What does it mean to be heterozygous for a trait?

Answer 1

One cannot really be heterozygous for a trait. You can be heterozygous for a gene, and based on the whether that gene is dominant or recessive will determine if you express that trait or not.

Humans (and most organisms) carry two copies of each chromosome. As such, for a given genetic sequence, there can be three possibilities (there are exceptions, but let's keep it simple for now). The genes A)both code for the trait, B) neither code for the trait, or C) One gene does and the other does not. The C option is is being heterozygous.

Let's get an example now:

Assume that in some animal, there are only two hair colors -- Black or White. Also, the Black Hair color is Dominant. The black hair color is coded by the uppercase letter "B" and the white hair color is coded by the lowercase letter "b".

An animal with the coding "BB" is HOMOZYGOUS for Black hair because BOTH genes code for black hair. Similarly, an animal coding "bb" will have White hair, because BOTH genes code for white hair.

Now, let's say these two animals mate and have a baby coding with "Bb". This baby will have BLACK hair because the Black hair color is dominant and overpowers the White hair gene.

To be Heterozygous (usually) means that you will express the dominant version of the trait, BUT your offspring/children can possibly get the recessive version of the trait.

Answer 2

Being heterozygous for a trait means having two different alleles for that specific trait. One allele is dominant and the other is recessive, resulting in a phenotype that shows the dominant trait. Heterozygous individuals can pass on either allele to their offspring.