biology sem 1 y10 Flashcards
What is an allele?
One of various versions of the same gene (at the same locus) distinguished by small differences in DNA sequence.
What is autosomal inheritance?
The passing on of a trait through a gene located on an autosome.
What is a chromosome?
In eukaryotes, chromatin condenses into linear structures visible under a light microscope; in prokaryotes, there is one circular chromosome.
What is a codon?
A set of three consecutive nucleotides found in a DNA or RNA molecule that carries the code for a specific amino acid.
What is crossing over?
The exchange of genetic material between maternal and paternal homologous chromosomes of non-sister chromatids that occurs during prophase-I.
What does dominant mean in genetics?
A phenotype that requires only one copy of its allele for it to be expressed in an individual.
What is diploid?
Describes a cell or organism that has a genome that contains two copies of each chromosome, represented by 2n.
What is evolution?
The process of cumulative, gradual, inheritable change in a population of organisms that occurs over many generations and a relatively long time.
What is fertilisation?
The union of haploid male and female gametes during sexual reproduction to produce a diploid zygote.
What is a gamete?
A male or female reproductive cell.
What is a gene?
A set unit of nucleotides that occupies a fixed position on a chromosome that codes for a polypeptide. They are the blueprint for all our hereditary information eg colour of eyes.
What is a genotype?
The specific combination of alleles for a particular gene locus.
What is haploid?
Describes a cell or organism that has a genome that contains only one copy of each chromosome; represented by n.
What does heterozygous mean?
A genotype with two different alleles for a single gene locus.
What is a homologous chromosome?
A pair of chromosomes that have the same size and shape; they have genes at the same locations; one is maternal and one is paternal.
What does homozygous mean?
A genotype with two identical alleles for a single gene locus.
What is a karyotype?
a photograph of the chromosomes in a cell that is used to check for abnormalities.
They are prepared by staining the chromosomes with dye and photographing them through a microscope.
What is a locus?
The position a gene occupies on a chromosome.
What is a monohybrid cross?
A cross between two organisms that are heterozygous at one gene locus for a dominant and a recessive allele.
What is a mutation?
A permanent change in the DNA sequence of a gene; a source of new alleles in a population’s gene pool.
What is a pedigree?
A diagram that depicts the biological relationships between an organism and its ancestors.
What is a phenotype?
The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
What does recessive mean?
A phenotype that requires two copies of its allele in an individual in order to be expressed.
What is a sex-linked trait?
A trait inherited on a sex-chromosome; the gene of interest on a sex chromosome is described as sex-linked.
What is a zygote?
A fertilized egg cell that results from the union of a female gamete (egg/ova) with a male gamete (sperm).
Describe the work of Miescher
- Identified nuclei (nucleic acids), essentially discovering the molecule DNA.
Describe the work of Franklin
- Discovered that DNA existed in a double helix structure through famous Photograph 51.
Describe the work of Wilkins
- Worked with Franklin on DNA’s structure as well as studying nucleic acids and secretly shared Photograph 51 without Franklins knowledge to Watson and Crick.
Describe Chargaff’s contributions
1950: Contributed to the structure of DNA in which the ratio of the nitrogenous bases is such that adenine is equal to thymine and guanine is equal to cytosine. Known as chargaffs ratios.
Describe the contributions of Watson and Crick
1953: discovered that DNA was made up of two chains of nucleotides that encodes for the genetic material of all living things.
DNA
deoxyribonucleic acid, a molecule that contains genetic information.
Genome
a complete set of genes - contains the information needed to build the entire human body.
What are phosphate groups:
Phosphate groups form phosphodiester (phosphate double bonds) bonds between sugar molecules to form a chain of molecules
What is the backbone of DNA made of?
The backbone of a DNA strand is made up of alternating deoxyribose (sugar) and phosphate units, liked by phosphodiester bonds. The backbone is labelled 5’ (with the point of the sugar pentagon pointing upward) and 3’ (the other side).
What are the 5 nitrogenous bases in RNA and DNA.
Adenine (A) and guanine (G) and Thymine (T), Cytosine (C,) Uracil (U). DNA contains adenine, guanine, cytosine and thymine. Conversely RNA contains Adenine, guanine, cytosine and uracil.
Complimentary base pairing + bonding
The four bases form loose hydrogen bonds (loose bonds hold when needed and can separate when needed as well) to create rungs that hold the double helix ladder of a DNA molecule. The bases always pair so that Adenine always pairs with Thymine and the two have a double bond. Cytosine always pairs with guanine so the two have a triple bond. This is called complimentary base pairing.
