Problem Description:
The image provided shows a karyotype, which is a visual representation of an individual's chromosomes. The task is to analyze the karyotype and identify any abnormalities compared to a normal human karyotype.
Step-by-Step Solution:
#### 1.
Understanding Normal Karyotypes:
- A normal human karyotype consists of 46 chromosomes (23 pairs).
- These include 22 pairs of autosomes (chromosomes 1–22) and one pair of sex chromosomes (XX for females or XY for males).
- Chromosomes are typically arranged in order of size, from largest to smallest, with the sex chromosomes placed at the end.
#### 2.
Analyzing the Provided Karyotype:
- The image shows a total of 47 chromosomes instead of the expected 46.
- Upon closer inspection, there are two X chromosomes and one Y chromosome, indicating that this is a male karyotype (XY).
- However, there is an extra chromosome present, which disrupts the typical pairing pattern.
#### 3.
Identifying the Extra Chromosome:
- The extra chromosome appears to be chromosome 21. This can be inferred because:
- Chromosome 21 is one of the smaller chromosomes in the karyotype.
- There are three copies of chromosome 21 visible, whereas there should only be two in a normal karyotype.
#### 4.
Diagnosis:
- The presence of three copies of chromosome 21 instead of two is indicative of
Trisomy 21, also known as Down syndrome.
- Trisomy 21 occurs when an individual has an extra copy of chromosome 21, resulting in a total of 47 chromosomes instead of 46.
#### 5.
Explanation of Trisomy 21:
- Trisomy 21 is the most common chromosomal abnormality and is associated with a range of physical and developmental characteristics.
- It typically arises due to nondisjunction during meiosis, where the chromosomes fail to separate properly, leading to an extra copy of chromosome 21 in the gamete.
Final Answer:
The karyotype shows
Trisomy 21 (Down syndrome). The individual has an extra copy of chromosome 21, resulting in a total of 47 chromosomes instead of the normal 46.
$$
\boxed{\text{Trisomy 21 (Down syndrome)}}
$$
Parent Tip: Review the logic above to help your child master the concept of answers worksheet 6 karyotype.
