Species area relationship

i. Latitudinal gradients

Species diversity decreases from the equator to the poles.

Tropics (latitudinal range of 23.5o N to 23.5o S) have more species than temperate or polar areas.

E.g. Number of bird species in different latitudes is given below:

• Colombia (near equator): about 1400 species. 
• India (tropical latitudes): > 1200 species. 
• New York (41o N): 105 species. 
• Greenland (71o N): 56 species. 

Tropical forest region like Equador has up to 10 times species of vascular plants as compared to a forest of equal area in a temperate region like the Midwest of USA.

Tropical Amazonian rain forest (South America) is the greatest biodiversity on earth. It contains

• > 40000 species of plants 
• 3000 species of fishes 
• 1300 species of birds 
• 427 species of mammals 
• 427 species of amphibians 
• 378 species of reptiles 
• > 1,25,000 species of invertebrates 

Biodiversity (species richness) is highest in tropics because

• Tropics had more evolutionary time. 
• Relatively constant environment (less seasonal). 
• They receive more solar energy which contributes to greater productivity. 

As the name indicates there is some sort of relationship between species of a particular region and the area in which they live which is particularly called as habitat. Alexander Von Humboldt observed that the diversity of species increases with increase in explored area upto a certain limit.

Species diversity is the  number of diversity or the variety of species in a particular region . It can be explained in 2 measures -
1.Species richness - The number of species present in a particular area.
2.Species even-ness (relative abundance ) In an environment it  refers to how close in numbers of each species to other in other words how evenly distributed the number of each species.

This relationship can be given by -

                            logS=log C +Z  log A 

In the log scale the graph is linear(straight line) .

Where,
           S=Species richness
           A=Area
           C=Y-intercept
           Z=Slope of the line (regression coefficient) Its range is 0.1-0.2 in case of smaller areas and 0.6-1.2 in large areas.

Power function species–area relationship goes as: S=cA^z

${\displaystyle S=cA^{z}}$

                                         Image source credit -https://courses.lumenlearning.com/biology2xmaster/chapter/the-biodiversity-crisis/

This relationship between species and area can be plotted to generate a species/area curve. Such a plot can give us useful information such as the total number of species in a region and the rate of species increase with area between different regions (calculated from the slope of the curve.

MCQs.
1. The curve of species area relationship looks like -
a. Sigmoidal 
b.Elliptical 
c.Rectangular hyperbola 
d.None of the above                                                                                   Ans.c

2.In larger area like continents slope tends to be-
a. Similar 
b.Steeper 
c.Both a and b 
d.None of the above                                                                                    Ans.b

3.In a species-area relationship -
a. the number of species in a sample increases as the area covered by that sample increases.
b.the number of species in an area of habitat increases as the area of that habitat increases.
c. the type of species observed in a habitat alters as the area of habitat alters.
d. species diversity increases linearly with island size.
Ans. b

4.Species richness tends to decrease with increasing altitude. Which of the following is not believed to play some part in this trend?
a. Higher-altitude areas tend to be younger, in evolutionary terms.
b.Higher-altitude areas tend to occupy relatively small areas. 
c.Productivity declines with altitude.
d.High-altitude habitats tend to be isolated from one another.

Ans.a

5.Which of the following plants have higher species diversity ?
a.Bryophytes
b.Algae 
c.Fungi 
d.Angiosperms 
Ans. c

Thank you for visiting my blog.Please feel free to share your comment on this

article ,Please subscribe and share the articles to get more such articles.

Recapitulation theory or Biogenetic law or Embyological parallelism

The very intresting example of recapitulation is the development of man . The recapitulation theory was proposed by Von Baer .This theory was revised and renamed by an embryologist (Ernst Haeckel in 1868) .We can compare the develpomental stages as follows-

1. The fertilised egg can be compared with the single celled ancestor of all metazoan .
2.The blastula may be compared to a colonial protozoan which might be the ancestor of metazoa.
3.Gastrula represents the coelenterate ancestor .
4.The embryo with the development of mesoderm represents tripoblastic stage like a flatworm .

