Genetic Pedigree Diagrams
What are genetic pedigree diagrams? Show how an inherited trait (characteristic) runs in a group of related individuals. You might have to interpret genetic diagrams to work out the genotypes or potential phenotypes of individuals.
Cystic Fibrosis Inherited disorder that causes the production of a thick mucus, which affects the lungs and digestive system. It is caused by a faulty recessive allele (f). A person with CF is homozygous from the allele (ff). (Ff) is a carrier of CF.
Unaffected male Unaffected Female Male with CF Female with CF Key shows what the shapes represent Two parents are joined by a horizontal line Vertical line goes from parents to children Children have a vertical line above them This female is CF (ff), but neither of her parents do. She must have inherited an f allele from each parent, so both parents must be carriers (Ff). This male has CF (ff), like his mother (ff). He's inherited an f allele from each parent, so his father must be a carrier (Ff).
Possible Question Work out the chances of the next child born to individuals 4 and 5 having CF.
Question Huntington's disease is caused by a dominant allele. The genetic pedigree diagram shows the inheritance of Huntington's disease in one family What is the genotype of individual 1? 2.What would the possible genotypes of the offspring produced by a cross between individuals 3 and 5? Affected female Unaffected Male
Answers 1.Heterozygous, e.g. Hh The cross between individual 1 and 2 has produced one affected child. As the unaffected child must have two recessive alleles, one from each parent, individual 1 must have one recessive allele and one dominant allele (Hh) to have the disorder and pass on an unaffected allele. 2.Heterozygous (Hh) and Homozygous recessive (hh). Individual 5 is unaffected so must be homozygous recessive (hh). Individual 3 has the disorder so must have at least one dominant allele, but they must also have one recessive allele from their unaffected parent (individual 2), so must be heterozygous (Hh)