Using Pedigrees to interpret Mode of Inheritance

Transcription

1 Using Pedigrees to interpret Mode of Inheritance

2 Objectives Use a pedigree to interpret the mode of inheritance the given trait is with 90% accuracy.

3 11.2 Pedigrees (It s in your genes) Pedigree Charts A pedigree chart shows the relationships within a family similar to a family tree or blood line of animals. Genetic counselors analyze pedigree charts to infer the genotypes of family members. Copyright Pearson Prentice Hall

4 A horizontal line connecting a male and a female represents a marriage. Reading a Pedigree A shaded circle or square indicates that a person expresses the trait. I II A circle represents a female. A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person does not express the trait. Roman numerals represent the generation # III

5 Interpreting a Pedigree The main question asked when looking at a pedigree is what is the mode of inheritance. The first thing to do is to decide whether the trait of interest is dominant or recessive? The second step is to decide whether the trait is Autosomal or Sex Linked (aka X-linked)

6 Interpreting a Pedigree Determine whether the disorder is dominant or recessive. If the disorder is dominant, one of the parents must have the disorder. Usually found in every generation

7 Interpreting a Pedigree If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous. Usually (but not always) skips generations

8 Fast Track to Pedigree Question 1. The recessive trait will be anyone with a phenotype that is different than both of their parents 2. It is autosomal if any girls with the recessive phenotype have a father OR a son with the dominant phenotype: If X-linked dominate affected fathers must pass the trait on to all their daughters Typically in X-linked recessive only males affected

9 Other Cheats to interpreting a pedigree Determine if the pedigree chart shows an autosomal or X-linked disease. If most of the males in the pedigree are affected, then the disorder is most likely X-linked If it is a 50/50 ratio between men and women the disorder most likely autosomal.

10 Pedigree Practice What is the mode of inheritance? X-linked Dominant- every gen. & father to all daughters

11 Pedigree Practice What is the mode of inheritance? X-linked recessive -Only males are affected and sons do not share the phenotype of their father

12 Autosomal Recessive- II-3 girl s father has dominant phenotype Pedigree Practice What is the mode of inheritance?

13 Pedigree Practice What is the mode of inheritance? Autosomal Recessive- II- 6 girl s father has dominant phenotype and she had dominant sons

14 Pedigree Practice What is the mode of inheritance? Autosomal Dom.- every gen. & in both male & female

15 Need more information? The following slides show the more complete way of assessing pedigrees and interpreting the mode of inheritance.

16 Rules of Inheritance Autosomal Dominant Appears in both sexes with equal frequency Both sexes transmit the trait to their offspring Does not skip generations Affected offspring must have an affected parent unless they posses a new mutation

17 Rules of Inheritance Autosomal Dominant When one parent is affected (het.) and the other parent is unaffected, approx. 1/2 of the offspring will be affected Unaffected parents do not transmit the trait

18 Rules of Inheritance Autosomal Recessive Appears in both sexes with equal frequency Trait tend to skip generations Affected offspring are usually born to unaffected parents When both parents are heterozygous, approx. 1/4 of the progeny will be affected Appears more frequently among the children of consanguine (blood) marriages

19 Rules of Inheritance X-Linked Dominant Both males and females are affected; often more females than males are affected Does not skip generations. Affected sons must have an affected mother; affected daughters must have either an affected mother or an affected father

20 Rules of Inheritance X-Linked Dominant Affected fathers will pass the trait on to all their daughters Affected mothers if heterozygous will pass the trait on to 1/2 of their sons and 1/2 of their daughters

21 Rules of Inheritance X-Linked Recessive More males than females are affected Affected sons are usually born to unaffected mothers, thus the trait skips generations Approximately 1/2 of carrier mothers sons are affected

22 Rules of Inheritance X-Linked Recessive It is never passed from father to son All daughters of affected fathers are carriers