Genetic Maps: Direct Meiotic Analysis

Abstract

Cytogenetic analyses provide a direct means of obtaining critical information on the patterns of meiotic recombination, at the genomic and chromosome‐specific levels, in both male and female germ cells. This information provides insight into the control of meiotic recombination in human germ cells and allows the construction of accurate sex‐specific genetic maps.

Keywords: genetic recombination map; crossing‐over; chiasmata; MLH1 foci; spermatocytes; oocytes

Figure 1.

Cartoon illustrating the generation of homologous pairs of chromosomes (bivalents) held together by chiasmata following crossing‐over at pachytene. Two chromosome pairs are illustrated: one acrocentric, the other metacentric. Centromere positions are indicated by filled circles. One homolog of each pair is dark, the other light. At the end of pachytene, intimate homologous chromosome pairing (synapsis) lapses and the two homologs are held together only at the positions of crossing‐over (chiasmata). The acrocentric pair, with one chiasma, forms a rod‐shaped structure; the metacentric pair, with two chiasmata, forms a ring structure.

Figure 2.

Human metaphase I spermatocyte. (a) Intact cell containing 22 pairs of autosomal bivalents and the XY bivalent. (b) Individual bivalents have been cut out and the positions of chiasmata are indicated by arrows.

Figure 3.

Cartoon illustrating the relationship of a crossover, as viewed directly (as a chiasma or MLH1 focus) or indirectly in the products of meiosis (gametes).

Figure 4.

Comparison of chiasma distributions (in 5% length intervals) along chromosomes 15 and 16. Chromosome 15 is acrocentric, chromosome 16 metacentric. Although both chromosomes are similar in length, they show different distributions.

Figure 5.

Pachytene male (a) and female (b) germ cells. In both, synaptonemal complexes are stained green and MLH1 foci red. In the spermatocyte (a), the centromeres are stained blue. The chromatin cloud that surrounds the synaptonemal complexes has been omitted to aid clarity. Arrowheads indicate the MLH1 foci.

Figure 6.

Comparison of the distribution patterns of MLH1 foci (in 5% length intervals) of chromosome 21 with one or two foci in fetal oocytes.

Figure 7.

Histograms illustrating the distributions of chiasmata in spermatocytes (blue) and MLH1 foci in oocytes (pink) on chromosomes 13, 18 and 21. Each chromosome pair is divided into 5% length intervals. These crossover distribution patterns are also displayed for each chromosome as recombination maps. These maps highlight the different patterns of crossover numbers and distributions in male and female germ cells and the consequent effect on the recombination map.

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References

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Further Reading

Barlow AL, Benson FE, West SC and Hultén MA (1997) Distribution of the Rad51 recombinase in human and mouse spermatocytes. EMBO Journal 16: 5207–5215.

Hassold TA, Sherman S and Hunt P (2000) Counting cross‐overs: characterizing meiotic recombination in mammals. Human Molecular Genetics 9: 2409–2419.

Hultén MA and Lawrie NM (1993) Chiasma density and interference maps of the normal and translocated chromosome 9 in the human male. First International Workshop on Chromosome 9. Annals of Human Genetics 56: 194–195.

Hultén MA, Lawrie NM and Laurie D (1990) Chiasma‐based genetic maps of chromosome 21. American Journal of Medical Genetics 7: 148–154.

Hultén MA, Palmer RW and Laurie DA (1982) Chiasma derived genetic maps and recombination fractions: chromosome 1. Annals of Human Genetics 46: 167–175.

Jones GH (1987) In: Moens PB (ed.) Chiasmata in Meiosis, pp. 213–244. Cambridge, UK: Cambridge University Press.

Laurie DA and Hultén MA (1985) Further studies on chiasma distribution and interference in the human male. Annals of Human Genetics 49: 203–214.

Laurie DA, Palmer RW and Hultén MA (1982) Chiasma derived genetic lengths and recombination fractions: Chromosomes 2 and 9. Annals of Human Genetics 46: 233–244.

Saadallah N and Hultén MA (1983) Chiasma distribution, genetic lengths and recombination fractions: A comparison between chromosome 15 and 16. Journal of Medical Genetics 20: 362.

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How to Cite close
Hultén, Maj, and Tease, Charles(Sep 2006) Genetic Maps: Direct Meiotic Analysis. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0006250]