Mix Examples - Heredity and Evolution Questions in English

(N/A) Heredity: It is the transmission of characters from parents to the next generation.
Variations: The changes that occur in the $DNA$ of an organism due to mutations,recombination,or environmental factors.
$(b)$ Dominant: The trait which is able to express itself even in the presence of a contrasting trait. It appears in all the progenies in the $F_{1}$ generation.
Recessive: The trait which can express itself only in a homozygous condition. It does not appear in the $F_{1}$ generation.
$(c)$ Natural selection: It is the gradual natural process by which biological traits become either more or less common in a population based on survival advantage. Example: Green beetles surviving better than red beetles in green foliage.
Artificial selection: It is the human-driven mechanism of selecting organisms with desirable characters to bring about major changes in plants and animals. Example: Different vegetables like broccoli,cauliflower,and kale derived from the wild cabbage variety.

(N/A) Geographical isolation refers to the separation of a population by physical barriers such as mountain ranges or large bodies of water,which prevents gene flow between the separated groups.
$(b)$ Consider a large population of red beetles living in a mountain area covered with green bushes. Various sub-populations exist in the neighborhood. Individuals within a sub-population reproduce sexually,and numerous variations accumulate over generations.
If a river forms between these sub-populations,they become geographically isolated:
$(i)$ Variations continue to accumulate independently in each isolated sub-population.
$(ii)$ Over many generations,processes like genetic drift and natural selection cause these sub-populations to diverge significantly.
$(iii)$ Eventually,the genetic differences become so great that individuals from the two groups can no longer interbreed,leading to the formation of a new species.

(N/A) Some of the vegetables generated from a common ancestor,$Wild \ Cabbage$,through artificial selection are:
$1$. $Cabbage$: Selected for short distances between leaves.
$2$. $Broccoli$: Selected for arrested flower development and thick stems.
$3$. $Cauliflower$: Selected for sterile flowers forming a large flower head.
$4$. $Kohlrabi$: Selected for a swollen edible stem.
$5$. $Kale$: Selected for large leaves.

(A) Gregor Mendel studied seven pairs of contrasting traits in pea plants.
Regarding the position of flowers,the two contrasting traits are $Axial$ and $Terminal$.
$Axial$ position is the dominant trait,while $Terminal$ position is the recessive trait.
Therefore,the contrasting trait pair is $Axial$ and $Terminal$.

(B) Males are considered heterogametic because they possess two dissimilar sex chromosomes,specifically $(X)$ and $(Y)$.
During the process of meiosis,these chromosomes segregate into different gametes.
As a result,males produce two distinct types of gametes: one type containing the $(X)$ chromosome and the other type containing the $(Y)$ chromosome.
This production of two different types of gametes is the definition of heterogamety.

(N/A) The two basic characteristics that decide about analogy and homology are:
$(i)$ Basic anatomical structure and embryonic origin.
$(ii)$ Function performed by the organ.
In homologous organs,the basic structure and embryonic origin are similar,but the functions are different (e.g.,forelimbs of humans and wings of birds).
In analogous organs,the basic structure and embryonic origin are different,but the functions are similar (e.g.,wings of butterflies and wings of birds).

(D) The evidence suggesting that modern humans originated in Africa includes:
$(i)$ Fossil records: The oldest fossils of anatomically modern humans ($Homo$ $sapiens$) have been discovered in Africa.
$(ii)$ Molecular phylogeny: Studies of mitochondrial $DNA$ and $Y$-chromosome $DNA$ indicate that all non-African populations share a common ancestry that traces back to Africa.
$(iii)$ Archaeological excavations: Tools and artifacts found in African sites provide a chronological timeline of human development and migration.
$(iv)$ Carbon dating: This technique helps in determining the age of fossils and artifacts, confirming their ancient origins in the African continent.

