Homozygous vs Heterozygous Alleles | Punnet Square Tips

A quick overview of the difference between homozygous and heterozygous alleles relating to Mendelian genetics.

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Thanks for stopping by. Today we are talking about homozygous vs heterozygous alleles. This is going to be a pretty quick video but I wanted to make it because I know it’s a tricky topic.

Let’s start by breaking down the terms. Any time you encounter the term “heterozygous” you should know it’s referring to two things being different or distinct from one another whereas “homozygous” refers to two things being the same.

Basically hetero=different and homo=same.

The same is true when referring to alleles. Using letters to represent alleles and referring to the most taught case of dominant vs recessive alleles. Two lower case letters such as “bb” would be a homozygous set of alleles, and in this case homozygous recessive. “BB” would also be homozygous, but would be homozygous dominant. “Bb” would be heterozygous. You wouldn’t assign dominant or recessive to the last pairing because it’s the only heterozygous option, so it needs no further distinction.

Alright, let’s do a quick recap. In dominant vs recessive alleles, if the two alleles are the same, the alleles are homozygous, the upper case being homozygous dominant and the lower case be homozygous recessive. If the two alleles are different, one uppercase one lowercase, then it’s heterozygous, just heterozygous.

I hope this clears up any confusion on the topic. Throw any additional questions in the comments and be sure to watch my other videos and share them with your friends.

I’ll catch you next time.