Study of Human Karyotype (Normal and Abnormal) Using Photomicrograph (Practical)

 

Study of Human Karyotype (Normal and Abnormal) Using Photomicrograph

 

Aim

To study and analyze human karyotypes (normal and abnormal) using prepared photomicrographs.

Background

A karyotype is the complete set of chromosomes in a cell, organized and displayed in a systematic arrangement. It is an essential tool in cytogenetics to identify chromosomal abnormalities, genetic disorders, and to study human genetics. Normal human karyotype consists of 46 chromosomes (22 pairs of autosomes and 1 pair of sex chromosomes). Abnormalities such as Down syndrome, Turner syndrome, and Klinefelter syndrome can be diagnosed by karyotyping.

Materials Required

1. Prepared photomicrographs of human karyotype (normal and abnormal)

2. Reference karyotype charts

3. White observation sheet

4. Pencil/pen for marking observations

Procedure

1. Observe the given photomicrograph of human chromosomes under study.

2. Arrange chromosomes into homologous pairs based on size, shape, and centromere position.

3. Identify and confirm the total number of chromosomes (46 in normal karyotype).

4. Check the sex chromosomes to determine male (XY) or female (XX).

5. Compare the observed karyotype with a standard reference chart.

6. Identify abnormalities such as extra or missing chromosomes, if any.

7. Record observations in tabular form for both normal and abnormal karyotypes.

Observation Table

Karyotype Type	Chromosome Number	Description
Normal Male	46, XY	22 pairs of autosomes + XY sex chromosomes
Normal Female	46, XX	22 pairs of autosomes + XX sex chromosomes
Down Syndrome	47, XY/XX, +21	Trisomy 21 (extra chromosome 21)
Turner Syndrome	45, X	Monosomy of sex chromosome (single X, no Y)
Klinefelter Syndrome	47, XXY	Presence of an extra X chromosome in males

 

Common Abnormal Karyotypes

1. Down Syndrome (Trisomy 21) – extra chromosome 21.

2. Turner Syndrome – monosomy X (45, X).

3. Klinefelter Syndrome – extra X chromosome in males (47, XXY).

4. Edward’s Syndrome (Trisomy 18) – extra chromosome 18.

5. Patau Syndrome (Trisomy 13) – extra chromosome 13.

Precautions

1) Use standard reference charts for comparison.

2) Ensure correct pairing of homologous chromosomes.

3) Avoid misinterpretation of chromosomal size or staining patterns.

4) Handle photomicrographs carefully to prevent damage.

Viva Questions

1. What is a karyotype?

2. How many chromosomes are present in a normal human cell?

3. Differentiate between male and female karyotype.

4. What is Trisomy 21?

5. Give one example of a sex chromosome abnormality.

FAQs

Q1. What is the importance of studying human karyotype?

It helps in diagnosing chromosomal abnormalities and understanding inheritance patterns.

Q2. Can karyotyping be done in prenatal diagnosis?

Yes, fetal cells obtained from amniocentesis or chorionic villus sampling can be used.

Q3. What staining techniques are used in karyotyping?

Giemsa banding (G-banding) is most commonly used.

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