Evolution And Genetics Yr10

SCIENCE Evolution and Genetics Focus 1+ 2. What is Darwin’s theory of natural selection and what observations did he base his theory on? • Define the theory of evolution by natural selection o Change of organisms over time o Change in the genetic composition of a population during successive generations, as a result of natural selection acting on the genetic variation among individuals, and resulting in the development of new species o Mechanics of evolution 1) Mutation  Gene Mutation: changes within DNA molecules are the main way new genes are introduced into a population. May produces traits entirely new to the populations. Most often recessive  Chromosome Mutation: changes involving whole chromosomes occur less frequently than gene mutations. Often have harmful (even fatal) effects on the organism 2) Natural selection o The process in nature by which only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.  Individual variation: Although members of a species resemble each other in general, they differ in detail, and except in special cases such as identical twins, no two individuals coming from sexual reproduction are ever exactly alike  Struggle for existence: Every species, without exception, reproduces itself in such numbers that if all were to survive long enough to reproduces in their turn; the earth would soon be covered with the progeny of a single pair  Darwin pointed out that the survivors in this “struggle for existence” would be those possessing variations which improved their adaptation to the environment. In particular, an individual possessing a mutation which gave it an advantage, would have more surviving offspring than other individuals of its species  Organisms with favourable characteristics in a given environment will survive to reproduces. The organisms with the favourable characteristics have a better chance in competing for available food and water  Populations of future generations of a species will therefore contain a greater proportion of individuals who have inherited these favourable characteristics  Gradually the preservation of favourable characteristics leads to a change in the characteristics of the natural population. As long as the environment does not change, the species becomes better adapted to its environment. The environment has effectively selected certain characteristics for survival (aka survival of the fittest) 3) Isolation o Isolating mechanisms provide the means by which different populations can become different species  Geographical Isolations: Occurs when mountains rise, coastlines sink, volcanic actions occur  Geographically separated populations form new species because:  They have initially different sets of genes  They will experience different mutations because mutations occur randomly  They will be exposed to different environmental factors that naturally select certain individuals  • Describe how Darwin developed his theory on natural selection by survival of the fittest o In 1830s, Darwin went on a 5 year voyage around the world on naval ship HMS Beagle o Visited South America, Galapagos Islands, Australia and South Africa o Darwin collected specimens of animals and plants and studied the geology of places he visited o Made numerous observations of animal anatomy and behaviour and also collected many fossils o Recognised that individuals within a population vary, and that those favourable variations survived to reproduce o Convinced that organisms gradually changed over long period of Earth’s history

Over the next twenty years, used these studies and other collected information to develop a theory to explain the process of evolutionary change Focus 3. What is a scientific theory? Why are scientific theories sometimes controversial? How is evolution an example of a theory? • Recall the function of a scientific model o Scientific model : a representation of a scientific feature, displaying the characteristics or mechanics of that figure and may change with new knowledge • Distinguish between theory and law o Theory: an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers. A theory explains a whole series of related phenomena. o Law: a statement of fact meant to explain in concise terms, an action or set of actions. Accepted to be true and universal, and can sometimes be expressed in terms of a single mathematical equation. A law governs a single action. • Discuss how Darwin’s work was accepted by society when it was first presented o Darwin’s work were dismissively discarded • Discuss why Darwin’s ideas were controversial o The theory was against the religious morals and beliefs of the period the ideas were raised o Those of the time period accepted the views of the church without any questions and doubt o

Focus 4 and 5. What further pieces of evidence have been used to support Darwin’s theory? • Identify evidence used to support the theory of evolution and how the evidence supports the theory. o Fossil evidence  Law of superstition: describes relative ages of rocks using the order in which they were formed. The fossils held in these layers can be given a relative age the same way  Fossils collected and analysed from various strata soon showed apparent that the fossils in deeper sedimentary strata were less complex in body structure than fossils in higher strata  Fossil evidence therefore supports the view that the earliest life forms were very simple and that they changed into more complex organisms over time  Fossils reveal the appearance of new life forms did not occur at an even rate over geological time and has shown that more than one new species sometimes developed form a pre-existing species. However, fossil record is incomplete since not all organisms become fossilised after death  Evolution of the modern horse (Equus) has been firmly established from fossils. Ancient ancestor of the horse (Eohippus) had four toes and was as small as a dog. Sequence of fossil forms thus shoes that the modern horse developed from a different organism in the distant past  Fossil evidence describing the development of the horse supports evolution because it shows that organisms change over a long time o DNA comparison  Chimpanzees and humans share identical amino acid sequences in several enzymes (proteins) found in their respiratory systems  Shows that the DNA base sequence code for these proteins is the same in both species  Humans and chimpanzees have 98.4% of DNA in common  This suggests that humans and chimpanzees shared a common ancestor about 4-5 million years ago and are closely related o Comparative biochemistry and anatomy and embryology  Biochemistry is the study of chemicals in living things  Cells in different organisms have a similar basic chemical structure e.g. blood proteins and DNA, suggesting common ancestry. These chemicals are very similar in closely related organisms  Anatomy indicate organisms that appear different may have evolved from a common ancestor