Nucleotides
a nucleotides contains one phosphate, one sugar (deoxyribose) and one base
DNA structure
Two chains of nucelotides hydrogen bonded by the bases to form a twisted ladder shape. DNA is a double helix. The backbones run in opposite directions so that they are antiparallel. DNA is asymmetrical and has a major groove and a minor groove.
DNA in eukaryotic cells
DNA s packaged as chromosomes in the nucleus. The DNA is tightly packed and coils around proteins called histone so that 2m of DNA coils into a few nanometres. The DNA and histones form chromatin which is the substance that forms chromosomes.
DNA in prokaryotic cells
In prokaryotic cells the DNA is all loose around the cell. It is one molecule that is loose in cytoplasm with no histone or chromatin.
Structure of chromosomes
Chromosomes are made of two identical chromatids attached at the centromere. When chromatids separate so there is one - that one is called a chromosome not a chromatid.
How are karyotypes arranged?
They are cut out and arranged in their homologous pairs (one from male one from female) in decreasing size order from largest to smallest.
How are karyotypes denoted?
Where the first number is the number of chromosomes and then the second two digits are either XX or XY depending on what the gender is (male or female respectively)
Autosomes in a karyotype
Within a karyotype eg for humans there are 23 pairs of chromosomes. Within that 22 pairs are autosomes meaning that they contain DNA and genes and then the other pair are of the sex chromosomes that depict gender.
Overview of DNA replication
Scientist proposed that DNA ‘unzipped’ as hydrogen bonds between the base pairs were broken. New polynucleotide strands could then be synthesised using the originals as a template. Each chromosome is replicated by semi conservation process where one DNA double helix comprises of one strand of DNA from original molecule and one from the newly synthesised strand.
Step 1 of DNA replication
- DNA helicase (enzyme) unwinds and separates the double strand by breaking the weak hydrogen bonds to expose the bases. Each half of the parents molecule is used as a template.
- The molecule is unwound a little at the time and helicase works in opposite directions.
- The point where it is divided is called the replication fork.
- As the helicase works in opposite directions, it creates a bubble in the middle and this is called the replication bubble.
- Single-strand binding proteins keep the DNA strand separated during replication because otherwise they would just join back together again.
Step 2 of DNA replication
- The enzyme RNA primase attaches a short sequence of RNA on both strands known as a primer to show DNA polymerase where to start adding nucleotides.
- These nucleotides come from free nucleotides that are floating around.
The RNA uses uracil instead of thymine when pairing with adenine.
- These nucleotides come from free nucleotides that are floating around.
Step 3 of DNA replication
- Complimentary nucleotides are added and linked together by the enzyme DNA polymerase.
- Synthesis of the new daughter strand is in a 5’ to 3’ direction.
- Adenine pairs with thymine and cytosine pairs with guanine.
DNA polymerase is also an error checker that checks the DNA is paired correctly.
Step 4 of DNA replication
- The leading strand is replicated continuously. This is because DNA polymerase builds the daughter strand 5’ to 3’.
- The lagging strand is replicated discontinuously in fragments. The daughter strands are made in short sections called Okazaki Fragments - each started with a primer, and then the polymerase finished.
- There are multiple primers and polymerase working across the DNA strand so that the process happens quicker.
Step 5 of DNA replication
- DNA ligase removes and replaces the primers and links the daughter strand into a continuous molecule.
- The result is the production of two identical DNA molecules that are each made of one parent strand and one new daughter strand.
The process is described as semi-conservative.
- The result is the production of two identical DNA molecules that are each made of one parent strand and one new daughter strand.
Point mutation overview
If an error is made during DNA replication, a point mutation can occur in the DNA of the daughter cell.
A substitution of one nucleotide pair causes the protein made using that gene to have one incorrect amino acid - less dangerous
Insertion or deletions errors can cause the proteins produced to be significantly different and it impacts a lot of proteins after this point. - more dangerous.
DNA helicase
separates the two DNA strands before replication by unwinding. DNA helicase breaks the hydrogen bonds between the nucleotides in order to unzip the strands apart.
DNA polymerase
catalyses the formation of a new polypeptide chain. It uses free nucleotides in order to create a matching pair in the daughter strand and synthesises this new strand. It works in a 5’ to 3’ prime directions and is also an error checker to check if the bases are paired up correctly.
