Question

The following variances were determined for measurements of body length, antennae bristle number, and egg production in a species of moth.  Which of these characters would be most rapidly changed by natural selection?  Which character would be most slowly affected by natural selection?

Variance                                            Body length               bristle #          Eggs

Total phenotypic variance (V_P)                   798                  342                  145

Additive variance (V_A)                                 132                  21                    21

Dominance variance (V_D)                            122                  126                  24

Interaction variance (V_I)                              118                  136                  34

Note that characteristics with a high narrow sense heritability value would change most quickly by selection.

Answer 1

Ans : To find out which character would be most rapidily and most slowly affected or changed by natural selection we have to calculate narrow sense heritability (h2).

Narrow sense heritability is defined as the fraction of phenotypic variance (VP) that can be attributed to variation in the additive effects of genes (VA).

i.e

Narrow-sense heritability, h2 = VA / VP

Calculating narrow sense heritability for characters (i) Body length, (ii) Bristle and (iii) Eggs

(i) Body length

Narrow-sense heritability, h2 = VA / VP VA = 132

= 132 / 798 VP = 798

= 0.1654

(ii) Bristle number

Narrow-sense heritability, h2 = VA / VP VA = 21

= 21 / 342 VP = 342

= 0.0614

(iii) Eggs

Narrow-sense heritability, h2 = VA / VP VA = 21

= 21 / 145 VP = 145

= 0.1448

It is noted that characteristics with a high narrow sense heritability value change the most quickly by natural selection and characteristics with a low narrow sense heritability value affect most slowly by natural selection.

Which of these characters would be most rapidly changed by natural selection?  

Ans : Body length has highest narrow sense heritability value(h2 = 0.1654) and hence it would be most rapidily changed by natural selection.

Which character would be most slowly affected by natural selection?

Ans : Bristle number has the lowest narrow sense heritability value (h2 = 0.0614) and hence it would be most slowly affected by natural selection.