Mix Examples - Heredity and Evolution Questions in English

(A) The exchange of genetic material,also known as genetic recombination,occurs during sexual reproduction.
In sexual reproduction,two parents contribute gametes (sperm and egg) which fuse during fertilization.
This process involves meiosis,where crossing over occurs between homologous chromosomes,leading to new combinations of genes.
This variation is a hallmark of sexual reproduction,whereas asexual reproduction (including vegetative reproduction and budding) typically produces clones with identical genetic material.

(C) The cross described is an example of incomplete dominance,where the phenotypic ratio of the progeny is $1:2:1$ (red:pink:white).
In this scenario,the pink flowers are heterozygous $(Rr)$.
When two pink flowers are crossed $(Rr \times Rr)$,the resulting genotypes are $1 RR$ (red),$2 Rr$ (pink),and $1 rr$ (white).
Since the question asks for the nature of the cross between two pink flowers,and the offspring are produced through the fusion of gametes from these two individuals,this is a form of cross-fertilisation (or cross-pollination) between two distinct plants of the same species.

(C) When a homozygous tall plant $(TT)$ is crossed with a homozygous short plant $(tt)$,all the $F_1$ generation offspring possess the genotype $(Tt)$.
Since the allele for tallness $(T)$ is dominant over the allele for shortness $(t)$,the phenotype of all $F_1$ progeny is tall.
This demonstrates the Law of Dominance,which states that in a heterozygote,one trait will conceal the presence of another trait for the same characteristic.

(D) Genes are segments of $DNA$ that contain the instructions for synthesizing specific proteins.
Since enzymes are proteins,there is a gene for every enzyme.
Many hormones are also proteins or peptides,which are encoded by genes.
However,fats (lipids) are not synthesized directly from a genetic template in the same way proteins are.
Fats are synthesized by enzymes,which are themselves encoded by genes,but there is no specific gene for every individual molecule of fat.
Therefore,the statement that there is a gene for every molecule of fat is incorrect.

(A) In this cross,the parent plants are $RRyy$ (round,green) and $rrYY$ (wrinkled,yellow).
During gamete formation,the $RRyy$ plant produces gametes with the genotype $Ry$.
The $rrYY$ plant produces gametes with the genotype $rY$.
When these gametes fuse during fertilization,the resulting $F_1$ generation offspring have the genotype $RrYy$.
According to the law of dominance,the dominant traits (round shape $R$ and yellow color $Y$) mask the recessive traits (wrinkled shape $r$ and green color $y$).
Therefore,all $F_1$ generation seeds will be round and yellow.

(B) In human males,the sex chromosomes are $XY$.
Unlike the autosomes,which exist in perfectly matched pairs,the $X$ and $Y$ chromosomes are morphologically different.
The $X$ chromosome is a large chromosome,while the $Y$ chromosome is a small chromosome.
Because they differ in size and genetic content,they do not form a perfectly matched pair.
Therefore,both the $X$ and $Y$ chromosomes are considered unpaired in terms of homologous pairing.
Thus,the correct answer is $(iii)$ and $(iv)$.

(C) 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 $(XY)$.
During fertilization,the mother always contributes an $X$ chromosome.
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 $XY$ chromosomes,which develops into a male child.
Therefore,the presence of the $Y$ chromosome is the deciding factor for maleness.

(D) In humans,the sex of an individual is determined by the sex chromosomes.
Females have $XX$ chromosomes,and males have $XY$ chromosomes.
During fertilization,the mother always contributes an $X$ chromosome to the zygote.
The father contributes either an $X$ or a $Y$ chromosome.
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 have $XX$ chromosomes and develop into a girl.

(A) The correct answer is $A$.
$1$. Reduction in weight due to starvation is an acquired trait caused by environmental factors (lack of food),not by changes in the $DNA$ of germ cells. Therefore,it is not genetically controlled and cannot be inherited by the next generation.
$2$. Option $B$ is correct because evolution is defined as the change in the frequency of alleles in a population over time.
$3$. Option $C$ is correct because weight is a complex trait influenced by both genes and environment; thus,low-weight parents can produce heavy-weight offspring if the environmental conditions (nutrition) are favorable.
$4$. Option $D$ is correct because only inherited traits (those present in the $DNA$ of germ cells) are passed to the next generation and contribute to the evolutionary process.

(B) 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 fundamental requirement for speciation.
$(ii)$ $A$ change in the chromosome number in gametes (such as polyploidy) can create reproductive isolation from the parent population,leading to 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 necessary for sexual reproduction and gene flow; lack of mating does not inherently cause speciation.
Therefore,statements $(i)$ and $(ii)$ are correct.