Structures resemble to chordate embryo -
1.Early human embryo with a dorsal hollow nerve cord .
2. A well developed notochord.
3.A series of gill-slits .

Structures resemble to fish embryo -
1. The development of piscine heart .
2.Paired of aortic arches .
3.Primitive pronephros and a tail .

Later on it resembles to reptilian embryo and then to mammalian embryo . It means embryonic development (ontogeny ) in man recapitulates or replay  the evolutionary history . (phylogeny ).

Ontogeny -Development of an individual organism .
Phylogeny -Evolutionary history or race of the species 
Recapitulates - Replay 

Evolution cannot go back and change the evolutionary history it can modify what is pre-existing .

Examples of recapitulation in plants -
1. Presence of flagellated sperm and water dependency for fertilisation in both terrestial plants (pteridophytes and gymnosperms ) and animals.
2.Presence of filamentous protonema during development of moss.(Funaria)
3.Seedlings of Acacia tree initially develop simple leaves which later get transformed into compound leaves .
4.Oak tree from southern united states retain their leaves through out the year ,whereas oaks from Northern  united states shed their leaves during winter and are deciduous .

MCQs-
1.Theory of biogenetic law was proposed by -
1) A. Weismann
2) E. Haeckel
3) De Lamark
4) A.R. Wallace                                                                               Ans. 2

2.Haeckel’s recapitulation theory states:

a)Ontogeny recapitulates phylogeny
b)High rate of reproduction
c)Mutations in the embryonic stage
d)Atavism                                                                                       Ans.1

3.In plants recapitulation theory in -

1-Oenothera lamarkiana
2-Pisum sativum
3-Acacia
4-none                                                                                           Ans.3

4.Presence of gill slits in the embryos of all vertebrates supports the theory of -

a. Organic evolution 

b.Biogenesis

c.Metamorphosis

d.Recapitulation                                                                               Ans.4

5."A good example for recapitulation theory" is

1) embryonic membranes of reptiles
2) tadpole larva of frog
3) placenta of mammals
4) canine teeth of frog                                                                      Ans.2

6.Basic principles of embryonic development were pronounced by

(a) Von Baer(b) Weismann(c) Haeckel(d) Morgan.                                                                                                                                                   Ans.1
7.In the developmental history of mammalian heart, it is observed that it passes through a two chambered fish like heart, three chambered frog like heart and finally four chambered stage. To which hypothesis can this above cited statement be approximated?

(a) Lamarck’s principle

(b) Mendalian principles

(c) Biogenetic law

(d) Hardy Weinberg law.                                                                     Ans.c

Explanation -As during embryonic development the mammalian heart first takes the form of fish, then frog and at last mammal.

8.Haeckel's biogenetic law of organic evolution receives support from -

1.palaeontological studies 

2.morphological studies 

3.embryological studies 

4.serological studies                                                                           Ans.3

Thank you for visiting my blog.Please feel free to share your comment on this

article ,Please subscribe and share the articles to get more such articles.

Artificial seed

It can be defined as artificial encapsulation of somatic embryos which is derived from plant tissue culture. The encapsulated somatic embryo functionally mimic seeds and can develop into seedling under suitable conditions.    
Unlike other eukaryotes,almost all plants have 
the capability to be regenerated from differentiated tissue.It is a technique which has been researched and developed since 1970s and allows the propagation of plants from artificial seeds. The use of synthetic varieties for commercial cultivation was first suggested in Maize .

In addition to using somatic embryos, axillary buds, adventitious buds and shoot tips have also been used in preparation of synthetic seeds . Among the different encapsulating agents,sodium alginate  was used for encapsulation of somatic embryo due to it’s solubility at room temperature and ability to form completely permeable gell with calcium chloride. 
   
 Characteristics- 
    
1.No seedcoat only encapsulated somatic embryos.
2.Embryos are not protected within any kind of maternal tissue.
3.Embryos do not pass through any kind of desiccation and they don't have any dormancy period.
4.They don't have their own storage tissue. 
    
