REVISION

1. Inheritance of Traits REVISION DSRU EP M3

2. Different types of variation People are similar, but not identical, to their parents or each other. The differences in a species are calledvariation. Variation can come about for two reasons. What are they? 1.People inherit characteristics from both of their parents and each person gets a different combination of features. This is called inherited variation. 2. Other characteristics are affected a person’ surroundings. This called environmental variation. Which features are environmental and which are inherited?

3. Variation – environmental or inherited?

4. Key words Gamete Zygote Allele Dominant Recessive Homozygous Heterozygous • This allele determines the development of a characteristic • This is formed when an egg is fertilised by a sperm • 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 • An egg or a sperm are called this • 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

5. Genes, Chromosomes and DNA

6. How genes work Some facts: - Made up of paired bases - Contain instructions on what a cell does, how the organism should work etc - The instructions are in the form of a code - The code is made up from the four bases that hold the strands together - The bases represent the order in which amino acids are assembled to make proteins - Each group of 3 bases represents one amino acid - There are only about 20 amino acids

7. The structure of DNA DNA contains information that determines inherited characteristics. DNA is made of very long strands which have four different compounds called bases. A sequence of three of these bases is the code for making a an amino acid. The order of bases on a DNA molecule controls the order in which amino acids are assembled to produce a particular protein

8. Daughter Mother Boy or Girl? Son Father

9. 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?

10. BB Bb bb Bb B B b b B b B b Bb Bb Bb Bb BB Bb bB bb Eye colour Example 1: A homozygous brown-eyed parent and a blue-eyed parent: Example 2: 2 heterozygous brown-eyed parents X X Parents: Gametes: (FOIL) Offspring: All offspring have brown eyes 25% chance of blue eyes

11. Bb bb b b B b bb Bb Bb bb Eye colour Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Equal (50%) chance of being either brown eyed or blue eyed.

12. Another method Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Father Mother

13. Example questions In rabbits, assume that the dominant allele (B) produces black fur. The allele (b) for white fur is recessive to B. (a) What colour fur will each of the following rabbits have? Rabbit 1 Rabbit 2 Rabbit 3 Rabbit 4 genotype BB Bb bBbb (b) Which rabbits are homozygous for coat colour? (c) If rabbits 1 and 4 were mated together and had 12 babies, how many of these would you expect to be black? (d) If rabbits 2 and 3 are interbred and produce several litters, totalling 48 babies, how many white babies would be predicted by the laws of genetics?

14. X Ff Ff X Cc cc X Ss Ss Inherited diseases 1) Cystic fibrosis – a disease that causes thick and sticky mucus to coat the lungs, gut and pancreas. It’s caused by recessive alleles: 2) Huntingdon's disease – a disease of the nervous system that causes shaking and eventually dementia. It’s caused by a dominant allele: 3) Sickle cell anaemia – a disease that alters the shape of red blood cells, thereby reducing their oxygen capacity, causing weakness and anaemia. It’s caused by recessive alleles:

15. X Modern Genetics 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:

16. Modern Genetics All the plants produced were tall. Now cross two of these plants… 3 out of every 4 plants were tall, leading Mendel to hypothesise that “for every characteristic there must be two determiners”

17. Plants can reproduce ASEXUALLY. The offspring are genetically ________ to the parent plant and are called _________. 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 Clones

18. Cloning 1) Cloning plants: 2) Cloning sheep:

19. 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 Jersey If, for example, I want lots of milk I would only breed Friesian cows with each other – this is SELECTIVE BREEDING. Hereford

20. Selective breeding vs. Cloning

21. Selective breeding vs. Cloning

22. Genetic Modification Possible uses of genetic modification of organisms: • Improving crop yield • Improving resistance to pesticides • Extend shelf-life • Manufacture a certain chemical (e.g. insulin) • Convenience

23. Genetic engineering Insulin is a hormone produced by the pancreas to help control blood sugar levels. Diabetics can’t produce enough insulin and often need to inject it. Insulin can be made by genetic engineering:

24. Genetic engineering - Insulin Step 1: Using RESTRICTION ENZYMES “cut out” the part of the human chromosome that is responsible for producing insulin. Step 2: Using another restriction enzyme cut open a ring of bacterial DNA (a “plasmid”). Other enzymes are then used to insert the piece of human DNA into the plasmid. 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 instruction to produce insulin. Commercial quantities of insulin can then be produced.

25. Evolution Charles Darwin (1809-1882)

26. Evolution Evolution is the slow, continual change of organisms over a very long time. All living things on the Earth have developed from the first simple life forms that arrived 3,000,000,000 years ago. • One of the effects of evolution is that species will become better adapted to their environment. If these species don’t adapt they may become extinct due to being unable to deal with any of these factors… • Increased competition • Changes in the environment • New diseases • New predators

27. Evolution • My key observations: • All living things produce more offspring than survive to adulthood • In spite of this, population sizes remain roughly constant • Variation exists among species • Characteristics can be passed on from one generation to the next. • These observations led me to the conclusion that species evolve over a along period of time by a mechanism called “Natural Selection”. The main evidence for this is from fossil records.

28. Natural Selection 1) Each species shows variation: • There is competition within each species for food, living space, water, mates etc Get off my land • The “better adapted” members of these species are more likely to survive – “Survival of the Fittest” Gutted! Yum • These survivors will pass on their better genes to their offspring who will also show this beneficial variation.

29. Bacteria Penicillin A smaller example… Consider the four steps of natural selection in the example of some bacteria that has become resistant to penicillin: • Variation – some strains of bacteria are resistant and some aren’t. • Competition – The non-resistant bacteria are killed by the penicillin. • Survival of the fittest – the resistant bacteria survive. • Passing on of genes – the resistant bacteria reproduce and pass on their adaptations to their offspring.