1. A Tale of Two Fishes Delving into genetic inheritance Continue here

2. Click on the information button before going further. In this activity you will investigate how characteristics are inherited. Remember to follow the instructions carefully on each slide. Investigation Test yourself Solve the problem Final challenge

3. Sexually reproducing organisms display a vast range of characteristics. In most cases a new individual arises as a result of the fusion between a male and female sex cell. This means the new individual has a combination of chromosomes and genes that is a mixture of both parents. This mixture is a major factor in determining the traits that the new individual will show. Over the next few slides you will investigate the inheritance of red or yellow body colour in a species of fish. Genetic inheritance investigation Continue here

4. What do you think the colour of the offspring will be if (i) both parents are yellow or (ii) if both are red? Click to find out. Continue here

5. Question: Which of the following best explains the observations on the previous slide when both parent fish are the same colour? A. Because the father is red all the children end up being red and this is the same with the yellow fish. B. It was just a coincidence because colour depends on how many red crabs the mother eats during pregnancy. Genetic inheritance investigation C. Red baby fish occur because they get a gene for red colour from each parent and the same for the yellow fish. D. Red parent fish can only have red babies because they do not have genes for yellow colour. ANSWER Write your thoughts down then click.

6. What do you think the colour of the offspring will be if one parent is yellow and one is red? Continue here Click to find out.

7. Question: Which of the following best explains the observations on the previous slide when parents are different colours? A. Each parent gives a red or yellow gene and therefore sometimes the offspring get two yellow genes and sometimes they get two red genes. B. It depends on the combination of genes that the parents have. Genetic inheritance investigation C. All the offspring get a red gene from one parent and a yellow gene from the other. For some reason the red gene hides the effect of the yellow and therefore they are all red. ANSWER Write your thoughts down then click.

8. Can two red fish produce yellow fish? What about two yellow fish producing a red fish? Continue here Click to find out.

9. Question: Which of the following best explains the observations on the previous slide when parents are same colours? A. Red fish can still be red if they have a red gene and a yellow gene, therefore the offspring could get a yellow gene from each of the red parents. B. The yellow fish occurred because the mother ate yellow crabs during pregnancy. Genetic inheritance investigation C. It is not possible for yellow fish to have red fish because each parent must only have yellow genes. ANSWER Write your thoughts down then click.

10. How can we explain the inheritance of characteristics? Genes are found on chromosomes which exist in pairs. In the case of the fish, each individual will have a gene for body colour that exists on two chromosomes (called homologous chromosomes). The gene has two different forms called alleles. A red allele and a yellow allele is possible. The colour of the fish depends on the combination of two alleles an individual has received, one from each parent. We often use symbols to represent these combinations. For example, there are three possible combinations for body colour. Genetic inheritance investigation R = red alleler = yellow allele RR (two red alleles)rr (two yellow alleles)Rr (one of each) homozygoushomozygousheterozygous continue here

11. Genetic inheritance investigation continue here R allele r allele As you can see red fish can either have a combination of RR or Rr whereas yellow fish must be rr. The fact that we see red colour when both types of alleles are present means that red colour is dominant and yellow colour is recessive.

12. Genetic inheritance investigation The combination of alleles, eg RR, Rr or rr is called the genotype. The characteristics that we can see, eg red or yellow colour is called the phenotype. When using symbols we use the upper case to represent the dominant trait and the lower case to represent the recessive trait. So lets see how two red fish can result in offspring that are yellow. Remember each parent provides one of their alleles to the offspring. This makes a total of three combinations. Rr RRRrRrrr continue here Press space bar to view the combinations

13. Genetic inheritance investigation Rather than draw diagrams all the time we can use a simple table called a Punnet square to predict what the genotype and phenotype of the offspring of the next generation will be, based on the genotypes of the parents. Two examples are shown below. continue here Rr Male parent Rr Female parent alleles Rr Male parent RR Female parent alleles R R r r Rr R R RRRr rr RR Rr We would expect 3 out of 4 fish (75%) to be red and 1 out of 4 (25%) will be yellow. We would expect all fish (100%) to be red and none to be yellow. =red =yellow Press the space bar to view combinations

14. Genetic inheritance investigation That completes the investigation. Below are some of the key ideas. The observable characteristics of an organism are referred to as the phenotype. The combination of alleles that produce a particular trait is called the genotype. A dominant characteristic only needs one of its allele to be present. A recessive characteristic requires both of its alleles to be present. Genes can have different forms called alleles. An individual is homozygous if both alleles are the same. An individual is heterozygous if they have one of each type of allele. Punnet squares are used to show all the possible combinations of the offspring. Sex cells (egg + sperm) will only carry one of the alleles that a parent has. Individuals therefore get one allele from each parent. Click on shark to return to home page

15. Test yourself See if you can answer the following questions. Green colour in frogs is dominant to red colour. a) Assign suitable symbols for the two alleles for frog colour. b) What is the genotype of (i) a homozygous red frog (ii) a heterozygous green frog? c) Is it possible for two red frogs to produce any green offspring? Explain Chickens can be white or brown. If two heterozygous brown chickens (Bb) mate: a) Which is the dominant colour? Why? b) Draw a punnet square showing the possible genotypes of the offspring. c) What is the chance that they produce a brown chicken? ANSWER Write your thoughts down then click.