Advantage-

1.Useful for plants which can't produce viable seeds.
2.It can be stored and transferred to soil for germination.
3.They are small in size therefore they are easy to handle.
4.Artificial seed help to study the role of endosperm and seed coat formation.
5.It gives the protection to meiotically unstable genotypes.
6.It can be directly used in fields.
7.Cereals ,fruits and some medicinal plants can be studied anywhere in the world using synthetic seeds.
8.Using synthetic seed technology endangered species can be propagated.
9.It helps in production of monocultures.
          
CONCLUSION-

Synthetic seeds technique is a rapid tool of plant regeneration because of its wide use in conservation and delivery of tissue cultured plants. Protocols of encap-sulation were already optimized for various plant species, 
but the commercial scale production of synthetic seeds was restricted to few species only due to several major problems, such as:asynchronous development of somatic embryos, improper maturation of somatic embryos, poor conversion rate of somatic embryos, lack of dormancy, and limited production of viable mature somatic embryos.

Q1.Synthetic seed is produced by encapsulating somatic embryo with 
a. Sodium chloride 
b.Sodium alginate 
c. Sodium acetate 
d. Sodium nitrate 
Ans. b

Q2.Artificial seeds are -
a. seeds produced in lab . condition 
b.seeds encapsulated in a gel
c.somatic embryos encapsulated in a gel 
d.zygotic embryos encapsulated in a gel 

Ans. c

Q3.The encapsulation is carried out by various types of hydrogels, which are 
a. soluble in water 
b. soluble in organic solvents
c.insoluble in water
d.insoluble in organic solvents 

Ans.a 

Q4 The preserved embryoids are termed as-
a. semi-synthetic seeds 
b. natural seeds 
c.synthetic seeds
d.fermented seeds

Ans.c

Thank you for visiting my blog.Please feel free to share your comment on this

article ,Please subscribe and share the articles to get more such articles.

Heterosis

It is a proven way  of increasing productivity of many crop plants . It is also called as hybrid vigour or outbreeding enhancement.  It leadsto  increase in such characteristics as size , growth rate , fertiity and yield of a hybrid organism . It actually results from crosses between two genetically different , highly inbreed lines. It is always associated with increased heterozygocity. Heterosis is often discussed as the opposite of inbreeding depression .

Types of Heterosis:

Heterosis is of two types-

1. True heterosis:

It is inherited.

It can be further divided into two types:

(a) Mutational true heterosis:

It is the sheltering or shadowing of the deleterious, un-favourable, often lethal, recessive mutant genes by their adaptively superior dominant alleles.

(b) Balanced true heterosis:

It arises out of balanced gene combinations with better adaptive value and agricultural usefulness.

2. Pseudo-heterosis:

Crossing of the two parental forms brings in an accidental, excessive and un-adaptable expression of temporary vigour and vegetative overgrowth. It is also called luxuriance.

For example: Gossypium Hirsutum (Cotton) has two varieties: one is a pure line variety (Variety-A) which is disease-resistant but with low ginning-percentage of cotton, while the other pure-line variety (Variety-B) has high ginning percentage, but is very susceptible to diseases like wilting or boll-worm. The farmer after sowing variety-B expects high commercial returns, but has to spend huge amount in spraying to protect it from diseases.

Cotton breeders cross these two varieties to produce a F1 hybrid which has high disease resistance as well as high ginning percentage of cotton. This hybrid gives the benefit of both the parent varieties and even more than the parents.

1.Heterosis lost due to continuous inbreeding known as
A)Hybrid vigour
B)Inbreeding depression
C)Outbreeding depression
D)none of these

Ans. b

2.When two unrelated individuals or lines are corssed, the performance of F1 hybrid is often superior to both its parents. This phenomenon is called

1. Metamorphosis
2. Heterosis
3. Transformation

4. Spheing

Ans. b

3.Heterosis is commercially exploited in:

A. Cross pollinated species B. Often cross-pollinated species
C. Self-pollinated species D. Vegetatively propagated species

Ans. a

4.Heterosis is -

a. superiority of hybrids over their parents

b. mixture of two or more traits

c. induction of mutation 

d. None of the above 

Ans. a

5. A mating among the following can not lead to heterosis

a.AAbb x aaBB
b.AABBccdd x AABBccdd
c.AABBccdd x aabbCCDD
d.aaBBcc x AABBCC

Ans. b

6.Maximum heterosis is found in -

a.single cross               c. triple cross

b . double cross            d. none of the above 

Ans. a

Thank you for visiting my blog.Please feel free to share your comment on this

 article ,Please subscribe and share the articles to get more such articles.

