Which of these genotypes are heterozygous?

A: TT
B: Tt
C: tt
D: none of these

B

Explanation:

Heterozygous genotypes are those that have one dominant allele and one recessive allele.

Dominant alleles are represented as capital letters, while recessive alleles are represented as lowercase letters. So, a heterozygote should have one capital letter and one lowercase letter.

Looking at the answer choices, only B fits this, so it's the answer.

Hope this helps!

4

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

read more on -