Question

1. Explain how the three mechanisms that are unique to sexual reproduction generate a great deal of genetic variation in sexually reproducing species?

Answer 1

Sexual Reproduction

Sexual reproduction is the combination of (usually haploid, or having a single set of unpaired chromosomes) reproductive cells from two individuals to form a third (usually diploid, or having a pair of each type of chromosome) unique offspring. Sexual reproduction produces offspring with novel combinations of genes. This can be an adaptive advantage in unstable or unpredictable environments. As humans, we are used to thinking of animals as having two separate sexes, male and female, determined at conception. However, in the animal kingdom, there are many variations on this theme.

Hermaphroditism

Hermaphroditism occurs in animals where one individual has both male and female reproductive parts. Invertebrates, such as earthworms, slugs, tapeworms and snails, are often hermaphroditic.

1 Hermaphrodites may self-fertilize or may mate with another of their species,

2 fertilizing each other and both producing offspring.

3 Self fertilization is common in animals that have limited mobility or are not motile, such as barnacles and clams.

Genetic Variation

Genetic Variation Definition

Genetic variation can be described as the differences between organisms caused by alternate forms of DNA.

Examples of Genetic Variation

Genetic Variation between Individuals

Look at the image of mussel shells below. All of these muscles belong to the same species, meaning they can all interbreed with each other. The differences in their patterns represents the total phenotypic variation in the population. Some of the variation comes from genetics, while some comes from the environment. To sort out what is genetic and what is environmental, scientist would have to conduct a series of experiments.

To get the genetic variation found in this population of mussels, the scientist would simply need to subtract the environmental variance observed with the clone from the total variance observed in the wild population. Another way of calculating the genetic variation is to sample the DNA of the population and measure the differences in the DNA directly. Since genetic variation is produced by differences in the DNA, these differences can be used in reverse to calculate the environmental variation in a population.

Sources of Genetic Variation

With all of the natural variety in the world, it is weird to think that all of the genetic variation comes from only a few simple sources. The simplest source is mutation

In fact, genetic variation is so important for species that many species reproduce sexually to aid the process of producing new varieties. Sexually reproducing organisms carry two copies of the genome, allowing mutations to lie dormant or express themselves more subtly. During sexual reproduction, genes are recombined in new ways. This process, known as recombination.