Question
Explain: Multiple allelism
✓
Answer
$\rightarrow$ It is the presence of more than two alleles of a gene to govern same character.
$\rightarrow$ E.g. $ \text{ABO}$ blood grouping $(3$ alleles: $I^A, I^B i).$
$\rightarrow$ In an individual, only two alleles are present. Multiple alleles can be found only in a population.
$\rightarrow$ A single gene product may produce more than one effect.
$\rightarrow$ Occasionally, a single gene product may produce more than one effect.
$\rightarrow$ For example, starch synthesis in pea seeds is controlled by one gene.
$\rightarrow$ It has two alleles $(B$ and $b).$
$\rightarrow$ Starch is synthesised effectively by $BB$ homozygotes and therefore, large starch grains are prdouced.
$\rightarrow$ In contrast, $bb$ homozygotes have lesser efficiency in starch synthesis and produce smaller starch grains.
$\rightarrow$ After maturation of the seeds, $BB$ seeds are round and the $bb$ seeds are wrinkled, Heterozygotes produce round seeds and so $B$ seems to be the dominant allele.
$\rightarrow$ But, the starch grains produced are of intermediate size in $Bb$ seeds.
$\rightarrow$ So, if starch grain size is considered as the phenotype, then from this angle, the alleles
show incomplete dominance.
$\rightarrow$ Therefore, dominance is not an autonomous feature of a gene or the product that it has information for.
$\rightarrow$ It depends as much on the gene product and the production of a particular phenotype from this product as it does on the particular phenotype that we choose to examine, in case more than one phenotype is influenced by the same gene.
$\rightarrow$ E.g. $ \text{ABO}$ blood grouping $(3$ alleles: $I^A, I^B i).$
$\rightarrow$ In an individual, only two alleles are present. Multiple alleles can be found only in a population.
$\rightarrow$ A single gene product may produce more than one effect.
$\rightarrow$ Occasionally, a single gene product may produce more than one effect.
$\rightarrow$ For example, starch synthesis in pea seeds is controlled by one gene.
$\rightarrow$ It has two alleles $(B$ and $b).$
$\rightarrow$ Starch is synthesised effectively by $BB$ homozygotes and therefore, large starch grains are prdouced.
$\rightarrow$ In contrast, $bb$ homozygotes have lesser efficiency in starch synthesis and produce smaller starch grains.
$\rightarrow$ After maturation of the seeds, $BB$ seeds are round and the $bb$ seeds are wrinkled, Heterozygotes produce round seeds and so $B$ seems to be the dominant allele.
$\rightarrow$ But, the starch grains produced are of intermediate size in $Bb$ seeds.
$\rightarrow$ So, if starch grain size is considered as the phenotype, then from this angle, the alleles
show incomplete dominance.
$\rightarrow$ Therefore, dominance is not an autonomous feature of a gene or the product that it has information for.
$\rightarrow$ It depends as much on the gene product and the production of a particular phenotype from this product as it does on the particular phenotype that we choose to examine, in case more than one phenotype is influenced by the same gene.
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