If several pea plants with the genotype ttyy are crossed with pea plants with the genotype ttyy what percentage of the offspring will be expected to have the ttyy allele combination

25%

Explanation:

A cross between two heterozygous plant can will result in the following pair.

To get this combination we need to cross the first pair individually and then the second pair individually.

    T         T                        Y         y

T   TT     TT                   y   Yy     yy

t    Tt       Tt                   y   Yy      yy

The ratio of TT= 1/2        The ratio of Yy= 1/2

The total ratio of TTYy= 1/2* 1/2 = 1/4 which is 25% of the total offspring produced by the cross between the pair TTYy and  Ttyy.

The offspring produced is heterozygous.

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.  

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