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Mut/Sel/Var
Genetics, Variation and Selection
| Question | Answer |
|---|---|
| Define variation. | The differences between species (interspecific variation) and within species (intraspecific variation). |
| Distinguish between the two types of intraspecific variation. | Discontinuous - variation in a feature with distinct categories, and no intermediates. Continuous - variation in a feature with a range of phenotypes between two extremes with many intermediates |
| What is the difference between a bar chart and a histogram? | A bar chart has spaces between each bar. A histogram has no spaces between each bar. |
| Which type of variation does height, body mass and hand span fall under? | Continuous |
| Which type of variation does the ABO system, ability to taste PTC and attached vs unattached earlobe fall under? | Discontinuous |
| On which axis of a graph should the independent (manipulated) variable always go? | x - axis |
| T or F. Discontinuous variation data is best represented on a bar chart whereas continuous variation data is best represented on a histogram. | T |
| Define mutation | A change in DNA |
| Give the name for mutations that only affect the organism in which they occur and are not passed on to the next generation. | Somatic mutation |
| Give the name for mutations that occur in gamete-forming cells and can be passed on to the next generation. | Germ line mutation |
| What is a chromosome mutation? | A change to the structure of a chromosome or to the number of chromosomes in the nucleus - occurs during nuclear division - either in mitosis or meiosis. |
| What is a gene mutation? | A change to the nucleotide sequence of a gene - occurs during DNA replication during interphase of the cell cycle. |
| List 3 types of chromosome mutations. | 1) Polyploidy 2) Aneuploidy 3) Translocation |
| Describe polyploidy. | An increase in the number of SETS of chromosomes. |
| Describe aneuploidy. | An increase or decrease in the number of INDIVIDUAL chromosomes. |
| Describe translocation. | Changes in the structure of a chromosome e.g. part of a chromosome is detached and reattached to another. |
| Down's syndrome is an example of which type of chromosome mutation? | Aneuploidy. |
| Down's syndrome is also called trisomy 21. Describe how this condition occurs. | Non-disjunction occurs during meiosis I in the formation of gametes (the ovum). A pair of chromosomes (chromosome 21) fails to separate and thus the ovum contains 2 chromosomes which forms a zygote with trisomy when fertilized. |
| Define trisomy. | The existence of three chromosomes of the same type. |
| T or F. The only survivable trisomies are those of the X chromosome and chromosome 21. | T |
| What is non-disjunction? | The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei. |
| T or F. Trisomies are NOT inherited; they arise because of non-disjunction during meiosis to form gametes. | T |
| List 3 types of gene mutation. | 1) Substitution 2) Frameshift 3) Stutter |
| Describe substitution. | The change of one base pair for another. |
| Describe frameshift. | The addition or deletion of one or more bases. |
| Describe stutter. | Repeat/duplication of base pairs. |
| What is a mutagen? | An agent/environmental factor that causes a mutation (change in DNA) e.g. radiation, certain chemical compounds such as benzpyrene in tobacco smoke. |
| What is a carcinogen? | Any agent that causes cancer. |
| Name the enzyme which does proof-reading to remove and replace any incorrectly placed nucleotides during DNA replication. | DNA polymerase. |
| What type of gene mutation causes sickle cell anaemia? | Substitution |
| Describe what causes sickle cell anaemia. | There is a change in the sixth triplet of the gene for Beta-globin of haemoglobin from CTC to CAC resulting in the amino acid valine(hydrophobic) instead of glutamic acid(hydrophilic) in the primary structure of B-globin. |
| What is the consequence of the mutation which occurs in sickle cell anaemia? | Abnormal haemoglobin (HbS) is formed instead of normal haemoglobin A (HbA). In low oxygen concentration, the molecules to stick together, become sickle-shaped and precipitate. |
| What is sickle cell crises? | The condition in which blood flow to major organs is reduced due to blockage of vessels with sickled cells. It usually includes pain, fever and difficulty breathing. |
| What is the life span of normal red blood cells? | 90 - 120 days |
| What is the life span of sickle-shaped red blood cells? | 10 - 20 days |
| The B-globin gene in haemoglobin is termed pleitropic. What does pleitropy refer to? | Genes which have multiple effects on the phenotype. |
| T or F. Sickle cell anaemia happens to people homozyous for the substitution mutation. | T |
| In some parts of the world, being a carrier(heterozygous) for sickle cell anaemia protects against contracting the malaria virus. Why? | The RBCs which become infected by the virus rupture prematurely so the parasite cannot reproduce. The mutant form of haemoglobin cannot be digested by the parasite thus reducing their ability to survive. |
| What does natural selection refer to? | The survival of individuals with particular features that adapt them to the conditions by an agent of the environment e.g. predators, competition and climate giving them a greater change of breeding and passing on their alleles. |
