Non-Mendelian Genetics High School Biology Worksheet With Answers
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1
2
3Eastern Regional High School
Name:______________________________
Honors Biology
Period:_________ Date:________________
Unit 13 – Non-Mendelian Genetics
A Human Pedigree – Tracing Hemophilia
Introduction:
A sex-linked characteristic is determined by an allele that is carried only on the X chromosome. The shorter Y
chromosome does not carry an allele for a sex-linked trait. Most sex-linked traits are recessive. Since there is only one
X in his 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.
Problems:
One sex-linked trait is hemophilia, a condition in which the blood does not clot properly. Most people who have
hemophilia are men. In this investigation you will determine why this is so.
1.
Study the pedigree for hemophilia shown in Figure A. In a pedigree a square represents a male. If darkened, he
has hemophilia; if clear, he has normal blood clotting. How many males in this pedigree have hemophilia?
How many are normal? ________3-H 8-Normal___________
2. A circle represents a female. If darkened, she has hemophilia; if clear, she has normal blood clotting. How
many females in this pedigree have hemophilia? How many are normal?
___1-Hemo 12-Normal_________________________
3. A horizontal line connecting a circle to a square indicates a marriage. How many marriages are there in
this pedigree? _____6_________________________________________
4. A line perpendicular to the marriage line indicates the offspring. If the line ends with either a circle or a square,
the couple only had 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 appears
to the left and the last to the right. How many children did the first couple have?
______5__________
5. Each level on the pedigree represents a generation on the pedigree. The first generation began with individuals
1 and 2. Label the other generations on the pedigree. How many generations are their total?
___________4___________________________________
6. The genotypes of the males in the pedigree for sex-linked inheritance are easy to determine since the normal
blood clotting (N) is dominant and hemophlia (n) is recessive. A male with a clear square will have the genotype
X
Y. One represented by a darkened square will be X
Y. Label the genotypes of all the squares in the
N
n
pedigree. How many males have the genotype X
Y?
N
____________8_________________________
7. Females who have hemophilia have an easy genotype to identify. They are all X
X
. Both recessive alleles must
n
n
be present in order for a female to have hemophilia. Label all the darkened circles with the genotype
X
X
. How many women in the pedigree have the genotype X
X
?
n
n
n
n
_____________1____________
8. Females that do not show the trait for hemophilia may be homozygous dominant (X
X
) or heterozygous
N
N
(X
X
). A heterozygous female is called a carrier. Carriers in a pedigree will be half shaded. Examining the
N
n
offspring and parents of a female can often determine the genotypes of the female. If any child (son or daughter)
has hemophilia, then the female must be heterozygous. If her son has hemophilia, he has the genotype X
Y). He
n
inherited the Y chromosome from his father, so the X
had to come from his mother. If the daughter has
n
hemophilia, she inherited an X
from each parent making the genotype fo the normal mother X
X
. Label all
n
N
n
the females in the pedigree X
X
that have children with hemophilia. Shade in half of the
N
n
circle for each female carrier. What is the genotype of the women in the first generation?
1
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