Heredity And Evolution

The given information is not sufficient to tell which of the traits, i.e., blood group B or O is dominant. But generally, blood group O is recessive in nature.

Here fathers blood group is B that means it can be either BB (homozygous) or BO (heterozygous) genotypically. Similarly, mother can have genes combination OO or OB. The daughter having blood group O will have received O type gene from each parent. The genes IO and IO combined to give blood group O. For this the father must be heterozygous (BO), and mother must be homozygous (OO). Recessive traits appear when both the parents contribute recessive genes.

In asexual reproduction, a single parent is involved in reproductions (i.e. through mitotic division), so the chromosomes are not different and there is less variation.

Whereas in sexual reproduction, two parents are involved in reproductions (i.e., through meiotic division), so there are two chromosomes inherited from parents to the offspring leading to variation.

Hereditary is transmission or passing of the traits or characteristics from parents to their offspring’s i.e., from one generation to the next generation, either through asexual reproduction or sexual reproduction. And it is due to this the offspring’s look like their parents in few traits or in all traits.

Monohybrid cross is cross between two individuals with a different variation of a single trait or single characteristic. That is Mendel crossed pure tall plant with the pure dwarf plant, here he considered height as the trait.

Dihybrid cross is a cross between two individuals differing in two different contrasting pairs of characters. That is Mendel crossed seeds of pea plant considering two characteristics of color (yellow and green) and texture (smooth and wrinkled).

The causes of genetic variations are:

(i) Change in genetic material

(ii) Mutation

(iii) Random mating

(iv) Random fertilization

(v) Recombination between homologous chromosomes during meiosis

(vi) And many environmental factors like light, temperature, nutrition, wind, water supply, etc.

A change in DNA that is useful for one property to start with, can become useful later for a different function means a change in DNA of an organism that may have helped it to adopt to an environmental condition can also become useful for a completely different function in the future.

For example feathers in birds, a character developed and selected during natural selection because it provided insulation in cold weather have become useful in later stages for flight. Some heavy birds and reptiles also have feathers, but they do not fly. Like dinosaurs had feathers, but they could not fly

i. The branch of biology dealing with the study of heredity and variation is known as genetics scientifically.

ii. The transmission of traits from parents to offsprings is known as hereditary.

In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY. Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female. So the offspring can be either male or female i.e., 50:50 chance.

Homologous structures are structures that have a common basic structure but perform different functions and appearance. For example fore limbs of reptiles, amphibians and mammals, etc.

Yes, homology means common, so homologous structures have a common ancestor but variously modified to carry out different activities.

Zygote is a diploid cell having 2n chromosomes. Zygote is a very early stage of sex determination and the sex determination can take place at embryo level in practical world. Theoretically for sex determination at zygote level is as follows:

Male is bearer of XY chromosome. Female is bearer of XX chromosome. From this we can understand that female chromosome does not decide the sex of the zygote/offspring. The pairing of male chromosome X with female chromosome X i.e XX pairing will result in female zygote/offspring and male chromosome Y pairing with X chromosome from female i.e XY pairing will result in male zygote/offspring.

Natural selection is key mechanism in evolution. It is a process where organisms better adapt their environment, and they tend to survive and produce more offspring’s.

The main concepts of Darwin’s theory of natural selection are as follows:

i. Variation - Within a population, some traits can be expressed in various ways and make individuals look and behave differently.

ii. Inheritance - Heritable traits are transmitted to the next generation.

iii. The high rate of population’s growth - At each generation, the population produces more offspring than what the local environment can support. It leads to substantial mortality.

iv. Differential survival and reproduction - Individuals with the best combination of traits to survive in the actual environment will produce more offsprings for the next generation.

“The sex of a newborn individual in some species is largely determined genetically, while in others it is otherwise” Examples to justify this statement is as follows:

i. Snails can change their sex when required. Hence sex is not determined genetically.

ii. For birds, reptiles and lizards; the sex of the child depends upon the incubation temperature, i.e., sex determination depends on environmental factors

iii. In some reptiles, the sex determination is temperature dependent, i.e., the temperature at which the fertilised egg is incubated before hatching, plays a role in sex determination of the offspring, e.g.: turtles and lizard.

iv. In some marine worms, the sex is determined by the physical contact between the larvae and female. If they mate with the female, they will become a male whereas if they do not mate, they will grow into females.

Acquired characters are characters that are gained during lifetime and are determined by environmental factors alone. These changes occur in the non-reproductive tissues; these cannot be passed into the DNA of the germ cells. i.e., since the genetic constitution does not determine these traits, they remain confined to the individual only and are never passed from parents to offspring. Hence acquired characters are not inherited.

For example, Weismann experimented with removing tails of 68 white mice, repeatedly over five generations, and reporting that no mice were born in consequence without a tail or even with a shorter tail.

The descendants of wild cabbage are cabbage, cauliflower, broccoli, kohlrabi, red cabbage and kale.

These vegetables are evolved from the same ancestor, i.e., wild cabbage by artificial selection.

Cabbage was developed by shortening the distance between the leaves.