What are the three theories of how DNA replicates
semiconservative, conservative and dispersive.
Conservative DNA replication theory
the DNA double helix replicates as a whole. Meaning when it replicates no part of the daughter DNA is made up of the parent DNA. This then continues through the replications. The whole molecule remains intact.
Semi-conservative DNA replication theory
A parents DNA split so that in the 2 new DNA each is made up of one parents strand and one new daughter strand. This then continues. The whole molecule doesn’t remain intact but the strands remain intact.
Dispersive DNA replication theory
replication results in two daughter DNA molecules that are mixtures of parental and daughter DNA. They are like patchwork including parts of one DNA and then parts of another -> the strands do not remain intact.
Evidence for semi-conservative process
Experiment done by Meselson and Stahl. Bacteria were grown in a heavy nitrogen (N15) medium for multiple generations meaning their DNA became fully labelled with the N15 isotope. They were then moved to a normal nitrogen medium of (N14) to replicate for one generation. They were then extracted and analysed and their DNA revealed that the DNA was not as heavy as N15 but not as light as N14 - it was in the middle. This suggested that part of the DNA was from N15 and part was from N14. If the process was conservative the DNA would have been fully N14 and if it was dispersive there would have been a gradual blend instead of a clear intermediate one.
Protein Synthesis
involves the production of a chain of amino acids that forms the primary structure of a protein. The sequence of amino acids are coded for by a gene.
Genetic Code
the sequences of bases along its DNA. It contains thousands of sections called genes or cistrons.
characteristics of the triplet code
The triplet code is where each three bases of DNA code for one amino acid on a protein. It is universal (whatever 3 bases make a specific protein are the same on all living things on Earth), degenerate (some triplets although different may make the same amino acids or other times they may be a stop or start protein), non-overlapping (each base on the strand is only a part of one triplet/codon and each triplet/codon will only code for one amino acid. )
DNA vs RNA
DNA is a double helix with two strands, contains deoxyribose as the sugar, contains thymine as a base. RNA is single stranded, contains ribose as a sugar and uracil as a base.
Transcription
The synthesis of mRNA from DNA where the sequence of nucleotides in the mRNA is complementary to the sequence in the stored DNA code. It occurs in the nucleus and is the first stage of protein synthesis. RNA polymerase (enzyme) binds to the start of the gene (promoter region), and separates the double helix (only a little bit at a time). It builds a chain of mRNA (messenger RNA) made from free nucleotides floating around the cell and uses complimentary base pairing with the DNA ‘template strand’.
In RNA it uses uracil instead of thymine and uracil still bonds with Adenine.
DNA base triplets are converted into mRNA codons.
All genes start with the same amino acid (methionine - A U G). - there are some codons that are coded to stop.
Translation
The synthesis of a polypeptide using the codon information in mRNA.
mRNA leaves the nucleus through a nuclear pore and finds a ribosome (a cellular structure on which the polypeptide chain will be built). Ribosomes can be found in the cytoplasm or on the rough endoplasmic reticulum. Two subunits on the ribosome bond around the mRNA.
Transfer RNA (tRNA) located in the cytoplasm brings the amino acids to the ribosomes when needed. Each tRNA is specific to one amino acid. tRNA molecules have a sequence of three baes called an anticodon. It is complimentary to the codon on the mRNA. The anticodon matches with the codon and brings the amino acid that that codon is coded for. Eg Codon AUG, has anticodon UAG and codes for the amino acid methionine (this is the start protein which starts every gene to exist). Ribosomes forms peptide bonds between amino acids to make a polypeptide chain. There are specific codons called stop codon which tell the ribosomes to stop bringing proteins and that the polypeptide chain is finished and should be released. The chain folds up to form a protein. The mRNA can be reused to make another polypeptide chain or it can be disassembled.
What happens to chromosomes during cell division:?
Within cell division a homologous pair chromosomes separates and each separate chromatid (once separated and individual are called chromosome), copies itself to form a sister pair.
Mitosis vs Meiosis: Function
In mitosis the purpose is to create two identical copies of a cell by nuclear and cellular division for growth, repair and asexual reproduction. The purpose of nuclear and cellular division for producing gametes.
Mitosis vs Meiosis: number of cell divisions
Mitosis is one and meiosis is two
Mitosis vs Meiosis: Number of chromosomes in daughter cells
In mitosis it is 46 or diploid (2n), in meiosis each of the 4 non-identical daughter cells contain 23 or haploid (n).