(N/A) This is a Dihybrid cross because it involves the study of the inheritance of two pairs of contrasting traits (pod shape and pod color).
$(b)$ In the $F_{1}$ generation,all plants obtained have inflated and green pods,as these are the dominant traits.
$(c)$ The rule observed is the Law of Independent Assortment. It states that when two pairs of traits are combined in a hybrid,segregation of one pair of characters is independent of the other pair of characters at the time of gamete formation.

(N/A) Besides humans,many other organisms such as cats,lions,monkeys,and dogs (all mammals) exhibit a genetic basis for sex determination.
$(b)$ In humans,the first $22$ pairs of chromosomes,known as autosomes,are similar in both males and females.
$(c)$ Autosomes carry genes that determine the somatic (body) characteristics of an individual,such as eye color,height,and skin texture,which are not directly related to sex determination.

(D) Gregor Johann Mendel studied the inheritance of traits in pea plants.
He selected the pea plant because it possesses several contrasting visible characters such as round/wrinkled seeds,tall/short plants,and white/violet flowers. Furthermore,pea plants are easy to cultivate and have a short life cycle.
Only the dominant traits are expressed in the first generation ($F_1$ generation).
In the second generation ($F_2$ generation) of a dihybrid cross,the traits with two contrasting characters are expressed in the ratio of $9: 3: 3: 1$.

(A-D) In a dihybrid cross between yellow round $(YYRR)$ and green wrinkled $(yyrr)$ seeds,the $F_2$ generation exhibits a phenotypic ratio of $9:3:3:1$.
$(a)$ $9 / 16$ represents the plants with both dominant traits: Round and Yellow seeds.
$(b)$ $1 / 16$ represents the plants with both recessive traits: Wrinkled and Green seeds.
$(c)$ $3 / 16$ represents the plants with one dominant and one recessive trait: Either Round Green seeds or Wrinkled Yellow seeds.

(C) When two sub-populations are separated by a natural barrier,genetic drift and natural selection accumulate different variations in each of the two geographically isolated sub-populations over several generations.
In due course of time,these two sub-populations become significantly different from each other.
Due to reproductive isolation,they eventually become unable to interbreed even if they are brought together.
Consequently,these two groups transform into two distinct new species.

(N/A) $(i)$ Darwin's theory of evolution explains how life evolved from simple to more complex forms through the slow and gradual process of natural selection. However,Darwin could not explain the mechanism by which variations arise in species.
$(ii)$ Mendel's work provides the missing link. He discovered that alleles of genes do not blend or change when inherited but remain distinct and separate in the offspring. This ensures that genetic variation is not lost but persists across generations,providing the necessary raw material for natural selection to act upon. Thus,Mendel's experiments support Darwin's view by providing the genetic basis for heredity,which is essential for the process of evolution.

(N/A) Each population survives and interacts within a specific environment. Any drastic change in ecological conditions can negatively impact the population,potentially leading to damage or even extinction. Organisms within a species that possess beneficial variations are more likely to survive these environmental changes. These surviving individuals can then reproduce and pass on their advantageous traits,eventually leading to the development of a new species or the adaptation of the existing one.

(N/A) If predators are more in a group,it will lead to a rapid decrease in the population of prey on which the predators are dependent. Eventually,due to the lack of food,the predator population will also decline,potentially leading to the elimination of both populations.
$(b)$ Organisms that survive accidentally often possess certain variations or adaptations that provide a survival advantage. These individuals have a better chance to reproduce,continue their lineage,and increase their population size.
$(c)$ Organisms that are not able to adapt or survive in changing environmental conditions fail to reproduce and pass on their genes. Consequently,these individuals are eliminated from the population,which may eventually lead to the extinction of the species.

(N/A) Through the process of artificial selection,humans have bred wild cabbage into various vegetables to suit specific dietary preferences:
$(i)$ Arrested flower development results in $Broccoli$.
$(ii)$ Sterile flowers result in $Cauliflower$.
$(iii)$ Very short distances between leaves result in $Cabbage$.
$(iv)$ Swollen parts result in $Kohlrabi$.
$(v)$ Broader leaves result in $Kale$.

