Exercise 6: Pedigree Analysis

Exercise 6: Pedigree Analysis [Adapted from TIBBETTS, MICHAEL F.. Pedigree analysis with PTC paper.. The analysis of the pedigree, a symbolic representation of a family history, is a c

Exercise 6:

Pedigree Analysis

[Adapted from TIBBETTS, MICHAEL F. Pedigree analysis with PTC paper Biology

Program, Bard College, 1994.]

INTRODUCTION

Mendel's methodical crosses were made possible by the ease with which

paren-tal types can be controlled in peas However, humans do not lend themselves to the

types of procedures that peas do Even without considering the impossibility of

controlled mating, the generation time is so long that directed studies would not be

feasible We must, therefore, employ special methods in the analysis of human

inheri-tance patterns

The analysis of the pedigree, a symbolic representation of a family history, is a

classic method of genetic analysis in humans Using carefully constructed pedigrees,

we can determine whether a given allele is behaving as a dominant or a recessive trait

and whether the gene is sex-linked In some special cases we can also determine if it is

linked (not assorting independently) to some other gene

The pedigree consists of a set of symbols that convey information about the

inci-dence of a trait in successive generations Figure 1 summarizes the symbols that are

most commonly seen in a pedigree

BIO 114: BIOLOGY OF NONINFECTIOUS DISEASE — LABORATORY MANUAL

EXERCISE 6: PEDIGREE ANALYSIS

Figure 1 Key to symbols commonly seen in pedigrees

PROCEDURE, PART I:

There are four hypothetical pedigrees printed on the next two pages Identify the type of inheritance pattern observed in each (dominant vs recessive; sex linked vs autosomal) At least one pedigree has no clear Mendelian pattern, and this should be noted, too

Label individuals in each pedigree with their apparent genotype (AA = homozy-gous dominant, Aa = heterozyhomozy-gous, aa = homozyhomozy-gous recessive) There are some individuals in each that you cannot be certain of In those cases give the potential genotypes

This portion of the laboratory can be handed in today for five points

PEDIGREE NO 1:

Is there a clear pattern of inheritance?

If so, is the trait dominant or recessive?

Is it sex-linked?

PEDIGREE NO 2:

Is there a clear pattern of inheritance?

If so, is the trait dominant or recessive?

Is it sex-linked?

BIO 114: BIOLOGY OF NONINFECTIOUS DISEASE — LABORATORY MANUAL

EXERCISE 6: PEDIGREE ANALYSIS

PEDIGREE NO 3:

Is there a clear pattern of inheritance?

If so, is the trait dominant or recessive?

Is it sex-linked?

PEDIGREE NO 4:

Is there a clear pattern of inheritance?

If so, is the trait dominant or recessive?

Is it sex-linked?

PROCEDURE, PART II:

The second part of the lab is to create a pedigree for your family If nothing else

this exercise will give an idea of the challenge researchers who need to make pedigrees

face Phenylthiocarbamide (PTC) is a chemical that has a bitter taste to some people

and no taste at all to others.1 You will be supplied with both PTC impregnated paper

strips (A) and control (non-PTC impregnated) paper strips (B) Test as many family

members as you can with each sheet Try to get siblings, parents, maternal and

paternal grandparents, and maternal and paternal aunts, uncles, and cousins You can

do the testing in person or through the mail The more members you test the easier it

will be to set up a pedigree

Using the symbols defined in Figure 1 make as complete a pedigree of your

family as possible for the ability to taste PTC As in Part I, where possible, you should

label individuals with their apparent genotype

RESULTS, PART II:

Your family's pedigree:

BIO 114: BIOLOGY OF NONINFECTIOUS DISEASE — LABORATORY MANUAL

EXERCISE 6: PEDIGREE ANALYSIS

CONCLUSIONS, PART II:

1 Is the ability to taste PTC a genetic trait in your family?

2 If yes then:

a Is it dominant or recessive?

b Is it sex-linked?

You have until 5:00 on the last day of classes to make your pedigree and answer the questions above, for 5 points