MAPPING GENES ON HUMAN CHROMOSoMES Geneticists have developed extensive linkage
ID: 211817 • Letter: M
Question
MAPPING GENES ON HUMAN CHROMOSoMES Geneticists have developed extensive linkage maps for suc aps has been slow. The reasons for this are fairly obvious, (1) Geneticists cannot carry out cont few individuals h organisms as Drosopbla, maize, certain se. By contrast, until recently, progress in preparing human linkage Fnusing humans. (2) Human families are relatively small and thus provide geneticists with too for measuring linkage relationships adequately. (3) The human generation time is long. use most abnormal genetic traits are rare, it is an extremely rare pedigree in which two such traits kmay not be linked) happen to occur in the same individual. For example,it is rare for two vidual. a study of recessive genes, such as those for hemophilia and color blindness, to occur in the same indi- To measure linkage intensities for X-linked genes using traditional pedigree techniques requires such genes. Thus, if a woman has the male children of women who are heterozygous for two erited the gene for color blindness from one parent and the gene for hemophilia from the other, her ons who express both mutant traits or neither mutant trait bear crossover X chromosomes. Establishing nkage of autosomal genes and measuring the intensity of that linkage are even more difficult. the li Although the techniques of classical genetics have allowed for some linkage relationships to be special established in humans, extensive mapping of human chromosomes is dependent on such technique ties aS ployed in somatic cell hybridization (see McKusick [1971, 19801 and Ruddle and Kucherlapati [1974D and in sttu hybridization of DNA probes to chromosomes. According to on line Mendelian Inheritance in Man (OMIM)I, by October 2014 some 22,587 possible gene loci were known, including 21,245 autosomal, 1,218 X-linked, 59 Y-linked and 65 mitochrondial. In addition to the genes assigned to the X and Y chromosomes, 13,958 autosomal genes have been assigned to specific chro In December 1999, it was announced that chromosome 22 had been completely sequ was followed in May 2000 with the announcement that chromosome 21 sequenced. The rest of the human genome was completely sequenced in mosomes, with many located at specific sites within their respective chromosomes. enced. This had also been completely Subse the estimated 3 billion base pairs in the human genome. This research will, of course, allow definitive assignment of all human genes to specific chromosomes and locations. (Investigation 26 looks at sev eral aspects of individual gene sequences and their specific chromosome locations.) quent research has concentrated on assigning specific functions to the genes encoded by Updated information on the number of human genes and the Human Genome Project can be obtained on the net at OMIM COnline Mendelian Inheritanc H e in Man, VA. McKusick, ed.) http://www.ncbi.nln.nih.gov/omm/Explanation / Answer
1. Yes, 4 out of 5 gene products are controlled by genes linked on the same chromosome.
Those gene products are A, C and B, E
Evidence for this is that, In hybrid cell line I, 2 human chromosomes are present and 4 gene products are present. Therefore which means, 2 gene product per human chromosome.
Similarly, in hybrid cell line II, 1 human chromosome is present and 2 gene products are present. Therefore, which means 2 gene products by 2 genes present on that particular human chromosome.
2. On chromosome no. 3 and 18, the linked genes are located.
Chromosome 18- A and C
Chromosome 3- B and E
Evidence for this is that, In hybrid cell line I, 2 human chromosomes (chromosome no. 3 and 18) are present and 4 gene products are present. Therefore which means, 2 gene product per human chromosome.
Similarly, in hybrid cell line II, 1 human chromosome (chromosome no. 18) is present and 2 gene products are present. Therefore, which means 2 gene products by 2 genes present on that particular human chromosome.
3. No, it is not possible to associate any other gene or genes with a particular chromosome.
4. Chromosome 12 and Chromosome 21
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.