(B) In a dihybrid cross involving seed shape (Round $R$ vs Wrinkled $r$) and seed color (Yellow $Y$ vs Green $y$),the parental generation is $RRyy$ (Round,Green) and $rrYY$ (Wrinkled,Yellow).
The $F_1$ generation is $RrYy$ (Round,Yellow).
When $F_1$ plants are self-pollinated,the $F_2$ generation exhibits four phenotypes in a $9:3:3:1$ ratio:
$1$. Round,Yellow (Parental type)
$2$. Round,Green (Recombinant/New combination)
$3$. Wrinkled,Yellow (Recombinant/New combination)
$4$. Wrinkled,Green (Parental type)
Therefore,the new combinations of characters are Round,Green $(ii)$ and Wrinkled,Yellow $(iii)$.

(D) Homologous structures are those that have a common evolutionary origin and similar basic structure, even if they perform different functions.
In the given options, carrot $(Daucus \text{ } carota)$ and radish $(Raphanus \text{ } sativus)$ are both modified taproots used for food storage.
Although they belong to different plant families, they are both homologous as they are derived from the same ancestral root structure.
Potato is a modified stem (tuber), and tomato is a fruit, so they do not share the same origin as the roots mentioned.

(B) Homologous organs are those that have the same basic structural design and developmental origin but perform different functions.
Analogous organs are those that have different developmental origins and structural designs but perform similar functions.
$1$. The tendril of a pea plant is a modified leaf,while the phylloclade of Opuntia is a modified stem. They perform different functions (support vs. photosynthesis/water storage) and have different origins,so they are not homologous.
$2$. Wings of birds and wings of bats are analogous because they perform the same function (flight) but have different evolutionary origins (the wing structure of a bird is different from that of a bat).
$3$. Wings of birds and limbs of lizards are homologous because they share a common ancestral skeletal structure (pentadactyl limb),despite performing different functions.
Therefore,the statement that tendril of a pea plant and phylloclade of Opuntia are analogous is incorrect,and the statement about wings of birds and wings of bat being homologous is also incorrect. The correct statement is that wings of birds and limbs of lizards are homologous (though not listed as an option here,based on standard biology,the provided options contain a common confusion). Re-evaluating: In many textbooks,wings of birds and wings of bats are considered analogous. Thus,option $B$ is often cited in contexts where these structures are compared as having different origins.

(B) The study of fossils provides evidence for evolution. According to the principle of stratigraphy,the layers of the earth are deposited sequentially over time. The deeper layers are older than the upper layers. Therefore,if a fossil is found in a deeper layer,it indicates that the organism lived and became extinct a long time ago (thousands of years ago) compared to organisms found in the upper layers.

(C) Variation refers to the differences in characteristics among individuals of a species.
$A$. Environmental factors select variants that are better adapted,which drives evolution. This is a true statement.
$B$. Changes in the genetic material $(DNA)$ lead to variations in offspring. This is a true statement.
$C$. Variations do not have an equal chance of survival. Some variations provide a survival advantage in specific environments,while others may be disadvantageous. Therefore,this statement is false.
$D$. Asexual reproduction involves a single parent and produces clones,leading to minimal variation. This is a true statement.

(D) In sexually reproducing organisms,offspring inherit genetic material from both parents.
Each parent contributes one set of chromosomes (containing $DNA$) to the zygote.
Since traits are determined by genes located on these chromosomes,the expression of a trait is influenced by the genetic contribution from both the mother and the father.
Therefore,both maternal and paternal $DNA$ play a role in determining the characteristics of the organism.

(A) In biological classification, the hierarchy follows the order: $Species < Genus < Family < Order < Class < Phylum < Kingdom$.
As we move from $Species$ to $Kingdom$, the number of common characters decreases.
Conversely, organisms belonging to the same $Species$ share the maximum number of common characters because they are the most closely related.
Therefore, two individuals of the same $Species$ will share the maximum number of common characters compared to the other options provided.

(B) According to the theory of evolution,speciation (the formation of new species) occurs primarily through the accumulation of small,heritable variations over many generations.
These variations arise due to genetic mutations,recombination during sexual reproduction,and natural selection.
Over a long period,these accumulated changes lead to significant differences between populations,eventually resulting in reproductive isolation and the emergence of a new species.

