Biology P4 random notes

[zeebujha]

Mutations:
Mutation refers to random, unpredictable changes in the nucleotide sequences of a gene or the number of chromosomes of a cell

Causes of mutations:
-Spontaneous mutations (Mutations occurring naturally during replication)
(i) Background mutation
(ii) Tautomeric shifts
(iii) Deamination

-Induced mutations:
Mutation due to exposure to mutagens

Types of mutations:

Two types of mutations based on the type of cell in which it occurs:
(i) Germline mutation
(ii) Somatic mutation

Two types of mutation based on what is effected (this should be written more elegantly, anyone?)
(i) Chromosome mutation
(ii) Gene mutation

Gene mutation (Also called point mutation as they happen at a point in the gene)
(a) Substitution mutation which can be:
-Silent
-Nonsense
-Missense
-Neutral missense

All are single point mutations

(b) Inversion
All are two point mutations

(c) Frame shift mutation
Either one or multiple point mutations

Chromosome mutation:
1. Re-arrangement of sequence of genes in chromosome

A. Deletion : A section of the chromosome is lost

B. Inversion: Middle of chromosome drops out rotates180 and then joins again

C. Translocation: Involves more than one chromosome which are non-homologous. A piece of one chromosome becomes attached to another non-homologous chromosome (It is different from crossing over in that in crossing over there is interchange of section of chromatid while this is one sided). This is one of the causes of Down's syndrome

D. Duplication: Part of chromosome repeated i.e. gene sequence is repeated several to hundreds of times. Cause of Huntington's diesease

2. No. of chromosome in the cell change
A. Aneuploidy
B. Polyploidy:
a. Autopolyploidy
b. Allopolyploidy

 

[zeebujha]

Some examples of effect of environment on phenotype:
(i) Height of plants and humans determined by their nutrient intake
(ii) While both worker and queen bee develop from fertilized egg, in order to become queen she is well fed during her larva stage
(iii) Temperature makes the primrose plant to produce different color. It becomes white at 32C whereas red at 24C
(iv) Himalayan rabbits are darker in color in the areas like ear, paw, nose and tail. They have homozygous gene for the production of melanine which is active only at low temperature

 

[MukeshG93]

Well, technically, the stuff that we need to know about mutations are:

A mutation is the alteration in the genetic base sequence of an organism.

There are three main types:
- Base substitution
- Base addition
- Base deletion

(*) Base substitution
- It is a point mutation
- A single base gets altered (it gets substituted for by another nitrogenous base)
- The protein that a section involving a single base substitution templates for is less likely to be altered because there are many codons that substitute for the same amino acids and they are usually just one base different
- Nevertheless, a single base substitution is the type that causes sickle cell anemia, cystic fibrosis and hemophilia because the rest of the protein is perfectly fine, it is just a single defective amino acid that alters the structure and hence impairs

(*) Base addition and base deletion (I'm putting them both in the same section because their effects are the same)
- They cause a "frame-shift" in the base sequence of the strand
- This causes a rather large change (often shortening) of the resulting polypeptide chain
- This is usually a very large defect in the cell and the cell is killed because it is defective and further mitosis of the cell could be dangerous

<NOT NEEDED> Neither of the aforementioned types of mutations are largely responsible for occurrences of cancer although they may lead to cancer </NOT NEEDED>

 

[MukeshG93]

Some examples of effect of environment on phenotype:
(i) Height of plants and humans determined by their nutrient intake
(ii) While both worker and queen bee develop from fertilized egg, in order to become queen she is well fed during her larva stage
(iii) Temperature makes the primrose plant to produce different color. It becomes white at 32C whereas red at 24C
(iv) Himalayan rabbits are darker in color in the areas like ear, paw, nose and tail. They have homozygous gene for the production of melanine which is active only at low temperature

Very nice examples.

Another PG (pretty good) example is that of the exposure of the gene of tallness in a human child's phenotype.

Although a child may inherit alleles for tallness from his/her parents, if he/she is not fed properly and not provided appropriate nutrition, it will not be seen in the phenotype.

 

[MukeshG93]

I need serious help with the long questions, any tips? I got like a 61 on my paper last terminal, largely because of my blundering in the last questions.

 

[princesszahra]

@ mukesh
what help exactly?
i mean u dont know what to write or how to write?

 

[zeebujha]

I need serious help with the long questions, any tips? I got like a 61 on my paper last terminal, largely because of my blundering in the last questions.

need to be more specific buddy

 

[MukeshG93]

@ mukesh
what help exactly?
i mean u dont know what to write or how to write?

I understand the question always, but then there doesn't seem to be enough stuff to write, you know, and I tend to go outside the boundary of the question and then I don't know what happens. Any sort of, you know, in general tips. You can even tell me which type of question to choose out of the two, I am pretty well learned when it comes to all the topics of our syllabus, I am confident I may be able to do better if there are particular topics that are "easier" or have more points than the rest.

