2029 a these results which were reported in 1933 were

Info icon This preview shows pages 5–7. Sign up to view the full content.

View Full Document Right Arrow Icon
20–29 A. These results, which were reported in 1933, were the first indication that the tendency to form breast tumors was maternally transmitted in mice. The results of the experiments in Table 20–1 cannot be readily explained on the basis of standard types of chromosomal mutations, be they recessive, dom- inant, or X-linked. If you assume that the ‘high’ strains are homozygous for a recessive mutation and the ‘low’ strains are homozygous for the wild-type allele, all the F1 progeny would be heterozygous and unaffected. For a dom- inant mutation, the males, as well as the females, should transmit the muta- tions to their offspring. X-linked mutations would be expected to give affected males in every other generation. Although it was unknown at the time these experiments were carried out, the pattern of inheritance shown in Table 20–1 matches the expectations for mitochondrial mutations, which are inherited via the egg cytoplasm. (See Problem 14–110 for more discus- sion of these patterns of inheritance.) B. The key to understanding how the tendency to form breast cancers is inher- ited is the foster-mother experiment. Although presented as an accident in this problem, it represented a critical insight at the time. Because foster mothers could pass this trait on to mice with which they shared no genetic connection, inheritance could not be due to chromosomal (or mitochon- drial) mutations. The link between mothers and daughters was identified as the milk. The so-called milk factor was later identified as a virus, which we now call mouse mammary tumor virus (MMTV). References: Little CC (1933) The existence of non-chromosomal influence in the incidence of mammary tumors in mice. Science 78, 465–466. Bittner JJ (1936) Some possible effects of nursing on the mammary gland tumor incidence in mice. Science 84, 2172. Paigen K (2003) One hundred years of mouse genetics: An intellectual his- tory. I. The classical period (1902–1980). Genetics 163, 1–7. FINDING THE CANCER-CRITICAL GENES DEFINITIONS 20–30 Oncogene 20–31 Transformation 20–32 Proto-oncogene 20–33 Retinoblastoma 20–34 Cancer-critical gene 20–35 Tumor suppressor gene TRUE/FALSE 20–36 False. Oncogenes, which are mutated, overactive forms of proto-oncogenes, can be detected in this way. Their addition to the genome can convert a cell
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
A462 Chapter 20: Cancer to a cancer cell. By contrast, tumor suppressor genes have their effects because they are inactive; it is their absence that causes cancer. One cannot use the same sort of transformation assay to detect something that is not there. 20–37 False. It is not that DMBA is a specific mutagen, but rather that the Ras gene is converted to its activated, cancer-causing form by a particular A-to-T alteration that leads to a very specific amino acid change. DMBA causes mutations throughout the genome, but only those at the specific site in the Ras gene give rise to cells that have cancerous properties and thus are iden- tified in the assay.
Image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern