Tag: pseudodominance with example

Pseudo-dominance – Recessive Allele Mimicking Dominant Pattern

Pseudo = false. Here it is pseudodominance that means it is false dominance.

Pseudodominance: is a condition where a recessive allele mimics the pattern of a dominant allele. 

To understand pseudodominance let’s start with the concept of dominant and recessive allele. In humans, since we are diploid organism we have two copies of every gene i.e. we have two alleles for every gene. And these alleles can be dominant or recessive. For a dominant allele to be expressed only one copy is enough. A dominant allele gets expressed even in heterozygous condition. But for a recessive allele to be expressed, there has to be two copies present i.e. it has to be in homozygous recessive condition for a recessive allele to be expressed.

But in pseudodominace, only one copy of recessive allele would get expressed. That’s why we say recessive allele mimics the dominant pattern.

Examples:

Sex Chromosome:

Females have two X chromosomes (XX) but males have only one X chromosome (XY). That means females would have two alleles of every gene present on X chromosome whereas males would have only one allele. So for a female to express any recessive allele on X chromosome it has to be in homozygous condition. But in case of male whatever allele is present on their single X chromosome that would get expressed. It can be either dominant allele or recessive allele. What I mean is, for males even one recessive allele is enough on X chromosome to express it because it doesn’t have homologous X chromosome. Therefore in case of males recessive allele on X chromosome mimics the dominant pattern and thus it is an example of pseudodominance.

Autosomal Chromosome:

Pseudodominance can be seen in autosomal chromosomes when in a homologous pair of chromosome, one allele is deleted and the other allele is recessive. So here that one recessive allele will get expressed because the other allele is deleted.

Why because of pseudodominance males are more commonly and severely affected with X-linked recessive genetic disorders?

X-linked genetic disorders such as hemophilia and color blindness are recessive genetic disorders which mean they require two copies of recessive alleles in order have the disorder. So for females there has to be homozygous recessive condition for this disorder but for males only one recessive allele would result in these disorders. Therefore, males are more susceptible than females.

I hope this helps 🙂

Watch a video on this topic here.