testcross

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a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring (同)test-cross

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/08/08 03:03:50」(JST)

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Punnett squares showing typical test crosses and the two potential outcomes. The individual in question may either be heterozygous, in which half the offspring would be heterozygous and half would be homozygous recessive, or homozygous dominant, in which all the offspring would be heterozygous.

In genetics, a test cross, first introduced by Gregor Mendel, involves the breeding of a phenotypically dominant individual with a phenotypically recessive individual, in order to determine the zygosity of the former by analyzing proportions of offspring phenotypes. Zygosity can either be heterozygous or homozygous. Those that are heterozygous have one dominant and one recessive allele. Individuals that are homozygous dominant have two dominant alleles, and those that are homozygous recessive have two recessive alleles. ^[1]

The genotype that an offspring has for each of its genes is determined by the alleles inherited from its parents. The combination of alleles is a result of the maternal and paternal chromosomes contributed from each gamete at fertilization of that offspring. During meiosis in gametes, homologous chromosomes experience genetic recombination and segregate randomly into haploid daughter cells, each with a unique combination of maternally and paternally coded genes.^[2] Dominant alleles will override the expression of recessive alleles.

Test crosses are used to test an individual's genotype by crossing it with an individual of a known genotype. Individuals that show the recessive phenotype are known to have a homozygous recessive genotype. Individuals that show the dominant phenotype, however, may either be homozygous dominant or heterozygous. The phenotypically dominant organism is the individual in question in a test cross. The purpose of a test cross is to determine if this individual is homozygous dominant or heterozygous.^[1]

Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. Analyzing the proportions of dominant and recessive offspring determines if the individual in question is homozygous dominant or heterozygous. If all offspring from the test cross display the dominant phenotype, the individual in question is homozygous dominant; if half the offspring display dominant phenotypes and half display recessive phenotypes, then the individual is heterozygous. Since the homozygous recessive individual can only pass on recessive alleles, the alleles the individual in question passes on determine the phenotypes of the offspring.^[1]

References

^ ^a ^b ^c Gai, J; He, J (2013). "Test Cross". Brenner’s Encyclopedia of Genetics, Second Edition 4. Elsevier. p. 1952.
^ Griffiths JF, Gelbart WM, Lewontin RC, Wessler SR, Suzuki DT, Miller JH (2005). Introduction to Genetic Analysis. New York: W.H. Freeman and Co. pp. 34–40, 473–476, 626–629. ISBN 0-7167-4939-4.

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English Journal

Analysis of quantitative trait loci affecting chlorophyll content of rice leaves in a double haploid population and two backcross populations.

Jiang G1, Zeng J2, He Y3.Author information 1National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research and National Center of Crop Molecular Breeding, Huazhong Agricultural University, Wuhan 430070, PR China; College of Life Science, Heilongjiang University, Haerbin 150080, China.2National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research and National Center of Crop Molecular Breeding, Huazhong Agricultural University, Wuhan 430070, PR China.3National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research and National Center of Crop Molecular Breeding, Huazhong Agricultural University, Wuhan 430070, PR China. Electronic address: yqhe@mail.hzau.edu.cn.AbstractChlorophyll content, one of the most important physiological parameters related to plant photosynthesis, is usually used to predict yield potential. To map the quantitative trait loci (QTLs) underlying the chlorophyll content of rice leaves, a double haploid (DH) population was developed from an indica/japonica (Zhenshan 97/Wuyujing 2) crossing and two backcross populations were established subsequently by backcrossing DH lines with each of their parents. The contents of chlorophyll a and chlorophyll b were determined by using a spectrophotometer to directly measure the leaf chlorophyll extracts. To determine the leaf chlorophyll retention along with maturation, all measurements were performed on the day of heading and were repeated 30days later. A total of 60 QTLs were resolved for all the traits using these three populations. These QTLs were distributed on 10 rice chromosomes, except chromosomes 5 and 10; the closer the traits, the more clustering of the QTLs residing on common rice chromosomal regions. In general, the majority of QTLs that specify chlorophyll a content also play a role in determining chlorophyll b content. Strangely, chlorophyll content in this study was found mostly to be lacking or to have a negative correlation with yield. In both backcross F1 populations, overdominant (or underdominant) loci were more important than complete or partially dominant loci for main-effect QTLs and epistatic QTLs, thereby supporting previous findings that overdominant effects are the primary genetic basis for depression in inbreeding and heterosis in rice.
Gene.Gene.2014 Feb 25;536(2):287-95. doi: 10.1016/j.gene.2013.12.010. Epub 2013 Dec 17.
Chlorophyll content, one of the most important physiological parameters related to plant photosynthesis, is usually used to predict yield potential. To map the quantitative trait loci (QTLs) underlying the chlorophyll content of rice leaves, a double haploid (DH) population was developed from an ind
PMID 24361205

Identification of quantitative trait locus (QTL) linked to dorsal fin length from preliminary linkage map of molly fish, Poecilia sp.

