Chromosome autosomal

To minimize problems with the detection and analysis of a gene that exists as a single copy on an autosomal chromosome, technology of extreme sensitivity needs to be employed. Although the standard Southern analysis combines reasonable sensitivity with greater specificity, it is labor-intensive, requiring the use of radioisotopes such as 32P, and a few days are required to complete an analysis. Several pitfalls of the Southern procedure can be eliminated by substituting the PCR technique (M4). 

Figure 13. Probability density functions of the skews Sja (a), Sac (b)- S = Sja + Sec (c) values computed in nonoverlapping 1-kbp windows from the DNA sequences of the 22 human autosomal chromosomes. Symbols have the following meaning (o) native sequences and ( ) repeat-masqued sequences.

Figure 15. Statistical analysis of the sharp jumps detected in the S profiles of the 22 human autosomal chromosomes by the WT microscope at scale a = 200 kbp for repeat-masked sequences [38, 39]. AS = S(3 ) — S(5 ), where the averages were computed over the two adjacent 20-kbp windows, respectively, in the 3 and 5 direction from the detected jump location, (a) Histograms Af( AS ) of AS values, (b) A( AS > AS ) versus AS. In (a) and (b), the black (respectively, grey) line corresponds to downward AS < 0 (respectively, upward AS > 0) jumps. R = 3 corresponds to the ratio of upward over downward jumps presenting an amphmde AS > 12.5% (see text).

Figure 16. Statistical analysis of the sharp jumps detected in the S profiles of the 22 human autosomal chromosomes by the WT microscope at scale a — 200 kbp for repeat-masked sequences [109]. The detected jumps have been classified into three categories according to the GC content found in a 100-kbp window centered at the position of the jump. Same as in Fig. 15 (a, a )...

A third embryonic hemoglobin, termed Hb-Portland 1, has recently been described (Cl, C2, H6, T8, W17). The protein was first discovered in a malformed newborn with a complex autosomal chromosomal mosaicism. However, it is probably also present for some 0.5 to 5% in newborn infants with a D, trisomy and in very small amounts (0.1-0.2%) in normal newborns. Hb-Portland 1 does not contain a chains but is composed of one pair of y chains and one pair of chains which have been termed C chains. The C chain is probably a normal embryonic hemoglobin chain. Hb-Portland 1 does react with free a chains to form Hb-F or aayz and a aafa component (T8). It seems, therefore, that the chain can combine with the a chain, but the afiSnity of the a chain for the C chain is apparently lower than for either the e chain or y chain. Embryonic hemoglobins have also been found in several mammalian species, such as the pig, cattle, and sheep (K13, K15). 

Chapter 9. This means that in normal individuals aU of the chromosomes other than the sex chromosomes come in pairs, and even the sex chromosomes are paired in one of the two sexes. In humans, for example, there are 22 pairs of autosomal (i.e. nonsex) chromosomes, together with two sex chromosomes, which form a pair in women (XX) but not in men (XY), making 46 chromosomes in total. As always in biology, it is more complicated than that, because even though women have two X chromosomes only one of these is expressed in any one cell. Thus, so far as expression is concerned, only the autosomal chromosomes are paired, and there is no difference between men and women in this respect. 

Different species have different numbers of chromosomes, and in Chinese hamsters, an example whose relevance will become clear later on, there are 10 pairs of autosomal chromosomes and one pair of sex chromosomes, making 22 in total. If no mistakes are made during cell division, the counts are preserved after each such division, but this is a highly complicated and still only partially understood process, and mistakes sometimes do occur as a result a daughter cell may contain one or three examples of an autosomal chromosome instead of the expected two. When this occurs in the germ line the result may be an individual with an abnormal number of chromosomes in every ceU, resulting, as noted briefly at the end of Chapter 1, in conditions such as Down syndrome and other trisomies. Errors also occur in somatic ceU division, usually with less-serious results as only a minority of cells are affected. In either case—in individual cells, or in whole organisms—the occurrence of an abnormal number of chromosomes is caUed aneuploidy. 

The genome, or total genetic content, of a human haploid cell (a sperm or an egg) is distributed in 23 chromosomes. Haploid cells contain one copy of each chromosome. The haploid egg and haploid sperm cells combine to form the diploid zygote, which continues to divide to form our other cells (mitosis), which are diploid. Diploid cells thus contain 22 pairs of autosomal chromosomes, with each pair composed of two homologous chromosomes containing a similar series of genes (Fig. 12.15). In addition to the autosomal chromosomes, each diploid cell has two sex chromosomes, designated X and Y. A female has two X chromosomes, and a male has one X and one Y chromosome. The total number of chromosomes per diploid cell is 46. 

One of the most surprising observations made with the aid of this new technique involved a change in the accepted number of chromosomes in humans. For years, the number of chromosomes in human cells had been assumed to be 48 now it is established that they contain only 46 chromosomes. The human diploid cell contains 22 pairs of autosomal chromosomes and one pair of sex chromosomes. In females, the sex chromosomes are identical in males, there is one sex chromosome of the X type and a sex chromosome of the Y type. Thus, the male is the heterogametic sex in humans as Wilson [47] postulated previously. 

In contrast to what happens with diseases linked to the sex chromosomes and therefore exhibited only in one of the sexes, diseases associated with the autosomal chromosomes are equally distributed in both sexes. 

An autosomal chromosome codes for the Na /K ATPase. Mutation to OU resistance is apparently dominant. A mutation in an Na /K" ATPase gene, which causes loss of functional enzyme, could not confer OU resistance, since the other gene product would still be OU-sensitive therefore, frameshift mutagens should not induce OU resistance. It has also been reported that treatments such as X rays do not induce OU resistance. 

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