(N/A) The insects that survive have developed resistance against the pesticide by generating variations in their $DNA$ in comparison to other insects. The insects that did not have these variations in their $DNA$ could not develop resistance against the pesticide and were thus killed (eliminated).
$(b)$ $A$ recessive trait is capable of expressing itself only when it is in a homozygous recessive state,i.e.,both chromosomes have the same type of gene representing the trait.
For example,in the case of plant height,the recessive trait (dwarfness) is expressed only in the genotype $tt$.

(N/A) Evolution: The gradual unfolding of organisms from pre-existing organisms through changes since the origin of life.
It occurs because there is an inbuilt tendency to variation during reproduction due to errors in $DNA$ copying and as a result of sexual reproduction.
Fossils provide evidence for evolution by showing that although organisms in the past appeared different from existing species,they often share certain features with them. This establishes evolutionary linkages between ancestral and modern forms. Furthermore,fossils provide information about extinct species that were distinct from those existing today,helping us reconstruct the history of life on Earth.

(N/A) Molecular phylogeny is an approach based on the principle that organisms which are more distantly related will accumulate a greater number of differences in their $DNA$ sequences over time. By comparing these genetic differences,scientists can trace the evolutionary relationships among different organisms,which provides a scientific basis for their classification and understanding of evolutionary history.

(N/A) The three primary ways that produce variant genotypes in a population are:
$(i)$ Gene mutations: These are sudden,stable changes in the $DNA$ sequence that create new alleles.
$(ii)$ Crossing over (recombination): This occurs during meiosis,where homologous chromosomes exchange genetic material,leading to new combinations of genes.
$(iii)$ Hybridisation: This involves the crossing of two genetically different individuals,which results in offspring with new combinations of parental genes.

(A) $(i)$ Since green $(G)$ is dominant over purple $(g)$,all $F_1$ progeny will have the genotype $Gg$ and will be green-stemmed.
$(ii)$ When $F_1$ $(Gg)$ plants are self-pollinated,the $F_2$ generation results in the ratio $1GG : 2Gg : 1gg$. The purple-stemmed plants $(gg)$ represent $1$ out of $4$ plants,which is $25\%$.
$(iii)$ In the $F_2$ progeny,the ratio of genotypes $GG$ to $Gg$ is $1:2$.

(N/A) $(i)$ Let $B$ be the allele for barking and $b$ for silent. Let $E$ be the allele for erect ears and $e$ for drooping ears. The cross is $BbEe \times BbEe$.
The expected phenotypic ratio is $9:3:3:1$.
$(ii)$ The different phenotypes observed are:

Barking dogs with erect ears	Barking dogs with drooping ears	Silent dogs with erect ears	Silent dogs with drooping ears
$9$	$3$	$3$	$1$

$(iii)$ This type of cross is known as a Dihybrid cross.

(A) $(i)$ Since the offspring show a $3:1$ ratio of black to white,both parents must be heterozygous. Thus,the genotype of both parents is $Bb \times Bb$.
$(ii)$ Black color is the dominant trait because it appears in the majority of the offspring,while white color is the recessive trait.
$(iii)$ This cross is called a monohybrid cross. The phenotypic ratio is $3:1$ (black:white).

(N/A) $(i)$ Both blood group $A$ and blood group $B$ are dominant (codominant).
$(ii)$ Blood group $O$ is recessive.
$(iii)$ Since the offspring include blood group $O$ $(OO)$,both parents must carry the $O$ allele. Therefore,the father's genotype is $AO$ and the mother's genotype is $BO$.
$(iv)$ The cross between $AO$ and $BO$ results in the following genotypes and phenotypes for the offspring:
- $AB$ (Phenotype: $AB$)
- $AO$ (Phenotype: $A$)
- $BO$ (Phenotype: $B$)
- $OO$ (Phenotype: $O$)
This cross explains the presence of all four blood groups in the offspring.