Keong BP1, Siraj SS2, Daud SK3, Panandam JM4, Rahman AN2.Author information 1Department of Aquaculture, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia. Electronic address: bunpoh@yahoo.com.2Department of Aquaculture, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia.3Department of Biology, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia.4Department of Animal Science, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia.AbstractA preliminary linkage map was constructed by applying backcross and testcross strategy using microsatellite (SSR) markers developed for Xiphophorus and Poecilia reticulata in ornamental fish, molly Poecilia sp. The linkage map having 18 SSR loci consisted of four linkage groups that spanned a map size of 516.1cM. Association between genotypes and phenotypes was tested in a random fashion and QTL for dorsal fin length was found to be linked to locus Msb069 on linkage group 2. Coincidentally, locus Msb069 was also reported as putative homologue primer pairs containing SSRs repeat motif which encoded hSMP-1, a sex determining locus. Dorsal fin length particularly in males of Poecilia latipinna is an important feature during courtship display. Therefore, we speculate that both dorsal fin length and putative hSMP-1 gene formed a close proximity to male sexual characteristics.
Gene.Gene.2014 Feb 15;536(1):114-7. doi: 10.1016/j.gene.2013.11.068. Epub 2013 Dec 11.
A preliminary linkage map was constructed by applying backcross and testcross strategy using microsatellite (SSR) markers developed for Xiphophorus and Poecilia reticulata in ornamental fish, molly Poecilia sp. The linkage map having 18 SSR loci consisted of four linkage groups that spanned a map si
PMID 24333858

Association between line per se and testcross performance for eight agronomic and quality traits in winter rye.

Miedaner T, Schwegler DD, Wilde P, Reif JC.Author information State Plant Breeding Institute, Universitaet Hohenheim (720), 70593, Stuttgart, Germany, miedaner@uni-hohenheim.de.AbstractKEY MESSAGE: We investigated associations between line per se and testcross performance in rye and suggested that selection for per se performance is valuable for several traits in multi-stage selection programs. Genotypic correlation between line per se and testcross performance is an important quantitative-genetic parameter for optimizing hybrid breeding programs. The main goal of this survey was to study the association of line per se and testcross performance at the phenotypic level. We used experimental data from the line per se and testcross performance of two segregating winter rye populations (A, B) with each of 220 progenies tested in six environments for eight agronomic and quality traits. Genotypic variances were considerably larger for per se than for testcross performance of all investigated traits resulting in higher heritabilities of the former in most instances. Genotypic correlations (r g) between testcross and line per se performance decreased with increasing complexity of the trait as shown by the respective heritabilities. They were highest (r g ≥ 0.7) for plant height and test weight in population B, and thousand-kernel weight, falling number and starch content in both populations. A selection of these traits for line per se performance in early generations will save field plots in further testing testcross performance and increase efficiency of hybrid breeding.
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik.Theor Appl Genet.2014 Jan;127(1):33-41. doi: 10.1007/s00122-013-2198-2. Epub 2013 Sep 27.
KEY MESSAGE: We investigated associations between line per se and testcross performance in rye and suggested that selection for per se performance is valuable for several traits in multi-stage selection programs. Genotypic correlation between line per se and testcross performance is an important qua
PMID 24072205

Japanese Journal

Construction of a high-density reference linkage map of tea (Camellia sinensis)

Taniguchi Fumiya,Furukawa Kazumi,Ota-Metoku Sakura,Yamaguchi Nobuo,Ujihara Tomomi,Kono Izumi,Fukuoka Hiroyuki,Tanaka Junichi
Breeding Science 62(3), 263-273, 2012
… A few linkage maps of tea have been constructed using pseudo-testcross theory based on dominant marker systems. …
NAID 130004057167

Genetic analysis of heterotic loci detected in a cross between indica and japonica rice (Oryza sativa L.)

Xin Xiao Yun,Wang Wen Xiang,Yang Jin Shui,Luo Xiao Jin
Breeding Science 61(4), 380-388, 2011
… In this study, using a set of introgression lines (ILs) and corresponding testcross F1 populations, we investigated heterotic loci (HL) associated with six yield-related traits in both Oryza sativa L. … The F1 testcross population showed superiority in most yield-related traits and was characterized by a high frequency of overdominant HL. …
NAID 130004146322

An AFLP-based Genetic Linkage Map of Ipomoea trifida (H.B.K.) G. Don., a Diploid Relative of Sweetpotato, I. batatas (L.) Lam.

Nakayama Hiroki,Tanaka Masaru,Takahata Yasuhiro
Tropical Agriculture and Development 54(1), 9-16, 2010
… Based on the "pseudo-testcross design" for analyzing F<SUB>1</SUB> …
NAID 130004544161

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