A STEP INTO GENETICS

First since we are now entering the genetics lets first pay our gratitude to the father of genetics,i.e., Sir Gregor Johann Mendel. *bows* okay so let's first know a bit about the experiments of mendel which led to the discovery of a whole knew subject, genetics. Well Mendel chose Pisum Sativum (garden pea) for his experiments reason bieng :
1. They have a short life span
2. They are easy to grow.
3. Control breeding is possible
4. It shows 7 pair of contrasting character or traits. for example:
+ Tall or Short plant
+ Violet or White flowers
+Yellow or Green seed
+ Round or Wrinkled seed
Mendel first took a pure tall and pure short pea plant. now pure means it contains a pair of genes which are simlar to each other (remember XX and XY) so pure are XX(lets say). He made a cross considering a pair of contrasting characters characters. this cross is known as monohybrid cross (since mono-one and one pair of characters was considered). When he raised first generation (by making breed the pure tall and pure short) he found all of them are tall. so he made the hybrid to self pollinate and found in seconf genration that some of them are tall. Now lets learn how he made the cross.

RULES TO MAKE A CROSS

(I) The dominant trait  (i.e, Violet, Tall, Yellow, and round) are denoted by the capital alphabets such a V,T,Y and R.

(II) the recessive trait (i..e., White, Short, Green and Wrinkled) are denoted by small alphabets which are used by the dominant trait such as v,t,y and r.

A CROSS BETWEEN PURE TALL AND PURE SHORT

 PARENT                       TT (Pure tall)      X                  tt (pure                                                                                                   short)

 GAMETE                          T                      x                       t

F1 GENERATION                                    Tt    x Tt                  (self                                                                                             pollinate)

F2 GENERATION                        TT     Tt     tT       tt

(i) Dominant trait is the trait which the plant shows in first generation for example (Tt) in above example which is tall. with the presence of dominant trait in the pair that trait is shown like in (Tt) there is a recessive gene t but due to the presence of T its charachters are overshadowed. 

(ii) Recessive trait is the trait which is shown in F2 generation 

(iii) the resultant ratio of F2 generation in monohybrid cross will always be 3:1 

for example TT Tt tT ARE THREE TALL WHILE tt IS THE ONLY ONE IS SHORT 

 for a better understanding since this is the base of the genetics do the following question:

Q- Do a cross between a pure round and pure wrinkled seed? if you want to get it checked, then put your answer in the comment box below and i will be there to check it xD

SEX DETERMINATION IN HUMAN BIENGS

We all know that  humans have 46 chromosomes. 23 paired chromosomes. out of them 22 pairs are the autosomes which define various charachteristics that we inherit. Last pair is called the sex chromosome. In woman the ovum is denoted by 'X' chromosome while in males there aretwo types of sperm 'X' & 'Y. the composition of the last pair in female is XX and in male is XY. so when the X ovum fuses with X sperm it forms a female embryo and if X ovum when fuses with Y sperm it forms male embryo. but surprisingly the sex ratio is decreasing at an alraming rate the reasons varied in various countries but the result will be the same extinction of homosapiens. So lets take an initaitive to spread awareness. spreading awareness doesnt always mean going on the roads and shouting. it can also be through various media such as the social networking sites, blogs etc. well the creativity is upto you but don't just take this as a lecture take it as a warning which taken lightly would seriously mean doom !

SEXUAL REPRODUCTION IN HUMAN

MALE REPRODUCTIVE SYSTEM:

In male reproductive system, there is 1 pair of testis. testis perform dual function. It produces sperm (male gamete ) and produces male sexual harmone, testosterone. It is present outside the abdominal cavity in a fold of skin called scrotum. Scrotum provides 2-3 degree less temperature as compared to the body. From testis originates a tube which carries the sperms called vas deferens.Vas deferens unites with a tube coming from the urinary bladder and forms a common passage called urethra. Prostate gland, cowper's gland and seminile vesicle secretes a fluid which when combines with sperms forms semen. This fluid helps in the transportation of sperms and supply important nutrients to the sperms and maintains the Ph important for their synthesis. 

FEMALE REPRODUCTIVE SYSTEM 

the female reproductive system has two functions :

1. the fertilization of zygote

2. the development of embryo 

the female reproductive system comprises of the following :

1.Ovary: a pair of ovary is present inside the abdominal cavity near the kidney. Like testis, the ovary also perform the dual function of producing the female gamete and producing female sex harmone, estrogen.

2. fallopian tube/oviduct: there are two fallopian tube on both the sides near ovaries. the fertilization takes place in the terminal end of fallopian tube. 