Mitosis vs Meiosis: Genetic Variation
In mitosis there is no genetic variation as they are all identical. In meiosis there is variation due to crossing over in prophase 1 and independent assortment in metaphase 2.
Mitosis vs Meiosis: Type of cell used
mitosis uses somatic cells and meiosis uses germ cells which form gametes.
Interphase
Not really apart of mitosis. At this point the chromosomes are unravelled and exist as chromatin. These 46 chromatin pieces replicate so that there are 46 pairs of chromatin pieces - in this pair both are identical copies of each other. The organelles of the cells also replicate including the centrioles. The cells also increase in size.
Prophase
The DNA collects together and coils around the histones so that they are in the shape of chromosomes which are visible. The two pairs of centrioles also become visible and move to either pole of the cell. The nuclear membrane breaks down so chromosomes are let loose and the nucleolus disappears. The spindle fibres or microtubules are formed from the centrioles.
Metaphase
The chromosomes are really distinctively visible in their shape. The chromosomes attach onto the spindle fibres and the microtubules tug and pull of the chromosomes until they are perfectly line dup at the equator of the cell or the metaphase plate.
Anaphase
The spindle fibres pull of the chromosomes so that the two chromatids are separated and they are pulled opposite ways to either pole of the cell. The chromatids are now called chromosomes. It is the shortest phase of mitosis.
Telophase
Two sets of chromosomes form groups at each pole. The DNA packages together into the nuclear membrane which is reformed and the chromosomes uncoil back into chromatin hence as soon as telophase is over you can’t see the shape of the chromosomes. The nucleolus returns. At the same time cytokinesis occurs so that the cleavage furrow is formed in the cell where the cell is dividing. The cleavage depends until the cytoplasm is split into two separate daughter cells.
What are the stages of mitosis?
Prophase, Metaphase, Anaphase, Telophase. Including interphase although it isn’t really a phase.
Eukaryotic cell cycle
the same sequence of events between mitotic divisions
Phases of Cell cycle
G1 Phase: cell growth before DNA replication. The cell carries out its normal metabolic functions
GO phase: a resting phase for cells. A cell may remain there for its lifetime or only temporary. Stem cells also wait here for replication, and then when called upon they come out of it and continue to life cycle.
S Phase: (Synthesis) DNA is replicated ready for cell division
G2 Phase: Cell prepares for division as there is cell growth and the organelles replicate.
M Phase: Mitosis (nuclear division) takes place - PMAT
C Phase: cytokinesis - cytoplasmic division takes place where the cell separates into two completely.
Gamete Formation
gametes are genetically unique because they are formed through meiosis. Only one chromosome from each homologous pair in the parent cell is copied to the gamete. This means human gametes have 23 chromosomes and are haploid. Gametes are formed through meiosis sometimes called reduction division because the amount of chromosomes are halved. Meiosis forms 4 unique daughter cells.
What are different stages of meiosis
In meiosis 1 there is IPMAT ending with 2 haploid daughter cells with 23 double stranded chromosomes, and in meiosis 2 there is PMAT ending with 4 unique haploid 23 single chromosome cells.
Interphase (Meiosis)
You begin with a germ cell that is diploid and has 46 chromatids. DNA replication occurs where 46 chromatids become 92. These 46 double chromosomes are sister chromosomes meaning they are identical to each other. The cell grows in size. All organelles are replicated (roughly 4 times so that there is sufficient amount for the 4 daughter cells produced at the end).
Prophase 1
The DNA condenses into chromosomes. Maternal chromosomes are attracted to paternal chromosomes and vice versa they are called homologues or homologous pairs. Once attracted they join and crossing over occurs. The nuclear membrane disintegrates and the nucleolus disappears. Centrioles move to opposite ends of the cell and the meiotic spindle beings to form.
metaphase 1
The chromosomes line up at the equator/metaphase plate of the cell still in their homologous pairs. Lining up is independent assortment as the pairs are lined up on one side or the other independent of each other. The chromosomes are attached to the spindle fibres which move them into place.
anaphase 1
The spindle fibres shorten, pulling on the centromere of each chromosomes. This separates the homologous pairs yet sister chromatids remain with each other and are pulled to either end of the cell.
telophase 1
New nuclear membrane forms and chromosomes unravel into chromatin. The spindle fibres disintegrate. Two daughter cells are formed which have 23 duplicated chromosomes that are not homologuss meaning that the cell is haploid as it doesn’t have a full set of chromosomes.
