Flashcards in 2. Blueprint of Life Deck (59):
Outline the two major conclusions Charles Darwin made in his book "On the Origin of Species by Natural Selection"
1. Species were not created in their present form, but have evolved from a natural ancestor
2. Natural selection is the mechanism for evolution
Define: Evolutionary adaptations
Inherited characteristics when enhance an organism's ability to survive to maturity, find a mate, produce fertile offspring in an environment
Recite the explanation of evolution by means of natural selection
The theory of evolution by means of natural selection relies on natural variation in a species and some of those organisms having favourable traits that better suit them to their environment, to that they are more likely to survive to maturity, find a mate, successfully reproduce to pass on those favourable traits to their fertile offspring, over thousands of generations. It thus depends in variation, inheritability and over-reproduction
Explain the impact of changes in the physical conditions of the environment on an organism, using examples
Peppered moth: some moths were naturally light coloured, whilst others were darker. As the Industrial Revolution occurred, the tree trunks became darker and thus natural selection favoured the darker coloured moths as they were better able to camouflage and avoid predators.
Explain the impact of changes in the chemical environment on an organism, using examples
Mosquitoes: to decrease the spread of malaria, mosquitoes were killed using DDT. However, due to natural variation, some mosquitoes were naturally resistant to DDT and were thus able to survive to maturity, find a mate, and produce fertile offspring to pass on favourable trait.
Explain the impact of competition on organisms
Introduced species create competition for organisms. The introduction of dingoes, feral cats and foxes disturbed the food chain as they did not have a natural apex predator. Organisms that were thus able to change their diet were favoured by natural selection
Identify the three major sections of evidence that Darwin used to support his theory of evolution
Fossil Records, behaviour of living animals and geographical distribution of similar organisms. Due to the technology in his period, genetic studies were not available
Describe the nature of fossil evidence in relation to supporting the theory of evolution and its limitations
When living organisms are compared with fossils from the record, a history of change can be observed, which is used to suggest a common ancestral relationship. Transitional forms are considered the 'missing link' between species. The Archaeopteryx is a small dinosaur which had both reptilian features and bird features.
Limitations: fossil record is incomplete and favours organisms that are easily fossilised, unequal representation of organisms, limitations of radiocarbon dating.
Describe the nature of comparative embryology in relation to supporting the theory of evolution
The study of similarities between embryos of different vertebrates. As these vertebrates begin their development with 'gill slits', they are used to suggest a common aquatic ancestor. As organisms have evolved to better suit their environment, the gill slits developed into other organs
Describe the nature of comparative anatomy in relation to supporting the theory of evolution
Compares similar structures (homologous structures) in vertebrate organisms. These homologous structures are used as evidence to suggest a common ancestral relationship. A common structure studied is the pentadactyl limb (forearm). The structure differences are a result of the specific functioning of the organism.
Describe the nature of biogeography in relation to supporting the theory of evolution
Biogeography is the study of the geographical distribution of organisms. Due to the movement of tectonic plates, organisms can become isolated in a specific region. As they evolve to better suit their environment over thousands of generations, they become unable to successfully reproduce with there initial species (speciation). Darwin noticed the unique flora and fauna on each continent and concluded that they must have a common ancestral relationship. Eg: ratite birds
Describe the nature of biochemistry in relation to supporting the theory of evolution
A comparison of organisms at a molecular level. Amino-acid sequencing is used to compare the structure and composition of amino acids in different organisms. 'Cytochrome-C' is present in all respiring organisms. Similarities indicate that the organisms have evolved from a common ancestor.
