Masked allele is a terminology that is sometimes used for recessive alleles, which should be suitable to your example. A common phrasing could be; "The wild type allele is masking the expression of the deleterious allele X.".

For your particular example you could use:

Deleterious mutations on the Y chromosome are more easily purged since they cannot be masked by alleles on a homologous chromosome.

An example can also be seen in the abstract to Otto & Goldstein (1992):

With two copies of every gene, a diploid organism is able to mask recessive deleterious mutations. In this paper we present the analysis of a two-locus model designed to determine when the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases ("alternation of generations").

Masked allele is a term that is sometimes used for recessive alleles, and it should be suitable to the situation you describe. A common phrasing could be; "The wild type allele is masking the expression of the deleterious allele X.".

For your particular example you could use:

Deleterious mutations on the Y chromosome are more easily purged since they cannot be masked by alleles on a homologous chromosome.

An example can also be found in the abstract to Otto & Goldstein (1992):

With two copies of every gene, a diploid organism is able to mask recessive deleterious mutations. In this paper we present the analysis of a two-locus model designed to determine when the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases ("alternation of generations").

Masked allele is a terminology that is sometimes used for recessive alleles, which should be suitable to your example. A common phrasing could be; "The wild type allele is masking the expression of the deleterious allele X.".

For your particular example you could use:

Deleterious mutations on the Y chromosome are more easily purged since they cannot be masked by alleles on a homologous chromosome.

Masked allele is a terminology that is sometimes used for recessive alleles, which should be suitable to your example. A common phrasing could be; "The wild type allele is masking the expression of the deleterious allele X.".

For your particular example you could use:

Deleterious mutations on the Y chromosome are more easily purged since they cannot be masked by alleles on a homologous chromosome.

An example can also be seen in the abstract to Otto & Goldstein (1992):

With two copies of every gene, a diploid organism is able to mask recessive deleterious mutations. In this paper we present the analysis of a two-locus model designed to determine when the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases ("alternation of generations").