Heredity And Evolution - Class 10 Biology - Extra Questions

$${F}_{1}$$ Generation. $${F}_{1}$$ or first filial generation is the generation of hybrids produced from a cross between the genetically different individuals called parents. For example, Tt individuals are produced in $${F}_{1}$$ generation from a cross between TT and tt parents.
$${F}_{2}$$ Generation. $${F}_{2}$$ second filial generation is the generation of individuals which arises as a result of inbreeding of interbreeding amongst individuals of $${F}_{1}$$ generation.

A gene is the segment of the DNA that controls the specific trait in organisms and an allele is the particular variant of the gene. For example, The colour of hair is a trait, that is determined by the gene. On the other hand, the different colours are the variant of the allele. We can also say that the different versions of the same gene are called alleles. 

In the given figure related to cross between TtYy and Ttyy plants the proportion of :

$$\textbf{Solution:}$$

$$\bullet$$ The study of evolution and classification of organisms are interlinked in phylogenetic classification system.

$$\bullet$$ Classification of different types of organisms in groups is based on similarities and dissimilarities between them.

$$\bullet$$ Phylogenetic classification refers to the classification of organisms based on their descent from a common ancestor.

$$\bullet$$ The evolutionary ancestry is the foundation of the phylogenetic classification system. It is based on life's evolution and depicts the genetic relationships between organisms. 

$$\bullet$$ It produces cladograms, which are groups of organisms that include an ancestor species and its descendants. 

Cross between TT and tt:

Formation of distinct and new species during the evolutionary process is called as speciation.  

Genes are the specific parts of a chromosome which determine the heredity characteristics. Genes are responsible for transmission of hereditary characters.

Analogous organs : The organs which have similar functions but are different in anatomical structures are called analogous organs. Examples of analogous organs are as follows:

In the first cross, the genotype of parents would be Tt and tt.

Gametes	T	t
t	Tt	tt
t	Tt	tt

Homology refers to similar structures but different functions. On the other hand, analogy refers to dissimilar structures but the same functions. The forelimb of a bird and a human are structurally similar but they differ in their functions. The forelimb of a bird is used for flying, whereas the forelimbs in humans are used for grasping. Therefore, the forelimb of a bird and a human are homologous organs.

i) The mechanism by which variations are created and inherited is known as heredity. 

Monohybrid cross is performed between two plants and only one character or trait is considered. For example, the flower color trait is considered for the cross. There is only one character considered and so the cross is known as monohybrid cross. For example, when pea plants with round seeds (RR) are crossed with plants with wrinkled seeds (rr), all seeds in F$$_1$$ generation were found to be round (Rr). When these round seeds were self-fertilised, both the round and wrinkled seeds appeared in F$$_2$$ generation in 3: 1 ratio. The genotypic ratio is 1:2:1. 

The phenotype is the physical appearance due to the presence of a trait. For example, tall and dwarf are the phenotypes for the trait height.

Monohybrid cross is performed between two plants and only one character or trait is considered. For example, the flower color trait is considered for the cross. There is only one character considered and so the cross is known as monohybrid cross. 

Africa is the region where the primitive man evolved. The fossils of the primitive man were found in the regions of Africa. There were ancestors of the modern man which lived in the Africa, Europe and other regions of Asia. This includes the organisms of the Hominidae group. 

The genotype of the homozygous dominant plant is TTRR, thus the gametes produced by this plant will contain TR genes. The genotype of the homozygous recessive plant is ttrr, thus the gametes produced by this plant will contain tr genes. Thus, the genotype of F$$_1$$ generation will be TtRr.

Gene are the functional segments of the DNA which express themselves and are responsible for a particular trait. Genes are located on the 23 pairs of chromosomes and  are responsible for transmission of hereditary characters from parents to offspring.

• There are two pairs of sex chromosomes. One of the sex chromosome is passed on to the offspring by the mother and the other is inherited by the father. 
• The mother (females) have two X chromosomes and the father (males) will have X and Y chromosome. 
• The chromosome which is inherited by the mother will be X. 
• The father can pass on either X or Y chromosome. 
• If the father pass on Y chromosome, the offspring will be male. If the father pass on X chromosome, the offspring will be female.
• Hence, the given statement is true. 

There is a total of 23 pairs of chromosomes in humans, out of which 22 pairs of autosomes, while one pair of chromosomes are sex chromosomes. 