Transcription unit and Rna polymerase enzyme

Transcription is formation of RNA from DNA by the help of enzyme Rna polymerase .

It occurs in the nucleus during the G₁ & G₂stage of the cell cycle.

Of the two strands of DNA only one strand called the template strand takes part in transcription.

TRANSCRIPTION UNIT:

A transcription unit in DNA consists of three regions:

A promoterThe structural geneA terminator.

Structural gene is the part of DNA from which RNA is formed.

It is polycistronic in prokaryotes and is monocistronic in eukaryotes.

Transcription occurs with the help of DNA dependent RNA polymerase.

Polymerization occurs in 5′ → 3′ direction.

The 3′ → 5′ strand of DNA acts as the template strand/ anti-sense strand.The 5′ → 3′ strand is the coding strand/ sense strand.

All reference points while defining the transcription unit is made with coding strand.

Lying towards 5′ end (upstream) of structural gene is the promoter. It is the binding site for RNA polymerase for transcription to start

Lying towards 3′ end (downstream) of structural gene is the terminator, where transcription ends.

RNA polymerase:

Single RNA polymerase synthesizes all type of RNA in prokaryotes.

RNA polymerase is a holoenzyme made of 5 polypeptide chains: 2α ( helps in chain initiation and interaction with regulatory proteins ) and , β( catalytic centre - chain initiation and elongation ), β′(Dna binding ) & σ factors.Sigma (σ)  factor recognizes the promoter  to which RNA polymerase binds and the ‘σ’ factor is released immediately after initiation.RNA polymerase without ‘σ’ factor is core polymerase.

                      Image source credit -http://www.slideshare.net/paulawaziry/lecture-6-biol3600-transcription-m-rna-processing-winter-2012-pw

There are 3 RNA polymerases in eukaryotes:

• RNA polymerase I synthesizes 28S, 18S & 5.8S rRNAs.
• RNA polymerase II synthesizes hnRNA (heterogeneous nuclear RNA) that forms mRNA.
• RNA polymerase III synthesizes t RNA, 5S rRNA & small nuclear RNAs.

Difference between prokaryotes and eukaryotes transcription -

1.Coupled transcription-translation that is called attenuation 
   is the rule in case of prokaryotes .

Coupled transcription translation is (Eukaryotes )

not possible.

2.Occurs in the cytoplasm.( Prokaryotes )

Occurs in the nucleus. (Eukaryotes )

3.Initiation of transcription does not need any proteins or initiation factors.( Prokaryotes )

Initiation of transcription requires proteins called transcription factors. These are TFIIA, TFIIB, TFIID, TFIIE, TFIIF AND TFIIH. These recognise TATA BOX.((Eukaryotes )  

4.. Transcription and translation nearly simultaneous.(Prokaryotes)

 The  process of mRNAProcessing of hnRNA includes:

        Addition of 5’cap(7 methylguanosine)

        Addition of 3’poly A tail. (Eukaryotes )

5..The 23S, 16S and 5S rRNAs are formed from a single primary transcript. (Prokaryotes)

The 28S, 18S, 5.8S and 5S rRNAS are formed from two primary transcripts.(Eukaryotes)

6. Inhibitors:

(Rifampin: RNA polymerase binds to β subunit.