(C) Acquired characters are those traits that an organism develops during its lifetime due to environmental factors,lifestyle,or physical training. These traits are not encoded in the $DNA$ of the germ cells and therefore cannot be passed on to the next generation.
$1$. Colour of eye,colour of skin,and nature of hair are inherited traits determined by the genetic makeup (genotype) of an individual.
$2$. Size of body is an acquired character. While genetics plays a role in potential height,the actual size of the body is significantly influenced by environmental factors such as nutrition,exercise,and health during the growth period. Since these changes occur in somatic cells,they are not inherited by offspring.

(D) In diploid organisms,every individual inherits two alleles (versions of a trait) for a specific character,one from the male parent and one from the female parent through gametes.
These alleles are located at the same locus (position) on homologous chromosomes.
Homologous chromosomes are essentially pairs of the same chromosome,where one is inherited from the father and one from the mother.
Therefore,the two versions of a trait are situated on copies of the same chromosome.

(A) 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 thousands of genes.
Therefore,the correct statements are $(i)$ and $(iii)$.

(A) $1$. In the $F_1$ generation,crossing $TT$ and $tt$ results in all heterozygous tall plants $(Tt)$.
$2$. When $F_1$ plants $(Tt)$ are self-pollinated,the $F_2$ generation genotypes are $TT$,$Tt$,$Tt$,and $tt$ in a ratio of $1:2:1$.
$3$. The phenotypes are $3$ tall plants and $1$ short plant.
$4$. Among the $F_2$ generation,the pure tall plants are $TT$ (genotype frequency $1$) and the short plants are $tt$ (genotype frequency $1$).
$5$. Therefore,the ratio of pure tall plants $(TT)$ to short plants $(tt)$ in the $F_2$ generation is $1:1$.

(C) In humans,the total number of chromosomes in a diploid zygote is $46$ ($23$ pairs).
Out of these $23$ pairs,$22$ pairs are autosomes and $1$ pair consists of sex chromosomes (allosomes).
In males,the sex chromosomes are $XY$,and in females,they are $XX$.
Therefore,the number of pair$(s)$ of sex chromosomes in the human zygote is $1$.

(D) The theory of evolution by natural selection was proposed by Charles Darwin.
He explained that individuals with variations that are better suited to their environment are more likely to survive and reproduce,a process known as natural selection.
Over generations,these advantageous traits become more common in the population,leading to evolution.

(A) The presence of feathers in both dinosaurs (reptiles) and birds suggests an evolutionary relationship.
Feathers were initially evolved in some dinosaurs for insulation or display,not for flight.
Later,these structures were adapted for flight in birds.
This indicates that birds share a common ancestor with these feathered dinosaurs,supporting the theory that birds have evolved from reptiles.

(N/A) The sex of an individual is genetically determined. Humans have $23$ pairs of chromosomes. Out of these,$22$ pairs are autosomes,and the $23$rd pair consists of sex chromosomes.
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 sex of the child depends on the chromosome contributed by the father:
$1$. If the father contributes an $X$ chromosome,the zygote becomes $XX$,resulting in a girl.
$2$. If the father contributes a $Y$ chromosome,the zygote becomes $XY$,resulting in a boy.

(B) No,the genetic combination of the mother does not play a significant role in determining the sex of a newborn.
Human females have a pair of $X$ chromosomes $(XX)$.
All children,whether boys or girls,will inherit an $X$ chromosome from their mother.
The sex of the child is determined by the chromosome inherited from the father; if the father contributes an $X$ chromosome,the child is a girl $(XX)$,and if he contributes a $Y$ chromosome,the child is a boy $(XY)$.

(N/A) Fossils provide evidence of the existence of ancient species that are now extinct.
$(b)$ Fossils help in establishing evolutionary relationships and lineages between modern organisms and their ancestors.
$(c)$ Fossils allow scientists to determine the geological time period in which specific organisms lived by analyzing the strata of sedimentary rocks.

(D) Human females have two $X$ chromosomes,which are their sex chromosomes.
During the process of meiosis,which occurs during gamete formation,the homologous pair of $X$ chromosomes separates.
As a result,each egg cell (ovum) receives exactly one $X$ chromosome.
Since females are homogametic $(XX)$,they produce only one type of gamete,all of which contain an $X$ chromosome.

(N/A) The sex of an infant is determined by the type of sex chromosome contributed by the male gamete. Human males produce two types of gametes: $50\%$ containing the $X$ chromosome and $50\%$ containing the $Y$ chromosome. When a sperm carrying the $X$ chromosome fertilizes an egg,the resulting zygote develops into a female $(XX)$. When a sperm carrying the $Y$ chromosome fertilizes an egg,the resulting zygote develops into a male $(XY)$. Since there is an equal chance of either an $X$-carrying or $Y$-carrying sperm fertilizing the egg,the statistical probability of having a male or female child is $50 : 50$.