Define: Divergent evolution and provide examples
Divergent evolution refers to system of evolution in which organisms becoming different in their form to common ancestors, as a result of speciation. Adaptive radiation is a mechanism which contributes to divergent evolution as organisms migrate ('radiate') and thus evolve to better suit their environment. Eg: Darwin's finches
Define: Convergent evolution
Organisms from distantly related ancestors come to resemble each other doe to similar environmental pressures
Describe an experiment conducted to model natural selection
Different coloured cards resembling variation in a species were used. A spinner was used to determine the organisms that became prey. Whilst this successfully modelled evolution by means of natural selection, it was oversimplified and so not all selective pressures were included. Assumptions were made regarding mating partners, population side and offspring
Describe a case study which explores who environmental changes lead to changes in a species
The environmental mosquitoes lived in changes due to the presence of DDT. Due to natural variation, some organisms were naturally resistant to DDT. As a result, they were more likely to survive to maturity, find a mate, successfully reproduce and pass on their favourable traits to fertile offspring. This meant that over thousands of generations. Most mosquitoes were naturally resistant to DDT.
Explain how advances in biochemical technology has changed scientific understandings of evolutionary relationships
Initially, it was believed that humans existed in their own classification (Homindae family) and that chimpanzees were in a seperate family (Pongidae family). However, due to the study of amino-acid sequencing (cytochrome-C), it was discovered that humans and chimps have the same sequencing and are thus more closely related. This mean that the chimpanzees are now also classified under the phylogenetic branch, Homindae
Outline the historical development of theories of evolution
1700s: natural theology
Curvier: nomenclature naming system. Implied no evolutionary relationships and hypothesised catastrophism
Hutton: hypothesised gradualism
Lamarck: first introduced the idea of evolution through suggesting that the parts of the body used extensively grow larger and stronger, whilst used parts become weaker and smaller. These changes are passed to offspring. Experimented by cutting the tails of mice and examining offspring.
Outline the experiments conducted by Gregor Mendel
He considered the inheritance of particular characteristics (traits) and discovered the basic principles of hereditary by breeding garden peas in carefully controlled experiments. He showed that inherited characteristics are passed as discrete 'units' from parents to offspring, allowing him to detect patterns in inheritance and predict ratios using mathematical formulae. He studied the inheritance of each monohybrid-cross individually.
Identify some the the characteristics that Mendel studied
Colour of seed contents
Shape of seed
Colour of flower
Colour of unripe pod
Outline some of the experimental techniques Mendel used which makes his experiments successful
1. He forced plants to cross-pollinate by removing immature stamens and hand-painting polled onto stigma. Covered plants with a bag
2. He started his experiments with pure-breeding plants
3. Used large sample sizes and kept accurate results
4. Used mathematical analysis (quantitative data)
5. Made justified conclusions about the Law of Segregation and Law of Independent Assortment
Describe Mendel's results from his experiments
From his experiments, he found that the F2 generation consistently had a 3:1 ratio of dominant to recessive factors expressed.
Describe the four conclusions that Mendel came to
1. Alternative versions of genes account for variation in inherited characteristics
2. For each character, an organism inherits two alleles, one from each parent
3. If two alleles differ, the dominant allele is always expressed
4. Two alleles for each character segregates during gamete production (Law of Segregation). Law of Independent Assortment refers to the idea that the segregation of alleles is completely random and is independent of other genes.
an organism's 'genetic makeup', comprises of an organism's two alleles. Whilst genotypes can be different, phenotypes can be the same
An organism having two identical alleles for a gene
An organism have two different alleles for a gene
Identify the two different types go genotypes an organism can have in a monohybrid cross
Heterozygous or homozygous
Define: allele, using examples
an alternative form of gene. Whilst there can be more than 2 alleles for a specific gene, an organism can only have two (eg. wrinkled seed and round seed are two alleles for he seed shape gene)
Define: gene, using examples
a discrete unit of hereditary information, consisting of a specific section (locus) of DNA. Each gene has two copies (alleles)
Define: Dominant allele
an allele that is always fully expressed
Define: Recessive allele
an allele that is completely masked by a dominant allele as is only expressed in the phenotype when in a homozygous pair
Identify some of the reasons why Mendel's work was not considered initially
Mendel presented his findings to scientists in 1865 and published a paper in 1866. His findings were not accepted as they were:
- radical and progressive
- only a small group of scientists heard him
- mathematical calculations were advanced
- he had no reputation and was shy
Describe the current use of pedigree trees in science
Pedigree trees are used to trace the inheritance of a gene within a family. They are currently used to trace genetic diseases/disorders to predict the likelihood of potential offspring inheriting the disorder.
