Karyotypes

Medical Case Study

The parents of a newborn child have some concerns.

Their child looks a little cross-eyed, its face seems a little
flat from the side, and there is a strong crease that runs
across the middle of the palms.

As a team of doctors, we are now responsible for

diagnosing this newborn and providing advice to the
parents. Let’s gather our information for our diagnosis.

Medical Case: Background Information

You believe this is a genetic disorder. Let’s figure
out how it might have occurred.

● Chromosomes-DNA wrapped around

proteins

● Humans have pairs of chromosomes one

from each parent

​Chromosomes - DNA wrapped around proteins
Humans have pairs of chromosomes. One from each parent.

Medical Case: Background Information

● Humans are diploid (2n)
● Diploid: pairs of (2n) chromosomes
● Haploid individual, unpaired (n) chromosomes

● Two copies of each chromosome are homologous

○ They have the same genes in the same location

but may have different versions of those genes

Multiple Choice

What are homologous chromosomes?

• chromosomes with different genes

• chromosomes with potentially different versions of the same gene

• all the DNA in an organism

Multiple Choice

If a diploid mouse cell has 40 chromosomes, how many chromosomes does the haploid cell have?

• 20

• 40

• 10

• 80

Medical Case: Background Information

We know the disorder is genetic and neither parent
has it.

Medical Case: Background Information

● Somatic Cells are diploid body cells
● Gametes are haploid sex cells

○ Egg or sperm cells
○ They allow traits to be combined in offspring

● Meiosis is the process that results in gametes unlike

mitosis

Mitosis vs. Meiosis

Mitosis- 2 Identical
cells

Meiosis- 4 different
cells

Non-Disjunction

● Nondisjunction is when the

chromosomes fail to
separate properly

● Results in an abnormal

distribution of chromosomes

Our Patient

It seems our patient had a
mistake in meiosis. What was the
cause of the mistake?

Multiple Choice

Which process can create gametes with the incorrect number of chromosomes? (like we see in our patients DNA)

• mitosis

• mitochondria

• crossing over

• nondisjunction

Karyotype

Now that we know our patient has an extra
chromosome. Let’s figure out which one.

A karyotype is a visual that shows the
chromosomes of an individual

You isolate chromosomes in fetus cell

Arrange in pairs according to size

​The 23rd pair of chromosomes in a karyotype are the sex chromosomes

A person who is biologically female will have two X chromosomes

A person who is biologically male will have one X and one Y (y is much smaller)

​Sometimes karyotypes are taken from before mitosis, and sometimes after. They may or may not show sister chromatids. The ones on the screen do not show sister chromatids, only homologous pairs. The ones on your paper show sister chromatids and homologous pairs.

Multiple Choice

What is the sex of this person?

• male

• female

• impossible to tell

Diagnosis

● Down syndrome is caused by

an extra chromosome in the
pair 21.

● It is called trisomy 21.

Diagnosis: Down Syndrome

● A chromosomal disorder resulting from a partial or

complete extra copy of chromosome 21

● Health Effects:

○ Short stature and distinct facial features
○ Mild to moderate physical and cognitive impairment
○ Increased risk of problems involving the heart,

respiratory, digestive, thyroid, vision and hearing

How can the family move forward with
this diagnosis?

After coming to the conclusion that their child has

Down Syndrome, you want to share with them how to
move forward. You show them the following video as a
way to better understand the needs of a child with Down
Syndrome.

How can the family move forward with
this diagnosis?