Name _______________________________________
Section 7.1 Chromosomes and Phenotype
Date __________________
Main Ideas:
 Two copies of each autosomal gene affects phenotype
 Males and females can differ in sex-linked traits
Vocabulary:
 Carrier
 Sex-linked gene
1. Remembering back to mitosis and meiosis, how many chromosomes does a normal human have? _____
Below is a karyotype of a human male and then a human female. A karyotype is a picture of the
chromosomes in a cell. Chromosome pairs # 1 – 22 are called autosomes or body chromosomes while the
last two are known as sex chromosomes.
Male
Female
2. How many autosomes does a normal male have? ______ Female? _______
3. What is the term for the XY and XX chromosomes shown on the above karyotypes? ________________
4. How is cystic fibrous inherited?
5. What is the term for someone who has a gene for the trait but also has a normal gene? ______________
6. Some traits on carried on the X sex chromosome and not the Y sex chromosome. These traits are called:
7. What type of sex chromosomes do males have? _______ Females? _______
8. If you are a male, who gave you your X chromosome? _______ Your Y? _________
9. If you are a female, who gave you your X chromosomes? _____________ & _____________
10. Look at the image of the X and Y chromosomes. What do you notice about the size of the X to the size
of the Y sex chromosome?
11. What happens when there is a gene on the top of the X chromosome say for colorblindness and there
isn’t one on the Y chromosome (because it is too short)? What if mom gave you a gene for
colorblindness and you are a male? Could dad give you the dominant normal gene to save you from
colorblindness?
Unmatched area – no homologous
genes present on the Y chromosome
12. If you are a male who is colorblind, who gave you the colorblind trait?
13. Let’s try a problem:
In humans, colorblindness is inherited on the X chromosome and is recessive. The gene for
normal color vision is dominant. Sex counts with these problems so put the genes on the top of
the X chromosome. Do not put anything on the Y because it is too small
N = Normal color vision gene
n = Colorblind gene
Cross a female who is a carrier of the gene (XNXn) with a normal male (XNY)
XN
Xn
a. What is the probability of them having a son who
has the colorblind gene (n) on his X chromosome
XN
and is therefore colorblind? ______%
b. What is the probability of them having a colorblind
daughter? She will need two colorblind genes to be
Y
colorblind? _______%