To solve this karyotyping problem, we need to organize the scattered chromosomes into pairs based on their size and banding patterns. Here is the step-by-step logic:
Step 1: Identify the Sex Chromosomes
First, look for the sex chromosomes (the 23rd pair). In humans, these are either XX (female) or XY (male).
- The X chromosome is a medium-sized chromosome with a distinct banding pattern.
- The Y chromosome is very small, much smaller than the X.
- Looking at the image, there is one medium-sized chromosome that matches the X pattern, and one very tiny chromosome that is clearly the Y.
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Conclusion: The presence of an X and a Y means this individual is
Male.
Step 2: Check for Autosomal Abnormalities (Trisomies)
Next, we group the remaining chromosomes (autosomes) by size to see if any number has three copies instead of the usual two. This is called a trisomy.
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Group 1 (Largest Chromosomes): Look for the biggest chromosomes. There are two very large ones with similar dark bands near the center. They form a perfect pair. No extra copy here.
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Group 2 (Medium-Large Chromosomes): Look for the next largest set. There is a distinct group of three medium-large chromosomes that look identical. They have a specific pattern of light and dark bands. Having three copies of this chromosome indicates
Trisomy 21 (also known as Down Syndrome). *Note: In many textbook diagrams, Chromosome 21 is depicted as larger than Chromosome 22, which appears to be the case here given the obvious trio.*
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Other Groups: If you pair up the rest of the chromosomes by matching their sizes and stripe patterns, they all form neat pairs of two. There are no other groups of three.
Step 3: Determine the Final Diagnosis
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Sex: Male (XY)
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Condition: Trisomy 21 (Down Syndrome)
Combining these findings gives us the full chromosomal notation. A normal male is 46, XY. A male with Down Syndrome has 47 chromosomes because of the extra #21.
Final Answer:
47, XY, +21 (Male with Down Syndrome)
Parent Tip: Review the logic above to help your child master the concept of karyotype lab worksheet answers.