Describe the process of hybridisation and give an example
hybridisation is the process in which two organisms from different breed/varieties, are cross-bred to produce an offspring with more favourable characteristics (hybrid vigour). Labradoodles are a cross-breed of labradors and poodle, with the aim of producing offspring that do not shed and have a tolerant temperament. Whilst hybridisation is able to produce hybrid vigour, offspring are often sterile so the process has to be repeated.
Describe the work of Theodor Boveri and the conclusions he made
He worked with sea urchin eggs, fertilising some with and some without a nucleus. He found that the normal eggs hatched into larvae with characteristics from both parents and the egg without the nucleus only had the characteristics from the sperm and has only half the number of chromosomes.
He thus concluded that a complete set of chromosomes is needed for normal development and that the inheritance of gene are found on chromosomes - they are the carrier of hereditary.
Describe the work of Walter Sutton and the conclusions he made
He studied the formation of sperm cells in grasshoppers. His observations revealed that chromosomes occurred in homologous pairs in diploid cells, during reduction division this number is halved (one chromosome in a homologous pair) and that fertilisation restores the diploid number.
He thus concluded that alleles of a gene occur on homologous chromosomes, which are separated (Law of Random Segregation) and that these genes on chromosomes seperate independently of genes on other chromosomes. He made the connection between the behaviour of chromosomes and Mendel's laws.
Discuss how Sutton and Boveri's work contributed to the Chromosomal Theory of Inheritance.
Both scientists identified the important of chromosomes during gamete formation, making the connection to Mendel's laws of hereditary. They thus concluded the several factors are present on one chromosome ('gene linkage')
Describe the chemical composition of chromosomes and genes
Chromosomes are comprised mostly of DNA. The DNA is wound around histones (protein) which forms a chromosomes. DNA is comprised of many genes, which contain a repeating subunit in a double-strand. The monomer is a nucleotide; a phosphate group, sugar and one of four nitrogenous bases. The bases complementarily pair to form the double strand.
Describe the composition of genes and briefly outline the discoveries which lead to this understanding
DNA is a polymer of nucleotides (phosphate group, pentose sugar and one of four nitrogenous bases). This discovery that the amount of adenine in DNA is similar to the amount of thymine (and likewise with cytosine and guanine) lead to the understanding that they were complementary pairs. Watson and Crick's understanding of the structure of DNA is dependant on Franklin and Maurice's crystallography images. The images indicated a double-helix, which supported their idea their idea of the complementary pairs forming 'rungs'
Identify and describe the three mechanisms of variation which involve the behaviour of chromosomes
1. Independent Assortment (only Metaphase 1): the orientation of the chromosomes in a homologous pair relative to the poles of each cell is random. The possible combinations are 2^n
2. Crossing Over (Metaphase 1 and Late Prophase): homologous chromosomes come together as pairs and line along the equator. Where they touch, the genetic information is switched.
3. Random Fertilisation
Identify the events in gamete formation which result in the variability of offspring
1. Random Segregation
2. Crossing Over
3. Independent Assortment
Describe how sexual reproduction influences the variability of offspring
Random fertilisation: the sperm which fertilises the ova is completely random.