(N/A) small population size leads to a higher frequency of inbreeding among individuals. This reduces the genetic diversity and limits the appearance of new variations within the population. Consequently,the species becomes less adaptable to sudden changes in the environment. Because the individuals lack the necessary genetic variation to cope with these environmental shifts,the population is at a higher risk of extinction.

(N/A) Homologous structures are those organs or body parts that share a common basic structural design and developmental origin but perform different functions in different organisms.
Example: The forelimbs of humans,whales,bats,and cheetahs have the same basic skeletal structure (humerus,radius,ulna,carpals,metacarpals,and phalanges) but are adapted for different functions like grasping,swimming,flying,and running,respectively.
Yes,it is necessary that homologous structures have a common ancestor. This phenomenon is known as divergent evolution,where structures evolved from a common ancestral form and were modified over time to suit different environmental needs.

(N/A) The occurrence of diversity of animals on Earth does not necessarily imply diverse ancestry. According to the theory of evolution,many diverse species share a common ancestor. This is known as adaptive radiation or divergent evolution,where organisms evolve from a common ancestor to adapt to different environments. While diversity is vast,molecular and genetic evidence often points to shared evolutionary lineages. Therefore,diversity in form and function is a result of natural selection acting on populations over millions of years,rather than an indication of multiple independent origins.

(N/A) The contrasting traits for the given characters in a pea plant are as follows:
$(i)$ Seed color: The contrasting pair is Yellow and Green.
- Yellow is the dominant trait.
- Green is the recessive trait.
$(ii)$ Seed shape: The contrasting pair is Round and Wrinkled.
- Round is the dominant trait.
- Wrinkled is the recessive trait.

(D) Gregor Mendel chose the pea plant $(Pisum \text{ } sativum)$ for his experiments due to several key reasons:
$1$. Short life cycle: The plant completes its life cycle in a short period, allowing for the study of several generations in a limited time.
$2$. Easily detectable contrasting traits: The pea plant exhibits several clearly defined, contrasting characters (e.g., tall/dwarf, round/wrinkled seeds).
$3$. Ease of pollination: The flowers are bisexual and naturally self-pollinating, but they can also be easily cross-pollinated artificially for experimental purposes.
$4$. Large number of offspring: Each plant produces a large number of seeds, which provides sufficient data for statistical analysis.
Therefore, all the given factors contributed to his choice.

(N/A) The sex of a child is determined by the sex chromosomes inherited from the parents.
$(a)$ $A$ woman is homogametic,meaning she produces only one type of ovum containing the $X$ chromosome.
$(b)$ $A$ man is heterogametic,meaning he produces two types of sperms: $50\%$ containing the $X$ chromosome and $50\%$ containing the $Y$ chromosome.
$(c)$ If a sperm carrying the $X$ chromosome fertilizes the ovum,the zygote will be $XX$ (female).
$(d)$ If a sperm carrying the $Y$ chromosome fertilizes the ovum,the zygote will be $XY$ (male).
$(e)$ Therefore,the father is responsible for the sex of the child. If a woman has only daughters,it implies that in every fertilization event,the sperm carrying the $X$ chromosome successfully fertilized the ovum,or the sperm carrying the $Y$ chromosome failed to produce a viable male zygote.

(YES) Yes,geographical isolation gradually leads to genetic drift. This may impose limitations on sexual reproduction of the separated population. Slowly,the separated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

(N/A) The concept of evolution does not necessarily imply a progression from simple to complex organisms.
$1$. If we define evolution based on morphological complexity,then human beings appear more evolved than bacteria.
$2$. However,bacteria are highly successful organisms that have survived for billions of years in diverse and extreme environments.
$3$. They possess efficient metabolic pathways and rapid reproductive rates,which are evolutionary advantages.
$4$. Therefore,evolution is not a linear process of increasing complexity,but rather a process of adaptation to the environment. Both bacteria and humans are highly evolved in their respective ecological niches.

(N/A) The evidence supporting the common ancestry of all human races includes:
$1$. Common body plan: All humans share the same basic anatomical structure,including the skeletal system,organ systems,and body organization.
$2$. Constant chromosome number: All human beings possess $46$ chromosomes ($23$ pairs),which is a fundamental characteristic of the species $Homo$ $sapiens$.
$3$. Common genetic blueprint: The $DNA$ sequence is remarkably similar across all human populations,indicating a shared evolutionary history.
$4$. Physiological and metabolic similarity: All human races exhibit identical physiological processes and metabolic pathways.
$5$. Ability to interbreed: All human races can freely interbreed and produce fertile offspring,which is the biological definition of belonging to the same species.

