Genetic basics


Genetic is a wonderful topic. Scientifics are not even beginning to understand what is going on about it. This is so vast and so complex that it's what makes it so interesting!  I know if you are new to genetic, it will look like Chinese to many. But with patience and work, you'll come to understand it! In my exemples, I'll use the gerbils, but this will work for any other living thing on earth.


The genes

These are part of the code that composes the chromosomes. The chromosomes are the "building manual" to build a life form. This building manual contains all the topics to build the life form. In genetic, this will be called, the traits. There is arms, hair, skin, nose, etc. For one topic, there is a list of things to think about. Like for the hair, you'll have to shape of the hair, the colour, the speed at which it grows, etc. Those are the genes. In gerbils, many types of pigements compose the fur color. This is the important thing to remember. There are 7 genes that code the colour in gerbils. (a-c-d-e-g-p-sp) I will speak about those in the next page. How the gerbil look like is called phenotype. The genotype is the code that gives a certain colour.

How it works?

Before going further, you'll have to understand how works genetics. Every animal or plants on the planet works the same way. Each gene as 2 alleles. Alleles are the parts of a gene. In gerbil colours, there is aa, cc, dd, ee, gg, pp and spsp. BUT! The only time there is one allele in a cell is in reproduction cell, which are female eggs and in male sperm. It may seem unusual to know that for now but it will be useful later.


A gerbil needs to give its genetic to the babies. If it would give 2 alleles, the baby would end up having 4 alleles because he has 2 parents. The nature found a way to solve the problem. Splitting the allele pair in half. So each parent gives 1 allele, from the pair he has, to the new baby. 


When each allele from each parent meets, it creates a totally new gerbil which has a part of his parent's genetic!



In the picture on the right, it explen the sex gene. The gene that tells if it is a male or a female. A male has the code: XY and a female is: XX (there is nothing to understand, this is it, that's all)


Row 1: The genotype of the parent, mom(maman) and dad(papa... french lesson!)


Row 2: The sexual cells. 

For mom: 2 female eggs (X) (X)

For dad: 2 sperm cells (X) (Y)


Row 3: Fecondation, the 2 possibles combinations. One sperm goes with one egg and the other sperm goes with the other egg. 


Row 4: Babies genotype. That is the babies possibilities. It can be a male or a female. There is 50% for each possibility. 






Alleles:  Part of the gene. The form they will take will change the appearance of the gerbil.


Dominant allele : This allele form will always win on the other in deciding how will be a gene. (wrote in CAPITAL) 


Recessive allele : This allele form need to be double to show on the gerbil. (Wrote in small letter)


Mutation: A change in a gene that modify the look of a trait. Can be a colour, a shape. Most of mutations are recessives.


Carrier: Said of a recessive allele present in a gerbil but which have no effect on the gerbil colour.

Ex: An Agouti gerbil, carrying a black gene, AaCEGP. 


Homozygote: For one gene, two identical allele; AA or aa 


Heterozygote: For one gene, 2 different allele; Aa 


Genotype: Is the genetic code for a certain colour. Ex: AaCEGgP


Phenotype: Is the appearanceof the gerbil.  Ex: Agouti


Conventions for writing genetic

Geneticist working all around the world, gave themselves rules to follow when writing genetics. This way, even if they don't speak the same language, they can understand each other. Here are the basic rules. 


1. The CAPITALES indicate the dominant allele. 

Aa C E G Pp 

2. The small letters indicate the recesive allele. 

aa Cch Ee G Pp

3. When 2 dominant alleles are present in a gene, write only one to make the writing easier. 

Good: A Cch Ee G P  

Bad: AA Cch EE Gg PP

4. When 2 recessive alleles are present in a gene, wrote both. It's important to know that they are there. 

Good: aa C ee G P

Bad: a C e G P


5. When there is a recesive and a dominant allele at the same time, the dominant one is wrote first. 

Good: Aa C Ee G Pp

Bad: aA C eE G pP

6. For the "Spoted" gene. Wrote only Sp at the end of the genotype. If the gerbil is a solid color, write nothing at the end

Aa C Ee GG pp Sp = spoted color

Aa C Ee GG pp      = non-spotted color


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