Pedigree Worksheet Biology Worksheet Template printable pdf download

CLASS SET!

Pedigree Worksheet #2

You can look at a pedigree and determine whether a trait is dominant or recessive, and you can also tell if it is sex-linked or

autosomal. A sex-linked recessive characteristic is determined by an allele that is carried only on the sex chromosomes.

Generally, alleles for sex-linked traits are carried on the X chromosome, because the shorter Y chromosome does not have

as many genes on it. Since there is only one X in a male’s genotype, XY, a male who carries a particular recessive allele on

the X chromosome will have the sex-linked condition. A female who carries a recessive allele in one X chromosome will not

show the condition if there is a dominant allele on her other X chromosome. She will express the recessive condition only if

she inherits two recessive alleles- one from each parent. Her chances of inheriting the condition are thus greatly reduced.

One sex-linked trait is hemophilia, a condition in which the blood does not clot properly. Most people who have hemophilia

are men. View the pedigree below and interpret the diagram to answer the questions.

A. Interpreting a human pedigree.

1. Draw the pedigree to right.

2. Number all the individuals on the pedigree at the top of each

shape.

3. In a pedigree, a square represents a male. If it is darkened he

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has hemophilia; if clear, he has normal blood clotting.

a) How many total males are there? ______

b) How many males have hemophilia? ______

4. A circle represents a female. If it is darkened, she has

hemophilia; if open she is normal.

a) How many total females are there? ______

b) How many females have hemophilia? ______

5. A marriage is indicated by a horizontal like connecting a circle to a square.

a) How many marriages are there? ______

6. A line perpendicular to a marriage line indicates offspring. If the line ends with either a circle or a square, the couple

had only one child. However, if the line is connected to another horizontal line, then several children were produced

each indicated by a short vertical line connected to the horizontal line. The first child born appears to the left and the

last born to the right.

a) How many children did the couple in generation I have? ______

b) How many children did the couple in generation III have? ______

7. Each row of individuals represents a different generation.

a) How many generations are there? ______

b) How many members are there in the fourth generation? ______

8. The genotypes of the males in a pedigree for sex-linked inheritance are easy to determine since normal blood

clotting (N) is dominant and hemophilia (n) is recessive. Since these alleles are on the X chromosome only, a

male represented by a clear square will have the genotype

. A darkened square will be

a) Label the genotypes under each individual on the pedigree.

b) What is the genotype for individual I-1? _____________ Phenotype? ________________________

c) What is the genotype for individual IV-1? _____________ Phenotype? ________________________

d) What is the genotype for the first born male in generation III? ______________ Phenotype? _______________

Pedigree Worksheet Biology Worksheet Template