Basic Genetics analyzing Pedigrees

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Basic geneticsAnalyzing Pedigrees The pedigree method consists of an analysis for aparticular trait, when the results have already been made. Usually diagrams orcharts are used to attempt to find patterns of inheritance. Pedigrees are theoldest methods of genetic information and are still used in studies of humaninheritance and animal breeding. The first step is to determine whether thegene being studied is dominant or recessive. Recessive genes are difficult tokeep track of, for they are hidden by their dominant alleles one generationafter another. An important thing to remember is that one can not determineoffhand which individual is a carrier of a specific trait, until the trait isexpressed in someone.Traits that are dependent on certain recessive genesmay suddenly appear without any previous record of a relative having thistrait. Recessives are more likely to become expressed in families where thefather and mother are closely related, or descended from a common ancestor. Nextone must identify the genotypes of as many family members as possible with theinformation given. For example if a man expresses the recessive gene for thetrait of adherent earlobes, the man must be homozygous (aa) for his genotype. Bothof his parents must be heterozygous (Aa) carriers for each to have contributeda gene to their son. One may then conclude that his brothers and sisters musthave the genotype of AA or Aa, but not aa for they do not express the trait ofadherent earlobes. The best probability is that each parent is Aa, thereforethe likelihood of a child having free earlobes with a genotype of Aa istwo-thirds and a genotype of AA, one-third. Without any more information onecan assume that the man's sibling's can be Aa with two-thirds probability and afifty percent chance for being a carrier of the recessive gene, if theirparents are also carriers.Family Pedigree Pedigrees are very similar to family trees, exceptpedigrees study a certain trait within a family. Every generation isrepresented by a Roman numeral, and each member of the generation by an Arabicnumeral. Males are represented by a square and females by a circle. If thesymbol is shaded that person expresses or has the studied trait. For example,the two generation pedigree below shows that the father expresses the trait, asdoes his daughter, but no other family members Making your own family pedigree is easy. All thematerials you will need is paper, a pencil or pen and a colored marker. Draw anoutline of your family starting with your grandparents, leading to yourparents, uncles, aunts and then yourself, any siblings or cousins. The abilityto roll one's tongue is a noticeable dominant trait. Anyone who can roll theirtongue has the dominant allele R while those who cannot have the genotype rr. Findout if you can roll your own tongue, if not enter your genotype on the pedigreeas rr. If you can, write your genotype as one R for you have the dominant gene.Ask family members on your pedigree if they are able to roll their tongues. Thenwrite down the appropriate genotypes by their symbol on the chart