UNIT 2:  GENETIC CONTINUITY

 

 

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SEX OR NO SEX?…THAT IS THE QUESTION!

 

1.  Asexual Reproduction and Genetic Continuity

 

·         some organisms are able to produce a new individual on their own

·         the hereditary information is passed on from one generation to the next through a process called asexual reproduction

·         this can happen through splitting, budding, or fragmentation of the parent

·         the genetic information is identical, unless a change occurs in the duplication process called a mutation

·         this means that the offspring will be the “clone” of the parent

·         this form of reproduction produces offspring relatively fast

·         for example, dividing bacteria could give rise to more than 2 million bacteria in 7 hours

·         the chance of variation is very low, and genetic continuity is maintained

·         Table 5.3, p. 144, outlines the methods of asexual reproduction:

o        Binary fission – bacteria/Amoeba, Paramecium, etc.

o        Budding – yeast/hydra

o        Fragmentation – flatworms/sea stars

o        Vegetative Propagation – wide range of plants

o        Spore Formation – ferns/bread moulds/mushrooms

 

2.  Characteristics of Sexual Reproduction

 

·         the products of meiosis are different from each other because of the random assortment of chromosomes and also because of the genetic recombination that occurs during prophase I

·         since there are many different possibilities for each gamete, the offspring that results will most likely be different that its parents

·         for sexual reproduction, two parents and two different gametes are require

·         the offspring will contain a mixture of hereditary information from both parents and will not look exactly like either one of the parents

·         the characteristic chromosome number and form for the species are maintained, but individuals produced in each successive generation will show variation

·         meiosis and sexual reproduction mean variation

 

3.  Sexual versus Asexual Reproduction and the Theory of Natural Selection

 

·         it is important to not that some organisms, such as plants, can reproduce offspring both sexually and asexually

 

Sexual Reproduction

Asexual Reproduction

Pros

Cons

Pros

Cons

 

·         all sexually-produced offspring are different from each other – this means that some individuals may be better adapted to certain environmental conditions than others

 

·         those that are better adapted have a higher reproductive success and will be the ones to perpetuate the species – those that are maladaptive do not

 

·         sexual reproduction is the preferred method of ensuring that at least some of the offspring will adapt to changing environmental conditions

 

·         sexual organisms may not produce a lot of organisms like asexual organisms but those they do produce are unique and may respond differently to different environmental conditions

 

·         offspring can be better adapted to their environment than their parents are

 

 

·         sexual reproduction involves much more time and energy

 

·         can still be risky – when individuals are searching for a mate they risk dying due to accidents, predation, etc.

 

·         sometimes, parental genes combine in ways that are not beneficial

 

 

·         asexual reproduction produces “clones” of the parent in a relatively short time, which makes reproduction fast and simple

 

·         when the environment is not changing, asexual reproduction will allow a well-adapted organism to rapidly produce a new generation of similarly well-adapted offspring

 

·         produce a lot of organisms quickly

 

·         if the environment changes, however, the asexually-produced offspring will have a hard time adapting to it, and therefore, a lower reproductive success itself

 

·         an environmental change that negatively affects one of the offspring will also affect all members of the population in the same way -- this could potentially wipe out the entire species

 

 

 

Homework:            p. 146, 1-6.