16. Problem solving challenge See if you can solve the following problem. Mice can be either white or black. A pure breed (homozygous) white and a pure breed (homozygous) black mouse were mated. They produced a litter of mice that were all black. The next time they produced a litter that were also all black. In fact, out of five litters all the offspring of these parents were black. These offspring are often referred to as the F 1 generation. Two black mice from the F 1 generation were then mated. a) Which colour is dominant? Why? b) What is the genotype of the F 1 generation? c) What is the likelihood of white mice being produced by two black mice from the F 1 generation? Use a punnet square to support your answer. ANSWER Write your thoughts down then click.

17. Final challenge See if you can meet the final challenge. A certain breed of cattle can either have a white coat or a brown coat. When pure breed brown and pure breed white individuals were mated they produced offspring that had hides that contained both brown and white colour. No offspring were purely brown and none were purely white. a) How can you explain this? b) How would you write the genotypes of the (i) brown cattle? (ii) white cattle? (iii) brown + white coloured cattle? c) If two brown + white coloured cattle were mated what sort of offspring would be produced? ANSWER Write your thoughts down then click.

18. Take your time to read each slide carefully. Do not use the mouse scroll under any circumstances. Follow instructions carefully. Some pages have timings so wait for them. Clicking on the shark icon in the top left corner will always take you back to the home page. It is important that you write your thoughts in your workbook before viewing answers. Good learning and may the fishes be with you! You may now click the shark icon to return to the home page and start the activity. Information page

19. If you chose B then you probably don’t have any idea even though the answer is not totally unrealistic. If you chose A you are not really correct, although males do determine some traits, such as the sex of the individual. Genetic inheritance investigation If you chose C or D then you are on the right track. However, as you will find out, it is a little bit more complicated. ANSWER Continue here Question: Which of the following best explains the observations on the previous slide when parents are the same colours?

20. Question: Which of the following best explains the observations on the previous slide when both parent fish are different colours? If you chose A then you are going down the wrong pathway. If you chose B you are on the right track but the answer is too general and vague. Genetic inheritance investigation If you chose C then you are on the right track. However, as you will find out, it is a little bit more complicated. ANSWER Continue here

21. If you chose B then you probably don’t have any idea even though the answer is not totally unrealistic. If you chose A you are on the right track but it is not the only possible explanation. Genetic inheritance investigation If you chose C you are also on the right track. Both A and C are possible explanations for both the observations. ANSWER Continue here Question: Which of the following best explains the observations on the previous slide when parents are same colours?

22. Test yourself Answers to questions. Green colour in frogs is dominant to red colour. a) Possible symbols might be G = greeng = red b) The genotype of a (i) homozygous red frog = gg (ii) heterozygous green frog = Gg c) It is not possible for two red frogs to produce a green frog. Red frogs contain only the g allele. Therefore the offspring will always receive one g allele from each red parent. This means they will always have the genotype gg and therefore be red. Chickens can be white or brown. If two heterozygous brown chickens (Bb) mate: a) The dominant colour must be brown because the chickens have one of each type of allele and brown is the phenotype that is observed. b) Possible genotypes are BB, Bb, bb press space bar to see the punnet square. c) 75% or 3 out of 4 would be brown. Continue here Bb Male parent Bb Female parent alleles B B b b BBBb bb =brown =white

23. Problem solving challenge Answers to problem solving. Mice can be either white or black. a) If the parents are both homozygous then the offspring must all get one of each type of allele. Since they all showed a black colour then the dominant colour must be black. b) The genotype of the F 1 generation is Bb. Press space bar to see diagram on right. c) When two F 1 mice are mated, the chance of a white mouse is 1 in 4 or 25%. Press space bar to see punnet square. Continue here Pure-breed BB or bb Bb Each offspring gets a “B” and a “b”. Bb Male parent Bb Female parent alleles B B b b BBBb bb =black =white

24. Final challenge Answer to final challenge. a) If both parents are pure breed they will each give one of the two types of alleles. So all the offspring have one of each type. Since both colours are shown this is an example of co-dominance. Neither trait is more “powerful” than the other or hides the other. b) Capital letters are used to represent each colour. (i) brown cattle have BB (ii) white cattle have WW (iii) brown + white coloured cattle have BW c) All three phenotypes could be produced if two brown + white coloured individuals were mated. The most likely are brown + white coloured offspring (50% chance). Press the space bar to see the punnet square. Continue here BW Male parent BW Female parent alleles B B W W BBBW WW =white =brown =brown + white

25. A tale of two fishes. Congratulations on completing this activity. Hopefully you have learnt about genetic inheritance. If you are unsure about anything or want something explained further feel free to ask questions in class.