Question

I'm doing a genetics lab and one of the questions are:

Mouth size is a trait that demonstrates partial dominance. For mouth size, what trait is expressed for the following gene combinations?
a. homozygous recessive
b. heterozygous
c. homozygous dominant
----------The combinations for the mouth are: TT, Tt, tt

How would I answer this question?

Answer 1

Let me give you a few facts that will help you.

~~~~~~~~~~~

(T T), (T t), and (t t) are all examples of GENOTYPES.

You see,
a GENOTYPE is made up of two letters.
A pair of letters.

~~~~~~~~~~~~~~~

A HOMOZYGOUS genotype is where both of the letters are the SAME.

For example....

(A A)
(a a)
(B B)
(b b)

Those are all HOMOZYGOUS genotypes.

~~~~~~~~~~~~~

A HETEROZYGOUS genotype is where both of the letters are DIFFERENT.

For example.....

(A a)
(B b)
(D d)

Those are all examples of HETEROZYGOUS genotypes.
Because in each genotype, the two letters are DIFFERENT.
One is capital, and the other is lower-case.

~~~~~~~~~~~~~~

DOMINANT genotypes have at least one CAPITAL letter.

For example.....

(A a)
(A A)
(B b)
(B B)

Those are all examples of DOMINANT genotypes.
Because there is at least one CAPITAL letter.

~~~~~~~~~~~~~~~~~~

RECESSIVE genotypes do not have ANY capital letters.
The letters are all LOWER-case.

For example.....

(a a)
(b b)
(c c)

Those are all RECESSIVE genotypes,
because in each genotype, both letters are LOWER-case.

~~~~~~~~~~~~~~~~~

Okay. So I've given you four facts.

Let's do some examples.


(A a) is a Heterozygous Dominant genotype.

(A A) is a Homozygous Dominant genotype.

(a a) is a Homozygous Recessive genotype.

(b b) is a Homozygous Recessive genotype.

(B b) is a Heterozygous Dominant genotype.

~~~~~~~~~~

You think you can do it on your own now?