Considering the relationship in the first pair, complete the second pair : rr: Homozygous :: Rr : Heterozygous. When two alleles of same gene are found in an individual then the individual is said to be  homozygous. These may be either recessive (rr) or dominant (RR). In contrast, when two alleles of different gene are found in an individual then the individual is said to be heterozygous (Rr).

The forelimb of whale and wings of bat are the examples of homologous organs. Organs having different functions but a similar structure are called homologous organs. They indicate a close relationship between their possessors. For example, the forelimbs of a whale, forelimb of human, the wing of a bird, leg of horse and flipper of a seal are all apparently different from one another in structure and function, yet they are all built on the same plan, having the same number of bones, muscles, blood vessels and nerves arranged in the same pattern and developed similarly.

$$\textbf{Solution:}$$

$$\bullet$$ The process by which characteristics or traits are passed down from generation to generation is referred to as heredity. 

$$\bullet$$ The traits are passed down through gametes that fuse during fertilization. One set of chromosomes is inherited from the mother, while the other set is inherited from the father.

$$\bullet$$ So the traits of our grandparents were passed down to our mother and father by their parents through inheritance.

$$\bullet$$ Similarly, our parents pass on these characteristics to us during the process of sexual reproduction.

$$\bullet$$ It is the inheritance pattern, in which characters are passed down from generation to generation and carried on.

Some of the fossil fuels formed by the decomposition of dead plants and animals are coal, petroleum, and natural gas.

Speciation is the formation of a distinct group of species with specific traits in course of evolution. Yes, geographical isolation will be a major factor in the speciation of an organism that reproduces sexually. The geographical isolation of organisms leads to change in gene frequency leading to the expression of one type of traits in a geographically isolated population.

Homologous organs	Analogous organs
The anatomy is the same.	The anatomy is different.
These structures develop in the related organisms.	These structures develop in unrelated organisms.
They perform different functions.	They perform the same functions.
The organs are inherited from the same ancestor.	The organs are not inherited from the same ancestor.
The structure and origin are the same.	The structure and origin are different.

Inheritance is the process by which genetic information is passed on from parent to child. The basic features of inheritance are:

Short-term adaptations	Long-term adaptations
Changes occurring are temporary	Changes occurring are permanent
These changes occur in response to momentary atmospheric changes.	These changes occur in response to major atmospheric changes.
These adaptations are not inherited.	These changes get inherited.
No mutation occurs in the DNA and hence, does not play a role in evolution.	Mutation take place in the DNA and so, their accumulation of can lead to speciation.
E,g.: Phototropism resulting in plant growth.	E.g.: White and scented night flowers to attract pollinators.

The process of transfer of genetical characters from parents to offsprings is called Inheritance. The basic features of inheritance are

(i) Characters are controlled by genes.
(ii) Each gene controls one character.
(iii) There may be two or more forms of the gene.
(iv) One form may be dominant over the other.
(v) Genes are present on chromosomes.
(vi) An individual has two forms of the gene whether similar or dissimilar.
(vii) The two forms separate at the time of gamete formation.
(viii) The two forms are brought together in the zygote.

This can be justified as follows - 

$$\textbf{Solution:}$$

$$\bullet$$ Fossils provide the most helpful evidences to study evolution.

The important features of the fossils that help in the study of evolution are given below:

$$\bullet$$ The ancient species are preserved through fossils.

$$\bullet$$ Fossils aid in the identification of evolutionary traits in organisms and their ancestors.

$$\bullet$$ Two different species of organisms can be connected by observing the physical structure of their fossils.

$$\bullet$$ Fossils aid in determining the time period during which those organisms lived.

Explanation-

In spite of the fact that creatures have a huge assorted variety of structures, they most likely don't have a typical family line, since regular heritage may extraordinarily restrict the degree of decent variety. The same number of these various creatures are possessing a similar living space, their development by land disengagement and speciation is likewise not likely. In this manner, a typical family line for every one of the creatures isn't the probable hypothesis.

When we consider T as the dominant trait and t as a recessive trait, TT and Tt represent tall plants and tt represent short plants.

(a) Difference between genotype and phenotype

The genes present in the DNA control characteristics or traits. The phenotypic or physical expression of a character depends upon the genotypic constitution. The expressed traits are a result of the specific genotypic combination of the alleles, which are a pair of genes . Also, a particular gene codes for a specific protein that determines the physical characteristics of an individual. This is how genes control the traits.

This can be demonstrated with help of Miller and Urey experiment: 
They took a blend of ammonia, hydrogen, methane and water.

