Inheritance, Variation and Evolution AQA Biology topic 6
6.1 Reproduction
Sexual Reproduction The human egg and sperm cell contain 23 chromosomes each. We have similar characteristics to our parents due to genetic information being passed down in genes through gametes: When fertilisation happens the gametes fuse together to make a single cell containing 46 chromosomes (23 pairs) - it contains information from each parent. The same happens in plants with pollen and egg cells.
Fertilisation summarised Egg 46 chromosomes in a fertilised egg 23 chromosomes in here Sperm 23 chromosomes in here Fertilisation
Cell growth 1 - Mitosis Each daughter cell has the same number of chromosomes and genetic information as the parent a clone is produced.
All gametes are genetically different from each other. Gametes will then join at fertilisation to restore the full number of chromosomes and divides by mitosis from then on. Gamete formation - Meiosis 1) A copy of the genetic information is made 2) The cell divides twice to form four gametes, each with a single set of chromosomes
Mitosis vs. Meiosis Mitosis: 1. Used for growth and repair of cells 2. Used in asexual reproduction 3. Cells with identical number of chromosomes and genetic information are produced ( clones ) Meiosis: 1. Used to produce haploid gametes for sexual reproduction 2. Each daughter cell has half the number of chromosomes of the parent During meiosis copies of the genetic information are made and then the cell divides twice to form four daughter cells.
Sexual vs. Asexual reproduction Sexual reproduction: 2 parents are needed Offspring will have pairs of chromosomes This will cause genetic variation Asexual reproduction: Only 1 parent needed Offspring are GENETICALLY IDENTICAL to parent ( clones ) Snuppy the first cloned dog (Aug 05)
Sexual vs asexual reproduction (Bio only) Advantages of sexual reproduction Advantages of asexual reproduction Increased variation, which may cause an evolutionary advantage Selective breeding can be used to increase food production Which form of reproduction is better? No need to find a mate More time and energyefficient Faster than sexual reproduction Produces a clone of a good animal
Reproducing Sexually and Asexually Some organisms can reproduce using both methods. Some examples: The malaria parasite reproduces asexually in a human but sexually in a mosquito Fungi can reproduce asexually using spores or sexually to give variation Many plants reproduce sexually but can also reproduce asexually by runners (e.g. strawberries) or by bulb division (e.g. daffodils)
Section of a chromosome: Genes Genetic information is stored by genes which are arranged on chromosomes: Genes for blood group: Genes for eye colour Genes for hair colour Each gene codes for a particular sequence of amino acids, to make a specific protein. The entire genetic makeup of an organism is called its genome.
Genes, Chromosomes and DNA DNA is a polymer made up of two strands forming a double helix structure. DNA is contained within chromosomes.
The Human Genome Project In 1990 an international project was launched called the Human Genome Project. The aim was to map the makeup of the human race and includes work from in 18 different countries. Possible benefits: Improved genetic testing Improved predictions and screening of diseases New gene treatments New knowledge of human patterns from the past Words scientists, genetic, migration, inherited, therapy
DNA detail (Bio only) Some facts: - It is made of four different nucleotides that consist of a and phosphate group - It contains instructions on what a does, how the organism should work etc - The code is made up from the four that hold the strands together with weak hydrogen bonds - A sequence of three bases represent the order in which acids are assembled to make specific - The DNA polymer is made up of repeating units - In the complementary strands, a C is always linked to a G and a T is always linked to an A Words amino, sugar, bases, cell, proteins, nucleotide
Making proteins (HT only) 1) DNA unravels and a copy of one strand is made 2) The strand copy is made to produce RNA 3) The mrna copy (with its code) then moves towards the ribosome 4) The ribosome decodes the mrna code which tells the ribosome how to make the protein 5) Amino acids are then joined together to form a polypeptide (protein)
Mutations (HT only) Cells contain a nucleus and the nucleus contains genes that carry instructions for what that cell should do: Genes Some facts: Some genes are switched off and don t do anything in that cell Genes basically tell the cell which proteins they should be producing Sometimes cells can mutate which may have a harmful effect on the cell and can be caused by natural or artificial means.
