A researcher interested in studying a human gene on chromosome 21 and another gene on the X chromosome uses FISH probes to locate each gene. The chromosome 21 probe produces green fluorescent color, and the X chromosome probe produces red fluorescent color.

If the subject studied is male, how many green and red spots will be detected? Explain your answer.

Key Concepts

Chromosome Structure and Function

Chromosomes are structures within cells that contain DNA, which carries genetic information. Humans have 23 pairs of chromosomes, including one pair of sex chromosomes (XX for females and XY for males). Each chromosome can carry multiple genes, and their arrangement is crucial for proper gene expression and inheritance.

Fluorescence In Situ Hybridization (FISH)

FISH is a molecular cytogenetic technique used to detect and localize the presence or absence of specific DNA sequences on chromosomes. By using fluorescent probes that bind to specific genes, researchers can visualize the location of these genes under a fluorescence microscope, allowing for the identification of chromosomal abnormalities or gene mapping.

Sex Chromosomes and Gene Dosage

In humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). This difference in sex chromosome composition affects gene dosage; males have only one copy of genes located on the X chromosome, while females have two. Therefore, in a male subject, only one red spot (for the X chromosome gene) will be detected, while two green spots (for the chromosome 21 gene) will be observed, assuming there are two copies of that gene.