Understanding Pedigree Problems

PEDIGREE PROBLEMS A pedigree is a representation of the genetic relationship among a group of individuals. Pedigrees can be used for a number of different purposes in the study of genetics including such things as determining the genotype of an individual in the group, predicting the chances of birth defects caused by certain alleles, and determining whether a trait is controlled by a dominant or recessive trait Determining if a trait is dominant or recessive: If the gene is dominant, every individual that has the trait must have a parent with the same trait If the gene is recessive, individuals may express without having parents with the same trait ** we are assuming no mutations have occurred Determining if a trait is autosomal or X-linked: If the gene is X-linked, mostly males will exhibit the trait If the gene is X-linked, if the affected individual is a female her dad must also exhibit the trait PEDIGREE 1: MYOPIA (nearsightedness) The following pedigree represents a family history with myopia. We shall assume the trait is transmitted by a single pair of genes. 1. Write the genotype for each individual on the line beneath it. 2. Use A and a to represent the dominant/recessive alleles 3. Is the trait controlled by a recessive or dominant allele? EXPLAIN using specific examples 4. Is the trait autosomal or X-linked? EXPLAIN using specific examples PEDIGREE 2: POLYDACTYLY (extra finger on each hand) The following pedigree represents a family history with polydactyly. We shall assume the trait is transmitted by a single pair of genes. 1. Write the genotype for each individual on the line beneath it. 2. Use E and e to represent the dominant/recessive alleles 3. Is the trait controlled by a recessive or dominant allele? EXPLAIN using specific examples 4. Is the trait autosomal or X-linked? EXPLAIN using specific examples PEDIGREE 3: RED GREEN COLOR BLINDNESS The following pedigree represents a family history with red green color blindness. We shall assume the trait is transmitted by a single pair of genes. 1. Is the trait controlled by a recessive or dominant allele? EXPLAIN using specific examples 2. Is the trait autosomal or X-linked? EXPLAIN using specific examples 3. Write the genotype for each individual on the line beneath it. 4 Use R and r to represent the dominant/recessive alleles PEDIGREE 4: TORTOISE SHELL (CALICO) COLORING OF CAT FUR The following pedigree is the inheritance of black, orange and tortoise-shell coat patterns( black and orange on a white background) in domestic cats (Felis catus). How this happens: In the development of the embryo, a certain cell which will grow into a large area of skin apparently becomes modified so that the hair which grows from it will only express the allele for orange. Another cell which will grow into an adjacent area of skin apparently becomes modified so that its offspring will only express the allele for black hair. 1. How many female calico cats are represented in the pedigree? male calico cats? 2. Explain how a male cat could have calico coloring. What do we call humans with this phenomenon? 3. What types of inheritance are shown with calico cat coloring? 4. Write the genotype for each individual on the line beneath it. 5. Use B for Black and O for Orange