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 female, how many green and red spots will be detected? Explain your answer.

Verified step by step guidance

1. Understand the problem: The researcher is using FISH (Fluorescence In Situ Hybridization) probes to locate genes on chromosomes. The green probe targets a gene on chromosome 21, and the red probe targets a gene on the X chromosome. The subject is female, so we need to determine how many green and red fluorescent spots will be visible.
2. Recall the chromosome composition of a female: Females have two X chromosomes (XX) and two copies of chromosome 21, as humans are diploid organisms. This means there are two copies of each autosome (chromosomes 1-22) and two sex chromosomes (XX for females).
3. Determine the number of green spots: Since chromosome 21 is an autosome and humans are diploid, there are two copies of chromosome 21 in each cell. Each copy of chromosome 21 will hybridize with the green FISH probe, resulting in two green fluorescent spots.
4. Determine the number of red spots: Females have two X chromosomes. Each X chromosome will hybridize with the red FISH probe, resulting in two red fluorescent spots.
5. Summarize the findings: In a female subject, the FISH analysis will detect two green spots (from chromosome 21) and two red spots (from the X chromosomes). This is consistent with the diploid nature of human cells and the presence of two copies of each chromosome.

Key Concepts

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. It involves using fluorescent probes that bind to specific parts of the chromosome, allowing researchers to visualize the location of genes. In this case, FISH probes are used to identify genes on chromosome 21 and the X chromosome by emitting different colors when bound.

Chromosome Number and Sex Chromosomes

Humans typically have 46 chromosomes, arranged in 23 pairs, including one pair of sex chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). In the context of the question, a female subject will have two X chromosomes, which is crucial for determining the number of red spots detected from the X chromosome probe.

Gene Dosage and Spot Detection

Gene dosage refers to the number of copies of a particular gene present in a cell. In the case of the female subject, there will be one gene on chromosome 21 (resulting in one green spot) and two genes on the X chromosome (resulting in two red spots). Therefore, the total number of spots detected will be one green and two red, reflecting the gene dosage from the respective chromosomes.