Biology Answers

QUESTION FOURTEEN: PEDIGREE TREESANSWER FOURTEEN: PEDIGREE TREESa) In this pedigree tree the phenotypes of the individuals are given to you.By doing genetic crosses you can work out the genotypes of eachindividual.b) Generation I male (No. 1): ddGeneration II female (No. 2): ddGeneration III female (No. 2): Ddc) (i) Carries out the following cross:DdddDd Dddd ddThere is a 50% chance of another child being affected with cystic fibrosis.c) (ii) To determine the parents genotypes or genotype of male (3) and female (4)you need to look at the offspring’s genotypes and work backwards. Male (3) isaffected so he must be homozygous recessive dd. Since there is one affectedchild female (4) must be heterozygous Dd. If she was homozygous dominant,there would be no possibility of having affected children.For Achievement your answer should have TWO correct statements.a) States that a pedigree tree shows the phenotypesb) Has 2 out of the 3 genotypes correctc) Has 1 genotype correct in the crossThe above diagram shows a pedigree tree for a family affected by cystic fibrosis.This is a recessive genetic disease which affects the entire body.(a) Explain how (in general terms) the genotypes of individuals can bedetermined from a pedigree tree.(b)(c)(i)Using the letters D and d state the genotypes of the following individuals:Generation I male (No. 1):Generation II female (No. 2):Generation III female (No. 2):Carry out a cross to determine the probability of the male (3) and female(4) in Generation II having another child affected with cystic fibrosis.(ii) Explain how you determined the genotypes of male (3) and female (4).For Merit your answer should have TWO correct out of:a) Explains that the genotypes can be deduced by doing crosses orlooking at parent combinations to ascertain heterozygotesb) Has all 3 genotypes correctc) (i) Has carried out the genetic cross correctly (but has not given thepercentage chance)(ii) Explains either male (3) genotype or female (4)For Excellence your answer should have ALL correct