Genetic mutations (Bio HT only) Here s a sequence of bases in DNA: A T C G G A T Q. What happens if this sequence is changed? Possible ways this sequence is changed: 1) A base is inserted A T C A G G A T 2) A base is substituted A T C G A G A T 3) A base is deleted A T C G G A T DNA mutations are the reason why we have genetic variation in the first place. Sometimes these changes won t affect a protein made from the DNA, sometimes the protein may function differently (changing the phenotype). Changes in non-coding DNA may influence phenotype by altering how genes are expressed.
Proteins (HT only) Proteins, when unfolded, are basically long chains of amino acids: Every different protein has its own number and sequence of amino acids which results in differently shaped molecules with different functions. Some example proteins: Name of protein Collagen Insulin Enzymes Function Give structure Hormones Help food digestion Not all parts of DNA code for proteins. Non-coding parts of DNA can switch genes on and off.
Mutations and effects on Proteins (HT) Enzymes are biological catalysts. Most enzymes are proteins and, as such, a mutation in DNA will affect them: An enzyme is basically a protein molecule made up of long chains of amino acids. These molecules are then folded to create a certain shape with high specificity : The enzyme s shape helps another molecule fit into it: Enzyme Substrate This shape can be affected by mutations in the DNA or the proten may lose its strength:
Basic genetics - Boy or Girl? Note that the Y chromosome is dominant and the X is recessive. The Y chromosome dictates the development of testes. X Y X Allele Girl XX XY Boy Phenotype Heterozygous Homozygous
Mother Boy or Girl? During sexual reproduction, children inherit two alleles of each gene (one from each parent). Son Father Daughter
Key words Genotype Phenotype Allele Dominant Recessive Homozygous This allele determines the development of a characteristic The characteristic caused by the genotype This allele will determine a characteristic only if there are no dominant ones This word refers to a pair of chromosomes being made of two different alleles of a gene The genetic make up in a nucleus This word refers to a pair of chromosomes being made of two of the same alleles of a gene An alternative form of a gene Heterozygous
Eye colour In eye colour the brown eye allele is dominant, so we call it B, and the blue eye is recessive, so we call it b: BB Bb bb Homozygous brown-eyed parent Heterozygous brown-eyed parent Blue-eyed parent What would the offspring have?
Eye colour Example 1: A homozygous brown-eyed parent and a blueeyed parent: Example 2: 2 heterozygous brown-eyed parents Parents: BB X bb Bb X Bb Gametes: B B b b B b B b (FOIL) Offspring: Bb Bb Bb Bb BB Bb bb bb All offspring have brown eyes 25% chance of blue eyes
Eye colour Example 3: A heterozygous brown-eyed father and a blue-eyed mother: B Bb b b bb b Equal (50%) chance of being either brown eyed or blue eyed. Bb Bb bb bb Note in reality, characteristics like this are usually depend on the instructions of multiple genes and other parts of the genome.
Another method the Punnett square Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Mother Father B b b Bb bb b Bb bb
Example questions 1) In mice, white fur is dominant. What type of offspring would you expect from a cross between a heterozygous individual and one with grey fur? Explain your answer with a genetic diagram. 2) A homozygous long-tailed cat is crossed with a homozygous short-tailed cat and produces a litter of 9 long-tailed kittens. Show the probable offspring which would be produced if two of these kittens were mated and describe the characteristics of the offspring (hint: work out the kitten s genotype first).
Inherited diseases 1) Cystic fibrosis a disorder or cell membranes. It s caused by recessive alleles so both parents need to be carriers : Ff X Ff 2) Polydactyly a condition where a person has extra fingers or toes. It s caused by a dominant allele so can be passed on by a parent who already has it: Pp X pp Embryos can be screened for alleles that cause these diseases before birth. Do you think this is right?
