The Pedigree. NOTE: there are no definite conclusions that can be made from a pedigree. However, there are more likely and less likely explanations

Transcription

1

2 The Pedigree A tool (diagram) used to trace traits in a family The diagram shows the history of a trait between generations Designed to show inherited phenotypes Using logic we can deduce the inherited genotypes NOTE: there are no definite conclusions that can be made from a pedigree. However, there are more likely and less likely explanations

3 Interpreting Pedigrees: 1. Each row on a Pedigree Represents a generation of the family Generation 1 P 1 Generation 2 F 1 Generation 3 F 2

4 Each shape in the pedigree represents an individual In a group of siblings the oldest is always placed on the left Shading is used to illustrate whether or not an individual displays a trait A pedigree MUST have a key (legend) explaining what trait a shaded or unshaded individual displays

5 Pedigree Symbols Pedigrees involve a number of symbols. Here are some of the more common ones that you will see: This symbol represents a Female p p This symbol represents a Male This symbol represents and Undetermined or Undesignated Gender This symbol represents a Deceased (dead) individual This symbol represents a Pregnant Individual (which biologically can only be a female)

6 This symbol represents a Mating (Or marriage, parents, couple or whatever ) This symbol represents a Divorce (Separation) This symbol represents a 2nd Mating This symbol represents a Consanguineous Mating (which is a fancy biological way to say that the mates are related) This symbol represents Siblings In a group of siblings the oldest is ALWAYS on the left

7 These symbols represent Identical Twins These symbols represent Fraternal Twins This symbol represents an Adopted Out Individual (individual put up for adoption) This symbol represents an Adopted In Individual (individual adopted into a family)

8 Determining whether a trait is Dominant or Recessive: The Key Pedigrees are useful for determining whether or not a trait is likely dominant or recessive When trying to determine whether a trait is dominant or not, look for this scenario in the pedigree: Both Parents (P 1 ) exhibit the same version of a trait Shaded = Brown hair Non Shaded = Blond hair Offspring (F 1 ) exhibit different versions of a trait than the parents In this case the parents phenotype is dominant and both parents must be heterozygous

9 Determining whether a trait is Dominant or Recessive: Consider: P 1 Shaded = Brown hair Non Shaded = Blond hair F 1 All offspring have brown hair which would suggest that Blond hair is dominant over brown hair in this case B = Blond b = Brown What is the likely genotype of this individual? Bb

10 Determining whether a trait is Dominant or Recessive: Pedigrees are useful for determining whether or not a trait is likely dominant or recessive BUT they can be ambiguous Consider: Shaded = Brown hair Non Shaded = Blond hair P 1 F 1 No Key All offspring have brown hair which would suggest that Brown hair is dominant over blond hair AND each of these individuals is heterozygous What is the likely genotype of this individual? Bb B = Brown b = blond

11 Determining whether a trait is Dominant or Recessive: BUT: Shaded = Brown hair Non Shaded = Blond hair: P 1 F 1 No Key All offspring have brown hair which could also be possible if Brown hair is recessive in which case each of these individuals is homozygous recessive B = Blond b = Brown What is the likely genotype of this individual? bb B = Blond b = brown

12 Practice Question #1: (a) What trait is dominant? Explain your answer. (b) Is Whirling a sex linked trait? Explain your answer. (c) What is the probable genotype of each numbered individual? Explain your answer.

13 Determining whether a trait is sex linked Pedigrees can also be used to determine whether a trait is likely sex linked Consider: Shaded = normal vision Non shaded = colour blindness F 1 P 1 What is the likely genotype of this individual? X B X b F 2 Notice: Normal vision seems to be dominant over colour blindness BUT the recessive trait appears predominantly in males This indicates that colour blindness is most likely sex - linked

14 Practice Question #2: (a) What trait is dominant? Explain your answer. (b) Is this a sex linked trait? Explain your answer. (c) What is the probable genotype of each numbered individual? Explain your answer

15