Overview of lectures & independent study Lecture 1. Introduction to genetic variation and inheritance Mendelian genetics: - monohybrid crosses - pedigree charts Independent study: Genetic dominance (not quite as simple as Mendel thought!) Independent study: Mendelian genetics: inheritance of X-linked traits Lecture 2. Mendelian genetics: - dihybrid crosses Recombination and linkage mapping Beyond Mendel: Multifactorial disorders Lecture 3. Population genetics: Hardy-Weinberg equilibium Independent study: Hardy-Weinberg online tutorial Independent study topics will be assessed! Quiz question: monohybrid cross In guinea pigs, rough coat (R) is dominant over smooth coat (r). A roughcoated guinea pig is bred to a smooth one, giving eight rough and seven smooth progeny in the F1. What are the genotypes of the parents and their offspring? In guinea pigs, rough coat (R) is dominant over smooth coat (r). A roughcoated guinea pig is bred to a smooth one, giving eight rough and seven smooth progeny in the F1. What are the genotypes of the parents and their offspring? Rough Smooth = dominant = recessive Parents : Phenotype: Genotype: Gametes: = RR or Rr = rr Rough RR or Rr R R or R r r r R Rr Rr R Rr Rr Offspring: 4/4 Rr = heterozygous = 100% rough X smooth X rr X r r r r R Rr Rr r rr rr 2/4 Rr = heteroz. = rough (50%) 2/4 rr = homoz. rec. = smooth (50%) Actual offspring: 8 rough (8*100/15) = 53%, 7 smooth (7*100/15) = 47% Mendel’s dihybrid crosses Mendel’s dihybrid crosses A dihybrid cross involves looking at the inheritance of two traits simultaneously E.g. Two traits of the seeds: Texture: Smooth (S) or Wrinkled (s) Colour: Yellow (Y) or Green (y) Dominant alleles are in CAPITALS Texture: Smooth (S) or Wrinkled (s) Colour: Yellow (Y) or Green (y) Parental cross Parental cross F1 generation (progeny) Texture: Smooth (S) or Wrinkled (s) Colour: Yellow (Y) or Green (y) F1 X F1 cross F1 X F2 progeny F1 What are the F2 progeny a) genotypes? B) phenotypes? F2 progeny Phenotypes (out of 16 seeds): Smooth yellow = Smooth green = Wrinkled yellow = Wrinkled green = F2 progeny: 9 3 3 1 9 different genotypes 4 different phenotypes (9:3:3:1 ratio) Mendel’s Second Law The Principle of Independent Assortment: Genes for different traits assort independently of one another in gamete production Worked example of a dihybrid cross Purple flowers (P) are dominant to white flowers (p) Fat pods (F) are dominant to thin pods (f) 1. What is the genotype of a plant heterozygous at both loci? 2. What is the genotype of a plant with white flowers and thin pods? 3. What are the genotypes and phenotypes of the progeny of a cross between these two plants? Worked example of a dihybrid cross Purple flowers (P) are dominant to white flowers (p) Fat pods (F) are dominant to thin pods (f) 1. What is the genotype of a plant heterozygous at both loci? Pp Ff Gam: PF Pf pF pf 2. What is the genotype of a plant with white flowers and thin pods? pp ff Gam: pf 3. What are the genotypes and phenotypes of the progeny of a cross between these two plants? pf PF Pf pF pf pP,Ff pP,ff pp,fF pp,ff = purple purple white Fat Thin Fat white Thin ¼ (25%) ¼ (25%) ¼ (25%) ¼ (25%) Mendelian inheritance: learning outcomes By the end of this topic (and independent study) you should be able to: 1) Understand the basis of Mendel’s Laws and how he derived them using experiments with pea plants. 2) Be able to explain the concept of dominance, including codominance and incomplete dominance. 3) Be able to carry out inheritance predictions in mono-hybrid and dihybrid crosses, including for X-linked traits, and apply this knowledge to simple problems. 4) Understand how Mendel’s Laws apply to the inheritance of monogenic traits in humans. NB This includes content covered in the first lecture, and independent study associated with this topic. What next? • Find these slides and lots of practice questions, as well as links to other learning resources on Canvas. • Investigate the independent study topics that go beyond the lecture material – this is essential for scoring high marks in assessments (if you are aiming for a bare pass, the lecture material alone is the bare minimum). • Have a go at the practice questions and quizzes. Where the answers are provided only use them once you have had a go yourself! • If you have questions or need further support either email me or book an appointment (see Canvas homepage). NB The images of Mendel’s crosses in this lecture are taken from the iGenetics text book (available in the library)