| Define intraspecific competition. | Competition between members of the same species. |
| T or F. All individuals of the same species have the same genes but they differ in the alleles of those genes. | T |
| List 4 observations which led to the theory of natural selection. | 1) Overpopulation 2) Populations remain stable over time 3) Variation exists within species 4) Offspring resemble parents |
| List 3 conclusions from the theory of natural selection. | 1) There is competition for resources which leads to high death rates 2) Individuals best adapted to obtain resources survive to breed and pass on their alleles 3) Populations consist of individuals best adapted to the existing conditions at that time. |
| What does evolution refer to? | The theory that organisms change over time and that natural selection is the mechanism by which it occurs. |
| List 4 examples which have been used to highlight how environmental factors act as forces of natural selection. | 1) Resistance to antibiotics 2) Peppered moth 3) Trinidadian guppies 4) Dominican anole |
| What was the agent of natural selection in the peppered moth population? | Bird predators which could see the moths on the bark of trees. When melanics were more visible, they were seen and eaten. When speckled were more visible, they were seen and eaten resulting in the other moths to survive and reproduce. |
| What is a selection pressure? | An external agent which affects an organism's ability to survive in a given environment. Selection pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait). E.g. predation, disease and competition. |
| Why is heritable variation important to natural selection? | Individuals with alleles that are advantageous survive and reproduce passing on their alleles to the next generation. The advantageous allele frequency increases. New combination of alleles occur in the next generation and variation continues. |
| What is stabilizing selection? | Selection in which the proportions of different types or forms within a population do not change from generation to generation. Selection pressures select against the extremes of a trait so the medium trait increases. |
| What is direction selection? | Selection which favours a rare form in a population, One extreme form is selected against so the distribution of the population's trait shifts toward the other extreme. |
| What is disruptive selection? | Selection which favours the extreme forms with selection pressures acting against the individuals in the middle of the trait distribution. A bimodal (two-peaked) curve results. |
| What does the biological species concept state? | It states that all individuals of a species are able to breed together to produce fertile offspring and are reproductively isolated from other species. |
| State three issues which arise with the need to test for production of fertile offspring in order to determine members of the same species. | 1) Difficulty in observing mating behaviour in the wild and checking the fertility of offspring. 2) Some species reproduce asexually. 3) Fossil species cannot breed. |
| What is the morphological species concept? | The definition of a species based on common distinctive features of morphology (outward appearance), behaviour, physiology, biochemistry and anatomy. |
| What is speciation? | The explanation provided for the formation of new species arising from existing species. |
| Explain allopatric speciation. | Formation of a new species from populations that are isolated from one another by geography. E.g. snapping shrimp separated by the Isthmus of Panama |
| Explain sympatric speciation. | Formation of a new species within a single population; common in plants where polyploidy occurs. E.g cord grass in salt marshes |
| What are isolating mechanisms? | Methods that prevent interbreeding between populations; allow populations to speciate and act to maintain separate species. |
| Explain reproductive isolation. | Separation of populations of organisms so that they are unable to interbreed successfully. |
| List 4 examples of pre-mating isolation methods. | 1) Geographical/ecological 2) Temporal of seasonal 3) Reproductive behaviour 4) Mechanical |
| List 2 examples of post-mating isolation methods. | 1) Production of hybrid prevented 2) Breeding of hybrid prevented |
| Features such as rivers, lakes, mountains, forests can separate populations so that they rarely meet e.g. the three sub-species of elephants in Africa. What type of isolating mechanism does this depict? | Geographical/ecological |
| Breeding can occur at different times of year e.g. two species of pine in California release pollen in February and April so they do not pollinate each other. What type of isolating mechanism does this depict? | Temporal/seasonal |
| Courtship rituals differ between species so males and females do not respond to signals and mate e.g. female anolis lizard only responds to signals from her species. What type of isolating mechanism does this depict? | Reproductive |
| Structural differences make the sex organs of males and females of different species incompatible. What type of isolating mechanism does this depict? | Mechanical |
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CAPE Biology Unit 1
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