What is the result of meiosis 1?
Two daughter cells that are haploid and have 23 duplicated chromosomes (46 chromatids)
is there DNA replication before meiosis 2?
No
Prophase 2
Chromatin condenses to form visible chromosomes again. New spindle fibres are produced. The nuclear membrane disintegrates.
metaphase 2
Individual chromosomes line up at the metaphase plate/equator. The spindle fibres attach to the sister chromatids at their centromere.
anaphase 2
The centromeres of each chromosome disconnect allowing sister chromatids to separate. The spindle fibres shorten pulling the chromatids apart to either end of the cell. In an animal cell the cleavage furrow beings to form and in plant cells a cell wall forms.
telophase II
chromosomes unwind, loosen and reform chromatin. 4 new nuclear membranes form around the nuclei one in each new daughter cell. The cells separate into 4 new non-identical haploid daughter cells.r
Why is genetic variation important?
It is important that unique gametes are produced as it ensures natural variation within a species. This is because every gamete produced is different to the others meaning that every combination is new and unique. Creating genetic diversity is vital to a species survival as it allows them to adapt to the changing environment around them.
How is genetic variation achieved?
Within meiosis there are two processes that determine this unique genetic make up.
1) Crossing over: occurs during prophase 1 in which homologous pairs of chromosomes swap parts of their genetic material for a specific trait eg an eye gene for an eye gene etc.
2) Independent assortment: chromosomes from each pair are randomly allotted to their daughter cells. There is no set sequences as to which chromosomes end up in which daughter cell it is all random and leads to a random assortment of chromosomes in a daughter cell.
After meiosis random fertilisation in which a random egg is released and a random sperm meets the egg also allows for genetic variation as all sperm and egg are genetically different.
How is the sex of an individual determined in the ovum?
- Within the egg there are XX chromosome pairs
- They crossover and swap genes
- Hence in an ova there is already an x chromosomes which holds a lot of important material.
- During telophase/cytokinesis when the cell splits producing the ovum the cells don’t split equally. There is one cell that is bigger and fuller with more nutrients - this is the egg. The other 3 smaller ones are polar bodies and useless.
The egg has no role in what the gender of the baby is but regardless it provides the X chromosomes
How is the sex of an individual determined in the sperm?
- They have an X chromosomes from female and a Y chromosome from the male which is white and runted and doesn’t hold much information from it.
- The sperm decides the gender of the baby.
- Half the sperm has x chromosomes and half of the sperm has y chromosomes.
- During telophase/cytokinesis all cells divide equally hence all that divides is all viable sperm.
Describe the work of Mendel
Gregor Mendel studied in 1850s to 1860s, he invented the terms dominant and recessive. All his work was before DNA was discovered. His work came from experiments with peas. He used peas because they grow quickly, available in pure-breeding (homozygous) strains. Many pea plants show discontinuous variation (either one form or another). By looking at homozygous green peas and homozygous yellow peas and making them reproduce in order to see what happened , he used the first generation to identify the dominant trait and the second generation to identify the recessive. This invented the idea of a cross between two genes.
Explain mendels laws of inheritance
MENDEL FIRST LAW: Law of segregation
Alleles cause variation in inherited characteristic. Organism inherits two alleles, one from each parent. Dominant alleles mask effects of recessive alleles. The two alleles for each characteristic separate during gamete formation.
MENDEL SECOND LAW: law of independent assortment
Genes for different characteristics are sorted independency during gamete production.
What was the work of Reginald C Punnet?
Reginald C Punnet created the visual tool named after him ‘Punnet Squares.” The tool is used in genetics in order to outline the different possible outcomes in the genotype and phenotype of off spring of two individuals.
Inheritance patterns: autosomal recessive
People with only one defective allele and one normal one are carriers. These people are most often not affected by the condition, however they can pass it onto their children. Parents of affected people are always at least carriers. Carrier have an unaffected phenotype because the dominant allele will silence the effects of the recessive allele that causes the condition.
Example of autosomal recessive inheritance pattern
sickle cell anaemia - an inherited disease that causes red blood cells to distort and form curved sickle shapes. It is cause by a single recessive allele which produce abnormal haemoglobin. A person would need HsHs to be affected and HAHs would be a carrier.
