pedigree charts the family tree of genetics what is a pedigree? constructing a pedigree interpreting...
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Pedigree ChartsThe family tree of genetics
What is a pedigree?
Constructing a pedigree
Interpreting a pedigree
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What is a Pedigree Chart?1. A Pedigree chart traces the inheritance of a
particular trait through several generations.
2. One GOAL of using a pedigree chart is to figure out who are carriers of the trait, because this information is typically unknown.
a. Carrier: someone who is heterozygous for a trait.
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Constructing a Pedigree
Male
Female
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1. Mated Pair:– Horizontal Line
2. Children: - Vertical line
3. More than one child:– a horizontal line is drawn
with a vertical line coming down for each sibling.
Constructing a PedigreeSlide # 4
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1. Fraternal twins- can be the same or different gender
a. Two line branching from the same point
b. two different eggs and two different sperm cells.
2. Identical twins-always same gender
a. Also called maternal twins
b. Same as fraternal twins but a horizontal line is added.
c. One egg and one sperm unite and later split to create two babies
Constructing a PedigreeSlide # 5
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I
II
III
Generations1. Roman numerals to the left of the pedigree show the generations.
2. Birth Order: children are listed in birth order with oldest on left and youngest on the right.
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More Symbols in a Pedigree Chart
1. Full Shaded:a. Affected person who
shows a disorder2. Half shaded:
– Autosomal carrier 3. Circle with dot:
– X-linked carrier –always female
4. Deceased
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1. Pedigrees are used to find out:
a. who are carriers of the disorder
b. the probability of having a future child with the disorder.
2. To begin to interpret a pedigree, first determine if the disorder is:
a. Autosomal dominant
b. Autosomal recessive
c. Sex-linked (carried on the X chromosome)
Predicting using Pedigree ChartsSlide # 8
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Interpreting a Pedigree Chart
First ask: Is it a Sex-linked or Autosomal Disorder?
1. If there is a much larger number of males than females who are affected then the disorder is Sex-linked.
2. If there is a 50/50 ratio between males and females who are affected then the disorder is autosomal.
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Interpreting a Pedigree Chart
1. If it is autosomal disorder then ask:Is it dominant or recessive?
2. If two parents do not show the trait and their children do show it, then it is an autosomal recessive disorder
- (parents are carriers or heterozygous)
3. If the disorder is autosomal dominant, then at least one of the parents must show the disorder.
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Note:1. The following pedigree charts show affected
individuals only.
2. Carriers are unknown at this point.
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Practice Examples Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer: Sex-Linked disorder much larger number of males are affected
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Practice Examples Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:Autosomal disorder 50/50 ratio between males and females
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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
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Practice Examples Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:Autosomal disorder 50/50 ratio between males and females
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Practice Examples Does this pedigree show a Autosomal
Dominant or Recessive disorder?
Answer:Autosomal recessive disorder Two parents do not show the trait but their children do show it (heterozygous parents)
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dddd dd dd
dddd
Dd Dd Dd Dd
Autosomal Recessive Genotypes and Carrier determinationD = Normal hearing d = deafness
Dd
Dd
D?
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