(A) In human males,the sex chromosomes are $XY$.
These two chromosomes are not identical in size and shape.
The $X$-chromosome is a large chromosome,while the $Y$-chromosome is a small chromosome.
Since they are not a homologous pair,they are considered the unpaired chromosomes in the male karyotype.
Therefore,both the $X$-chromosome and the $Y$-chromosome represent the unpaired condition in males.

(B) In humans,the sex of a child is determined by the sex chromosomes inherited from the parents.
Females have two $X$ chromosomes $(XX)$,while males have one $X$ and one $Y$ chromosome $(XY)$.
During fertilization,the mother always contributes an $X$ chromosome to the zygote.
The father can contribute either an $X$ chromosome or a $Y$ chromosome.
If the sperm carrying the $Y$ chromosome fertilizes the egg,the resulting zygote will have an $XY$ genotype,which develops into a male child.
Therefore,the presence of the $Y$ chromosome is the deciding factor for maleness.

(C) In humans,the sex of an individual is determined by the sex chromosomes inherited from the parents.
Females have two $X$-chromosomes $(XX)$,while males have one $X$ and one $Y$-chromosome $(XY)$.
The mother always contributes an $X$-chromosome to the zygote.
If the father contributes an $X$-chromosome,the resulting zygote will have $XX$ chromosomes,which develops into a girl.
If the father contributes a $Y$-chromosome,the resulting zygote will have $XY$ chromosomes,which develops into a boy.
Therefore,a zygote inheriting an $X$-chromosome from the father will develop into a girl.

(D) Evolution is defined as the change in the frequency of genes in a population over several generations. This is a correct statement.
Traits that are not inherited (acquired traits) do not cause evolution because they are not passed on to the next generation. This is a correct statement.
Low weight parents can have heavy weight progeny due to variations in genetic makeup or environmental factors affecting growth. This is a correct statement.
Reduction in weight due to starvation is an acquired trait caused by environmental factors (lack of food). It is not genetically controlled and will not be inherited by the offspring. Therefore,this statement is incorrect.

(A) Speciation is the evolutionary process by which populations evolve to become distinct species.
$(i)$ Significant changes in the $DNA$ of germ cells lead to variations that are inherited by the next generation,which is a primary driver of speciation.
$(ii)$ Changes in chromosome number in gametes (such as polyploidy) can lead to reproductive isolation,preventing interbreeding with the parent population and resulting in the formation of a new species.
$(iii)$ If there is no change in the genetic material,the offspring will be identical to the parents,and no new species will be formed.
$(iv)$ Mating is essential for sexual reproduction and gene flow; lack of mating does not inherently create a new species.
Therefore,statements $(i)$ and $(ii)$ are correct.

(B) Acquired traits are those that an organism develops during its lifetime due to environmental factors,lifestyle,or practice. These traits do not change the $DNA$ of the germ cells and are therefore not inherited by the next generation.
$1$. Colour of eye,colour of skin,and nature of hair are inherited traits determined by the genetic makeup $(DNA)$ of an individual.
$2$. Size of body is an acquired trait because it can be influenced by nutrition,physical exercise,and environmental conditions during an individual's life,and these changes are not passed on to offspring.

(C) In diploid organisms,every somatic cell contains two copies of each chromosome,one inherited from each parent.
These are known as homologous chromosomes.
Each gene (which determines a trait) exists in two versions,called alleles.
These alleles are located at the same locus on the two copies of the same chromosome (homologous chromosomes).
Therefore,the two versions of a trait brought by the male and female gametes are situated on copies of the same chromosome.

(D) Statement $(i)$ is correct because genes are segments of $DNA$ that contain specific sequences of nucleotide bases.
Statement $(ii)$ is incorrect because the primary function of most genes is to code for specific proteins or polypeptides.
Statement $(iii)$ is correct because genes have fixed positions (loci) on specific chromosomes within a species.
Statement $(iv)$ is incorrect because a single chromosome contains hundreds to thousands of genes.
Therefore,statements $(i)$ and $(iii)$ are the correct characteristics of genes.

