variation and selection

VARIATION AND SELECTION PT.1

by Giulia Maria Ciccani and Dafne Porri

17.1 VARIATION

differencies between the individuals of the same species

17.1 Variation can be...

population: a group of organisms of one species living in the same area at the same time

... disconinuous:

... continuous:

variation in which there is a continuous range of phenotypes between two extremes ex. height in a histogram and a line graph:

variation in which there are distinct categories of phenotype, with no intermidiate ex. blood groups in a bar chart:

17.1 causes of Variation

Enviromental:

Mutation:

a random change in a gene, which can produce new alleles; mutaton involves a change in the base sequence in DNA (: it determines the aminoacids sequence in the protein that are made, and changing it may the protein may not be able to carry out its function)

Discontinuous variation is almos always caused only by genes, while continuous variation is also affected by the eniroment (ex. body fat) Only variation caused by genetics are passed on to an oranism's offspring ; variation caused by enviroment is not passed on.

They are unpredictable but there are some factor that make mutation more likely:

• radiations
• mutagens (heavymetals)

17.2 Selection

Adaptive feaure: an inherited feature that helps an organism to survive and reproduce in its enviroment

HYDROPHYTES

XEROPHYTES

A plant that has adaptive features that

A plant that has adaptive features that

help it to survive in water

help it to survive in an enviroment where water is scarce

Eicohhotnia crassipe-water hiacinth

reducing surface

closing stomata

• float freely in the water
• hallow spaces in stem and leaves to float (so they gets lot of light)
• somata on both sides of the leaves

area of the leaves

waxy cuticleand/or hairy leaves

Cabomba

sunken stomata on the underside of the leaves

• completely under water
• feathery leaves so that they spread out easily and get plenty of sunlight and prevent damadges

deep or spreading roots

other plants have just deep root to hold them

... now some exercises!

exercises

page 352

1. State if each of these features shows continuous or disontinuous variation:

• blood group in humans
• foot lenght in humans
• leaf lenght in a species of trees
• presence of horns in a cattle

2. Suggest if they are caused by genes alone, or both genes and enviroment.

4. A maize cob:

3. In peas, seeds can be either yellow or green. Plants grown from green seeds are pure breeding, but plants grown from yellow seeds can produced some green seeds if they are bred together.

• Is this an example of continuous or discontinuous variation?
• Explain how this variation is caused.

• Does the colour in the maize kernel shows a continuous or discontinuous variation?
• Estimate the ratio white kernels: brown kernels.
• Suggest suitables symbols for the alleles, and the genotypes of the parents that produced this maize cob

5. State how new alleles are formed

5.1 List four ways in which genetic variation in caused

exercises

page 353 page 356

7. Copy and complete the table comparing xerophytes and hydrophytes.

6. This is a Tarsier: they feed on insects, which they hunt in the trees at night. What adaptive features can you see in the photograph?

THANK YOU!