Lots of possible answers.  Could you provide a few more details?  If these tetrads are the result of mating two haploids, can you post the genotypes of the haploids that you crossed?  If you are not doing a cross and are instead dissecting ascospores from a sporulted stable diploid, please provide that strain's genotype.

I agree with Christopher,

Some of possible answers: Haploids may contain alleles lead to shift of optimal growth environmental conditions compared with diploids. Or even complete loss of growth ability due to lethal mutations in some cells which are masked by diploid state.

Nevertheless more information needed to find an answer...

Thank you for the reply Christopher and Maria,

1. These tetrads are not result of any mating experiment, I am dissecting ascospores from a sporulated stable diploid.

2. Christopher can you please elaborate as in what more information regarding genotype do you seek for ? When mat-allele typing of this strain was done using mat A and Alpha primers, I did get two distinct bands - indicating its A-Alpha strain.

Moreover when I did mat typing of one of the segregants I did get a single mat allele band (of A)

Hi Jaideep. Regarding the genotypes: most laboratory strains have mutations in various genes that cause nutritional auxotrophies. For example, deletion or mutation in the ura3 gene (that functions in the uracil biosynthsis pathway) abolishes the cell’s ability to synthesize uracil. For these strains, you need to add uracil in the medium to permit their growth. Such auxotrophic markers are present in laboratory strains so that you can manipulate them genetically. The reason I asked about the genotype of your strain is so that I could see what auxotrophic markers are present in your strain and I could better think about possible causes of your poor viability. So, if you can get a list of any genetic markers (genotype) your strain has, it could be informative.

Without knowing the genotype, I would speculate on a few possibilities (there are more) based on what you have described. Often times when one sees spores germinating, forming a few cells, and not growing further, it is a sign that:

1) the cell has a nutritional requirement that is not be rescued by nutrients provided in the growth medium (eg. the ura3 mutation described above and not enough uracil being provided in the medium). In your case, you are dissecting onto rich medium, so I am less worried about amino acids being present, but auxotrophies in nucleotides like uracil or adenine sometimes require some extra supplementation of ura or ade in the medium (even in rich medium).

2) the parent diploid was heterozygous for an essential gene. In spores that are generated after meiosis, two spores would contain wild type allele of this gene and they would grow. Two spores would contain the mutant allele of the gene. They would try to grow with 1-2 rounds of division, then would stop. Again, the genotype of the strain would inform us if this is a possibility.

3) for some strain backgrounds, spore viability can be low. However, this generally results in spores that do not germinate at all…this may account for a portion of what you are seeing (those spores that do not germinate). In this case, my advice would be to dissect more tetrads.

Perhaps Maria or others will jump in with their thoughts. I hope this is helpful.

Hi Christopher, thanks a lot for explaining the genotypes in details.

I do not have information about genotype of the strain, I would try to get information regarding the same and/or try adding uracil or adenine in media used for dissecting spores.

I think the 2nd point that you say, ie, of parent strain being heterozygous for an essential gene, might be the causative/responsible thing in my case.

Thanks once again.