(A) $1$. In the $F_{1}$ generation,the cross between $TT$ and $tt$ results in all heterozygous tall plants $(Tt)$.
$2$. When $F_{1}$ plants $(Tt)$ are self-pollinated to produce the $F_{2}$ generation,the genotypes obtained are $TT, Tt, Tt,$ and $tt$.
$3$. The phenotypic ratio is $3$ tall : $1$ short,but the question asks for the ratio of pure tall $(TT)$ to short $(tt)$ plants.
$4$. In the $F_{2}$ generation,the genotype $TT$ appears once and the genotype $tt$ appears once.
$5$. Therefore,the ratio of pure tall $(TT)$ to short $(tt)$ plants is $1:1$.

(B) Homologous structures are those that have a common evolutionary origin and similar basic structure, even if they perform different functions or look different.
In the given options, both the carrot $(Daucus \, carota)$ and the radish $(Raphanus \, sativus)$ are modified taproots.
They share a common structural origin as roots, despite being different species.
Therefore, carrot and radish are considered homologous structures.
Potato is a modified stem (tuber), and tomato is a fruit, so they do not share the same structural origin as the roots mentioned.

(B) $1$. Homologous organs are those that have the same basic structural design and developmental origin but perform different functions.
$2$. Analogous organs are those that have different origins but perform similar functions.
$3$. The tendril of a pea plant (modified leaf) and the phylloclade of Opuntia (modified stem) are both modified plant parts that perform the function of support or photosynthesis,but they have different evolutionary origins,making them analogous structures.
$4$. Wings of birds and wings of bats are analogous (both used for flight,but different structures),while wings of birds and forelimbs of lizards are homologous (same skeletal structure,different functions).

(D) The study of fossils provides evidence for evolution. According to the principle of stratigraphy,the Earth's crust is formed in layers. The deeper layers of the Earth were deposited earlier than the upper layers. Therefore,fossils found in deeper layers are older than those found in the upper layers. If an organism's fossil is found in a deeper layer,it indicates that the organism lived and became extinct a long time ago (thousands of years ago).

(A) The correct answer is $A$.
$1$. Not all variations have an equal chance of survival. Variations that provide a survival advantage in a specific environment are selected by nature,while others may be eliminated.
$2$. Genetic changes (mutations,recombination) are the primary source of variation.
$3$. Natural selection acts on these variations,which is the fundamental mechanism of evolution.
$4$. Asexual reproduction involves a single parent and minimal genetic recombination,leading to very little variation compared to sexual reproduction.

(B) In sexually reproducing organisms,offspring inherit genetic material from both parents.
Each parent contributes one set of chromosomes (containing $DNA$) to the zygote during fertilization.
These $DNA$ segments contain genes that code for specific traits.
Therefore,the expression of a trait in an organism is influenced by the combination of $DNA$ inherited from both the mother (maternal) and the father (paternal).

(C) The phenotypic ratio obtained is $1:2:1$ (red:pink:white). This is a classic example of incomplete dominance,which is observed in $Antirrhinum$ $majus$ (Snapdragon).
When two pink flowers $(RW)$ are crossed,the offspring are $RR$ (red),$RW$ (pink),$RW$ (pink),and $WW$ (white).
Since the parents are of the same phenotype (pink) and are being crossed to produce this specific ratio,the process is known as self-pollination (or selfing).

(D) In a cross between a homozygous tall plant $(TT)$ and a homozygous short plant $(tt)$,the $F_1$ generation offspring all receive one allele from each parent,resulting in a genotype of $(Tt)$.
Since the allele for tallness $(T)$ is dominant over the allele for shortness $(t)$,the phenotype of all $F_1$ individuals is tall.
Therefore,the observation that all progeny are tall confirms that tallness is the dominant trait.

