3.10 Menstrual cycle

Oestrogen and progesterone are both hormones, which is produced in the structure called endocrine gland. Hormones will travel through the blood to the target tissue, where the hormone will have effects on.

The ovary is the endocrine gland for (produces) oestrogen that will travel through the blood stream to the lining of the uterus.

The effects of estrogen include:

1. The lining of uterus (wall of endometrium) thickens

2. Flows through the blood stream to out brain and brings the release of sex hormone (LH). It reaches its peak by day 13 of the cycle and causes the ovary to release an egg into the oviduct, where it is possible for fertilization to occur. 

During this first half of menstrual cycle, a circular structure becomes larger and larger. Inside this falloco is the egg. The cells around the fallocal are producing oestogen. It reaches it maximum size by day 13 and causes its wall to rapture and the egg is released. 

LH causes ovulation, the release of the egg.

Now that the fallico is released, the now emptied structure changes its function and develops into the yellow color. This gives us the name corpusinteum that produce progesterone. 

Progesterone travels through the blood stream to the lining of uterus. 

3. This prevents the lining of uterus from breaking down. This makes it possible that the fertilized egg then can plant into the wall of endometrium and develops into pregnancy. 

4. If no fertilized egg is planted into the wall of endometrium, then it will break down and form what we known as menstrual period/bleeding. 

This mark the end of one menstrual cycle. When the lining is broken down completely, the whole process would repeat. 

(credits to michelle biology)

3.34 Causes of Mutation

Mutation is the change in base sequence of the genes which creates new alleles.

Causes:

• Radation - Xrays or sunshine (UVB) in this case of UVB this can cause a mutation which leads to skin cancer

• Chemicals - effects of tars and tobacco which causes a change in the base sequence which can also lead to cancer.

Chemicals which cause mutation are called mutagens and those that cause cancers are called carcinogen.

3.33 Antibiotic resistance

An example of this:

Staphlococcus aureus can lead to skin and lung infections.
People with this bacteria can be treated with Methecilline Antibiotics which can kill Staphlococcus aureus.  The Staphlococcus aureus that can be killed by this antibiotic is called the susceptible form. MSSA (Methecilline susceptible Staphlococcus aureus).

What happened was there was a random mutation to the geno of Staphlococcus aureus and when the antibiotics Methecilline is applied it doesn't die and this is called the resistant form. (Methecelline Resistant Staphlococcus aureus)

The mutation has created genes that allowed the bacteria to break down the antibiotics, resisting it so it  can survive. As antibiotics are used across time this type of bacteria increasingly surivives and becomes more common. In time this has become a serious problem in hospitals.


(Credits to Daniel biology)

3.32 Types of mutation

New alleles can be: beneficial, neutral or harmful.

Example of 


Beneficial mutation might be to improve an efficiency of an enzyme. 


Harmful mutation might be a production of an enzyme that does not work


If the mutation has no particular effect, we call it a neutralmutation. 
Although the neutrality may change due to environmental change which can lead to harmful or beneficial mutations.

3.31 Evolution

Describe the process of evolution by means of natural selection.

• Evolution can be a change in the form of organisms
• Evolution can be a change in the frequency (how many) of alleles.

Natural selections is the mechanism of evolution and was first proposed by Charles Darwin.


Example:

A bacteria staphlococcus aureus which can lead to skin and lung infection is introduced.

The original form of such bacteria is sustained to be kill by methecilline, which is a type of antibiotic.

 (They are susceptible to the antibiotic.) 

What happens is that a random mutation to the genome of the bacteria allowed us a characteristic of 'breaking down methecilline.' This means that it is no longer killed by the antibiotic. This new form is called the Resistant form, MRSA.

[Refer to definition number 1 of evolution]

Because the MRSA is resistant to the antibiotic, they became increasingly common (increase in frequency of the allele) 

[Refer to definition number 2 of evolution]

Two features of natural selection (process not a thing):

1. Random mutation - produce MRSA form 

2. Non-random selection - due to anti-biotic which is selecting the MRSA to survive and MSSA to be selected and killed

3.30 Mutation

• The base sequence ( A,C,T,G,A,A,C,C) of a DNA is what constitute the gene. 
• The form of the gene is called an allele.
• Certain events and certain processes can result in a change in the base sequence .

->  This change create a new version of the allele  and it is possible that this process will result in an entirely different protein and therefore creating an entirely different phenotype ( how it looks).

The reasons why dominant alleles and recessive alleles exist is because of this process.

3.29 Species Variation

Every individual has a phenotype and the appearance for an individual for any of the characteristics is because of their genotype which is be variant to various degrees accordingly to the environment. 

Individual Phenotype = Genotype + Environment

Differences in the appearance of the indiviuals in an species is because they have different genotypes and they are surviving and living in different environments.

Vpop = Vgeneration + Venvironment

Example to this :


In the first example it shows variation that depends entirely on the genotype with no role of the environment. For example the blood groups.

In the second example it shows where the variation depends on the environment. With one example such as height, one might have been inherited the genotype to be short, however, a good diet may affect his height.
In the third example, it shows a variation in population which depends entirely on the environment. Genes have no roles to play here, for example, languages.

3.20 Pedigree diagrams

Pedigree can be use to interpret that the affected condition is caused by dominant or recessiveallele. 

3.21 Genetic Probabilities

Crossing parents (RR) and (rr)

Crossing heterozygous parents (Rr) and (Rr)

3.18c Codominance

Codominance refers to a relationship between two alleles of a gene in which both phenotypes of the genes are visible and do not over power each other in phenotype. 

This happens when both alleles are dominant. 

The offspring will result in an unusual third phenotype as the parents both contribute to the phenotype. The offspring's genotype would be a heterozygous of both dominant alleles.