Variation and Inheritance

1. Variation and Inheritance WJEC Biology Module 1 2011 Specification

2. Variation WJEC Biology Module 1 2011 Specification

3. Learning Outcomes • Examine the variation in height/length in individuals of the same species by collecting and analysing data and know that variation may be due to environmental or genetic causes. • Understand that variation may be continuous or discontinuous.

4. Clones Fertilisation Inheritance Chromosome Exposure Gamma rays Mutation Ultraviolet radiation X-rays Continuous Discontinuous Environmental factors Genes Mutation Phenotype Variation Sexual reproduction Asexual reproduction Keywords

6. Variation • Look at variation in the class • Try to write down at least 20 ways in which individuals vary from one another.

7. Variation • Variation can be described as either • Continuous variation • a range of measurements from one extreme to the other. E.g. height • Discontinuous variation • individuals fall into distinct categories. E.g. ability to roll the tongue; attached or free ear lobes

8. Continuous variation • Use a tally chart and plot results in a histogram

9. Discontinuous variation • Plot results in a bar chart

10. Variation • Differences in the characteristics of different individuals of the same kind may be due to differences in • The genes they have inherited – genetic causes • The conditions in which they have developed – environmental causes • Variation is normally a combination of both genes and the environment.

11. Phenotype • The phenotype is the outward appearance of an organism • It depends on both the organism’s genes and its environment.

12. Variation in Snails - Practical • Snails of two closely related species of Cepaea are common in woodland and grassland in Britain. • They show a pattern of variation known as polymorphism. • This means that there are several different ‘types’. The shell may be either yellow or pink/brown, and it may have dark stripes or be plain.

13. So, the four types of the snails are as follows: Pink/brown, plain Yellow, plain Pink/brown, striped Yellow striped Even within each type, there is variation, so that the pink/brown variety may be distinctly pink, or brown, or even greyish, and the striped forms may have different numbers of stripes, for instance.

14. Variation in Snails - Practical • Pick 50 snails at random for the grassland • Use the table to create a tally chart recording the number of each type of snail found in the grassland • Write your results onto the main table • Calculate the percentage of each snail type • Repeat the stages above for woodland snails

15. Conclusion • What differences do you notice in the distribution of the different types of snail? Describe any trends seen. [2] • Describe one difficulty in the method that might have reduced the accuracy of the results [1] • The size of the sample can affect the accuracy of the results. In using a sample, do you think a sample size of 50 was big enough? Give a reason for your answer

16. Evaluation • Plan a similar activity to find out if the snails grow bigger in woodland or grassland. • Describe, in detail, the procedure you would use. • Suggest any difficulties you may have in obtaining valid results • Suggest how these difficulties may be avoided.

17. Learning Outcome • Understand that sexual reproduction leads to offspring that are genetically different from the parents unlike asexual reproduction where genetically identical offspring called clones are produced from a single parent. Sexual reproduction therefore gives rise to increased variation.

18. Genetic Variation • Sexual reproduction • Egg and sperm fuse at fertilisation, to form a zygote • The zygote has a set of genes from the mother and a set from the father. • Offspring are genetically different from their parents

19. Asexual reproduction • No fertilisation, no mixing of genes • Offspring are genetically identical to each other and the parents • Produces clones

20. Cloning • Cloning can be used to mass produce economically important organisms • Animals • IVF – In vitro fertilisation • Plants • micropropagation

21. Prep • WJEC Science Page 34 • What are continuous and discontinuous variation? • Question 1

22. Inheritance WJEC Biology Module 1 2011 Specification

23. Learning outcomes • Understand that genes are sections of DNA molecules that determine inherited characteristics and are in pairs. Genes have different forms, called alleles. • Know that chromosomes are linear arrangements of genes and that chromosomes that are found in pairs in body cells are strands of DNA. DNA contains coded information for the production of different types of proteins. These proteins determine how cells function.

24. Chromosomes and Genes • Our cells contain genetic information this is your DNA. • This information on DNA is in units called genes. • Our genes are on chromosomes. • Chromosomes always come in pairs in our body cells.

25. Genetics and DNA • Each chromosome is made up of thousands of genes; • the genes carry genetic information that affects how we grow and what we look like. • A chromosome is made up of a long thread, made up of deoxyribonucleic acid (DNA). • One gene is made up of a short length of DNA.