Genetic Diagrams Here s what happens (genetically) when an egg is fertilised: Mother xx Father xy x x x y Equal (50%) chance of being a boy or a girl xx xy xx xy
Genetic Diagrams Here s another way of drawing it: Father Mother x x x y
6.2 Variation and Evolution
Variation Variation is the name given to differences between individuals of the SAME species. Variation is due to GENETIC or ENVIRONMENTAL causes. There is often extensive variation within a species. For example, consider dogs: 1) Ways in which they are the same: 2) Ways in which they are different:
Environmental differences Some of this variation is due to our parents, but some of it is due to our upbringing and the environment in which we live this is called Environmental variation. Variation due to inheritance only Variation due to environment only Variation due to a bit of both
Beneficial Mutations - the peppered moth All variations arise from mutations. Most mutations have no effect on phenotype whereas some do. If the new phenotype is more suited to its environment then it can lead to a rapid change in the species. For example
Evolution Charles Darwin, 1809-1882 Evolution is the slow change in organisms that happens over a long period of time. All life on Earth has evolved from simple life forms that existed around 3 billion years ago. It happens through a process called natural selection, which basically says this: 1) Different species show variation 2) The better adapted ones survive 3) They then have kids who also have the better phenotypes
Definition of Species A species is defined as when organisms reproduce with each other to produce fertile offspring. Different species can sometimes mate and have offspring but they would be infertile. Some examples: Mule Liger Zebroid Geep
Selective breeding I raise cows. Each type of cow is good at a certain job. The Friesian cow produces large quantities of milk, the Jersey cow produces very nice milk and the Hereford cow produces lot of beef. Friesian If, for example, I want lots of milk I would only breed Friesian cows with each other this is SELECTIVE BREEDING. The only trouble is that I m reducing the gene pool by doing this. Jersey Hereford
Examples of Selective Breeding Other examples can include plants with larger flowers and disease resistance in crops. Some breeds may be particularly prone to diseases or inherited defects due to selective breeding.
Basics of Genetic Engineering Genetic engineering is basically the idea of modifying a genome using a gene from a different organism in order to improve characteristics. For example: With genetic engineering I can produce milk that contains: Extra protein Lower levels of cholesterol Human antibodies Genetic Engineering has also been used to make disease-resistant plants with bigger fruits and to produce insulin on large scales.
Genetic Modification Advantages Improving crop yield Improving resistance to pesticides Extend shelf-life Manufacture a certain chemical (e.g. insulin) Convenience Current medical research into using genetic modification to overcome inherited disorders Disadvantages Genetically modified organisms may be expensive Need for long term studies Effects may be passed on to other crops, e.g. weed resistance spreading from crops to weeds Ethical issues about abortion Risk of miscarriage or false positives with amniocentesis
Summary Here are the basic steps: Identify the desired gene Remove the gene from the DNA Cut open the DNA in the other organism Insert the removed gene using enzymes again Clone the organism to produce lots of copies
How Genetic engineering is done (HT only) Step 1: Cut out the part of the human chromosome that is responsible for the desired characteristic. Step 2: Using another restriction enzyme cut open a ring of bacterial DNA (a plasmid or vector ). Other enzymes are then used to insert the piece of human DNA into the plasmid. Most of the cells don t take up the vector so the ones that have need to be marked. Step 3: Place the plasmid into a bacterium which will start to divide rapidly. As it divides it will replicate the plasmid and make millions of them, each with the desired characteristic.
Cloning Plants (Bio only) Plants can reproduce ASEXUALLY. The offspring are genetically to the parent plant and are called. The only variation between then will be due to environmental factors. Two examples: 1) This spider plant has grown a rooting side branch ( stolon ) which will eventually become. 2) A gardener has taken cuttings of this plant (which probably has good characteristics) and is growing them in a atmosphere until the develop. Words clones, damp, independent, roots, identical
Cloning Plants by tissue culture (Bio only) 1) Scrape off a few cells from the desired plant 2) Place the scrapings in hormones and nutrients 3) 2 weeks later you should have lots of genetically identical plants
Cloning Animals 1 (Bio only) Method 1 Embryo transplants A developing embryo is split before the cells specialise and the identical embryos are implanted into host mothers.
