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1. PEDIGREE ANALYSIS (4)

2. INTRODUCTION
A pedigree is a chart that shows the inheritance of a trait over several generations.
 It is commonly created for families, and it outlines the inheritance patterns of
genetic disorders and traits.
 It can help predict the probability that offspring will inherit a genetic disorder.
 From studying a pedigree, scientists can determine if a trait is sex-linked or
autosomal (not carried on the sex chromosome).
 Human genetics are different from Mendelian pattern of inheritance since one
cannot force humans to mate with someone they do not like.
 Human inheritance patterns are identified by examining the family trees.
 Mendelian- inheritance laws are still followed.

3. SYMBOLS USED IN HUMAN PEDIGREE ANALYSIS
• In a pedigree, squares symbolize males, and circles represent females.
• A horizontal line joining a male and female indicates that the couple had offspring.
• Vertical lines indicate offspring which are listed left to right, in order of birth,
oldest on the left.
• Shading of the circle or square indicates an individual who has the trait being
traced.
• In the following pedigree, the inheritance of the recessive trait is being traced.
• A is the dominant allele, and a is the recessive allele.

4. Generations

5. Pedigree analysis
• Affected persons have at least one affected parent
• Each generation will have an affected individual if the trait is dominant
• If the trait is recessive, individuals expressing the trait will have 2
phenotypically Normal parents.
• Two affected parents will have an affected child
• If it is a recessive X linked trait, there will be no father to son
transmission, since the males are affected.
• Traits may skip a generation.
• If a child is affected but parents are not, then both parents are
heterozygous for the trait

6. Mode of inheritance
Pedigree analysis is used to determine mode of inheritance:
• Autosomal dominant
• Autosomal recessive
• X- linked

7. Autosomal dominant
Dominant mutant alleles produce mutant phenotypes because of
GAIN OF FUNCTION MUTATIONS >>gene products
• Traits do not skip a generation
• There is an equal # of affected males as females
• Affected parents can have un affected children

8. Autosomal recessive inheritance
• Affected individuals have 2 normal heterozygous parents
• The trait appears in the F1 as a 25% of the progeny being
HOMOZYGOUS of the recessive allele
• If a homozygous recessive person mates with a homozygous normal
person, they will produce a heterozygous individual, who will not
show the trait.
• Recessive traits skip a generation.
• When both parents are affected; they are HOMOZYGOUS for the
recessive trait.

9. Sex linked
• Sex linked characters usually affect the males and are caused by a
recessive allele on the X chromosome.