For instance, the limbs of mammals show a common pattern and are similar in structure, but they appear different because they have evolved in different environments. Some have been modified for running e.g. horse, some for swimming e.g. whale, and others for flying e.g. bat  Embryos of vertebrates look very similar even though as adults they look different, suggesting they have evolved from a common ancestor o Biogeography  Study of the geographical distribution of species, both present day and extinct  Plants and animals in different areas have different characteristics, which are believed to have evolved because of separation or isolation. Focus 6 and 7. How did Lamarck’s theory explain evolution? Are new scientific theories always accepted with an open mind by the rest of the scientific community? • Compare Darwin and Lamarck as examples of models used to explain observations o o o o • Describe Lamarck’s theory of acquired inheritance and compare it to Darwin’s model o Lamarck proposed in 1810 that evolution occurred when organisms acquired characteristics by use or disuse o Put forward the idea that using body parts strengthens them, whereas disuse causes them to disappear o Believed that features acquired by use are inherited by offspring o E.g. Lamarck proposed that the giraffe acquired its long neck by continually strengthening it while stretching for food o Extinction does not occur o Spontaneous generation of organisms from inanimate matter occurs continuously throughout earth’s history • Describe the theory about acquired inheritance proposed by Dr Ted Steele (practicing Australian scientist) and explain why these ideas have not been widely accepted o o o o



Focus 8. What are the mechanisms of sexual reproduction and how does this contribute to variation within a population? • Identify the organs involved in human reproduction and describe their functions o Male Reproductive System  Scrotum: External sac holding the testes; helps to regulate the temperature of testes  Testes: Site of sperm production; glands that produce male hormones such as testosterone  Vas deferens (sperm duct): Tube that carries sperm away from the testes  Glands (prostate; seminal vesicles; Cowper’s gland): Produce protective and nutritive fluids for the sperm; the combination of sperm and these fluids is called semen  Urethra: Tube that carries semen during intercourse; tube that discharges urine from the bladder  Penis: Organ used to deposit semen in the vagina of the female during intercourse o Female Reproductive System  Ovaries: Site of egg production; glands which produce female hormones such as oestrogen and progesterone  Fallopian tubes (oviducts): Tubes through which an egg moves following ovulation; site of egg fertilisation if sperm are present in the reproductive tract  Uterus (womb): Muscular organ in which a fertilised eff will implant and grow to produce a baby

Vagina: Canal in which semen is deposited during intercourse; canal through which a baby is born Define the terms gamete, ova, testes, sperm, ovaries, zygote o Gametes: reproductive cells (e.g. egg and sperm). They carry genetic material (genes), which is transferred to the next generation during fertilisation. Gametes are formed by meiosis o Ova: female reproductive cell o Testes: makes sperm and the hormone testosterone o Sperm: male reproductive cell o Ovaries: produces the egg and the hormone oestrogen o Zygote: the new cell with 23 pairs of chromosomes formed when a sperm cell fertilises an egg cell



•

Focus 9. What is DNA and how is it involved in reproduction? • Describe the basic structure and function of DNA (deoxyrubonucleic acid) The shape of the DNA molecule is a double helix The two strands of the double helix resemble a spiral staircase The separate strands are composed of molecules called nucleotides o Nucleotides are composed of three parts  Phosphate group  Deoxyribose sugar molecule  Nitrogen base o ‘Spiral steps’ composed of the nitrogen bases o Four types of nitrogen bases are: Cytosine (C), Guanine (G), Thymine (T) and Adenine (A)  Cytosine (C) and Guanine (G) always bond  Thymine (T) and Adenine (A) always bond o Sides of the ‘spiral staircase’ are composed of the phosphate groups and deoxyribose sugar molecules Identify that DNA consists of genes o Molecules make up chromosomes, which contain genes and control cell activities o DNA contains a code that provides instructions for making proteins in cells o The code is contained in the order of the bases along the length of the DNA molecule o Only certain genes are ‘switched on’ so that the same genetic material is not expressed equally in all cells Relate the structure of DNA to the process of cell division o When cell division occurs to make new cells, new DNA is made for these cells – DNA replication o DNA replication is the process of making new DNA when new cells are made during cell division (mitosis and meiosis). If the DNA is not replicated exactly, then mutations occur and the new cells or organisms can be quite different from the original o DNA Replication steps:  Nitrogen bases that form the ‘spiral steps’ start to split apart at one end of the DNA ladder  New nucleotides are transported into place and linked together to produce a complementary strand according to the rule for base paring (C with G and A with T)  Two new double helices from when this process is completed o o o

•

•

Focus 10. What are mitosis and meiosis, and what role do they play in reproduction and inheritance? • Describe the process of mitosis and explain its importance in the sexual reproduction o Process of division that creates body cells o Enables organisms to grow and repair tissue o During mitosis chromosomes (DNA) make copies of themselves (DNA replication) and each new cell receives the same number and type of chromosomes and genes as the parent cell o Process:      • Describe the process of meiosis as producing sex cells with half the number of chromosomes as a normal cell o Process of cell division that produces gametes o Occurs in the ovaries and testes of most organism o Referred to as reduction division – because cells formed have half the number of chromosomes ( haploid number or n) that are found in body cells (diploid number or 2n) o Body cells in humans have 46 chromosomes (diploid), in the egg and sperm there are 23 chromosomes (haploid). During fertilisation the diploid number is restored o Genetic diversity or variation is increased in meiosis by crossing over of chromosomes and independent separation of chromosomes into new cells (random segregation of chromosomes) o Process:     

