Question

6. The world's first cloned pet, the kitten CC (a play on the words Copy Cat and Carbon Copy) was the result of a nuclear transfer experiment in which the nucleus from the diploid somatic cells of a female calico cat named Rainbow was injected into an egg (from an unnamed donor cat) whose own nucleus had been removed previously (similar to the "Three Parent Baby" experiment described in Lecture 12). The reconstituted egg was then implanted into the uterus of a surrogate mother Both cats are tabby (their colored fur has a mottled pattern) and both have white regions, mainly on their bellies and legs (see photos on the first page of Ch 12 in your textbook). However, a major difference exists in their appearances. Rainbow is a calico tabby; she has black and orange spots controlled by alleles of the X-linked O gene, where the dominant trait is black (X°X) and the recessive trait is orange (X"X). However, Rainbow's clone, CC, is a black tabby; she lacks the orange spots What is Rainbow's (and CC's) genotypes for the O gene? a. b. Given that CC was made from a single one of Rainbow's somatic cell nuclei, explain the difference between CC's and Rainbow's appearances Would every clone of Rainbow's be a black tabby like CC, or do other possibilities exist? Explain. c.

Answer 1

a. Since CC is the clone of rainbow both of them will have the same genotype. Both of them will be heterozygous for this genotype X^OX^o .  

b. The reason for difference in appearance between CC and rainbow is because of the random inactivation of one of the X chromosome (Lyonization). Where ever the cells with the X chromosome containing the dominant allele X^O is inactivated are, there will be orange spots and where ever the cells with X chromosome containing the recessive allele X^o is inactivated are, there will be black. In CC cat all X chromosome containing the recessive allele X^o is inactivated in the colored part of the fur, hence it does not have any orange spots.

c. Since X chromosome inactivation is random other possibilities do exist.