Explain by co-dominance and sex-linkage are variation to Mendel's ratios
Mendel's experiments were mono-hybrid crosses, meaning that each character he studied was only influenced by one gene
Define and explain co-dominance
When both alleles inherited from homozygous parents are simultaneously expressed, producing a third phenotype (e.g. Roan Cattle)
Define and explain sex-linkage
When a particular gene is found on the 23rd pair of chromosomes. As a result, a particular gender is favoured for the inherence of a gene. Common X-linked genes are haemophilia and muscular dystrophy
Describe Morgan's contribution to the understanding of sex-linkage
Thomas Morgan studied fruit flies (Drosophilia melenogaster) as they bred every two weeks and only had 4 pairs of chromosomes. After a year of breeding a simple male with white eyes was produced (mutation). He breezed this fly with a female red-eyed fly and found in the F2 generation that only male flies has white eyes. He thus deduced that the loci for eye colour was on the X-chromosome, as males only need a simple copy of the mutant recessive gene for it to be expressed. He concluded that linked gene could only be inherited separately if crossing-over occurred.
Define the Chromosomal Theory of Inheritance
1. The behaviours of pairs of alleles can be explained by the movement of chromosomes during meiosis (Sutton and Boveri)
2. Pairs of alleles are carried on pairs of homologous chromosomes (Morgan)
3. Mendel's laws are explained by the separation and recombination of pairs of alleles if they are not sex-linked and they show dominance
Outline how the environmental affects the expression of a gene
The environment can affect the phenotypic expression of a gene. Hydrangeas change colour flower in soil of different pHs.
Outline an experiment conducted to observe the effect of environment of the expression of a gene
Three different pertinent dished of grass seed were placed in different conditions (no light, indirect light, direct light). As a result, the seeds with no light grew the most, thus revealing how the environment affects the expression of genes
Outline the process of DNA Replication
1. Two strands of DNA separate
2. Free nucleotides in the nucleus complementary base pair to the existing strand of DNA
3. Nucleotides longitudinally link
Explain the significance of DNA Replication
DNA replication is the process of a DNA strand completely duplicating, so that two identical DNA strands are produced. This is necessary for both mitosis and meiosis as otherwise an incorrect number of chromosomes would be present in the daughter cells. As DNA complementary base pairs, each single strand contains the information to reconstruct its complementary strand.
Outline the process of Protein Synthesis
1. Transcription: synthesis of RNA under the direction of DNA. RNA is formed by complementary base-pairing with the non-coding strand of DNA, so that the mRNA strand is identical to the coding strand of DNA. This is achieved by a gene being 'unzipped' by helices (enzyme) forming a transcription bubble. The formed mRNA then leaves the nucleus through a nuclear pore the the ribosome
2. Translation: synthesis of polypeptide chain. mRNA is translated in series' of three base pairs (codons) to procure an amino acid. This is achieved by the tRNA, which carries a specific amino acid from the cytoplasm to the ribosome, which complementary base pairs with a codon (anti-codon).
Identify the the need for mRNA is protein synthesis
DNA can not leave the nucleus. So, mRNA transcripts the genetic code from DNA and transports it the ribosomes for translation.
Explain the impact of mutation to the generation of new alleles
Mutations are random changes to DNA information, which can lead to the expression of new alleles. They are a source of variation necessary for evolution by natural selection
Identify and describe the two types of mutation
1. Chromosomal mutation: large changes to genetic code on chromosomes (duplication, inversion, translocation, amplification)
2. Point mutation: chemical changes to one base pair. (Substitution - point mutation, Deletion/Insertion - frameshift mutation) Point mutations can affect the the codon structure and thus the proteins that are produced.
Outline the contributions made by Wilkins and Franklin to the understanding of DNA
Made a crystal of DNA (cystallography) and obtain X-ray diffraction patterns to study its structure. Wilkins was also to produce crystalline molecules for examination and Franklin was able to produce clear diffraction images
Outline the contribution made by Watson and Crick to the understanding of DNA
Accredited with discovering the structure of DNA, particularly in regards to the complementary base pairs that joined inwardly, giving the idea for a mechanisms of replication. They worked together making large models to deduce DNA's structure.
Assess the quality of collaboration and communication between Watson, Crick, Wilkins and Franklin
Overall poor, whilst Watson and Crick worked well, Wilkins and Franklin has district so did not communicate well. Wilkins allowed Watson and Crick to see Franklin's work without consent