Pedigrees Lecture

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The family tree of genetics

Pedigree charts1

Overview

I. What is a pedigree?

a. Definitionb. Uses

II. Constructing a pedigree

a. Symbols

b. Connecting the symbols

III. Interpreting a pedigree

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Autosomal dominant

If this were autosomal recessive, you would not expect individual #7 to not express the trait. Note that matings between non-expressing individuals always produce non-expressing offspring. This tells you that the expressed trait is dominant.

What is a pedigree?

• A graphic representation of how a trait is passed from parents to offspring.

• A chart of the genetic history of family over several generations.

• A genetic counselor would find out about your family history and make this chart to analyze.

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Constructing a pedigree

• Male

• Female

Connecting pedigree symbols

• Fraternal twins• Identical twins

Examples of connected symbols:Examples of connected symbols:

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Connecting pedigree symbols

Parents

Examples of connected symbols:Examples of connected symbols:

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Siblings

Example

What does a pedigree chart look like?

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Pedigree Chart Symbols

Deceased

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Affected

Carrier

X-linked

Interpreting a pedigree chart

Determine if the pedigree chart shows an autosomal or X-linked disease.• If most of the males in the pedigree are

affected the disorder is X-linked • If it is a 50:50 ratio between men and

women the disorder is autosomal*.

* autosomal is a chromosome which is not a sex chromosome.

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Example of pedigree charts

1. Is it Autosomal or X-linked?

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Answer 1

•Autosomal

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Interpreting a pedigree chart

Determine whether the disorder is dominant or recessive.

• If the disorder is dominant, one of the parents must have the disorder.

• If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

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2. Dominant or Recessive?

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Answer 2

Dominant

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3. Dominant or Recessive?

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Answer 3

•Recessive

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Additional SymbolsSlide

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Queen Victoria Descendants & HemophiliaPedigree showing inheritance of hemophilia, an X-linked trait.

Many descendants in the 3rd & 4th generations omitted as no mutant gene.

Offspring whose status is uncertain are indicated with a question mark.

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Problem 1

• In humans, albinism is a recessive trait. • The disorder causes a lack of pigment

in the skin and hair. • This results in an albino appearing very

pale with white hair and pale blue eyes.• This disorder also occurs in animals, a

common albino found in a laboratory is the white rat. • The pedigrees below trace the

inheritance of the allele that causes albinism

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Salif Keïta (born August 25, 1949) is an afro-pop singer-songwriter from Mali. He is unique not only because of his reputation as the "Golden Voice of Africa" but because he has albinism and is a direct descendant of the founder of the Mali Empire, Sundiata Keita.

Problems

• 1. Given the following genotypes, describe the phenotypes (normal or albino)• AA =

_______normal______Aa = ______normal_______aa = _____albino_________• 2. Fill out the blanks on the

pedigree below. Remember that gray squares indicate that the person has the two recessive alleles (aa) and is an albino• aa x Aa

Aa, Aa, aa

Answers

1. Given the following genotypes, describe the phenotypes (normal or albino)• AA = normal• Aa = normal• aa = albino

2. Fill out the blanks on the pedigree below. Remember that gray squares indicate that the person has the two recessive alleles (aa) and is an albino• aa x Aa• Aa, Aa, aa

aa Aa

Aa aaAa

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Problems

3. How many children does this family have? ______

4.What are the sexes of the children? ______

5. Fill out the blanks of the pedigree below (AA, Aa, aa)

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Answers

3. How many children does this family have? 2

4.What are the sexes of the children? Female, Male

5. Fill out the blanks of the pedigree below (AA, Aa, aa)

Aa Aa

Aaaa

Aa

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Aa

aa aaaa

Aa Or

AA

Problems

10. How many children does the original couple have? ______

11. How many grandchildren? ________

12. What are the sexes of the children? ___________

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Problems

10. How many children does the original couple have? 2

11. How many grandchildren? 3

12. What are the sexes of the children?

Female, Male

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Summary

• Pedigrees are family trees explaining your genetic history.

• Pedigrees are used to find out the probability of a child having a disorder in a particular family.

• To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.

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Homework

•Find out which family members (as many as you can; siblings, parents, grandparents, aunts, uncles, cousins, great-grand parents, etc.) with listed traits.

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HomeworkSlide

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Education

Pedigrees Lecture