Cloning Animals 2 (Bio only) Method 2 Fusion: Animals can be cloned by taking the nucleus from an adult body cell and transferring it to an empty, unfertilised egg and giving it an electric shock to stimulate the egg to form an embryo: Host mother Clone
6.3 The Development of understanding of Genetics and Evolution
Evolution (Bio only) Charles Darwin, 1809-1882 Evolution is the slow change in organisms that happens over a long period of time. All life on Earth has evolved from simple life forms that existed around 3 billion years ago. I came up with this theory after observations around the world and after years of experimentation and observations. Evolution happens through a process called natural selection, which looks like this:
4) These survivors will pass on their better genes to their offspring who will also show this beneficial variation. The smallernecked giraffe will eventually die out. Natural Selection (Bio only) 1) Each species shows variation here are some long-necked giraffes and short-necked giraffes: Get off my land 2) There is competition within each species for food, living space, water, mates etc 3) The better adapted members of these species are more likely to survive Survival of the Fittest Harsh Yum
Controversy about Darwin s Work (Bio only) I published my work On the Origin of Species in 1859. However, it attracted a lot of controversy because: 1) It challenged the theory that God made every animal and plant on the Earth 2) There wasn t a lot of evidence at the time 3) The mechanism of natural selection was not known until around 50 years later
An example of Natural Selection antibiotic resistant bacteria Bacteria 1) Mutation some strains of bacteria can develop to the antibiotics. Penicillin No effect!! 2) The non-resistant bacteria are by the. 3) The resistant bacteria and pass on their mutations to their - an example of Words offspring, resistance, killed, antibiotics, reproduce, natural selection
Darwin vs Lamarck Darwin wasn t the first to come up with evolution he was simply the one credited with explaining how it worked (i.e. Natural Selection). An earlier scientist called Lamarck explained evolution by different means: The giraffe has a long neck because it stretches its neck to reach the food, and these long necks are passed on to their offspring. Organs which aren t used will eventually disappear. However, we now know that changes like these cannot be inherited. Jean Baptiste Lamarck (1744-1829
Speciation (Bio only) I independently proposed the theory of evolution by natural selection at around the same time as Darwin. I am best known for my work on warning colours in animals and my theory of speciation the formation of a new species. One example of speciation is geographic isolation : Alfred Wallace 1823-1913
Geographic Isolation Different species can be formed by geographic isolation, for example, consider an African elephant: 1) Elephants are separated by a geographic feature e.g. a 2) Elephants on each side of the mountain have different in their pool 3) Some offspring have characteristics that help them survive 4) Their weaker die out and the offspring are so genetically removed that they re incapable of with each other they re now different Words species, mutations, mountain, gene, ancestors, reproducing
Mendel s Work (Bio only) Guten tag! My name is Gregor Mendel. I am the father of modern genetics because of the work I did on pea plants in 1865 Mendel s experiment: Take two plants; one which is pure-bred for tallness and one pure-bred for shortness, and cross them: X
Modern Genetics All the plants produced were tall. 3 out of every 4 plants were tall, leading Mendel to hypothesise that for every characteristic there must be two units that determine the characteristic Now cross two of these plants
Modern Genetics Achtung! Unfortunately, nobody knew about chromosomes or genes when I published my findings so no one believed me until after my death, when more powerful microscopes were available. Three key developments that led to Mendel s ideas being accepted: 1) By the late 19 th Century behaviour of chromosomes during cell division had been observed 2) By the early 20 th Century it was observed that chromosomes and Mendel s units behaved in similar ways therefore, the units (now called genes) are located on chromosomes 3) In the mid-20th Century the structure of DNA was determined.
