2n 8 how many gametes

Then, the goodness-of-fit of the candidate regions with centromeric region was evaluated based on the transmission rate. Simulation method developed in this study was implemented in PedigreeSim version 2. Supplementary material is available at G3 online. In the simulation of the 2n gametes population, we first assumed an individual and simplex markers with known linkage phase across the genome, and simulated transmission in 2n gametes.

As expected, the transmission of the alternative allele across the genome showed different patterns between the broad sense FDR and SDR mechanisms. Changes in simplex transmissions along the genome resulted from recombination.

The simplex transmission patterns represented the heterozygosity restitution rate reported in diploid species Cuenca et al. Markers in the centromeric region showed only simplex transmission in FDR gametes and equal fractions of duplex and nulliplex transmissions in SDR gametes. Due to recombinations between the centromere and the markers, the duplex transmission increased toward the telomeres in FDR gametes but decreased in SDR gametes.

Multivalent formation decreased the net allele transmission i. Increased quadrivalent formation resulted in an increase in the duplex inheritance rate, and a decrease in the simplex inheritance rate, in both gamete types. In order to discriminate the mechanisms, we focused on the pattern of the duplex to simplex transmission ratio across the genome Supplementary Figure S6. In the FDR gametes, this ratio reaches its minimum value in the centromere and increases toward the telomere.

In contrast, in SDR gametes, the duplex:simplex ratio is at its maximum value in the centromeric region and decreases toward the telomere. In order to apply this ratio for the discrimination, it is required to measure an allele frequency of genome-wide markers in a 2n gamete population or in hybrids resulted from 2n gametes. When the mechanism for an individual gamete or hybrid needs to be discriminated, allele transmission pattern through a single 2n gamete across the genome can be a primal focus Figure 3.

In other words, beyond the 2nd recombination point, there could be a mixture of markers that are simplex and that are nulliplex or duplex depending on which homologous chromosome carried the simplex allele and which homologous chromosomes were involved in the recombinations, and thus those regions cannot be used for discriminating the mechanisms.

Simulation of the range of allele transmission in 2n gametes. A—D Simulated 2n gametes produced by a hexaploid individual. More than 5 million 2n gametes were generated for each experiment. It should be noted that we assumed chromosomes with only one arm during this simulation. Each color bar represents different homologous chromosomes in a 2n gamete produced by a hexaploid individual.

Recombination events at the recombination breakpoint RB in the figure were assumed. It should be noted that the reported counts of recombination in this figure took place in one of the two 2n gametes generated by a single meiosis but the other was not considered. This type of scan is achieved by fitting the nulliplex, simplex, and duplex transmission ratio in a given region to the possible transmission model at the centromere. When the SNPs are far from the centromere and recombination among homologous chromosomes occurs, both mechanisms produce simplex, nulliplex, or duplex status in the gametes Figure 4.

Specifically, allelic dosage doubling can only occur by recombination between marker and centromere in the FDR case but occurs over the entire chromosome including the centromere in the SDR case, leading to different distribution patterns.

A model of the allelic dosage doubling mechanism in 2n gamete formation. The SNPs with doubled alleles are highlighted in yellow.

There are limitations to this method. Therefore, this method can only be applied to polyploid species and cannot discriminate the mechanisms in diploid species where a single recombination results in the centromeric transmission pattern of the alternative mechanism. Besides, the discrimination power differs between the formation mechanisms. Since the subject is a single hybrid, in the following, we focused on the allele transmission pattern through a single 2n gamete across the genome.

In total, 25,, SNPs, which are heterozygous in at least one of the parents, were identified using our SNP selection criteria. The inheritance ratio was In order to discern the origin of the 2n gamete and the formation mechanism, we focused on simplex SNPs in the parents and analyzed the allele transmission in the progeny.

The simplex SNPs in the parents should transmit to the progeny with a specific ratio depending on the 2n gamete formation mechanism, genetic distance from the centromere, and pairing pattern Figures 2 and 3. Therefore, the RSS value was used to report on the goodness-of-fit for the nulliplex:simplex transmission pattern in the progeny against expected ratio for n gamete to identify the 2n gamete origin and possible formation mechanism.

The simplex MIA showed nulliplex , loci , simplex , loci , and duplex 17, loci transmissions in the progeny Figure 6A. The value in each figure represents RSS value of the goodness-of-fit of the nulliplex:simplex ratio against the model. Additionally, it appeared that regions with a high ratio of duplex inheritance matched regions with a low ratio of simplex inheritance Figure 7, A and B.

Genome-wide inheritance pattern of the simplex PIA. A Genome-wide distribution of duplex inheritance of the simplex PIA. B Genome-wide distribution of simplex inheritance of the simplex PIA. In this SDR mechanism, the simplex SNPs in the pericentromeric region of the parent, which offered the 2n gamete, should be duplex or nulliplex with equal probability in the progeny, whereas they should be entirely simplex in the FDR mechanism Figure 4.