 

[zeebujha]

what is a linkage group and how does crossing over break linkage groups??

 

[MukeshG93]

what is a linkage group and how does crossing over break linkage groups??

This is in reference to?

 

[zeebujha]

what is a linkage group and how does crossing over break linkage groups??

This is in reference to?

how meiosis results in genetic variation

 

[MukeshG93]

what is a linkage group and how does crossing over break linkage groups??

This is in reference to?

how meiosis results in genetic variation

Crossing over as in chiasmata, right? Linkage groups are groups of genes on the loci of the chromosomes that are "linked" together as in bound together and when crossing over occurs, these break and reform between parts of the paternal and maternal chromosomes.

 

[zeebujha]

Crossing over as in chiasmata, right? Linkage groups are groups of genes on the loci of the chromosomes that are "linked" together as in bound together and when crossing over occurs, these break and reform between parts of the paternal and maternal chromosomes.

What prompted me to ask the question was the fact that if they are "linked together" as in they are close together on chromosome and thus have high probability of being inherited together, why are they broken? Shouldn't it be more probabilistic that the linked genes be inherited together and it is the combination of linked genes on a chromosome that gets changed? Man I don't even know what I am asking anymore :x

 

[MukeshG93]

Crossing over as in chiasmata, right? Linkage groups are groups of genes on the loci of the chromosomes that are "linked" together as in bound together and when crossing over occurs, these break and reform between parts of the paternal and maternal chromosomes.

What prompted me to ask the question was the fact that if they are "linked together" as in they are close together on chromosome and thus have high probability of being inherited together, why are they broken? Shouldn't it be more probabilistic that the linked genes be inherited together and it is the combination of linked genes on a chromosome that gets changed? Man I don't even know what I am asking anymore :x

Yes, your questions are getting vaguer and vaguer. Well, the point of crossing over is: out of the paternal and maternal chromosomes in the cell undergoing meiosis, only one of them will be present in the gametes. Crossing over make sure that the same genes from the grandmother/grandfather (whose chromosomes also, of course, had crossed over) don't get passed directly into the child and there is some variation with the other parent's genes in the chromosome as well. Hope you understand what I'm getting at.

 

[zeebujha]

Crossing over as in chiasmata, right? Linkage groups are groups of genes on the loci of the chromosomes that are "linked" together as in bound together and when crossing over occurs, these break and reform between parts of the paternal and maternal chromosomes.

What prompted me to ask the question was the fact that if they are "linked together" as in they are close together on chromosome and thus have high probability of being inherited together, why are they broken? Shouldn't it be more probabilistic that the linked genes be inherited together and it is the combination of linked genes on a chromosome that gets changed? Man I don't even know what I am asking anymore :x

Yes, your questions are getting vaguer and vaguer. Well, the point of crossing over is: out of the paternal and maternal chromosomes in the cell undergoing meiosis, only one of them will be present in the gametes. Crossing over make sure that the same genes from the grandmother/grandfather (whose chromosomes also, of course, had crossed over) don't get passed directly into the child and there is some variation with the other parent's genes in the chromosome as well. Hope you understand what I'm getting at.

okay, lemme put my question in another way.
Suppose we have genes ABCDE in a part of the chromosome. A and B being close together are linked and thus form a linkage group. So, if crossing over occurs, it is highly probable that AB will be translocate together. So, how is the linkage group comprising of A and B broken?

 

[NIXORCollege]

The alleles move from one chromatid on one homologous chromosome to the corresponding non-sister chromatid on the other member of the homologous chromosome pair.

http://www.youtube.com/watch?v=m2Rd6iW_Ncw

(What he's doing is breaking linkage groups)

 

[zeebujha]

how many layers of podocytes are there?? From what I understand , podocytes wrap around the basement memabrane surrounding the capillaries of the glomerulus. But now I read that podocytes form the wall of the renal capsule too. So, are there two layers of basement membrane and two layers of podocytes? =@

 

[zeebujha]

I haven't found anything satisfactory on the role of Distal Convoluted Tubules. So, I would like to post what I have understood, please correct the mistakes in my answer:
DCT conceptually behaves both as the ascending loop of Henle and Distal convoluted tubule
(i) Reabsorption of sodium ions in the tissue fluid by active transportation of Na+ ions from the lumen of DCT to the tissue fluid . The hormone aldosterone increases the rate of Na+ secretion and K+ absoprtion. So, partly responsible for regulation of sodium and potassium concentration in the tissue fluid
(ii) Formation of ammonium ions in DCT membrane cells from ammonia and proton which are then actively secreted into the DCT lumen. So, partly responsible for regulation of pH of tissue fluid

 

[MukeshG93]

What are the required details of the Krebs cycle?

 

[abuhantash]

Detail you missed out on:

Higher temperatures --> Larger rates of respiration --> Increased stomatal closure --> Decreased carbon dioxide intake --> Decrease in the rate of photosynthesis

why would an increse in resipration rate increase stomatal closure?