Milk testing and the wonders of genetic inheritance (Day 25)

Ok, so onto another day of testing milk. Today we looked at the enzyme functionality of milk (aka how do you stop milk going off) and pasteurization which was pretty cool.

Checking perioxidase to confirm proper heat treatment of milkGreat joys, I found I had a sample of raw milk (unpasteurized) as my sample turned blue (yay!). To be honest this class is making me a little nervous of buying milk here as I cannot read the labels yet and for milk that is semi-skinned/skinned the milk fat is replaced with vegetable oil. Its interesting just how much work goes into you being able to pour that milk over your cereal or into your coffee in the morning.

After a short break it was then time for Genetics. Today was on the mendalian laws and genetic inheritance and pedigree classification which is probably one of the most important parts of genetics. It not only reflects in inherited diseases, but also plays a major role in natural selection and genetic convergance.

Within genetics there are two words that are really important: genotype are the genes that are the code for a specific trait, and phenotype which is the physical trait that is caused by the gene

Basically there are two copies of every gene in nearly every living organism with one from the mother and one from the father which code for different traits such as eye color, hair color, height etc. A gene is made up of alleles which are proteins and occupy a specific position on a chromosome. These two alleles may be completely different in which case one will be dominant and one will be recessive (heterozygous), or they may be the same (homozygous) either both dominant or both recessive..

The basis of this was discovered by Gregor Mendel (who is sometimes called the Father of Genetics) who worked with garden pea plants and documented in 1866 the fact that two tall plants often produced a tall plant whilst a tall and short plant didn’t. From over 29,000 different pea plants (the thought of that much data without a computer makes my head hurt!) he drew three laws of inheritence up.

  1. The law of Dominance
  2. The law of Segregation
  3. The law of Independant Assortment

These laws form the basis of genetics today. The first law distinguishes that some alleles are dominant over other alleles and will always take priority over the recessive allele (except in very special cases).

The second law says that during the formation of gametes (sperm and ovum) that alleles will seperate from one another to be “reconnected” at fertilisation. This means that with heterozygous genes that 75% of the time the dominant allele will take priority however for 25% of the time the recessive alleles will form a homozygous pair and take priority for the trait. This forms the first phenotype ratio of 3:1.

Taking this as an example, say B (dominant) = blue eyes and b (recessive) = brown eyes if the parents both have the gene Bb then on average three of their offspring will have blue eyes to every one that has brown eyes.

The third law is that of Indepandant Assortment that genes for different traits are transmitted to offspring independently of each other. This means that height does not affect the eye color or hair color for example. With parents with heterozygous genes when we are calculating the probability of offspring having both traits that we are looking for we have a new phenotype ratio of 9:3:3:1.

This is something I will come back to in more detail in another post, but for now its back to revision!

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