Nondisjunction Notes
Name
Period
Nondisjunction is the improper separation of chromosomes during meiosis. As learned, the tetrads separate in meiosis I
and the sister chromatids separate in meiosis II. Numerous structures ensure proper separation of chromosomes
including centrioles, spindle fibers, and centromeres. If any part malfunctions, the result may be disastrous.
Study the drawing below. Fill in the diploid number of this fictitious creature. In the haploid gametes, how many
chromosomes should be present?
.
A normal human karyotype should show 22 autosomes, or non-sex chromosomes and 2 sex chromosomes- either an XX
for female or an XY for male. The total number of human chromosomes should include
. However, as shown in
the diagram mistakes may occur in the process of meiosis.
For normal offspring, the diploid number must be the same as the original parent following fertilization. In this case the
diploid number is
. How many chromosomes would the offspring inherit if the egg cell in the top right
corner was fertilized?
. How many if the bottom right egg was fertilized?
.
Obviously, the result may be a chromosomal abnormality. The abnormalities result from nondisjunction and result in an
atypical number of chromosomes, or a structural abnormality in one or more chromosomes.
Karyotypes, or pictures of chromosomes, allow doctors and scientists to look for chromosomal abnormities. Creation of
a karyotype requires the condensed (visible) chromosomes, which occurs in
of the cell cycle.
The number of autosomes in this karyotype includes
The number of sex chromosomes in this karyotype includes
The total number of chromosomes in this karyotype is
What is the gender of the person?
How do you know?
Abnormal Karyotype #1 Examine the abnormal karyotype below and circle the area of concern. Where is the trisomy?
How many autosomes in this karyotype?
How many sex chromosomes?
What is the gender of the person?
Bullet point a nondisjunction scenario below:
what is the name of this disorder, often referred to as trisomy 21?
What are symptoms or side effects of trisomy 21?
Abnormal Karyotype #2 Examine the karyotype and circle the area of concern.
Gender determination may be difficult in this
case, but what is the most likely gender?
.
Circle the area of concern on this karyotype
Research the condition:
Name
Life expectancy
Side effects/symptoms
Think: Since nondisjunction mostly happens in the formation of female egg cells, did the male of the female contribute
the X chromosomes? Explain.
Abnormal Karyotype #3 Examine the karyotype and circle the area of concern.
Gender determination may be difficult in this case, but
what is the most likely gender?
.
Circle the area of concern on this karyotype
Research the condition:
Name
Life expectancy
Side effects/symptoms of karyotype #3:
Abnormal Karyotype # 4 Examine the karyotype and circle the area of concern: Where is the trisomy?
Gender
Name of chromosomal disorder
Life expectancy
Symptoms/side effects
Abnormal Karyotype # 5 Examine the karyotype and circle the area of concern. Where is the trisomy?
Gender
Name of chromosomal disorder
Life expectancy
Symptoms/side effects: