I explained discontinuous and continuous variation. I talked about the man named Gregor Mendel what work he did and what laws he discovered. I also wrote about monohybrid phenotypic ratio and dihybrid phenotypic ratio such as heterozygous parents which is known as F2 cross and results 9:3:3:1. I g...
Discontinuous variation
The categories of phenotypes (characteristics and traits of an organisms) are discrete and
distinct. They are noticeable from other in a qualitative way. Another part of the
discontinuous variation is there are no intermediates which means you are either that trait
or you are not that trait. For example, male or female, tall or short. The reason why
discontinuous variation is distinct which means separate is because the characteristics and
trait are controlled by a single gene which is called monogenic.
Continuous variation-
Continuous variation is the genetic variation between the individuals within a population
which shows a range in phenotypes and there is intermediates. The difference between
continuous and discontinuous variation is that in discontinuous variation only a single gene
control the characteristics and traits, in continuous variation a lot of genes control the
characteristics and traits which is called polygenic. The example of continuous variation is
length, height, mass, yield. The length is how long something is. The height is how tall
something is this can be a human. Mass is how big, medium or small you are and is
measured in kilograms. Yield can be used in wheat and other food that is important to our
environment.
Mendel’s law of inheritance
First, he studied pea plant and their genetic and he particularly focuses on the range of
characteristics and their trait for example seeds. Gregor Mendel next was breeding plants
with different characteristics for example colour green and yellow. His results for the parent
flower was breeding the purple plant with the white plant the seeds he got were all light
violet.
Mendel result caused him to say that the violet flower that was breeding first called the
dominant trait and the trait that has disappeared was the recessive trial.
He carried on finding out what would happen when they fertilise again.
There was a 3:1 ratio violet to white.
Mendel model for the inheritance of a Single characteristics. Parents travel across genes
which as we said before controls and regulates the characteristics. The gene has two copies
yd or xx which is called an allele and the allele is split into two one is dominant which is the
one that hides the recessive allele. The genotype of an organism is understood by the pair of
alleles. Genotype is controlled by the phenotype. Like I said above if the pairs of alleles YY
are the same then the gene is homozygous. If it not the same pair this also means one is
capital and the other is not capital, then it is heterozygous.
The law of segregation
Each gene has two alleles. During the process of meiosis which is the cell division the diploid
parent cell has 46 chromosomes, and it is halved. There are two genes the gametes which is
the egg, and the sperm gets one copy. The egg and the sperm join together a process which
is called fertilisation.
The law of independent assortment is that the alleles that the gamete obtains from the
gene does not affect the allele obtained by another gene. The reason why independent
assortment happens is due to the formation of the gametes during meiosis 1. The first place
, when independent assortment happens when the chromosomes independently and
randomly assort of each homologous pair.
During meiosis 2 independent assortment takes place again this time it happens to the
chromatids. The principal of independent assortment says segregation occurs each trait
does so independently from another trait. During meiosis 1 chromosome alignment on the
metaphase plate is random, such that these chromosomes can segregate from each other.
Monohybrid crosses
In pea pods the dominant allele for colour is the green allele G and the reccesive allele is the
yellow allele. The dominant one is the one that shows itself. Pea pods are always
homozygous the green pod will have GG phenotype and the pure breeding yellow pods will
have a gg phenotype.
The offspring called the F1 generation is When a green pea pod is crossing and breeding
with a yellow pea pod
1.) We use punnet square to work out what the genotypes and phenotypes the F1
generation will be
Parents Green Yellow
Phenotypes green yellow
Genotype GG gg
2.) write out the parental gametes
G for green pea pod
G for yellow pea pod
2.) Work out the offspring genotypes
Parental gametes G for green G for green
g for yellow Gg Gg
g for yellow Gg Gg
The first generation will be the green pea pod because they all have a capital G and the
dominant one take over the recessive allele.
A monohybrid cross with the F1 generation
Two different pure breeding pods are crossed the resultant F1 generation are all
heterozygous which means the allele are different.
When two green pea pods from the F1 generation are crossed with each other the
offspring are called the F2 generation.
We do same process using punnet squares.
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