Evidence for Evolution Fossil records, showing the development of an organism over a long period of time Antibiotic-resistant bacteria, giving evidence for natural selection Now that the mechanism of natural selection has been understood and with evidence like fossils and antibioticresistant bacteria, the theory of evolution is widely accepted.
Fossils Fossils are the remains of organisms from millions of years ago and are found in rocks. They provide evidence of early life and could have been formed in many ways. Four examples: This fossil of a bat was formed due to hard parts of the animal not decaying This fossil was formed by parts of its body being replaced by minerals This bee and orchid pollen were preserved in amber the amber lacked some of the conditions needed for decay to happen Fossilised footprints
Fossil records Fossil records can provide a useful way of observing a species development: The Stenheim skull, found in Germany in 1933 Oh no The problem is, many early forms of life only had soft bodies and the few remaining traces of them have been destroyed by geological activity. This makes it difficult for scientists to know what happened in the distant past.
Extinct Species Extinction is when every member of a species dies out. Some examples: Sabre-toothed tigers and mammoths Dodo
Recap antibiotic resistant bacteria Bacteria 1) Mutation some strains of bacteria can develop to the antibiotics. Penicillin No effect!! 2) The non-resistant bacteria are by the. 3) The resistant bacteria and pass on their mutations to their - an example of Words offspring, resistance, killed, antibiotics, reproduce, natural selection
Using Antibiotics Antibiotics are used to cure bacterial by killing infective bacteria inside the body. The development of new antibiotics is usually slower than the development of new of bacteria. There are some issues with using antibiotics: 1) Patients should always complete their 2) Antibiotics should be used as bacteria can grow to them, e.g. the MRSA superbug. 3) Agricultural use of antibiotics should be Words course, immune, strains, diseases, sparingly, restricted
6.4 Classification of New Organisms
Classification How would you construct a key to classify these organisms?
Classifying organisms All organisms are classified into groups. For example: What is the main difference between these? Plants Organism Animals Kingdoms Vertebrates Invertebrates Amphibians Birds Reptiles Fish Mammals Notice that the number of similarities increases as you go down this tree Species Dogs Cats
Why use classification? Dog Canis lupus familiaris Wasp vespula germanica Human homo sapien I invented the modern system of naming species. I did this so that species would have the same name in every language and so that we would have a greater ability to understand different species and how they have evolved. Carolus Linnaeus, 1707-1778
Classification Organisms are classified using the following levels: Kingdom Phylum Class Order Family Genus Species
Classification Consider, for example, a dog: Kingdom - Animalia Phylum - Chordata Class - Mammalia Order - Carnivora Family - Canidae Genus - Canis Species C. lupus
The 5 Kingdoms The 5 Kingdoms that organisms are classified by are: Animalia Plantae Fungi Protoctista Prokaryotes Multicellular, don t have cell walls or chlorophyll Multicellular, have cell walls and chlorophyll Multicellular, have cell walls but no cholophyll Unicellular, have a nucleus Unicellular, have no nucleus
Classification A modern way of doing it As microscopes became more powerful and our knowledge of DNA improved, new models of classification were proposed. Due to evidence from chemical analysis I devised a threedomain system: Carl Woese, 1928-2012 Archaea (primitive bacteria usually living in extreme conditions) Bacteria (true bacteria) Eukaryota (which includes protists, fungi, plants and animals)
Common Ancestors Modern DNA research shows that all forms of life share a lot of their DNA. This is used as evidence to suggest that all forms of desecnded from common ancestors (the Theory of Evolution). 85% shared DNA 98.8% shared DNA
The Evolution Tree Similar species are proposed to have common ancestors but also will have differences due to the habitats they live in. Family Hylobatidae (Lesser Apes) Subfamily Ponginae Family Hominidae (Great Apes) Subfamily Hominidae Scientists use current classification data and older fossil data to help them develop this tree Tribe Panini Tribe Gorillini Tribe Homini Gibbons Orangutans Chimpanzees Gorillas Humans