Genetic variation and change the short version

Transcription

1 Part 1: Biodiversity and variation Genetic variation and change the short version Define biodiversity and describe its advantages. Why is variation important to a species? What is DNA? A chromosome? A gene? An allele? Describe the structure of DNA 1

2 Describe the structure of DNA Did you include? / can you add? Phosphate Deoxyribose sugar Base Double helix Nucleotide Hydrogen bond Thymine Adenine Cytosine Guanine How does DNA replicate? Watch DNA replication vid? ch?v=8kk2zwjrv0m Use these key words to write a description DNA Helicase DNA Ligase Unzip Okazaki fragments Nucleotides Unwind DNA Polymerase RNA Polymerase Leading strand Lagging strand 3 end 5 end Double helix Leading Strand DNA polymerase adds nucleotides in 5 3 direction Helicase unzips DNA 5' 3' RNA polymerase makes a short RNA primer Lagging Strand DNA polymerase extends primer in 5 3 direction with short lengths of DNA Okazaki fragments Why is DNA replication a semiconservative process? RNA primers DNA polymerase enzyme digests primer Okazaki fragments 3' DNA ligase joins 5' 5' Okazaki fragments 3' How is DNA structure related to protein structure? What is our genetic code? 2

3 What is a mutation? What are some types of mutations? What is a mutation? What are some types of mutations? Gametic Somatic Change in DNA or chromosome structure Duplication Deletion Substitution Inversion How can mutations affect proteins? Describe the structure of a chromosome. Chromatid Centromere Histone Chromatin Autosome vs sex chromosomes? Define quick write! Homologous Haploid Diploid 3

4 Define Discuss define and compare Describe the process of mitosis Sexual reproduction Asexual reproduction Watch mitosis vid? &feature=iv&src_vid=gwcwszifklm&v=f-ldpgefahi Use key words to create your answer Prophase Metaphase Anaphase Telophase Interphase What is the purpose of mitosis? Describe the process of meiosis Watch meiosis vid? Use key words to create your answer Prophase Metaphase Anaphase Telophase Interphase What is the purpose of meiosis? PMAT Draw a diagram to show crossing over during meiosis Use the term chiasma How does crossing over produce recombinant chromosomes within the gametes? Draw a diagram to show crossing over during meiosis Chiasma Source of variation 4

5 How do mutations, crossing over and sexual reproduction cause variation in organisms? How do mutations, crossing over and sexual reproduction cause variation in organisms? Mutations create new proteins or altered proteins Crossing over breaks up gene combinations Sexual reproduction shuffles the genes when it halves chromosome numbers in meiosis What is an example of continuous variation? An example of discontinuous variation? What is an example of a variation caused environmentally instead of genetically Part 2: Inheritance Quick write: define the following Gene Allele Genotype Phenotype Homozygous Heterozygous Dominant Recessive F1 F2 5

6 Quick write: define the following Gene A length of DNA coding for a characteristic Allele An alternate form of a gene Genotype the genetic makeup of an organism Phenotype what the organism looks like Homozygous where both alleles are the same Heterozygous where the alleles are different Dominant the allele that overrides the recessive if both are present. Recessive Must be homozygous to be expressed in the phenotype F1 offspring of two homozygous parents F2 the result of crossing the F1 generation Dihybrid crosses Are we comfortable with these? If not: Do page 137-> in your workbook Check out the worked example in the revision folder Ask for more practice questions to work through. What do you cross to get the 9:3:3:1 ratio for F1? What phenotypes does the 9:3:3:1 ratio refer to? 2013 exam: Q1: DIHYBRID INHERITANCE In the sweet pea plant, Lathyrus odoratus, the allele for purple (P) flower colour is dominant over the allele for red (p) flower colour. A second gene determines the shape of the pollen. Long (L) pollen is dominant over round (l) pollen. (a) A purple, long-pollen plant, PPLL is crossed with a red, round-pollen, ppll plant. Give the genotype of the F1 generation: Two F1 generation plants were crossed to produce the F2 generation plants. (b) Use a Punnett square to show the gametes and the expected genotypes of all the possible F2 offspring from these two F1 plants. Give the expected phenotype ratio for the cross you have completed. Can you interpret a pedigree chart? 6

7 Define independent assortment and segregation using the dihybrid cross as an example Define independent assortment and segregation using the dihybrid cross as an example Means that the two genes can go into gametes independent of each other so they get separated Eg red/ tall x white/ short: the red gene may end up with the tall gene OR with the short gene. Why does independent assortment increase variation? Discuss: Compare and contrast codominance and incomplete dominance Genes Genotype Phenotype ratio Explain the effect of lethal alleles 7

