3. Genetic Problems

12. Outline Mendel’s monohybrid experiments and the discovery of dominant/recessive traits (time permitting/ extension).

13. Explain the process of dominant/recessive inheritance.

14. Solve problems on inheritance using Punnet squares.

15. Use the terms genotype, phenotype, allele, dominant, recessive.

2.0 Inheritance vs Environment

Genetic and Non-genetic Inheritance

Some characteristics are from non-genetic inheritance. 

• What are some examples of this?

Our genes control many of the characteristics of organisms that we see.

• What are some examples of this?

Some characteristics are controlled by a number of genes such as our height, eye, hair and skin colour. This can result in a wide range of variation in these factors.

To complicate things, some characteristics can be influenced by both genetics and non-genetic factors

• What are some examples of this?

Genes and Environmental Factors

Besides genes determining characteristics of an organism, which we will look into next, the environment can play a strong role. 

The growth of a plant can be affected by amount of water,  temperature and type of soil. Any variation in these factors can result in a very different plant in terms height, density of foliage and the frequency of flowers and fruits. This variation in plants is not due to genetics but the environment they are in.

The same can apply for animals, including humans. If a person is suffering from malnutrition and disease, their growth can be significantly stunted, their immunity low and the mental development limited. Environmental variation for humans is not restricted to nutrition but also their education, climate (compare typical body shapes of those in hot dry climates to those in extreme cold environments) and exposure to chemicals and other things such as UV light.

It's often easy for us to understand the role that the environment plays in determining our characteristics, but the role of our genes is more complex. Many of our characteristics are pre-determined by our genetic code.

Meiosis produces half-cells that combine to form a new individual. The rearrangements of chromosomes during meiosis allow for genetic variety. 

But what does genetic variety mean? How does it happen?

Each chromosome carries multiple lengths of DNA called genes. These genes are  coding agents; their different sequences of base-pairs are codes that tell specific cells of the body to synthesise a particular protein. These proteins carry out the functions of the body. 

Some examples are the genes that:  

• produce the pigment melanin that controls eye, hair and skin color [if this gene doesn't work at all, the condition called albinism results]

• produce hormones eg insulin, which is made by the pancreas and allows your body to use sugar (glucose) from carbohydrates in the food that you eat for energy or to store glucose for future use (if this gene is defective, Type 1 diabetes is the result)

• regulation of the chemical processes of the body eg amylase, the enzyme found in saliva that starts the digestion of carbohydrates

The study of how the genes are inherited, and how those genes are expressed is called genetics.  

Our genes work in pairs (with a small number of exceptions involved with inheritance linked with sex ), one coming from each parent. Because the genetic information of two parents joins (not necessarily with equal mixing of traits), the offspring will be different from the parents. But why and how does what your genes code for (your genotype) become what is expressed in your body, observable traits (your phenotype)? 

Note: people can pronounce these as jen-o-type or jean-o-type, and fen-o-type or fee-no-type. It is usually jen-o-type and   for some reason, but any combination is fine.