Transcript File
The Post-Mendel Era Exceptions to Mendel Problem • Cross a homozygous red flowered plant with a homozygous white flowered plant. (R and r) • What offspring do you expect? • After the time of Mendel we have discovered most genes are more complex then simply dominant and recessive • Examples – Incomplete dominance – Codominance – Multiple alleles Incomplete Dominance • The blending of two different traits in a heterozygous genotype • Example: red and white crossed making pink • WW RR RW Practice Problem • Incomplete Dominance – If color exhibits incomplete dominance in violets, what will be the phenotypes of the offspring of a homozygous red and a homozygous white plant? Incomplete Dominance Incomplete Dominance W W R R RW RW RW RW Codominance • In a heterozygous genotype both genes are fully expressed. • Example yellow begonias crossed with red Codominance Practice Problem • Codominance – Cross a cat with black fur (B) with a cat that has tan fur (b). If we assume that fur color exhibits codominance, what will be the phenotypes of the offspring. (Hint: black and tan fur together make a color called “tabby” in cats). Practice Problem • Codominance – What if we wanted to get some cats that have tan fur, some with black, and some tabby? What would have to be the phenotypes of the parents? Multiple Alleles • More then two alleles can exist for one trait. • Each individual can only have two. This leads to more than three possible genotypes. • In the example of blood type where 3 alleles exist there are 6 genotypes and 4 phenotypes possible I A I B i • Above are the three possible alleles for blood type. You have a combination of two of these. • Phenotype (blood type) Genotype A I I or I i A A B AB O Bl II A II ii B B B A or Ii B • IA and IB are codominant • i is recessive Practice Problem • Multiple Alleles – What are the chances of a woman with Type AB and a man with Type A having a child with Type O? Practice Problem • Multiple Alleles – Dr. Paul is blood type O. His father was blood type A and his mother was blood type B. What were the genotypes of his parents? California Court Case • 1946 the California supreme court ruled that Charlie Chaplin was the biological father of child he claimed was not his. • His defense was that the baby had type B blood. He had type A and the woman who sued him had type O • Was the court correct? 19 AA, AO = Type A i i A Ai Ai i ii ii BB, BO = Type B AB = Type AB OO = Type O The judge should take a course in genetics! 20 Polygenic • Describes a trait that is controlled by more than one pair of alleles • This allows for a variety of intermediates • Human height, skin and hair color, body build. Polygenic traits tend to form a bell curve Sex linked inheritance • • • • A trait that travels on the X chromosome. Results that men can not be carriers Women can be carriers For a woman to be afflicted she has to have an afflicted father and a mother that is either afflicted or a carrier