Genetics-Year-9-Key-Stage-3-Troilor.pptx

Genetics

1. Title: Genetics LO: Today we are learning about how characteristics are passed from parents to their offspring. After this topic you will be able to: Use a Punnett square to show what happens in a genetic cross. Explain dominant and recessive alleles of genes.

2. Starter Task What is the function of the nucleus of a cell? Female human gametes (sex cells) are called eggs. What are male human gametes called? What type of molecule is genetic information contained in? What is fertilisation? Humans have 23 pairs of chromosomes in each cell. How many is this in total? Extension: In as much detail as you can, explain how species change through the process of natural selection.

3. Starter Task (Answers) The nucleus stores genetic material (DNA) and controls the cell. Male human gametes (sex cells) are called sperm. The molecule that genetic information is stored in is called deoxyribonucleic acid (DNA). When an egg and a sperm cell meet, they fuse to form one new cell. This is fertilisation. Humans have 23 pairs of chromosomes in each cell; 46 in total. Extension: In as much detail as you can, explain how species change through the process of natural selection.

4. Group Reading Reader 1: Chromosomes come in pairs. One of each type comes from the mother and one from the father. These chromosomes contain many genes . Each gene controls one characteristic ; for example eye colour. You have two copies of each gene, one from each parent. These genes may be the same (e.g. both brown) or different (e.g. one brown, one blue). Reader 2: Different types of the same gene are called alleles . For example blue and brown are different alleles of the same gene. Usually only one of the two alleles is expressed . The one which is expressed is the dominant allele, and the other is the recessive allele.

5. Group Reading Reader 3: A dominant allele will always be expressed. We write alleles as a single letter and the dominant one is always a capital letter. The allele for brown eyes is a dominant allele (B). The allele for blue eyes is recessive (b). We inherit one allele from each parent. Whatever combination a person has, if a brown (B) allele is present, the person’s eyes will be brown. Reader 4: We use these letters to perform a genetic cross. A genetic cross can be used to predict the characteristics of offspring from two parents. Each sperm and egg cell will have one of the two alleles. A Punnett Square like this shows the possible combinations at fertilisation. BB = Brown Bb = Brown bb = Blue Father: Bb (brown eyes) Mother: bb (blue eyes) B b b b Bb (brown) Bb (brown) bb (blue) bb (blue)

6. Keywords Match each keyword to its correct meaning, then write down the keyword with its definition. Gene Characteristic Alleles Recessive Expressed A small section of DNA which controls a characteristic. Different versions of the same gene. A feature of an organism e.g. eye colour or height. The allele which is not expressed. The characteristic appears in the organism. Extension: Explain how it is possible for a parent with brown eyes to have a child with blue eyes, even though brown is the dominant allele. Dominant The allele which is expressed.

7. Keywords (Answers) Match each keyword to its correct meaning, then write down the keyword with its definition. Gene Characteristic Alleles Recessive Expressed A small section of DNA which controls a characteristic. Different versions of the same gene. A feature of an organism e.g. eye colour or height. The allele which is not expressed. The characteristic appears in the organism. Extension: Explain how it is possible for a parent with brown eyes to have a child with blue eyes, even though brown is the dominant allele. Dominant The allele which is expressed.

8. Task Boxes Choose at least two of the task boxes below to complete. How many alleles are there of each gene? Which is the dominant allele for eye colour; blue or brown? Questions Different types of the same gene are called ________ . For example blue and brown are different alleles of _____ _______ gene. Usually only one of the two alleles is __________. The one which is expressed is the __________ allele, and the other is the __________ allele. the same expressed recessive alleles dominant Copy and Fill in the Blanks Copy the Diagram: Can a father with the alleles BB (dominant brown) have a baby with blue eyes? Explain why/why not. Challenge Mother Rr Father RR Eggs R r Sperm R R The baby could have: RR Or Rr

9. Task Boxes (Answers) Choose at least two of the task boxes below to complete. There are two alleles of each gene. Brown is the dominant eye colour over blue. Questions Different types of the same gene are called alleles . For example blue and brown are different alleles of the same gene. Usually only one of the two alleles is expressed . The one which is expressed is the dominant allele, and the other is the recessive allele. the same expressed recessive alleles dominant Copy and Fill in the Blanks Copy the Diagram: A father with the alleles BB (dominant brown) cannot have a baby with blue eyes because the baby must receive a B allele from him. Only one B allele is needed for the eyes to be brown. Challenge Mother Rr Father RR Eggs R r Sperm R R The baby could have: RR Or Rr

