3 2 4 Distinguish Between Homozygous And Heterozygous Genoty

Homozygous and Heterozygous…lol

So, let's deconstruct the words

Mono: means one (singular)
Homo: Same (but you already knew that)
Hetero: Opposite of different
Hybrid: combination of two things


Now, using this a monohybrid is the combination of two different parent animals with only one different trait

i.e. a brown cow and a white bull mate and produce a calf with either brown, white or (in the event of codominance – where both traits are dominant) a brown + white cow —> [wateva the fk that colour is]


Homozygous:

Within this, there are to sub-categories – homozygous dominant
homozygous recessive

Homozygous refers to an organism that possesses the same pair of allele (either a pair of dominant or recessive)

Thus, when an organism is homozygous dominant is posses the same pair of dominant alleles

i.e. using the example of cows again, white (R) would be the dominant trait and brown (r) the recessive. So a homozygous dominant would be a fully white cow (RR) and homozygous recessive would be a fully brown cow (rr)


But sir, sir what happens if we breed a brown and a white cow?

Breeding any organism that is either a homozygous dominant + homozygous recessive will create a heterozygous organism.

But this organism inherits both the dominant and recessive allele from its parents. Resulting in the dominant phenotype being physically shown. This, however, does not mean the recessive allele is not present within the gene, merely dormant.

i.e White cow (RR) + Brown cow (rr) = 100% White cow (Rr)
-> as white is the dominant allele


One of the most important aspects of this dot point would be the interaction between two heterozygous organisms.

Breeding two heterozygous organisms (Rr) result in:

  • 25% homozygous dominant (RR)
  • 50% heterozygous (Rr)
  • 25% homozygous recessive (rr)

As you can see these produce a variety of different Allele of offspring, with 3 expressing the dominant phenotype and one the recessive.

During Mendels research he also noticed this, and dubbed the "the golden ratio" wherein the second Filial (of initially breeding a homo and hetero – LOL) the recessive trait would eventually show in the ratio of 3:1

**– Nathaniel Tran

nathanieltran.jpg (hit me up on IG)**