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L3 Biology: Human Pedigree Analysis

Introduction

A pedigree chart is used to study the passing of a trait through a number of generations. People who raise show animals, such as dogs and cats, often use these charts for their animals so the inheritance of desired traits from generation to generation can be traced. Pedigree charts also are used to study the inheritance of certain diseases or disorders in humans, such as sickle-cell anemia.

Standard symbols

Male female

[pic] [pic] [pic] [pic] [pic] [pic]

Parents shows trait carries trait (heterozygous)

Offspring (two boys, followed by a girl)

Generations: I, II, III, etc.

[pic] [pic] [pic] Individuals: 1, 2, 3, 4

(within generations)

Practice problems

1. Study the pedigree chart for sickle-cell anemia and answer the accompanying questions.

I [pic] [pic]

1 2

II [pic] [pic] [pic] [pic] [pic]

1 2 3 4 5

III [pic] [pic] [pic] [pic] [pic] [pic] [pic] [pic] [pic] [pic]

1 2 3 4 5 6 7 8 9 10

IV [pic] [pic] [pic] [pic] [pic] [pic] [pic] [pic] [pic] [pic]

1 2 3 4 5 6 7 8 9 10

a. How many generations are represented in the chart for sickle-cell anemia? _______________

b. Identify the carriers shown in the chart.

c. Which individuals in the chart were born with sickle-cell anemia?

d. From which parent did the second generation children inherit the sickle-cell allele?

e. How can you tell if sickle-cell anemia is a dominant or recessive allele? Explain (hint: look at the inheritance of every individual that has sickle-cell anemia)

2. Use the data chart for deafness to construct a pedigree for deafness in this family. Be sure to use the proper symbols. Use a separate sheet of paper and remember neatness counts.

D = allele for normal hearing; d = allele for deafness.

|Generation I |Generation II |Generation III |

|Genotype |Sex |Genotype |Sex |Spouse’s genotype |Grandchildren’s |

| | | | | |genotypes/sex |

|Dd |M |DD |M |Dd |DD/M; Dd/F |

|Dd |F |Dd |F |DD |Dd/F |

| |dd |M |Dd |dd/F; Dd/M |

3. A woman finds out she is having twins, a boy and a girl. She goes to see a genetic counselor because she is concerned about passing a disease on to her children. This woman’s maternal grandfather (her mother’s father) had the disease hemophilia. The woman’s husband and father both came from families with no history of hemophilia. How would you counsel this woman? What are the odds of either of her twins getting the disease?

Draw a pedigree chart for this woman on a separate piece of paper showing appropriate symbols (remember half-colored circles). Next to each circle or square on the chart, write the two-letter genotype of that individual. *Hint: the genotype letters that may be used (depending on the individual) are XH (normal), Xh (hemophilia) and Y. When the genotype is not known with certainty, make a notation of the possible genotypes (a Punnet square on a scrap of paper may help you figure out possible alleles). Be sure to include on the pedigree the future twins and their appropriate symbols. Finally write a sentence or two explaining your findings.

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