Chapter 5 – Evolution and inheritance
Consider the following statements and click to reveal the answer.
1. Judging by the genes and species names, how closely related are the blue tit (Parus caeruleus) and the coal tit (Parus ater) compared with the carrion crow (Corvus corone corone) and the hooded crow (Corvus corone cornix)?
Look at the genus and species names. The tits are in the same genus and so are very closely related, but the two crows are varieties of the same species and readily interbreed where their ranges overlap. (The hooded crow is common in north Scotland, while the carrion crow lives in south Scotland and England.)
2. In Australia and New Zealand, there are many endemic species, i.e. species that are found nowhere else on Earth. Why is this?
New Zealand and Australia were isolated from the other continents by a fairly wide expanse of ocean and so evolution proceeded along different lines.
3. Are there more chromosomes in brain cells or skin cells?
The same number in both – 46
4. Are there more chromosomes in a human egg just emerging from the ovary or in a fertilised egg? Explain your answer.
The egg has 23 chromosomes – those from the mother only. The fertilised egg has 46 chromosomes – the mother’s and the father’s.
5. Two normal parents, both of whom have the recessive gene for sickle cell disease, have two children, both of whom have the disease. The parents think that they would be unlikely to have a third child affected by the disease. Is this the case?
Their next child runs exactly the same risk of having the disease as the other two. The next child runs a one in four chance of inheriting the disease.
6. In two sentences, summarise why you are for or against the genetic modification of crops.
An example of a for argument: Genetically engineered organisms, such as the vitamin-rich rice, will have considerable benefits to poor people. The risks will be controlled by scientists who will not allow harmful food to be eaten or to cross with other organisms,
An example of an against argument: Genetic engineering will mainly benefit rice companies, who pay little regard to the possibility of their new organisms crossing with living things in the environment with highly unpredictable results. The food produced by genetic engineering may have consequences unforeseen by the scientists who produced it.
7. Of the five groups of vertebrates, which developed first and which are the most recent innovations?
Fish developed first, followed by amphibians, reptiles, birds and mammals.
8. In order of specificity, what are the features that distinguish humans from the other great apes?
Humans can walk upright, have a large brain, use tools extensively, bury dead with ceremony and create art.
9. Summarise the evolutionary pressures that led to the development of whales and dolphins. Explain why they continue to breathe through lungs rather than gills.
After the demise of the dinosaurs there were significantly fewer large carnivorous marine animals. The ancestors of the whales and dolphins were land-based carnivores which were able to exploit the niche left by the dinosaurs. Sea-going characteristics such as streamlined shape and top-of-head breathing holes were selected since the individuals which possessed them had an advantage over more land-adapted types in the struggle to get food. Whales and dolphins did not evolve gills because they are mammals with a highly developed form of breathing which could easily adapt to marine existence.
10. Comment on the idea that humans are evolving towards bodily perfection.
Humans evolved like all other animals in response to evolutionary pressure. Evolution occurs by chance and often the response to a pressure in the environment is not perfect. For instance, backache is a result of imperfect spines evolving as a response to upright gait.