Therefore, no simplex inheritance of the PIA to the progeny in the pericentromeric region would occur, and the nulliplex:simplex:duplex ratio should be Figures 3J and 4.

The presumed pericentromeric regions identified in the SDR scenario were defined based on the high fraction of duplex inheritance, and the regions of Chr2: Subsequently, the major concern is that whether the simplex dosage inherited from simplex PIA in these regions is negligible. If so, these regions are supported to be authentic pericentromeric regions in the SDR scenario.

If not, the SDR scenario will be rejected. Additionally, the nulliplex:simplex:duplex ratio was fit best with the model, in comparison to the model, for the remaining eight regions Figure 8, B—I.

Thus, the putative centromere regions, defined based on the duplex inheritance pattern in SDR, did not show TR-SDRc, but fit more to the transmission ratio at a region with a chromosome combination formed by one recombination from the SDR centromere combination, which could be present in FDR gametes Figure 3, I and J.

The former and latter values in each figure represent RSS values of the goodness-of-fit of the nulliplex:simplex:duplex ratios to the and models, respectively. In order to further verify this inference, the simplex PIA on the presumed pericentromeric regions under the FDR scenario was selected for further analysis. It is worth noting that more than one presumable pericentrometric region was defined in many chromosomes according to this criterion in Figure 7B. Two mechanisms resulted from this phenomenon: 1 a portion of the regions is located between the centromeres and a recombination break, which is the closest to centromere; and 2 recombination and chromosome segregation during meiosis produce a parental chromosomal combination, which is same as that of centromere.

This suggests that the regions are located between the centromere and a recombination break, which is the closest to centromere; whereas this pattern could also be obtained with a combination of parental chromosomes mixed by recombination, as mentioned above. This result exclusively fits the broad sense FDR mechanism, as illustrated in cross-combination I Figure 2.

The former and latter values in each figure represent RSS values of the goodness-of-fit of the nulliplex:simplex:duplex ratio to the and models, respectively. In this study, a new strategy for uncovering mechanism used to produce 2n gametes in polyploid plants was proposed. We showed that even without any information on the location of centromere, it is possible to discriminate between the two possible mechanisms associated with the 2n gamete formation and the parental origin of the 2n gamete.

Since the genotypes of simplex centromeric markers are not affected by ploidy or the occurrence of multivalents, the strategy presented in this study can be tested on the products of any hybridizations involving 2n gametes in polyploid species. The mechanisms resulting in individual 2n gamete can be distinguished by analyzing the goodness-of-fit of the observed transmission to the expected transmission ratio at the centromere, assuming that any recombinations do not produce a chromosome combination expected at the centromere under the alternative hypothesis.

This approach also allows to identify the centromeric region, given that a gamete has arisen by either the FDR or SDR scenario. Quadrivalent formation in normal meiosis affects allele transmission pattern, whereas the effect in the transmission through 2n gametes has not been well characterized.

Here, it was shown that increased quadrivalent formation increases duplex transmission of parental simplex alleles in 2n gametes Supplementary Figure S3. In SDR gametes, the increased amount of duplex transmission in the quadrivalent is due to the situations where the chromosomes involved in crossing over go toward the same pole.

We have no clear explanation for FDR gametes, but the increased duplex transmission in the FDR gametes could be related to the increased opportunities for recombination with quadrivalent formation Sved ; Voorrips and Maliepaard Interestingly, allelic doubling was almost exclusively detected at the telomeres of the D.

This is probably a consequence of polyploid breeding. Progeny bred by the FDR-derived 2n gametes tends to be superior to that not derived from 2n gametes and that derived from SDR-type 2n gametes, due to the increased allelic diversity, resulting in heterosis Yao et al.

The assumed superiority of FDR-derived 2n gametes was confirmed with respect to yield in potato Hutten et al. The FDR gamete is likely to be a useful model to study the recombination landscape in polyploid species, as well as for breeding. Apart from some reports suggesting polysomic inheritance in the astringency-controlling locus based on genotype segregation Akagi et al. Further analysis combining cytology, double reduction, and 2n gamete formation may be helpful for understanding the chromosomal evolution of Diospyros.

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Received : 21 July Accepted : 09 January Published : 01 July Issue Date : 01 July Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Euphytica Scientific Reports Plant Cell Reports Advanced search.

Skip to main content Thank you for visiting nature. Download PDF. Introduction In plants, sexual polyploidization by the formation of unreduced 2 n gametes is an important feature in both nature and breeding programs.

Full size image. Materials and methods Plant materials Four diploid clones that were derived from crosses between the diploid species S. Evidence for postmeiotic restitution in 2n-egg formation In order to provide genetic evidence for postmeiotic doubling of chromosomes, it is essential to show genotypes of 2 n -eggs that are recombinant as well as completely homozygous. Implications of PMR 2n-gametes For the breeding of potato at the diploid level, it is important to realize that 2 n -eggs are not always of SDR origin.

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