Heredity and Variation

Mitosis

is the type of cell division that results in the formation of two daughter cells, each with the same number and kind of chromosomes as the parent cell. All cells produced by mitosis from a single parent cell are collectively called a clone.

The Importance of Mitosis

• it ensures that each daughter cell has the same number and type of chromosomes as the parent cell

• it is the method by which all cells of a multicellular organism are formed, hence it is essential for growth and to repair damaged tissues

• it is the method by which organisms reproduce asexually

Meiosis

Is the type of cell division that results in the formation of four daughter cells, each with half the number of chromosomes as the parent cell. Each cell contains the haploid number of chromosomes. Meiosis occurs only in reproductive organs during the formation of gametes.

Meiosis Importance

• each daughter cell or gamete has the haploid number of chromosomes so that the diploid number can be achieved during fertilization

• Genetic variation among offspring

Variation

refers to the differences that exist between individuals and it arises from a combination of genetic causes and environmental causes.

Phenotype VS Genotype

the observable characteristics of an individual is the phenotype while genotype is the composition of gens within the cells of an individual

Causes of Genetic Variation

Genetic Variation is controlled by genes and can be passed on from one generation to the next. It arises in several ways

1. Meiosis - every gamete produced by meiosis has a different combination of genes as a result of crossing over and chromosomes randomly aligning themselves at the equator of cells

2. Sexual Reproduction

3. Mutations - a change in the structure of a single gene, the structure of part of a chromosome containing several genes or in the number of chromosomes in a cell.

Causes for Environmental Variation

Environmental Variation is caused by different factors is an organism’s environment. It is not caused by genes and cannot be passed on from one generation to the next. Environmental factors affecting humans are:

1. Type and quantity of food

2. drugs

3. climate

4. upbringing and living conditions

5. education

Continuous Variation

is where characteristics show continuous gradation form one extreme to the other without break. e.g. height, weight, hand span, skin color

Discontinuous Variation

is where characteristics show clear cut differences with no intermediates. Individuals can be divided into distinct categories. Examples, gender, ABO blood groups and tongue-rolling ability. Characteristics are usually controlled by a single gene and environmental factors have little, if any, influence.

Importance of Variation

• better chance of survival

• adapt to the environment

• evolve

Monohyrbid Inheritance

is the inheritance of a single characteristic.

Genetic Engineering

involves changing the traits of one organism by inserting genetic material from a different organism into its DNA. The organism receiving the genetic material is called a transgenic organism or genetically modified organism.

Purpose of Genetic Engineering

• Improving the quality of a food product, such as increasing its nutritional value

• Improve the yields of livestock and crops, such as size and growth rate

• Protect agricultural crops against environmental threats, such as pathogens, pests and low temperature

• Make organisms produce materials that they do not usually produce, such vaccines and drugs

Genetic Engineering and Food Production

1. Golden rice - by inserting two genes into rice plants, the rice grains are stimulated to produce beta-carotene which the body converts into Vitamin A.

2. BST Hormone - increase milk and meat production in cattle

Genetic Engineering and Medical Treatment

1. Insulin - by transferring the gene that controls into bacteria, the bacteria produce human insulin which is used to treat diabetes

2. Human growth hormone - by transferring the gene controlling the production of HGH into bacteria, the bacteria produce the hormone which is used to treat growth disorders in children

Advantages of Genetic Engineering

• Yields can be increased, which should increase the world food supply and reduce food shortages

• the nutritional value of foods can be increased by genetic engineering which should reduce deficiency diseases worldwide

• the need for chemical pesticides that harm the environment can be reduced by genetically engineering crops to be resistant to pests

Disadvantages of genetic engineering

• plants genetically engineered to be toxic to pest may also be toxic to organisms, e.g. insects which bring about pollination. This could reduce reproduction in crops, reducing food production

• Unknown health risks may occur as a result of eating genetically modified plants and animals

• large companies with funds and technology to develop genetically modified organisms could make large profits at the expense of smaller companies and poorer nations