Variation

Types of variation

• Variation means differences between species (remember dichotomous key) or differences within a species

• Types of variation:1.Continuous variation2.Discontinuous variation

Continuous variation• Variation with a continuous range of unit, such

as the range of weight from light to heavy. • Determined by genes and other factor such as

nutrition and activity (environment)• Example: length of leaves or stems

range of height from shortest to tallest

There are no clear divisions between the intermediates

Discontinuous variation• Variation in a limited number of phenotypes

with no intermediates. • Example: various human blood type

different color of flowerear lobe

Inheritance versus Variation

• Identical twins develop from the same embryo and are genetically identical. However, they are different in many ways!how this is happen?

• A Mexican hat plant reproduce asexually to make lots of tiny plantlets all around its leaves. How you would investigate the environmental factor that effect the variety of this plant?

Inheritance versus Variation

Mutations

Mutation

• It is a change in a gene or a chromosome that may cause a change in a phenotypic characteristic

• Mutation can be harmful but some are beneficial and some have no effect

Gene mutation• Mutation of the red color eye of a fruit fly into

white eyes. It is caused by the changes of gene that no longer coded for the production of the red pigment.

• Albino, mutation of melanin pigment that responsible to protects skin and eyes from ultra violet light. The gene can mutate and stop produce melanin. This trait is a recessive allele and albino is a homozygous recessive.

Gene mutation • Sickle cell anemia (SCA) is an inherited disease

of the blood. It’s the result of an allele that causes the abnormality form of haemoglobin (C shaped of red blood cell ) which makes it difficult for the red blood cells to carry oxygen.

Chromosome Mutation • Down syndrome, is a mutation that occurs

during meiosis when two of the chromosomes do not separate properly. Instead of the egg having 23 chromosomes there is an extra chromosome.

• If the egg is fertilised the baby will have 47 chromosome

• Down’s syndrome affects about 1 in 1000 babies

Meiosis KM 12

Causes of mutation

• Damage to DNA or failure in the copying process before nuclear division

• Mutation occur naturally at random but is increased by exposure to radiation, such as: ultra violet, X rays and gamma rays

• Mutation also increased by some dangerous chemicals, such as: benzpyrine in cigarette smoke.

Effect of Mutation• Mutation may lead to cancer (as happened

after atomic bomb in Japan and the nuclear power station in Chernobyl in the Soviet Union)

• Mutation on red blood cell and cause heterozygous cause resistance to malaria and since they still have normal red blood cell they do not have problem in transporting oxygen.

Natural Selection• The process by which organisms that

are well adapted to their environment have a greater chance to breed and pass on their genes to the next generation than those that are less well adapted

The process of natural selection• Variation

• Over population• Competition • Adaptation • Evolution

Search from the Biology book or article to explain how the process above may lead to the natural selection