(N/A) Inherited characters are traits that are genetically passed from parents to offspring through $DNA$. These traits are present from birth and are encoded in the germ cells. Example: Eye colour or hair texture.
Acquired characters are traits that an individual develops during their lifetime due to environmental factors,lifestyle,or physical changes. These traits are not encoded in the $DNA$ of germ cells and therefore cannot be transmitted to the next generation. Example: Learning a skill like cycling or loss of a finger due to an accident.

(N/A) Acquired characters are changes that occur in the somatic cells of an organism during its lifetime due to environmental factors or usage/disuse of organs.
These changes do not affect the $DNA$ of the germ cells (reproductive cells).
Since only the information present in the $DNA$ of germ cells is passed on to the next generation,acquired characters cannot be inherited.
Only those traits that are encoded by genes in the germ cells are heritable.

(N/A) The statement is correct. While organisms show immense diversity in their size,form,and morphological features due to adaptation to different environments,the molecular machinery remains highly conserved. At the molecular level,diverse organisms exhibit remarkable similarity. For instance,the fundamental biomolecules such as $DNA$,$RNA$,proteins,and carbohydrates are structurally and functionally similar across almost all living organisms. This suggests that while morphological traits evolve rapidly to suit ecological niches,the core molecular processes are essential for life and have remained stable throughout evolutionary history.

$(a)$ Since both parents are homozygous dominant $(RR YY)$,all offspring will be $RR YY$,which are Round and Yellow.
$(b)$ This is a dihybrid cross of heterozygous parents $(Rr Yy)$. According to Mendel's law of independent assortment,the phenotypic ratio is $9:3:3:1$. The progeny will be: Round and Yellow,Round and Green,Wrinkled and Yellow,and Wrinkled and Green.
$(c)$ Since both parents are homozygous recessive $(rr yy)$,all offspring will be $rr yy$,which are Wrinkled and Green.
$(d)$ This is a cross between homozygous dominant and homozygous recessive parents. All offspring will be heterozygous $(Rr Yy)$,which are Round and Yellow.

(RRYY) In a dihybrid cross,the $F_1$ generation consists of heterozygous individuals with the genotype $RrYy$. Self-pollination of the $F_1$ generation involves crossing $F_1$ individuals with each other. Therefore,the cross is $RrYy \times RrYy$. The blank should be filled with $RrYy$.

(D) The cross represents a dihybrid cross. The $F_1$ generation is self-pollinated,so the cross is $RrYy \times RrYy$.
The combinations of characters in the $F_2$ progeny and their phenotypic ratios are:
$(i)$ Round,yellow: $9$
$(ii)$ Round,green: $3$
$(iii)$ Wrinkled,yellow: $3$
$(iv)$ Wrinkled,green: $1$
The phenotypic ratio is $9 : 3 : 3 : 1$.

(N/A) $(i)$ Characters are controlled by genes.
$(ii)$ Each gene controls one character.
$(iii)$ There may be two or more forms of the gene (alleles).
$(iv)$ 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 (Law of Segregation).
$(viii)$ The two forms are brought together in the zygote during fertilization.

(B) The appearance of new combinations of characters in the $F_2$ progeny is due to the Law of Independent Assortment.
According to Mendel's dihybrid cross,when two pairs of contrasting traits are considered,the inheritance of one pair of traits is independent of the inheritance of the other pair.
This means that during gamete formation,the alleles of different genes segregate independently,leading to new combinations of traits such as round-green or wrinkled-yellow seeds in the $F_2$ generation,which were not present in the parents.

(N/A) The primary reason for this situation is $Natural \text{ } Selection$. Green beetles are better adapted to their environment (e.g., green leaves) as they are camouflaged from predators. Consequently, they survive more frequently and reproduce more successfully than blue or red beetles, leading to an increase in their population over generations.

(B) The reappearance of dwarf plants in the $F_{2}$ generation indicates the Law of Segregation. According to this law,the alleles of a gene pair segregate from each other during the formation of gametes,so that each gamete carries only one allele for each character. Even though the recessive trait (dwarfness) is masked in the $F_{1}$ generation,it reappears in the $F_{2}$ generation because the alleles do not blend and remain distinct.

(C) Human beings possess a total of $46$ chromosomes, which are organized into $23$ pairs.
Out of these, $22$ pairs are autosomes, and $1$ pair consists of sex chromosomes ($XX$ in females and $XY$ in males).