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Pedigree Charts The family tree of genetics What is a pedigree? Constructing a pedigree Interpreting a pedigree Some History Hemophilia has played an important role in Europe's history The disease began to crop up in Great Britain's Queen Victoria’s children It became known as the "Royal disease" because it spread to the royal families of Europe through Victoria's descendants How it Spread it spread through the Royal Houses of Europe as monarchs arranged marriages to consolidate political alliances. We can trace the appearance of hemophilia as it popped up in Spain, Russia, and Prussia by looking at the family tree. The Royal Family Tree What is a Pedigree Chart? A Pedigree chart traces the inheritance of a particular trait through several generations. One GOAL of using a pedigree chart is to figure out who are carriers of the trait, because this information is typically unknown. Steps to Creating a Pedigree 1. A genetic counselor will first gather information regarding who the family members are and how are they related. This will go back a few generations. 2. The genetic counselor will then ask who has the trait of interest. (Shows the trait) 3. After researching, the genetic counselor uses all of this information to construct a Pedigree chart, with all the family members’ names and genotypes written below each symbol. Constructing a Pedigree Male Female Constructing a Pedigree Married Couple– Horizontal Line Siblings – Vertical line More than one Sibling: – a horizontal line is drawn with a vertical line coming down for each sibling. Constructing a Pedigree Roman numerals to the left of the pedigree show the generations. Birth Order: children are listed in birth order with oldest on left and youngest on the right. I II III Constructing a Pedigree Fraternal twins– Two line branching from the same point – two eggs and two sperm cells. Identical twins– Also called Maternal Twins – Identical or Maternal Twins (first set above) are drawn branching off of the same point, but are also connected to each other More Symbols in a Pedigree Chart Full Shaded: – Affected person who shows a disorder Half shaded: – Autosomal carrier Circle with dot: – X-linked carrier –always female Deceased Sex-Linked Traits Genes located on the X chromosomes (some cause diseases) The Y is much smaller, contains few genes Sex Linked Disorders – Color Blindness (red-green) – Hemophilia ("bleeders disease) – Duchenne Muscular Dystrophy (weakening/loss of skeletal muscles) More common for males to display disorders Sex-Linked Traits Consider hemophilia How do you find the genotypes of the persons in the chart? Start with the person showing the trait. Look at parents of this individual and ask yourself: what would the parent’s genotypes have to be (in a Punnett square) to produce an offspring with this genotype? If there is not enough information to figure out the entire genotype then a question mark is used to take the place of the uncertain allele. Ex. T? Example Problem Shaded=deaf (D) is normal hearing (d) is deaf Is deafness a dominant or recessive trait? recessive To show deafness, what genotype does this son have to have? dd For two parents who have normal hearing to have a deaf son, they both must be carrier. What are the parent genotypes? Dd Example Problem Write the genotypes for the parents and son under the correct circle/boxes, half-shading carriers. Shaded=deaf (D) is normal hearing Dd Dd (d) is deaf dd Predicting using Pedigree Charts Pedigrees are used to find out: – who are carriers of the disorder & – the probability of having a future child with the disorder. To begin to interpret a pedigree, first determine if the disorder is: – Autosomal dominant – Autosomal recessive – Sex-linked (carried on the X chromosome) Interpreting a Pedigree Chart First ask: Is it a Sex-linked or Autosomal Disorder? – If there is a much larger number of males than females who are affected then the disorder is Sex-linked. – If there is a 50/50 ratio between males and females who are affected then the disorder is autosomal. Interpreting a Pedigree Chart If it is autosomal disorder then ask: Is it dominant or recessive? – If two parents do not show the trait and their children do show it, then it is an autosomal recessive disorder (parents are heterozygous) – If the disorder is autosomal dominant, then at least one of the parents must show the disorder. Note: The following pedigree charts show infected individuals only. Carriers are unknown at this point. Practice Examples Does this pedigree show a Sex-linked or Autosomal disorder? Answer: Sex-Linked Disorder much larger number of males are affected Practice Examples Does this pedigree show a Sex-linked or Autosomal disorder? Answer: Autosomal Disorder 50/50 ratio between males and females Practice Examples Does this pedigree show a Autosomal Dominant or Recessive disorder? Answer: Autosomal Dominant Disorder At least one parent of the affected children show the disorder Practice Examples Does this pedigree show a Sex-linked or Autosomal disorder? Answer: Autosomal Disorder 50/50 ratio between males and females Practice Examples Does this pedigree show a Autosomal Dominant or Recessive disorder? Answer: Autosomal Recessive Disorder Two parents do not show the trait and their children do show it (heterozygous parents) Autosomal Recessive Genotypes and Carrier determination D = Normal hearing Dd dd Dd dd Dd dd Dd d = deafness Dd dd dd Dd dd D?