26. DNA is twisted into a double helix, where bases pair up: Adenine with thymine Guanine with cytosine Every 3 bases along the strand codes for a particular amino acid, this means that DNA controls the proteins that are made DNA

27. DNA and Genetics GCSE Practical

28. What is DNA? • DNA is packed tightly into chromosomes inside the cell, it is a gigantic molecule, very long but very thin. • DNA from a single cell can be 2 metres long, but is so thin that it can hardly be seen with a powerful microscope. • When DNA is released from cells it clumps together to form strands, which are colourless and jelly like. • Extraction of DNA from cells is the first step in many experiments in genetic engineering. DNA can be extracted from both plant and animal cells.

29. How to extract DNA from kiwi fruit!

30. Kiwi fruit White tile Scalpel Tap water Warm water 600C Ice cold ethanol Washing up liquid Coffee filters Plastic measuring cylinders Funnels 250ml beaker Boiling tube Boiling tube bung Equipment

31. Method – Stage 1 • DNA extraction mixture: • Mix 10ml washing up liquid + 3g salt + 100ml water in a 250ml beaker • Finely chop the kiwi fruit and place in boiling tube. • add DNA extraction mixture • Place bung on top and shake carefully. • Leave for fifteen minutes at 60oC

32. Method – Stage 2 • Filter the mixture through the coffee filter into a 100ml beaker to separate the chopped kiwi fruit from the clear liquid. (the DNA is invisible as it is dissolved in the clear liquid) • Transfer 5 ml of the clear liquid into a clean test tube. • Add 5ml of cold (4oC) absolute alcohol down the side of the tube. • DNA will appear as “fluffy” white solid.

33. Final “tricky” stage • The DNA can be pulled out using a fine wire.

34. Learning Outcomes • be able to understand and complete Punnett squares and explain the outcomes of monohybrid crosses including ratios. • The following terms should be understood: • genotype, phenotype, dominant, recessive, F1, F2, selfing, heterozygous, heterozygote, homozygous and homozygote • An understanding of simple Mendelian ratios.

35. Inheritance • Things to remember: • Chromosomes are strings of genes and chromosomes occur in pairs in each cell. • There are two copies of each gene in each cell • These genes may be identical or may be different versions (alleles) of the same gene.

36. Glossary • Homozygous • 2 identical alleles for a particular characteristic • Heterozygous • 2 different alleles for a particular characteristic • Genotype • alleles for a particular characteristic • Phenotype • outward effect of those alleles

37. Dominant allele which controls the development of a characteristic when it is present on only one chromosome. Recessive allele which control the development of a characteristic if present on both chromosomes. Glossary

38. Further definitions • F1 – first generation • F2 – second generation • Selfing • Manually pollinating a flower by placing its pollen on its own stigma • Self pollination

39. Monohybrid Inheritance • The study of how a single gene is passed on from parents to offspring. • A punnet square can be used to predict an outcome

40. Genetic Cross - Tips • When you write out a genetic cross, make sure you state what the symbols represent • Make sure you label each line in the cross (phenotype, genotype, etc) • It is a good idea to circle the gametes to show that meiosis has happened • Read the question carefully – are you asked to state the outcome in terms of the genotype or the phenotype?

41. A cross between a pure-breeding tall pea plant and a pure-breeding dwarf pea plant

42. A cross between two F1 pea plants

43. A cross between a heterozygous tall pea plant and a dwarf pea plant

44. Now try this ……. • You need to be able to predict the genotypes of the parents from descriptions of them. • Work out the following genotypes, based on peas that can be round or wrinkled, with round being dominant to wrinkled. • A heterozygous round pea • A wrinkled pea • A pure-breeding round pea

45. Learning Outcomes • Understand that most characteristics are controlled by more than one gene. • consider the scientific process of observation, experimentation and deduction that led Gregor Mendel to propose the mechanism of inheritance. • Discuss why the significance of the work was not recognised and validated by scientists for many years.

46. Gregor Mendel • Gregor Mendel was a monk who did experiments looking at the inheritance of height in pea plants. • He did not publish any of his results in scientific journals, so no one took any notice of his work during his lifetime. • He is now regarded as one of the greatest scientists of all time.

47. Learning Outcome • know that in human body cells, one of the pairs of chromosomes, XX or XY, carries the genes which determine sex. These separate and combine randomly at fertilisation.

48. Inheritance of Sex in humans • The sex chromosomes X and Y determine the sex of an individual • Males XY • Females XX • The presence of the Y chromosome results in male features developing

49. Inheritance of sex

50. Learning Outcomes • understand that when gametes are formed the chromosome number is halved and the genetic composition of the daughter cells is not identical (the term, meiosis, and knowledge of stages are not required). Fertilisation restores normal chromosome number.