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Question Video: Describing How to Use a Karyotype to Identify Down Syndrome Biology

A karyotype is an image of a person’s chromosomes that can be used to determine chromosomal abnormalities. Which syndrome will likely be developed as a result of the chromosomal abnormality shown in the karyotype provided?

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Video Transcript

A karyotype is an image of a person’s chromosomes that can be used to determine chromosomal abnormalities. Which syndrome will likely be developed as a result of the chromosomal abnormality shown in the karyotype provided? (A) Turner syndrome, (B) Down syndrome, or (C) Klinefelter syndrome.

This question asks us about a syndrome resulting from a chromosomal abnormality which occurs when an individual inherits a different number of chromosomes than usual. Normally, an individual will gain one copy of each chromosome from the biological mother and one copy from the biological father. In a karyotype, we arrange these chromosomes in order by height.

The matching chromosomes from each parent are called homologous chromosomes. During gamete or sex cell formation, an individual’s chromosomes are divided in half. Typical human body cells will contain 46 chromosomes, while sex cells will only possess 23. Of these chromosomes, 22 will be autosomes that once fertilization occurs will make up one-half of a homologous pair, while one will be a sex chromosome.

Sex chromosomes are either X or Y, and they contain genes specific for sexual development. When these gametes come together during fertilization to form a new individual, there will be 46 chromosomes in total. Either a male or a female will be produced. Sometimes the process of sex cell formation will incorrectly separate the chromosomes so that they aren’t divided evenly. If this sex cell is involved in the process of fertilization, or the joining of a sperm and an egg, it can result in an offspring with a chromosomal abnormality.

Now, let’s take a look at the karyotype in our question. You can see that the individual possesses three copies of chromosome 21. But normal body cells should only contain two copies of each chromosome: one from the biological mother and one from the biological father. These chromosomes must have been incorrectly split during sex cell formation, resulting in a trisomy, or three copies.

In our question, the individual contains a trisomy 21, which results in a condition called Down syndrome. Characteristics of Down syndrome include heart defects, a flattened facial profile, and short stature. In addition, these individuals may develop intellectual disabilities.

Now that we have reviewed chromosomes and conditions that can develop from their incorrect separation during gamete development, we should be able to answer our question correctly. We’re asked which syndrome will likely develop as a result of the chromosomal abnormality shown in the karyotype provided. The correct answer is (B), Down syndrome.

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