Genes and Environment

The environment can alter the expression of genes. In fruit flies, the expression of the mutation for vestigial wings (short-shrivelled wings) can be altered by temperature. When raised in a hot environment, fruit flies that are homozygous, recessive for the vestigial wings, can grow wings almost as long as normal wild-type wings. 

Probability in Genetics:

Probability is the likelihood that a particular event will happen. It cannot predict whether a particular event will actually occur. However, if the sample is large enough, it can predict an average outcome.

If a pea plant has a genotype TT, the probability that a gamete will contain gene T is 1.

If a pea plant has genotype Tt, the plant can form two types of gametes. One type of gamete will contain gene T, while the other contains gene t.

The probability that a gamete will contain gene t is ¹/₂ and the probability that a gamete will contain gene T is also ¹/₂.

Application of the Principles of Genetics:

A. Inbreeding and Outbreeding:

Inbreeding is the reproduction with close relatives while outbreeding is the reproduction with related members of the species.

Inbreeding is used to maintain pure lines i.e. maintain desirable characteristics.

Outbreeding is used to introduce new recombination and hybrid vigourHybrid vigour, also known as heterosis or outbreeding enhancement, is the phenomenon that a hybrid offspring has improved traits, such as growth rate, biomass, stress tolerance, and fertility. For example, hybrids... More.

B. Agriculture:

 i) Production of high-yielding varieties of plants and animals.

 ii) Production of crops with improved quality of fruits.

 iii) Early maturing crops are produced.

 iv) Production of diseases resistance varieties of crops.

C. Medicine:

(i) Hereditary Diseases and Marriage Counselling: Diseases such as sickle cell anaemiaAnaemia is when the body does not have enough healthy red blood cells or haemoglobin. Red blood cells and haemoglobin (the molecule in red blood cells that makes them red) are... More, and haemophilia are hereditary. Marriage between carriers is not recommended.

(ii) Blood Transfusion: The blood group of humans are A, B, AB and O. Blood group is an inherited trait determined by a pair of homologous chromosomes.

Blood groups contain specific proteins called antigens in the red blood corpuscles and antibodies in the plasma. An antigen is a substance that induces the formation of an antibody.

Blood groups of patients must be compatible for transfusion to be successful. If the blood groups are not compatible, the red blood cells from the donor’s blood are caused to clump together (agglutinate) by the antibody in the recipient’s blood. This may lead to death.

(iii) Determining the Father of a Child:

In cases of disputed paternity of a baby, the correct father may be ascertained by determining the respective blood groups of the child, the mother, and two male claimants.

Traits used for this purpose are discontinuous variations, such as blood groups, eye colour, and the ability to roll the tongue or taste PTC.

• For example, a group A or O man and a group A or O woman cannot produce a group AB child.

matings	possible children	impossible children
O × O	O	A, B, AB
O × A	O, A	B, AB
O × B	O, B	A, AB
O × AB	A, B	O, AB
A × A	O, A	B, AB
A × B	O, A, B, AB
A × AB	A, B, AB	O

• A green-eyed man and a blue-eyed woman usually cannot produce a brown-eyed child.
• A man and woman who are both not capable of rolling their tongues, usually cannot produce an offspring who can.

The unborn baby’s health and the rhesus factor can also be determined.

Note:  All the applications listed above sum up the relevance of biology to life in what is now termed biotechnology. In biotechnology, DNA is now being manipulated to the benefit of humanity.

Biotechnology is the application of biological processes to produce things for human use. The technique used in biotechnology is called genetic engineering.