3.Uterus: The two fallopian tubes end up in a elastic muscular bag like structure called uterus. it is where the zygote gets implanted and undergoes development for nine months (called gestation period) 

4. vagina: Also called birth canal (you know why right?) vagina is the one who takes the sperms during sexual intercourse. 

LET'S GET TO THE REAL DEAL- HUMAN REPRODUCTION *evil laugh*

Amazingly when the girl child is born, she contains thousands of the immature eggs. On reaching the puberty (when your body undergoes changes such as cracking of voice in boys and starting of menstruation in girls and secretes respective sex harmone) 10-12 eggs start maturing and only one of the egg is released. the release of egg is called ovulation. The egg is picked up by the fallopian tube where the fertillization occurs. the thousands of sperms which are deposited during sexual intercourse in vagina reach up the fallopian tube and the lucky one reaches the ovum first wins xD i.e. it forms zygote. the zygote slowly moves down to the uterus and gets attached to the wall of unterus this is called implantation. after implantation there is development of a special tissue called placenta.Placenta is a disc like structure between the embryo and walls of  uterus. it has blood villi on the embryo's side and blood space on the mother's side. it gives a surface area for the exchange og glucose and various gases. Also, the excretory and unwanted products from the embryo is also taken from the placenta to the mother's body. so it has dual functions too lol xD. after this after nine months the embryo is slowly brought down to vagina where after rhythemic muscular actions child is finally born *phew*

 

SEXUAL REPRODUCTION IN PLANTS

lets first look and study carefully the reproductive part of the plant- FLOWER. there are two types of flower - unisexual  (which contains either stamen or pistil) and bisexual (which contains both stamen and pistil)

PARTS OF THE FLOWER

1. Sepals: 

they are the green leaf-like structure present in the flower. their main function is to protect the the bud from the adverse environment condition as bud is sensitive.

2. Petals: 

they are the colorful and soft part of the plant (mainly the reason why half the plants break before they reproduce by kids) they are colorful so as to attract the bees, butterfly etc. so that they could help them in pollination.

3. stamen: 

it is the male reproductive part of the flower. it consists of anther and filament. filament are long tube like structure and anther is present on the tip of the filament. anther contains pollen grain. pollen grains are yellowish in colour. 

4. Carpel/ Pistil 

it is the female reproductive part of the flower. It contains stigma, style and ovary. Stigma is the one which recieves the pollen grain and is present in the tip of style. style is long tube like structure which helps in transportation of male gametes. and ovary is the bottom and large structure where female gamete is present.

POLLINATION

the transfer of pollen grains from the anther to stigma is called pollination.

pollination are if two types-self pollination and cross pollination. the transfer of pollen grains from anther to stigma of same flower or any other flower of same plant is called self pollination. when there is transfer of pollen grains from anther to stigma of any other flower of same species remember same species but not the same plant it is called cross pollination.

FERTILIZATION 

as discussed earlier fertilization is the process of fusion between male and female gamete to form zygote. now let's step by stem consider the sexual fertilization in plant. at first the pollen grains falls on the stigma, absorbs water and nutients anf produces a pollen tube which passes through style, ovary and finally reach ovules. it carries male gamete over to the female gamete which is present in the embroyonal sac which is in the ovule where male and female gamete fuses and you know what comes after this right?

SEXUAL REPRODUCTION

   1. Sexual reproduction involves two parents namely male and female.

    2. There is involvement of two gametes, i.e., male gamete (sperm) and female gamete (ovum).

3.   3.The offspring produced are not identical to their parent. As sexual reproduction is a source of variation due to involvement of two different organisms (variation is the tendency of an organism to differ from other)

   WHAT ACTUALLY HAPPENS IN SEXUAL REPRODUCTION?

   1. As we already know that male gamete (sperm) and female gamete (ovum ) are involved in sexual reproduction so in their respective bodies the gametes undergo mieosis. mieosis is a process in which the the chromosomes are halved as compared to the other cells. so we can conclude that sperms and ovum have half the no. of chromosomes as compared to other cells and hence are called haploid cells. 

2  2. the male gamete is motile,i.e., it can move freely while female gamete is large and stores food.

    3. when the male and female gamete fuse together they form zygote (future baby) this process is called fertilization. 

   4. zygote undergoes mitosis. mitosis is a process in which the there are complete no. of chromosomes. (complete opposite of mieosis ,a 't' can do wonders in your biology paper xD) and hence is called diploid cells. now think about it if there were no mieosis then the chromosome in zygote would be double of the parents and boom the baby might turn into hulk ! but half from male and half from female gamete controls it all. and hence the DNA (Deoxyribo Nuclic Acid) content of the zygote equals the parents.