Example of autosomal dominant inheritance pattern
Huntington’s disease - a rare and fatal inherited disease of the central nervous system. Cause my a single dominant allele meaning that heterozygous individuals will develop it.
Inheritance pattern: autosomal dominant
Autosomal dominant: a single allele is responsible for the occurrence of a phenotype. Each affected person usually has an affected parent and the phenotype occurs in every generation. A single copy of the affected allele is enough to cause the condition. A parents with a single copy of dominant allele )heterozygous will theoretically pass it on to 50% of offspring, if the parent is homozygous for the trait then 10% of offspring will be affected.
What do pedigree’s show?
The genetic data that is used to show these is pedigree charts. Females are circle and males are squares. If it is shaded in then the person is affect but you can’t tell the difference between EE or Ee in autosomal recessive pedigrees as they are both unshaded and EE and Ee are both shaded in autosomal dominant pedigrees.
Codominance
there is more than one dominant allele and both dominant alleles are expressed. Eg ABO blood group, A and B are co dominant and O is recessive hence the blood type AB exists.
Incomplete dominance
sometimes two different alleles are neither full dominant or recessive to each other. In heterozygous individuals this creates a phenotypes that is an immediate mix of the other two. Eg red snapdragon crosses with white snapdragon to form a pink snapdragon.
Polygenic traits
It is a characteristic such as height, weight and eye colour that is influenced by two or more genes. Polygenic traits do not follow the patterns of Mendelian inheritance. Many polygenic traits are also influenced by the environment like weight is also affected by how much food you eat not just your genes.
Continuous variation
varies over a range of values and cannot easily be places in individual categories. It is caused by a combination of genes and environment and may be polygenic. Eg height, mass
discontinuous variation
they can be placed in distinct categories (the organism has the characteristic or not). It is controlled by a small number of genes and the environment has little effect eg eye colour
Fixed/free earlobes: monogenic trait
free earlobes in the dominant trait E and fixed earlobes is the recessive trait e. EE or Ee will result in free earlobes and ee will result in fixed earlobes. This trait is only determined by one gene hence making it monogenic, it is also discontinuous variation as it is only one or the other.
Height: polygenic trait
It is influenced not only by multiple genes which all play a small part leading to continuous variation eg children have heights between their parents but not exactly the same as either one. Environmental factors like nutrition also play an important role in the height of someone. Hence it is an example of polygenic inheritance.
What is the work of Paley in evolution?
Believed that God created the world and decided the characteristics of everything
What is the work of Lamark in evolution?
Believed that species evolved because they inherited traits acquired through the over or under use of body parts eg giraffes have long neck because they use them so much to reach the tree and every time they did they stretched it.
What is the work of Darwin in evolution?
believed that the similarity between different species pointed to common ancestry that new species form by gradual changes over the generations.
What is the work of Wallace in evolution?
Proposed the idea of natural selection which is the mechanism by which the most successful changes are passed on allow organism to evolve to suit their environment.
Darwins theory (acceptance) + evidence
Although’s Darwin’s work was accepted in the scientific community it was opposed in the religious community by the churches who till believed that everything was created by a divine power.
Darwins theory is considered more compelling than lamarcks due to the evidence that he had.
Darwins EVIDENCE:
1) Fossil record: specially gradually changed over millions of years showing progressive evolution.
2) Comparative anatomy: Seemingly unrelated animals chare anatomical features that are similar
3) Biogeographical evidence: evolution of species happens with separation of land masses
Direct observation: artificial selection in animal and plant breeding.
Darwin and Wallaces definition of evolution
evolution is the process that results in cumulative, heritable changes in a population, spread over many generations.
Modern definition of evolution
evolution is the cumulative changes in allele frequencies in a population over a very long time
Modern evidence for evolution
MODERN EVIDENCE (all organisms share a number of molecular characteristics):
- All have DNA and RNA as their genetic material
- The genetic code is universal
- ATP is the universal molecule for energy storage
- The proteins in all organisms are formed from the same 20 amino acids
- All have phospholipid membranes
- Vital physiological process follow very similar metabolic pathways in all organisms.
what are evolutionary tree charts?
- Tracks changes in proteins in living things in order to create an evolutionary tree
what are the four mechanisms of evolution
Mutations: the formation of new genetic material/combinations
Natural selection: The process by which a selection pressure can change a population
Genetic drift: chance events can cause significant changes to a population
Gene flow: Migration can change populations over time
What is a gene pool?