10. Handout Sheet Task Use this information to help you to complete your handout sheet: Extension: Look at the diagram of these crossbred rabbits and their offspring. Explain in detail why the baby rabbits are different colours and suggest other characteristics that they might inherit from their parents. We use these letters to perform a genetic cross. A genetic cross can be used to predict the characteristics of offspring from two parents. Each sperm and egg cell will have one of the two alleles. A Punnett Square like this shows the possible combinations at fertilisation. This cross has a ½ (or 50%) chance of producing a blue-eyed baby. Father: Bb (brown eyes) Mother: bb (blue eyes) B b b b Bb (brown) Bb (brown) bb (blue) bb (blue)

11. Long fur is: Dominant Recessive Short fur is: Dominant Recessive Delete the incorrect words: A chromosome is a long string of carbohydrate/DNA . Chromosomes come in trios/pairs . One of each type comes from the offspring/mother and one from the father. These chromosomes contain many genes/nuclei . Each gene controls one/several characteristic; for example eye colour. You have two/several copies of each gene, one from each parent, and these ribosomes/genes may be the same (e.g. both brown) or different (e.g. one brown, one blue). A = long fur rabbit a = short fur rabbit Complete the Punnett squares to find the probability of the offspring having short fur. Male: Aa (long fur) Female: Aa (long fur) A a A a A A A a Chance of each offspring having short fur: 0% 25% 50% 75% 100% Chance of each offspring having short fur: none 1 in 4 1 in 2 3 in 4 all Ratio of short hair : long fur in offspring 0 : 1 1 : 3 1: 1 3 : 1 0 : 1 Chance of each offspring having short fur: ¼ ½ 1/3 1 Male: AA (long fur) Female: Aa (long fur) Male: AA (long fur) Female: aa (short fur) Male: aa (short fur) Female: Aa (long fur) A a a a

12. Long fur is: Dominant Recessive Short fur is: Dominant Recessive Delete the incorrect words: A chromosome is a long string of carbohydrate / DNA . Chromosomes come in trios / pairs . One of each type comes from the offspring / mother and one from the father. These chromosomes contain many genes / nuclei . Each gene controls one / several characteristic; for example eye colour. You have two / several copies of each gene, one from each parent, and these ribosomes / genes may be the same (e.g. both brown) or different (e.g. one brown, one blue). A = long fur rabbit a = short fur rabbit Complete the Punnett squares to find the probability of the offspring having short fur. Male: Aa (long fur) Female: Aa (long fur) A a A a A A A a Chance of each offspring having short fur: 0% 25% 50% 75% 100% Chance of each offspring having short fur: none 1 in 4 1 in 2 3 in 4 all Ratio of short hair : long fur in offspring 0 : 1 1 : 3 1: 1 3 : 1 0 : 1 Chance of each offspring having short fur: ¼ ½ 1/3 1 Male: AA (long fur) Female: Aa (long fur) Male: AA (long fur) Female: aa (short fur) Male: aa (short fur) Female: Aa (long fur) A a a a AA (long) Aa (long) Aa (long) aa (short) AA (long) AA (long) Aa (long) Aa (long) A A a a Aa (long) Aa (long) Aa (long) Aa (long) Aa (long) Aa (long) aa (short) aa (short)

13. Comprehension Questions Complete these questions in your book. If you get stuck ask for help or try the next one! Lillian’s mother has brown eyes (Bb) and her father has blue eyes (bb). Lillian’s mother is expecting another baby. Draw a Punnett Square and use it to work out the odds of Lillian’s new brother or sister having brown eyes. Lillian has brown eyes like her mother. She says that this means her own alleles must also be Bb. Is she correct? Which allele combination (BB, Bb or bb) would mean that a parent could never have a child with blue eyes? 4. Jack has some pet mice. Half of his mice have white fur (W) and the other half are albino (w). Which colour is dominant? 5. Jack breeds a white mouse (WW) with an albino mouse (ww). Does it make a difference to the colour of the offspring which mouse is the female? Challenge Questions: White Albino 6. Draw a Punnett square to show the odds of the offspring being albino. 7. Could the offspring of the first pair have albino offspring of their own?