When the cloned cat Carbon Copy (CC) was born, she had black patches and white patches, but completely lacked any orange patches. The knowledgeable students of genetics were not surprised at this outcome. Starting with the somatic ovarian cell used as the source of the nucleus in the cloning process, explain how this outcome occurred.

Verified step by step guidance

1. Understand the genetic basis of coat color in cats: Coat color in cats is determined by the X-linked gene responsible for orange and black pigmentation. Female cats (XX) can be heterozygous for this gene, meaning they can carry one allele for orange (Xᴼ) and one allele for black (Xᴮ). Due to X-chromosome inactivation, one X chromosome is randomly inactivated in each cell during early development, leading to a mosaic pattern of orange and black patches in heterozygous females.
2. Recognize the role of X-chromosome inactivation: In the somatic ovarian cell used for cloning, one of the two X chromosomes was already inactivated. This inactivation is a random process and is maintained in all descendant cells. If the X chromosome carrying the orange allele (Xᴼ) was inactivated in the donor cell, only the X chromosome carrying the black allele (Xᴮ) would remain active.
3. Understand the cloning process: In cloning, the nucleus from the donor somatic cell is transferred into an enucleated egg cell. The genetic material in the nucleus, including the inactivated X chromosome, is preserved. Therefore, the cloned organism will inherit the same pattern of X-chromosome inactivation as the donor cell.
4. Explain the absence of orange patches: Since the Xᴼ chromosome was inactivated in the donor somatic cell, all cells in the cloned cat (CC) will have the Xᴮ chromosome active. This means that CC will only express the black pigmentation gene and will lack any orange pigmentation, resulting in black and white patches but no orange patches.
5. Conclude with the importance of X-chromosome inactivation: This phenomenon explains why the cloned cat CC does not have orange patches. The pattern of X-chromosome inactivation in the donor somatic cell is faithfully replicated in the cloned organism, leading to the observed coat color phenotype.

Key Concepts

Cloning and Somatic Cell Nuclear Transfer (SCNT)

Cloning, particularly through Somatic Cell Nuclear Transfer (SCNT), involves transferring the nucleus of a somatic cell into an enucleated egg cell. This process allows the genetic material from the somatic cell to dictate the traits of the resulting organism. In the case of Carbon Copy, the somatic cell used was derived from a cat, which determined her genetic makeup and the expression of specific coat colors.

Genetic Expression and Coat Color in Cats

In cats, coat color is determined by multiple genes, including those responsible for black, white, and orange fur. The presence of black and white patches in Carbon Copy indicates that the genes for these colors were expressed, while the absence of orange patches suggests that the genetic material from the donor cell did not include the allele for orange fur. This selective expression is crucial in understanding the phenotype of cloned animals.

X-Chromosome Inactivation

In female mammals, including cats, one of the two X chromosomes is randomly inactivated in each cell, a process known as X-chromosome inactivation. This phenomenon can lead to a mosaic pattern of coat colors, as seen in tortoiseshell cats. Since Carbon Copy was cloned from a somatic cell, the inactivation pattern of the X chromosomes in the donor cell influenced the absence of orange patches, resulting in her unique coat coloration.