1 The authors state In mildly stressful conditions a few ben

1. The authors state: “In mildly stressful conditions a few beneficial mutations may exist [a], and the fraction of mutations that are beneficial will increase with the level of stress, up to the point where the breakdown of fundamental biological processes hinders or entirely prevents any alleviation [d]. The overall rate of beneficial mutation is the product of the mutation supply rate, which falls with increasing stress [b], and the fraction of mutations that are beneficial, which rises with increasing stress [c]”. Why are these things (a-d) true?

2. Populations can also include sub-groups that differ from one another. For instance, how would you expect height to differ between males and females? Draw a graph depicting this.

3. Sometimes traits of individuals can co-vary, so that having value A for one trait predicts having value B for another trait. Consider the length and width of your hand. You would not expect these traits to be completely independent – some combinations of hand length and width are just not seen in humans. Draw a graph with hand width across the knuckles on one axis and hand length from wrist joint to tip of middle finger on the other. If you were to draw dots on this graph representing trait combinations of everyone in the class, what would you expect that graph to look like? Would you expect any patterns relating to maleness/femaleness? What about patterns relating to the individual’s height?

Solution

In response to environmental stress beneficial mutations in the population get advantage of stress tolerance and the proportion of population bearing the beneficial mutation to encounter stress get upper hand in the altered stressful environment and positively selected. The fraction of the population having beneficial mutation will grow in response to the stress level up to a certain limit but when the stress level increases to a critical level where there is no mutation to counter that level of stress the selection process or evolution ceases. The situation or environmental stress specific mutation may also exert metabolic burden or other disadvantage to the normal functioning of the organism hence there is a certain limit of tolerating any stress for some population when the threshold level is achieved the growth of the particular fraction ceases.

Unlike other mammals sexual dimorphism and body growth in male and female is not very influenced as there is no longer reproductive success in larger body sized man. Unlike other mammal where STAT5b effecting only male growth both male and female growth in humans is dependent on GH-dependent STAT5b regulation of IGF-I expression. But still on average men are five inches taller than woman in general as male growth hormone testosterone level helps gain more height in men (genetically determined). Body parts like land length and width varies proportionately i.e. co varies which means width of the hand increases and decreases with length of the hand.

The graph with hand width across the knuckles on one axis and hand length from wrist joint to tip of middle finger on the other will produce a straight line. So, if graph is drawn with dots representing trait combinations of everyone in a class, a straight line is expect in that graph.

The graph will look like a straight line.

The graph line of female will be straighter than male as musculization affects as secondary sexual growth development in men. Patterns relating to the individual’s height will be similar as height will be truly co vary with other body measures proportionately.