Pedigrees Lecture
-
Upload
lorraine-stratton -
Category
Education
-
view
76 -
download
2
Transcript of Pedigrees Lecture
Overview
I. What is a pedigree?
a. Definitionb. Uses
II. Constructing a pedigree
a. Symbols
b. Connecting the symbols
III. Interpreting a pedigree
2
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.
3
Connecting pedigree symbols
• Fraternal twins• Identical twins
Examples of connected symbols:Examples of connected symbols:
5
Connecting pedigree symbols
Parents
Examples of connected symbols:Examples of connected symbols:
6
Siblings
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.
9
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.
12
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.
Slide18
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
Slide19
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
Slide21
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)
Slide22
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
Slide23
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? ___________
Slide24
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
Slide25
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.
Slide26
Homework
•Find out which family members (as many as you can; siblings, parents, grandparents, aunts, uncles, cousins, great-grand parents, etc.) with listed traits.
Slide
29