Focus 11. What is genetics and how was the concept first scientifically studied? • Extract information on Gregor Mendel to explain what he did o German speaking Austrian Augustinian priest and scientist o Born Johann Mendel, he took the name Gregor upon entering monastic life o Sent to the University of Vienna to studyin 1851, returning to his abbey in 1853 as a teacher, principally of physics o Inspired by both his professors at university and his colleagues at the monastery to study variation in plants, and he conducted his study in the monastery’s garden • Evaluate his work as a piece of scientific research o Collected information about inheritance by breeding pea plants in the 19th century o Between 1856 and 1863 Mendel cultivated and tested some 29,000 pea plants o Examined seven different characteristics (e.g. pea shape and plant height) o Study showed that one in four pea plants had purebred recessive alleles, two out of four were hybrid and one out of four were purebred dominant o His experiments bought forth two generalisations which later became known as Mendel’s Law of Inheritance • Explain how genetic information is transferred to offspring in the process of sexual reproduction o Each characteristic is controlled by two factors or genes (e.g. T tall, t short) o All cells in the body, except eggs and sperm, have two genes for one characteristic (TT, Tt or tt for height) o Each egg and sperm receives only one of these genes o Fertilisation brings gene pairs together again o When an individual is a hybrid (Tt) the individual shows the dominant characteristic (T). The characteristic that is hidden is recessive (t).

Focus 12. How can knowledge of patterns of inheritance be used to predict features in a population of offspring? • Define the terms genotype and phenotype, homozygous and heterozygous, recessive and dominant o Genes: units of inheritance o Allele: different forms of a single gene o Genotype: type of allele e.g. Bb o Phenotype: Physical expression of the genotype, resulting from genes and environment o Homozygous :A homozygous organism has two alleles the same (TT or tt) o Heterozygous: A heterozygous organism, or hybrid, has two different alleles (Tt) o Recessive: Alleles that are only expressed when with another recessive allele. The hidden feature. Represented by the lower case letter o Dominant: The allele that masks a recessive allele. Represented by a capital letter

•

Perform punnet square crosses to predict the genotypes of offspring from parents of known genotype o Used to calculate possible ratios or percentages of the different types of offspring produced in a genetic cross

Focus 13. How can further variation in a population be produced? • Define genetic mutation and identify causes of mutation o Change in the DNA of a cell in an organism, which may cause this cell and other cells formed from it to appear and behave differently from normal cells o Mutations may occur naturally, but the number of mutations is increased by radiation and some chemicals (e.g. nicotine, benzene) • Relate the occurrence of mutation to natural selection and determine advantages and disadvantages of exact DNA replication and mutation o Mutations occurring in gametes (egg and sperm) may be passed to offspring o Many mutations are harmful and cause disease o Some are useful and increase variation (genetic diversity) in the population and so are important in natural selection and evolution Focus 14. What factors affect the expression of our genes? • Explain how phenotype is influenced by genotypes and environmental factors through the use of specific examples o Both genotypes and environmental factors contribute to the appearance and functioning of an individual o For instance, a person may have genes for dark hair but environmental factors such as the sun may cause it to lighten Focus 15. What is genetic engineering and why is it so controversial?

•

•

Describe examples of how genetic engineering is used by humans including agriculture, treatment of genetic disease and pharmacology o Process in which the genes of an organism are altered or new genes are added by technology developed by humans  Organism 1 supplies the new gene  Gene is cut out using enzymes  A) Gene is injected into cell of organism 2  B) Gene is transplanted into bacterial DNA (circular and called a plasmid)  B1) Cells of organism 2 are infected with bacteria containing plasmid with new gene. The new gene is incorporated into the DNA of organism 2, resulting in a new characteristic (e.g. frostresistant tomatoes)  B2) Bacteria with the new gene are cultured. They make useful substances e.g. human insulin o Humans manipulated inheritance by selective breeding, cloning and genetic engineering in order to:  Improve produce such as fruit, vegetables and cereal crops  Produce medical substances such as insulin and growth hormones  Provide cures for diseases and tread genetic disorders such as cystic fibrosis (gene therapy)  Produce organisms with a special purpose (e.g. bacteria that ‘eat’ oil and can be used to combat oil spills in the ocean) Discuss issues surrounding the use of gene technology o ‘Improved’ organisms will be favoured while wild types or organisms of less commercial value will be discarded o Should humans be interfering with nature in this way and do they have the right to impose genetic change on future generations? o Can genetically modified organisms spread and interfere with natural ecosystems? o Will these procedures change genetic diversity and have an effect on natural evolution? o Are genetically modified foods safe to eat?