Actinomycin-Intercalates to interrupt transcription.)- Prokaryotes 

Inhibitors:

α amanitin: Inhibits RNA polymerase 2 most srongly- Eukaryotes

1.The complex of RNA polymerase, DNA template and new RNA transcript is called-

A. transcription bubble B. replication bubble C. a translation bubble D. none of these Answer: Option A

2.Multiple copies of 5S genes, located at a chromosomal site distinct from the other rRNA genes-

A. are transcribed by rRNA polymerase III and the 5S rRNA B. are transcribed by rRNA polymerase II C. are transcribed by rRNA polymerase I and the 5S rRNA D. are transcribed by DNA polymerase I Answer: Option A 3.Transcription begins- A. at the start codon B. upstream from the start codon C. downstream from the start codon D. none of these Answer: Option B

Thank you for visiting my blog.Please feel free to share your comment on this
 article ,Please subscribe and share the articles to get more such articles.

Pheromones

A chemical substance produced and then released into environment by an animal (Mammal or an ants) which affects the behaviour and physiology of others of same species.

Pheromones are first identified in 1959 .Gustav Jager was the first to propose the idea of pheromones. He called them anthropines.

Main goal -

Communicate with other members of its own species .

Insect pheromones -(Ants and honeybess )
Insects have an alarm pheromone to attract other insects of same species during emergency.Once the period is over the insects return quietly to their former occupations .

Mammal pheromones -(Dogs and Cats )

Many mammals deposit chemicals in and around, as these vaporize they signal to the other member of the same species.


Domestic rabbit mothers release a mammary pheromone that triggers immediate nursing behaviour by their babies. Humans may have pheromones .

Characteristics of pheromones-

• It is similar to hormones but work outside of the body .
• It induce activity in other individual of same species.
• Virtually all insects use pheromones to communicate .
• It is a exocrine secretion .

                                            Image source credit -http://24.media.tumblr.com/tumblr_l7xo7jsjKj1qbtjkwo1_500.png

Types of pheromones insect produce -

• Sex pheromone - It brings together opposite sexes for mating. 
• Aggregation pheromone- Attracts both sexes generally for feeding on food source or for mating.
• Alarm pheromone- Alerts other individuals to some source of danger .
• Trail pheromone- It marks a trail laid by pioneering individuals towards a source of food or refuge .Other individuals follow it to reach the source .
• Social pheromone - It governs interaction among organized societies .

Types of pheromone-

There are four principal kinds of pheromones:

• Releaser pheromones - they elicit an immediate response, the response is rapid and reliable. They are usually linked to sexual attraction.

• Primer pheromones - these take longer to get a response. They can, for example, influence the development or reproduction physiology, including menstrual cycles in females, puberty, and the success or failure of pregnancy. They can alter hormone levels. In some mammals, scientists found that females who had become pregnant and were exposed to primer pheromones from another male, could spontaneously abort the fetus.

• Signaler pheromones - these provide information. They may help the mother to recognize her newborn by scent (fathers cannot usually do this). Signaler pheromones give out our genetic odor print.

• Modulator pheromones - they can either alter or synchronize bodily functions. Usually found in sweat. In animal experiments, scientists found that when placed on the upper lip of females, they became less tense and more relaxed. Modulator hormones may also affect a female's monthly cycle.

Functions-

1.Pheromone products for women contain ovulation pheromone, which make them more attractive, obtainable, and profitable.

2.Pheromone products for men contain the alpha-male pheromone, which make them more sexually aggressive.

3.Monitoring of insect pests .

   Q1.Which of the following is not a function of pheromones?

A)sex attractants
B)trigger alarm behaviors
C)trail markers
D)All of these are functions of pheromones.

Ans . D.   

Q2 .Q. The chemical, which attracts opposite sex insects of a species, is known as -
1) Hormones
2) Allomones
3) Kairomones
4) Pheromones

Ans. 4

Q3.Pheromone is-

a. a product of endocrine gland
b. used for animal communication
c. Messenger RNA
d. Always protein

Ans. b

Q.4 'Pheromones trap 'attracts -

   A.female moths 
   B.male moths
   C.caterpillar
   D.female bugs

  Ans.  b

Thank you for visiting my blog.Please feel free to share your comment on this
 article ,Please subscribe and share the articles to get more such articles.