8 Explain multiple alleles Describe how genes can be linked, and how this affects variation Describe how genes can be linked, and how this affects variation Two genes located at a particular. on the same.. are said to be linked. This results in variation s there are combinations of alleles present. Part 3: Evolution This reduction in variation can be countered by recombination. What is evolution and genetic equilibrium? What is evolution and genetic equilibrium? Evolution when the allele frequency of a population changes (mainly due to natural selection). Genetic equilibrium A population that is not changing (this state does not exist as natural selection is always occurring). 8

9 Describe how the relationships between variations, gene pools, and natural selection can lead to changed allele frequencies and this evolution Terms to use: Gene Allele Population Gene pool Gene flow Allele frequency Competition Mutation a group of organisms of one species ( a population) have a number of variations in their gene pool due to mutations occurring or new genes coming in with immigrants (gene flow). Any mutation that results in a useful variation means this organism will be better in competition and will produce more offspring so the gene or allele will increase in frequency: ie natural selection favours it, and evolution has occurred. Describe the relationship between these terms: selection pressure and adaptation Describe the relationship between these terms: selection pressure and adaptation Adaptations that are harmful are selected against, and those that are useful are selected for. This selection is called selection pressure the more harmful / useful the greater the selection pressure What are the three types of natural selection: define each and state how they can cause genetic change What are the three types of natural selection: define each and state how they can cause genetic change Stabilising - favours middle range of adaptive phenotype so population is very similar for that feature no extremes eg plants all a similar height, no extra tall or extra short Directional favours one extreme of adaptive phenotype so no. of population with that allele increases Disruptive Favours both extremes of adaptive phenotype so population ends up as two groups with the extremes and few in the middle range eg only tall or short, no mid height plants 9

10 Define the terms species and speciation Define the terms species and speciation Species: to be the same species two organisms must be able to interbreed and produce fertile offspring. Speciation means to form a new species we know it has happened when the two groups no longer interbreed Describe the process of speciation by isolation Describe the process of speciation by isolation isolation means mutations that occur in one group are not shared with the isolated group (no gene flow). Over time enough different mutations occur in both groups so that even if they were no longer isolated, they couldn t interbreed successfully (eg mightn t have right behaviour or structures to be able to interbreed) Give examples of geographic barriers and reproductive barriers to gene flow Give examples of geographic barriers and reproductive barriers to gene flow Geographic: Mountains are barriers to lowland species, rivers and seas are barriers to organisms that cannot swim or tolerate salt, deserts are barriers to organisms that need moisture, land is a barrier to lake dwelling organisms. Reproductive: mating or courtship behaviour might be different, might flower or ovulate at different times of day or season, sperm might not be able to penetrate egg, offspring might be sterile eg mule 10

11 Define bottleneck effect, genetic drift, and founder effect and describe how they can lead to genetic change and reduced variation Bottleneck: species number has dropped to very few individuals eg black robin and cheetah. Those that survive cannot have all the variations the bigger population used to have. This means some alleles are not present any more so allele frequency has changed (ie genetic change = evolution) Founder effect has similar effects to bottleneck. A population establishes from a small group of organisms who cannot have all the variations of their bigger group eg a small group of hedgehogs were brought to NZ they did not bring all the variations that were in the English ones so the allele frequency is different in NZ, or a few birds are blown to an island and establish a new population there but lack some of the alleles of their parent population so the allele frequency is different Genetic drift: chance causes there to be low numbers that do not have a representative selection of alleles to build up a new population. Eg a tree that had a lot of dark lizards on it is burnt leaving a higher proportion of the light coloured ones. So the allele frequency has changed from mostly dark to mostly light. Populations need to be small to start with for genetic drift to make a difference. Define and give examples of factors that can change gene/allele frequencies (and therefore cause evolution) Define and give examples of factors that can change gene/allele frequencies (and therefore cause evolution) Mutations: eg allele giving black speckled moths became more common in polluted towns Natural selection: by favouring some alleles and not others eg more speckled moths eaten than black ones Gene flow: immigration brings in new alleles or emigration takes some out eg low IQ go to Aussie Population size: if it is small genetic drift can occur Genetic drift and bottlenecks Unequal mate selection where some never get to mate eg bottom of the peck order Environmental change eg climate change, floods leaving silty valleys, fire: variations that may not have been adaptive before may now be better adapted than the existing ones so natural selection will start favouring them instead. Therefore what are the factors that cause genetic equilibrium (no evolution) Therefore what are the factors that cause genetic equilibrium (no evolution) no mutations (but they are always occurring) no natural selection pressure (but it is always occurring) no gene flow (would have to be very isolated) big population size no genetic drift and bottlenecks Equal mate selection where all get to mate no environmental change 11