    

VEGETATIVE REPRODUCTION

Vegetative reproduction is an asexual mode of reproduction where the new individual rises from the vegetative parts of the plant, like stem, roots and leaves. For example:

1.       Stem: onion, ginger, potato etc.

2.        Roots: sweet potato, dahlia, guava etc.

3.       Leaves: bryophyllum

Due to the presence of adventitious cells on the vegetative parts of the plants they are able to give rise to new individual.

TYPES OF VEGETATIVE REPRODUCTION

1.      Budding:  

In bryophyllum, the adventitious cells are present in the notches of the leaf margins where new individual rises and separates itself for the parent and drops into the soil. This is also practiced in agriculture. This is called budding.  (You can relate it to the budding in yeast that we studied earlier right? Like the separation part then how the individual is identical to the parent.)

2.      Layering: 

In jasmine, the stem is taken and buried around 6-9 inches under the ground. The stem grows roots and a new individual rises. (Imagine a whole jasmine garden can be created with this with just one jasmine flower wow!). This is called layering.

3.     Grafting: 

In plants like roses, mangoes and oranges their reproductive capacity is less. So they are made to reproduce through grafting. In grafting the stem of a plant is cut and is replaced by stem of another plant of same species.  

ADVANTAGES OF VEGETATIVE REPRODUCTION

1.      1.  The plants produced by vegetative reproduction grow faster meaning they bear fruits and flowers faster as compared to the one grown from traditional seed method.

2.     2.   The offspring will be identical to the parent. (identical means perfectly similar just like doppelganger )  

3.       3. The plants that have less reproductive capacity (like rose, mangoes, oranges) can be grown through this method.

REPRODUCTION (ASEXUAL)

Reproduction is a process by which all living organisms give rise to new individuals which are very much similar to their parents.

ASEXUAL REPRODUCTION

1.   In this only one parent is involved

2.   No gametes are involved

3.     In this process, the off springs are identical to their parent.

4.    It occurs in lower classes of organisms. For example amoeba, plasmodium, planaria etc.

TYPES OF ASEXUAL REPRODUCTION

BINARY FISSION

This occurs in amoeba. At first, the nucleus divides itself into two separate nuclei. Then a constriction is formed in the cytoplasm. The constriction begins to deepen resulting in the formation of two daughter amoebas which have their own cell apparatus which is identical to their parent. It can occur in any plane in amoeba but in leishmania it can only happen in longitudinal plane due to the presence of flagella on one end.

MULTIPLE FISSION

This occurs in plasmodium (the malarial parasite). In this process, the living organisms divide themselves into many daughter cells which are identical to their parent.

BUDDING

This takes place in yeast. Yeast gives rise to two unequal daughter cells. The smaller bud appears on the parent yeast and a long chain is produced which separates to grow further.

FRAGMENTATION

In this process the living organism divides itself into smaller fragments which then grow into new individuals. For example: spirogyra. Unlike regeneration no specialized cells are involved in fragmentation. For example: spirogyra.

REGENERATION 

This is another mode of reproduction in which the organisms have the ability to regenerate the lost body parts. Surprisingly, even if it is cut into 1/6th mm parts of its body it is able to regenerate and form a new individual. 

REGENERATION vs. FRAGMENTATION

Now, students often get confused between regeneration and fragmentation  so here you go

1. in regeneration specialized cells are involved. These cells revive and differentiate to form tissues, tissues forms organs and organs form the .....individual (ta-dah) Since it is performed in highly orderly manner this process is called development (lame right?)while no such procedure is followed in fragmentation. 

2.  In fragmentation, the fragments formed grow into an individual but in regeneration the lost parts may/may not form into a new individual. for example: lizard. the tail it drops i mean shed off does not regenerate to become a new lizard! (thank god the idea in itself is horrible!)

3. GIVE EXAMPLES!

4. DEFINATION (i know it should have been the first ): )

SPORE FORMATION

It occurs in fungi. I personally think it is most interesting of all asexual reproduction method ! So in this method the spores drifting in the air falls on suitable substratum like bread (i wanted to sound cool okay?) when it falls it germinates to form a white cottony thread like structure called hyphae. the nutrients and misture is taken by the roots who emerge from hyphae called rhizoids. the vertical hyphae are called sporangiophore which have sporangium on their tips.(so spore-ish) the sporangium contains spores and when it bursts it various spores pack their bags coolly saying adios to their parent in search of suitable substratum (-.-' i know) the spore have thick walls which protects them against adverse environmental condition.