GAUTENG DEPARTMENT OF EDUCATION SENIOR SECONDARY INTERVENTION PROGRAMME LIFE SCIENCES GRADE 12 SESSION 3 (LEARNER NOTES)
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TOPIC 1: MENDEL’S 1ST LAW, SEX AND BLOOD GROUP DETERMINATION Learner Note: Mendel’s Laws are very important and you must understand the basic concepts of Genetics. You must understand the concepts of dominance and how this plays a role in monohybrid crosses (mono = one = one characteristic or trait). Be aware of confusing the word ‘cross/ crossing’ with ‘crossing over’ in Meiosis. You cross individuals and calculate the chances of a characteristic or trait being in the offspring. “Crossing over’ takes place in Meiosis during prophase where pieces of chromosomes cross over from the male chromosomes to the female chromosomes to ensure a mix of the characteristics in the offspring. You must be clear of the difference between these two terms. Questions on blood group inheritance and sex determination are often asked during examinations. The more examples of genetic crosses you do, the better you will be. QUESTION 1: 6 minutes (Taken and adapted from Study & Master Biology Grade 11) 1. Blood typing can be used to identify a parent in that the blood type can prove that a person is not the parent of a child rather than determine without question who the parent is. A, B, AB and O blood groups are the result of three alleles. Allele A and B are co-dominant and O is recessive to both A and B. Should the discrepancy continue, tissue typing and DNA fingerprinting will be used. Read through the following information and answer the questions below: In a maternity ward of a hospital, two newly born babies were mixed up. One baby is blood type O and the other is type A. Both mothers believe the baby with blood type O is their baby. Can you sort it out? On testing the parents’ blood it was found that: 1. Mr. Xhosa is blood group AB and his wife is blood group B 2. Mr. Mbundwini is type A.
Who owns baby ‘O’ and who owns baby ‘A’? Explain / show your reasoning.  (Remember that in blood groups there are three alleles A, B and O. A and B are co-dominant over O which is recessive. There must be two of the same alleles if a recessive trait is present in the individual) SECTION A: TYPICAL EXAM QUESTIONS – PLEASE adhere to the time allocations. GAUTENG DEPARTMENT OF EDUCATION SENIOR SECONDARY INTERVENTION PROGRAMME LIFE SCIENCES GRADE 12 SESSION 3 (LEARNER NOTES)
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QUESTION 2: 11 minutes (Taken and adapted from Study&Master Biology Grade 11) 2. The diagram below shows the inheritance of eye colour in humans. The squares represent men and the circles, women. The individuals represented in shaded symbols have brown eyes and the unshaded symbols have blue eyes. Brown eye colour (B) is dominant over blue eye colour (b). 2.1. Use the letter B and b as indicated and write down the genotypes of the individuals numbered 1 to 5. (5) (Remember that genotype will be what is in the genes and not what you can see) 2.2. Draw a diagramatic representation of all the genetic combinations with regard to eye colour, of the descendants when 6 marries a woman with the same genetic composition as 3. Use the letters B and b to show the genotype and phenotype of this F1 generation. (6) (Remember to use a Punnit square. Refer to your notes to check that you write all the information required or you will loose unnecessary marks) 
QUESTION 3: 13 minutes (Taken from DoE Additional Exemplar 2008 Paper 1) 3. Study the family tree below which shows the inheritance of sex and type of earlobes over four generations of a family. In humans, free earlobes (F) is dominant over attached earlobes (f). GAUTENG DEPARTMENT OF EDUCATION SENIOR SECONDARY INTERVENTION PROGRAMME LIFE SCIENCES GRADE 12 SESSION 3 (LEARNER NOTES)
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3.1. How many members of the family have free earlobes? (1)
3.2. What proportion of offspring in the fourth generation are females with attached earlobes? (2) 3.3. If the genotype of person A is FF,...
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