(A) Genes are segments of $DNA$ that contain the instructions for synthesizing specific proteins.
Since enzymes are biological catalysts made of proteins,their production is also controlled by genes.
Many hormones are also proteinaceous in nature (peptide hormones),and their synthesis is directed by genes.
However,fats (lipids) are not synthesized directly from genetic templates in the same way proteins are.
Fats are synthesized through complex metabolic pathways involving various enzymes,which are themselves gene products,but there is no 'one gene-one fat molecule' relationship.
Therefore,the statement 'for every molecule of fat there is a gene' is incorrect.

(B) According to the theory of evolution,speciation occurs when a population of a species becomes reproductively isolated from the original population.
This process is driven by the gradual accumulation of genetic variations (mutations and recombination) over many generations.
As these variations accumulate,the population undergoes significant changes in its genetic makeup,eventually leading to the formation of a new species that can no longer interbreed with the ancestral population.
Therefore,the correct answer is the accumulation of variations over several generations.

(C) The presence of feathers in dinosaurs (which were reptiles) and their presence in modern birds suggests an evolutionary link.
Since dinosaurs existed long before birds,it indicates that birds evolved from feathered reptiles (dinosaurs).
This is a classic example of evolutionary adaptation where a trait (feathers) originally evolved for a different purpose (likely insulation or display) in reptiles and was later co-opted for flight in birds.

(B) The statement is $False$. Humans have $23$ pairs of chromosomes in total. Out of these, $22$ pairs are autosomes, and only $1$ pair consists of sex chromosomes (allosomes). In males, the sex chromosomes are $XY$, and in females, they are $XX$.

(A) The statement is $True$. In many species of snails, sex determination is not strictly genetic but is influenced by environmental factors, such as temperature, population density, or social cues. This phenomenon allows individuals to change their sex during their lifetime, a process known as $sequential \text{ } hermaphroditism$.

(B) In humans,the sex of a child is determined by the sex chromosomes inherited from the parents.
Females have two $X$-chromosomes $(XX)$,and males have one $X$ and one $Y$-chromosome $(XY)$.
$A$ father contributes either an $X$ or a $Y$-chromosome to the offspring.
If the father passes an $X$-chromosome,the child will be a girl $(XX)$.
If the father passes a $Y$-chromosome,the child will be a boy $(XY)$.
Therefore,a child who inherits an $X$-chromosome from her father will be a girl,not a boy.

(B) In humans,the sex of a child is determined by the sex chromosomes inherited from the parents.
Females have $XX$ chromosomes and males have $XY$ chromosomes.
$A$ father contributes either an $X$ or a $Y$ chromosome to his offspring.
If a father passes an $X$ chromosome to his child,the child will be a girl $(XX)$.
If a father passes a $Y$ chromosome to his child,the child will be a boy $(XY)$.
Therefore,inheriting an $X$ chromosome from the father results in a girl,not a boy.

(B) In humans,the sex of a child is determined by the sex chromosomes inherited from the parents. Females have $XX$ chromosomes and males have $XY$ chromosomes.
When a child inherits an $X$-chromosome from the father,the child will be a girl $(XX)$.
When a child inherits a $Y$-chromosome from the father,the child will be a boy $(XY)$.
Therefore,the statement that a child inheriting a $Y$-chromosome will be a girl is false.

(A) The statement is True.
Variation is an inherent feature of reproduction.
In asexual reproduction,variations arise primarily due to minor errors in $DNA$ copying during cell division.
In sexual reproduction,variations are more significant due to the combination of $DNA$ from two different parents,the process of crossing over during meiosis,and random fertilization.

(A) Evolution is defined as the change in the heritable characteristics of biological populations over successive generations. At the genetic level,this corresponds to changes in the allele frequencies within a population's gene pool over time. Therefore,the statement that the frequency of certain genes in a population changes over generations is the fundamental essence of the theory of evolution.