Cauliflower was developed by producing sterile flowers.

Broccoli was developed by arresting the flower production.

Kohlrabi was developed by producing swollen stem.

The red cabbage was developed by shortening the distance between the leaves in a plant with the purple leaves.

Kale was developed by producing plant with broad leaves.

Variation arise in an organism during reproduction that is during the DNA copying some error may occur by chance which gives rise to variations, and this is passed down to their offsprings.

Variations can be beneficial or detrimental that is variation is sometimes useful for the survival of the species; this is justified with the following examples:

i. If the temperature of the water increases suddenly, then most of the bacteria living in that water would die. Only a few variances that are resistant to heat would be able to survive. However, if this variance were not there, then the entire species of bacteria would have been destroyed. Thus, this variant help in the survival of species.

Hence if some variations are there, few individuals might survive. Depending on whether the variations are useful to the change in the environment some variants survive whereas others do not.

Fossils are the remains of plants, animals or other organisms that once existed on earth. These are formed when plants or animals buried in mud and soil. The soft tissues decay easily by leaving the hard bones and shells. Over a period of time sediment builds over these bones and shells, then hardens to form rock.
Fossils help in tracing the organic evolution in the following ways:-

a. Fossils represent modes of preservation of ancient species.

b. Fossils help in establishing evolutionary traits among organisms and their ancestors.

c. Fossils help in establishing the time period in which organisms lived.

d. Fossils provide good evidence of the structure and lifestyle of animals (and even plants) from the past.

e. They provide a record of the remains of long-extinct species.

For ex:

i. A Fossil Bird called Archaeopteryx looks like a bird, but it has many other features which are found in reptiles. Hence it is a connecting link between the reptiles and birds and hence suggests that the birds have evolved from reptiles. Thus, Fossil provides evidence that the present animals and plants have originated from the previously existing ones through the process of continuous evolution.

ii. Earliest fossils are of Monera, followed by Protoctista and then fungi. Plants and animals appeared later. Even among the vertebrates, the oldest fossils are those of the fishes, followed by amphibians and progressively mammals are the latest organisms to appear on earth.

iii. Human fossils show a progressive increase in skull sizes to the present age while evolutionary stages of the horse have been reconstructed on the basis of increased complexity of fossil limbs.

Human beings are more evolved than bacteria cannot be just answered on the basis of their complexity, i.e., it’s not necessary that a complex organism is always more evolved.

If the appearance of complexity is concurrent with evolution, then human beings are certainly more evolved than bacteria. But if we take the totality of life characteristics into account, then it is hard to label either of the organisms as evolved.

Some similarities between humans and bacteria are:

a. Both bacteria and human beings are still evolving from 6 billion years.

b. Bacteria spend their time in evolving characteristics that made them adaptable in almost any environmental conditions.

c. Both are well adapted to ecological niches they exist in.

d. Both of them now co-exist.

Dinosaurs were much more complex organisms which got disappear followed by the appearance of birds on earth (an organism with less complex body structure as compared to dinosaurs). Although bacteria are simpler organisms as compared to human but have evolved with the time that enables them to withstand extremes of climatic conditions and to develop many adaptive traits to survive under harsh conditions (antibiotic resistance). Thus, the evolutionary process does not prove that bacteria being less evolved organisms as compared to a human.

Homologous organs are organs that have common basic structure but perform different functions and appearance.

Flippers of whales and wings of birds considered as homologous organs because they both have the same anatomy, i.e., they have same skeletal structures, and they perform different functions. Flippers of whales are used to swim whereas the wings of birds are used for flight.

As whales and birds have flippers as homologous organs show that they have evolved from very closely related ancestors. Even though they have the same origin, they both have been adapted for different functions.

According to Darwin’s theory of evolution:

1. There is natural variation within any population, and some individuals have more favourable variations than others.

2. The population remains fairly constant even though all species produce a large number of off springs.

3. This is due to ‘competition’ or struggles for existence between same and different species.

Organisms produce more offspring than the available food and space, so there is a struggle for existence this ensures that the best among them survive.

Natural selection states that there is ‘struggle for existence’ within a population and variation exists in a population. The continuous competition between individuals for environmental resources creates ‘struggle for existence’, and this struggle makes sure that certain organisms would survive or reproduce leaving back the others that are not a better fit in the environmental conditions. Hence the less suited organisms are eliminated, and better-adapted organisms survive and pass their traits to the next generation leading to variation.

Struggle for existence preserves advantageous traits and weed out disadvantageous traits.

Here the parents are dihybrid in nature as dihybrids are two individuals differing in two different contrasting pairs of characters. In the given example the parents are differing in two characters, i.e., shape (round and wrinkled) and color (yellow and green). A cross between two pure-breeding dominant and recessive parents gives heterozygous dominant offspring. All F₁ progeny in this cross will have genotype RrYy and will exhibit round and yellow phenotype. Self cross in F₁ progeny gives F₂ generation and follow law of independent assortment of characters.

So,

F₁ – Rr Yy X Rr Yy

Round, yellow Round, yellow