Chapter 8 Principle of Inheritance (Part 2) PDF

10/1/20 Chapter 8 Principle of Inheritance (Part 2) Complex Pattern of Inheritance • Dihybrid Cross: genetic crosses involving two traits simultaneously - Mendel’s pea experiment: seed color and shape are controlled by genes on different chromosomes - Seed color: yellow (dominant) green (recessive...

10/1/20 Chapter 8 Principle of Inheritance (Part 2) Complex Pattern of Inheritance • Dihybrid Cross: genetic crosses involving two traits simultaneously - Mendel’s pea experiment: seed color and shape are controlled by genes on different chromosomes - Seed color: yellow (dominant) green (recessive) - Seed shape: smooth (dominant) wrinkle (recessive) 1 10/1/20 Punnett Square: Complex Pattern of Inheritance • Incomplete Dominance: one allele for a specific trait is not completely dominant over the other allele Flower color in snapdragons: x Red = RR = White = rr Pink = Rr Figure 7.3 2 10/1/20 Complex Pattern of Inheritance • Codominance: neither allele is dominant to the other; heterozygote shows both traits Coat color in cattle: x Red = R1R1 = White = R2R2 Roan = R1R2 (patchy red and white) Figure 7.4 Complex Pattern of Inheritance • Sex-Linked Trait: result of genes located on the sex chromosomes - X-linked: located on the X chromosome - X-linked recessive trait: e. g. baldness, red-green colorblindness - X-linked dominant trait: less common, genetic disorder - Y-linked: located on the Y chromosome - Very few, e.g. hairy ear 3 10/1/20 (Karyotype: the arrangement of chromosomes) XX Male Female 4 10/1/20 X-linked Recessive Trait • For an X-linked recessive trait, if the mother is the carrier: - None of her daughter will be affected - 50% of her sons will be affected X-linked Recessive Trait • If the dad is affected and the mum is not a carrier, what is the chance of his daughters and sons to be affected? - None of the daughters and sons will be affected - The daughters are carriers, who pass the traits to 50% of the grandsons! • Males are more likely to express recessive X-linked traits than females 5 10/1/20 X-linked Dominant Trait • For an X-linked dominant trait, if the mother is the carrier of a gene: - 50% of her daughters will be affected - 50% of her sons will be affected X-linked Dominant Trait • For an X-linked dominant trait, if the father is the carrier of a gene: - All of his daughters will be affected - None of his sons will be affected 6 10/1/20 Complex Pattern of Inheritance • Blood Typing (ABO): three alleles of one gene - IA and IB are codominant to each other - i is recessive to both other alleles - An individual will have two of these alleles Red blood cell phenotype Red blood cell genotype Type A Sugar A I AI A or I Ai Type B Sugar B I BI B or I Bi Type AB Sugars A and B Type O I AI B ii Figure 7.5 7 10/1/20 Lecture Activity: Use blood typing to exclude potential parents and predict child blood types • In 1944 Charlie Chaplin was involved in a legal battle over the paternity of a child born to Joan Barry. The baby was blood type B, the mother type A, and Chaplin type O. • At the time of the trial, blood group evidence was not admissible in California courts. Charlie Chaplin was declared responsible for the child's support. Lecture Activity: Use blood typing to exclude potential parents and predict child blood types • The woman has type A blood, her father had type O blood and her mother type AB. • Her husband has type AB blood, his mother had type A and his father type B. • What’s the percentage of this couple's children expected to have type AB blood? 8 10/1/20 Blood Transfer: Sugar (antigen) on red blood cell + Its antibody in plasma = immune response - bad in this case! Receive blood from: O A or O B or O A, B or O DNA Fingerprinting • It is a modern method used for unambiguous identification of people • The basis for DNA fingerprinting: differences in nucleotide sequences of their DNA • Steps: - Extract DNA out of the body - Cut DNA into fragments with restriction enzymes - Separate them on basis of size and visualize them 9 10/1/20 - Each person will have a unique pattern of bands - All bands of the child should be found in the parents Adult 1 Adult 2 Adult 3 Adult 4 Adult 5 Adult 6 Child 1 Child 2 Child 3 Figure 7.18 Lecture Activity: Extract DNA from Everything! • Handout online downloaded from: http://learn.genetics.utah.edu/content/labs/extract ion/howto/ • Take photos while you work on each step. Paste them into a PowerPoint slide and show me. • Count for 5 extra credits in Exam 2 10