Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give suitable explanation.
No, all the gametes formed from a parent organism do not have the same genetic composition.
It can be better understand with the help of the explanation given below
Sexual reproduction in organisms generally involves the fusion of gametes from two different individuals. These gametes form by the process of gametogenesis. In the heterogametic species, gametes are of two types namely male and female. Gametes are haploid though the parent body from which they arise may be either haploid or diploid.
(a) A haploid parent like Monera, fungi, algae and bryophytes produce gametes by mitotic division. The number of chromosomes, i.e., the genetic composition remain same after such type of division.
(b) The diploid parent like pteridophytes, gymnosperms, angiosperms and most of the animals including human beings produces gametes by meiosis. In such organisms (diploid), specialised cells called meiocytes (gamete mother cell) undergo meiosis.
At the end of meiosis only one set of chromosomes gets incorporated into each gamete. It means the gametes formed contain a haploid number of chromosomes in contrast to the number of chromosomes in mother cells.
Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organisms in kingdom-Animalia and Plantae prefer this mode of reproduction. Give atleast three reasons for this.
Follwing are the three reasons for the mode of sexual reproduction in higher group of organisms
(i) The sexual mode of reproduction ensures creation of new variants.
(ii) Genetically varied offsprings are produced that adapt to changes in environment and survive in all climatic conditions.
(iii) Sexual reproduction ensures the genetic recombination that results in variation which gives rise to evolution.
Differentiate between (a) oestrus and menstrual cycles; (b) ovipary and vivipary. Give an example for each type.
(a) The differences between oestrus and menstrual cycle are as follows
| $$ \text { Oestrus cycle } $$ |
$$ \text { Menstrual cycle } $$ |
|---|---|
| The cyclic changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase of non-primate mammals is called oestrus cycle. | The cyclic changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase of primate mammals is called menstrual cycle. |
| Females show strong irresistible sexual urge. | Females do not show irresistible sexual urge. |
| There is estrus/heat production at the time of ovulation and copulation occurs only at that period. | There is no heat period and copulation occurs during any time of the cycle. |
| The shedding of endometrium and bleeding do not occur. e.g., cows, sheep, rats, deers, dogs and tigers etc. | The shedding of endometrium and bleeding occurs. e.g., monkeys, apes and humans. |
$$ \text { (b) The differences between ovipary and vivipary are as follows } $$
| $$ \text { Ovipary } $$ |
$$ \text { Vivipary } $$ |
|---|---|
| In ovipary, animals lay eggs. | In vivipary, animals give birth to young ones. |
| The eggs are covered by hard calcareous shell. | Ovum are not covered by calcareous shell. |
| The development of zygote takes place outside the female's body. | The development of zygote takes place inside the female's body. |
| Females lay eggs in a safe place in the environment, but the chances of survival are less e.g., all birds, most of reptiles are egg laying mammals. | Females deliver young ones and the chances of survival are more. e.g., mammals except monotremes egg laying mammals. |
Rose plants produce large, attractive bisexual flowers, but they seldom produce fruits. On the other hand a tomato plant produces plenty of fruits though they have small flowers. Analyse the reasons for failure of fruit formation in rose.
Rose plants produce large, attractive bisexual flowers, but they seldom produce fruits. The reasons for failure of fruit formation in rose are as follows
(i) Rose plants may not produce viable pollens, hence, no fertilisation can take place.
(ii) Rose plants may not have functional eggs.
(iii) Rose plants may have defective and non-functional ovule ,which is the female gametophyte generator.
(iv) There may be self-incompatibility.
(v) There may be internal barriers for pollen tube growth or fertilisation.
(vi) As rose plants are hybrids and reproduce vegetatively, there are chances for them to be sterile.