The total information from all the genes and allele of the breeding individuals in a population at a particular time.
The frequency of alleles within a gene pool can be changed over time by several different mechanisms:
- Natural selection
- Sexual selections (alleles for more sexually attractive traits become more frequent)
- Mutations
- Genetic drift (changes in allele frequency due to random chance)
Gene flow (changes in allele frequency due to migration)
species
a group of organisms that can reproduce with one another in nature and produce fertile offspring.
population
a group of individuals of the same species living and interbreeding within a given area.
different types of mutation and impact on variation
All mutations have a negative impact on the body making it more prone to diseases such as cancer or can cause other things like a shorter life span.
Somatic mutation: only affects the body cells. The mutation is passed on during mitosis but will not be inherited.
Germline mutation: Copied to gametes during meiosis so they will be inherited.
Chromosomal mutations: Chromosome mutations can come in many forms and the effects of chromosomal abnormalities are very wide ranging. These changes can occur during cell division. In meiosis these changed would be heritable (inherited by the next generation). In mitosis these changes would NOT be inherited - but they could cause diseases like cancer. The different types are deletion where genes are deleted from a chromosome or translocation where a piece of one chromosome breaks off and attaches onto a different chromosome.
Point Mutations: If an error is made during DNA replication, a point mutation can occur in the DNA of the daughter cell.
A substitution of one nucleotide pair causes the protein made using that gene to have one incorrect amino acid. In some cells this can cause life in death but in many it just means the cells dies or can’t do its job.
Insertion or deletions errors can cause the proteins produced to be significantly different and it impacts a lot of proteins after this point. The effect of these are dangerous and they can cause death or very bad mutations.
causes of mutation
Mutation can be induced through things cause mutagens. The 3 mutagens are radiation like gamma rays and x rays, carcinogenic chemicals like cigarette smoke and infections such as HPV.
Not all variation is inherited.
selection pressures + types
Selection pressures: are environmental factors that can be survived by those individuals in a population who possess a beneficial trait but not others. It can contribute to changes in allele frequency in a population gene pool.
Types of selection pressures: resources (presence/lack of food, prey or shelter), abiotic factors (temperature, water availability, pH), biotic factors (pathogens, disease carrying organisms, predators).
speciation
Speciation: the formation of a new species. Occurs when gene flow has effectively stopped between population where it has previously existed.
Allopatric speciation: species become geographically isolated and can no longer produce offspring with each other leading to speciation. Due to geographic isolation these populations independently adapted to their different changing environments due to natural selection and diverged and turned into different species.
Sympatric speciation: the species evolved in the same place, but the stopped making offspring with each other due to temporal (active at different times of the day), behavioural (different behaviours to select a mate), or morphological (vastly different sizes) aspects. After which natural selection weighed upon both populations independently causing the groups to change and adapt differently.
allopatric speciation
Allopatric speciation: species become geographically isolated and can no longer produce offspring with each other leading to speciation. Due to geographic isolation these populations independently adapted to their different changing environments due to natural selection and diverged and turned into different species.
sympatric speciation
Sympatric speciation: the species evolved in the same place, but the stopped making offspring with each other due to temporal (active at different times of the day), behavioural (different behaviours to select a mate), or morphological (vastly different sizes) aspects. After which natural selection weighed upon both populations independently causing the groups to change and adapt differently.
main stages of natural selection
1) There is variation in a population due to mutations and/or sexual reproduction.
2) There are more individuals produced in a population than the environment can support. Not all individuals can survive.
3) Due to limited resources, the selection pressures favour those with better suited/more advantageous characteristics. They outcompete those who do not possess the favourable trait.
4) Those with the advantageous traits survive and reproduce. (survival or the fittest).
5) When the survivors reproduce, they pass on their advantageous traits to offspring as the trait is heritable.
6) Over many generations the frequency of the alleles for the favourable traits increases, The less favourable alleles will decrease in frequency.
When apply the concept make sure you cater the response to the scenario.
divergent evolution
Divergent evolution: occurs when two separate species evolve differently from a common ancestor. It is the accumulation of differences between groups which can lead to the formation of a new species. These differences can be caused through the selection pressures placed on them that results in natural variation.
convergent mutation
occurs when species have different ancestral origins but have developed similar features. The two species independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. These may evolve similar because they have the same selection pressures of having to find prey/food or shelter within their environment hence natural selection means they have similar advantageous traits.