 The scientific terms used to represent the following are:
(a) The branch of biology which studies heredity and variation -Genetics.
(b) The transmission of traits from parents to offspring - heredity.
(c) Differences in a trait in human beings - variation.
(d) A recognisable feature of an organism - character.

The traits that are expressed by the parent when also expressed by the progeny it is known as inheritance.

$$3:1$$ Monohybrid $$:: 9 :3:3:1:$$ Dihybrid cross

This can be illustrated with the help of the following examples:
(a) The thick and tall stem can be a desirable trait in sugarcane but the dwarf stem is desirable in rice plants.
(b) More leaves are desirable in spinach but it may not be the case in a mustard plant.

• Sexual reproduction involves the fusion of two types of gametes i.e., the male and the female gametes. 
• The zygote formed contains a fusion of both the sperm nucleus and the egg nucleus. 
• Due to this, the new individual has characteristics that are similar to both the parents while some characteristics are different from both the parents. 
• Thus, the new individual formed from sexual reproduction inherits the characteristics of both the parents. 
• For example, if the father has black hair while the mother has brown hair, the chances are that their offspring may have either black or brown hair. 

Height is a genetic trait but it also depends on the type of nutrition we take, type of exercise we do, amount of growth hormone secreted in a person and diseases they suffer from. 

Sexual reproduction results from the fusion of gametes produced by male and female. Sexual reproduction causes more viable variations because:
$$\rightarrow$$ There might be an error in the copying of DNA, though the event is rare.
$$\rightarrow$$ Segregation of chromosome of maternal and paternal origin at the time of gamete formation is random.
$$\rightarrow$$ There is an exchange of genetic material between homologous chromosomes during formation of gametes.
In case of asexual reproduction, variation is significantly less since only a single parent is involved. Very small changes occur due to inaccuracies during DNA copying that pass on to the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.

When a tall plant is crossed with a short plant, the first (F$$_{1}$$) generation plants obtained is all tall. But when the F$$_{1}$$ generation plants are crossed, the second (F$$_{2}$$) generation plants obtained are not all tall: there are both tall and short plants. 
This shows that the F$$_{1}$$ plants inherits their trait from the short plants but do not express it in the presence of the tallness (dominant character), and transfer it to the next generation.

TtRr TtRr	TR	Tr	tR	tr
TR	TTRR (tall plant, red flower)	TTRr (tall plant, red flower)	TtRR (tall plant, red flower)	TtRr (tall plant, red flower)
Tr	TTRr (tall plant, red flower)	TTrr (tall plant, white flower)	TtRr (tall plant, red flower)	Ttrr (tall plant, white flower)
tR	TtRR (tall plant, red flower)	TtRr (tall plant, red flower)	ttRR (dwarf plant, red flower)	ttRr (dwarf plant, red flower)
tr	TtRr (tall plant, red flower)	Ttrr (tall plant, white flower)	ttRr (dwarf plant, red flower)	ttrr (dwarf plant, white flower)

Analogous organs have similar functions but different origins. Flippers of penguin and dolphin have a similar function (helps in swimming) but different origin so they are called analogous organs. Penguin and dolphin are not closely related to each other but evolved similar traits (flippers) which represent convergent evolution.

Monohybrid cross.

A monohybrid cross is a genetic cross between two individuals,  who have homozygous genotypes, or genotypes that have completely dominant or completely recessive alleles, which result in opposite phenotypes for a certain genetic trait.

Monohybrid crosses are used by geneticists to observe how the offspring of homozygous individuals express the heterozygous genotypes they inherit from their parents. Typically, this cross determines the dominant genotype.

• The genotype of both the parents is MmBb for myopic brown eyes.
  
• The genotype of the child is mmbb. (recessive for both the traits).

Women have two X chromosomes and men have one X and one Y chromosome. Hence a female produces gametes which are all of the same kind and only contribute in one chromosome to the zygote. The other chromosome comes from the male and it can be either X or Y chromosome.

In evolutionary terms, all the organisms we see today have evolved in millions of years because they were fitter and better compared to their ancestors. All of them have evolved according to the habitats they occupy or the ecological role they play. For example,  bacteria is a very simple unicellular organism that can survive even in extreme conditions and multiply to increase its population in a couple of hours. On the other hand, if we see a more complex organism like a chimpanzee, even though it has a stronger body or limbs; it requires a longer time period to reproduce and increase its population size.