Question

3. Describe the twofold cost of sex, the cost of males, and the cost of recombination.
4. What are the differences between sexual and natural selection? Define and explain each (including the basic principles of evolutionary changes and natural selection) with examples from the readings and class.

please explain in about 3-4 paragraph so that I could understand clearer please.

Answer 1

Ans. Two-fold cost of sex :- All else being equal , an asexually reproducing population will grow at twice the rate as a sexually reproducing population. The reason for this is that the members of a sexually reproducing population must produce both sexes, but effectively only half of them can give birth to offspring of their own. In contrast , all offspring of an individual from an asexually reproducing population can potentially give birth. This is the two-fold cost of sexual reproduction.

• Cost of males :- The males do not produce offspring( not directly). The amount of new individuals that can be created in a population only depends on the number of females (given that there is atleast one male ).e.g. If a female produce only two daughters, and these would also produce two daughters, in four generations there would be 8 offspring. But , if a female produce one daughter and one son, and the daughter produce again one daughter and one son , in four generations there would be only 2 offspring present in the population.
• Cost of recombination :- In sexual reproduction half of genes in an offspring came from father and half from mother. The genetic relatedness between parent and offspring is therefore much lower than when the offspring is a direct genetic copy of the parent . Alleles have only 50% chance of being passed on to next generation every time an offspring is created. From the viewpoint of genes this is costly ; twice as many offspring need to be created to have same allele frquency in next generation as compared to asexual reproduction.

Difference between sexual and natural selection :-

Natural selection :- The process whereby organisms better adapted to their environment tend to survive and produce more offspring.

Sexual selection is a special kind of natural selection in which mating prefrences influence the traits of organism

Sometimes , natural selection and sexual selection are in direct opposition to one another. e.g. population of wild guppies that live in streams in Trinidad in the Carribean have different colour patterns depending on where they live. Male guppies living in streams that have a crayfish predator are drab green in colour, but males living in streams that lack the crayfish predator have bright red tails. Apparently females prefer to mate with males with red tails , but in streams with crayfish predator that has good colour vision , not enough red-tailed males survive to reproduce