no variation
Compare the terms haploid and diploid
Diploid cells are body cells, whereas haploid cells are germ cells
Diploid cells have a full set of chromosomes, whereas haploid cells only have half this amount
Explain the role of meiotic cell division in halving the chromosome number to form gametes
This maintains diploid cells when gametes combine, and acts as a source of genetic variation
Explain single gene inheritance
Refers to the inheritance of traits that are controlled by one gene pair (one from the father and one from the mother)
Explain the process of meiosis
-4 non-identical cells form from one cell
-cells in reproductive organs divide by meiosis to form gametes, which only have one copy of each chromosome
Stage 1:
-chromosomes are copied
-chromosomes line up along the middle of the cell in pairs (one from each parent)
-one member of each pair is pulled to opposite ends of the cell
-often when they are pulled apart, sections of DNA are swapped
-the cell divides in two, so two separate cells are formed
Stage 2:
-chromosomes line up along the middle of each of the 2 new cells
-this time each chromosome is pulled in half
-a single copy of each chromosome goes to opposite ends of the cell
-each cell then divides into 2, resulting in 4 haploid cells
Describe the development of our understanding of genetics (i.e. the work of Mendel)
-Gregor Mendel worked in the monastery gardens and observed the characteristics passed on between generations of plants
-he carried out experiments on pea plants using smooth, wrinkled, green and yellow peas and observed which characteristics had been inherited by offspring
-he concluded that:
-offspring have some characteristics that their parents have because they inherit hereditary units from each
-one unit is received from each parent
-units can be dominant or recessive, and cannot be mixed together
-his work was only realised posthumously and helped people realise later on chromosomes and genes behaved similarly
describe the impact of developments in biology on classification systems
Artificial classification:
-classification is based purely on observations and human judgement
-system created by Carl Linnaeus, based on artificial classification. Living things were divided into kingdoms, phylum, class, order, family, genus, species.
Natural classification:
-where molecular techniques are used to see similarities between species, such as DNA sequencing to compare protein structures
-phylogenetics: the study of how closely related two organisms are, allowing us to see where species originated from
-current classification system has been developed based on some key advances in biology, including:
-DNA evidence
-improvements in microscopes
-studies of biochemistry
-Carl Woese added three large groups called domains above kingdoms by using molecular techniques:
○ Archaea: primitive bacteria which live in extreme environments such as hot springs
○ Bacteria: true bacteria (despite having similar features to archaea)
○ Eukaryota: organisms who have a nucleus enclosed in membranes, includes the kingdoms protists, fungi, plants and animals
-the binomial system gives each organism a name which is used worldwide (overcomes language barriers). The first part is their genus and the second part is their species.
What is evolution
A change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
explain how evolution occurs through the natural selection of variants that have given rise to phenotypes best suited to their environment
-within a population, there is usually large amounts of genetic variation between individuals of the species, as small mutations occur which provide variation between organisms
-if a mutation provides a survival advantage, the organism is more likely to survive to breeding age
-the mutation will then be passed onto offspring
-over many generations, the frequency of the mutation will increase within the population
What is speciation
As evolution continues to occur through the appearance of random mutations, a species’ population may become so different to that they can no longer interbreed to produce fertile offspring
This means they have become a new species
Describe the evidence for evolution
Fossils
The remains of organisms from many years ago, which are found in rocks. They are formed by:
1. Parts of organisms that have not decayed because oxygen or moisture were not present,
meaning that the microbes that cause decay cannot survive.
2. Parts of the organism such as teeth, shells and bones are replaced by minerals as they decay,
forming a rock structure of the original part.
3. Preserved traces such as footprints, burrows and rootlet traces (the plants roots) remain due to
the ground hardening around them and forming a cast.
Fossils are used to show how the anatomy of organisms has changed over time. They can be used to compare how closely related two organisms are, through looking at the number of similarities they have. This information is used to create evolutionary trees
Antibiotic resistance in bacteria
Bacteria are organisms that reproduce at a very fast rate and therefore advantageous genes, such as those for antibiotic resistance, can become prominent within a population very quickly.
Exposure to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive and those without die. As a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring and so the population of antibiotic resistant bacteria increases.
An example is the MRSA ‘superbug’ that is resistant to many different types of antibiotics. It is found in hospitals as it spreads when doctors and nurses move between different patients
Describe the work of Darwin and Wallace in the development of the theory of evolution by natural selection
Explain the impact of these ideas on modern biology
Darwin
Darwin’s work was published in his book ‘On the Origin of Species’:
● Variation exists within species as a result of mutations in DNA
● Organisms with characteristics most suited to the environment are more likely to survive to
reproductive age and breed successfully – called survival of the fittest. www.pmt.education
● The beneficial characteristics are then passed on to the next generation
● Over many generations the frequency of alleles for this advantageous characteristic increase
within the population
There was lots of controversy surrounding his ideas for many reasons:
1. It contradicted the idea that God was the creator of all species on Earth.
2. There was not enough evidence at the time as few studies had been done on how organisms
change over time.
3. The mechanism of inheritance and variation were not known at the time
Wallace
Wallace worked alongside Darwin to help prove evolution, but his work focused more on the theory of speciation.
The process of speciation:
1. Variation exists within a population as a result of genetic mutations.
2. Alleles which provide a survival advantage are selected for through natural selection.
3. Populations of a species can become isolated, for example through physical barriers such as a
rock fall preventing them from breeding together.
4. Different alleles may be advantageous in the new environment, leading to them being selected
for.
5. Over time the selection of different alleles will increase the genetic variation between the two
populations.
6. When they are no longer able to breed together to produce fertile offspring, a new species has
formed.
