Statement I: A father can never pass an X-linked recessive trait directly to his son.
Statement II: Sons inherit their X chromosome exclusively from their mothers.
- Statement II correct
- Statement I correct
- Both are correct
- Both are incorrect
Explanation: Both are true. Since a father provides only the Y chromosome to his son, he cannot pass an X-linked trait to him. (Avoided 'explanation' as A format).
Mendel’s work remained unrecognized for many years primarily because:
- Lack of experiments
- Poor documentation
- He used animals
- Mathematical approach
Explanation: His use of statistics and mathematics to explain biological phenomena was totally new and unacceptable to many contemporary biologists.
According to Mendel’s Law of Segregation, the two alleles for a trait are separated during which biological process?
- Gamete formation
- Seed germination
- Vegetative propagation
- Cellular respiration
Explanation: The Law of Segregation states that the two alleles for a heritable character segregate during gamete formation and end up in different gametes.
The physical appearance or observable characteristics of an organism is called its:
- Phenotype
- Genotype
- Karyotype
- Haplotype
Explanation: Phenotype refers to the observable physical properties of an organism; Genotype refers to the underlying genetic makeup.
If a color-blind man marries a woman with normal vision (non-carrier), what is the probability of their sons being color-blind?
- 50 percent
- 0 percent
- 100 percent
- 25 percent
Explanation: A father passes his Y chromosome to his sons. Since color blindness is X-linked, he cannot pass it to his sons; they will have normal vision.
The term 'Homozygous' refers to an individual that has:
- Identical alleles
- Different alleles
- Extra chromosomes
- No alleles
Explanation: Homozygous means having two identical alleles for a particular gene (e.g., TT or tt).
Which of the following violates Mendel’s Law of Independent Assortment?
- Polygenic inheritance
- Pleiotropy
- Linkage
- Codominance
Explanation: Linkage occurs when genes are located close together on the same chromosome and tend to be inherited together, violating independent assortment.
Which cross is performed by swapping the sources of male and female gametes for the same traits?
- Monohybrid cross
- Back cross
- Reciprocal cross
- Test cross
Explanation: In a reciprocal cross, the phenotypes of the male and female parents are reversed to see if the sex of the parent influences inheritance.
Which of the following represents the 'Genotype' of an organism?
- Tall stature
- Yellow seeds
- The letters 'Tt'
- Axillary flowers
Explanation: Genotype refers to the specific genetic makeup (alleles) of an individual, usually represented by symbols.
For a female to express an X-linked recessive trait like Hemophilia, her genotype must be:
- Homozygous recessive
- Heterozygous
- Hemizygous
- Homozygous dominant
Explanation: Since females have two X chromosomes, they must have the recessive allele on both ($X^{h}X^{h}$) to express the disease.
Mendel’s Law of Independent Assortment is best demonstrated by which type of genetic cross?
- Dihybrid cross
- Reciprocal cross
- Monohybrid cross
- Back cross
Explanation: Independent Assortment describes how different genes independently separate from one another when reproductive cells develop, observed in dihybrid crosses.
A cross between a homozygous dominant and a homozygous recessive individual results in an $F_1$ generation that is:
- All heterozygous
- Homozygous recessive
- Homozygous dominant
- Fifty percent each
Explanation: Crossing $AA imes aa$ results in 100% $Aa$ offspring.
A woman who is a carrier for hemophilia (XHXh) marries a normal man (XHY). What percentage of their daughters will be hemophilic?
- 0 percent
- 100 percent
- 50 percent
- 25 percent
Explanation: Daughters inherit an X from the father. Since he is normal (XH), all daughters will have at least one normal allele and won't be hemophilic.
Why are sex-linked recessive traits like color blindness more frequently observed in human males?
- Lack of autosomes
- Hormonal differences
- Y chromosome dominance
- Single X chromosome
Explanation: Males are hemizygous (XY). A single recessive allele on their lone X chromosome is sufficient to express the trait, unlike females (XX).
In a monohybrid cross between two heterozygous (Tt) pea plants, what is the expected phenotypic ratio?
Explanation: A monohybrid cross of Tt x Tt results in 75% dominant (TT, Tt) and 25% recessive (tt) phenotypes, creating a 3:1 ratio.
Mendel’s Law of Independent Assortment is applicable to genes located on:
- Y chromosome only
- Different chromosomes
- X chromosome only
- Same chromosome
Explanation: Independent assortment occurs because homologous chromosome pairs align randomly during meiosis, provided the genes are on different chromosomes.
Mendel’s 'Factors' that are passed from parents to offspring are known today as:
- Chromatids
- Alleles
- Genes
- Proteins
Explanation: Mendel used the term 'factors'. We now know these are discrete units of inheritance called genes.
Mendel's Law of Segregation is based on the fact that alleles do not show any:
- Dominance
- Mutation
- Assortment
- Blending
Explanation: Alleles do not blend; both traits are recovered as such in the $F_2$ generation even though one is hidden in $F_1$.
When an F1 hybrid is crossed with either of its parents, the cross is known as a:
- Test cross
- Reciprocal cross
- Back cross
- Monohybrid cross
Explanation: A back cross is a cross between a hybrid and one of its parental genotypes.
The term 'Allele' is defined as:
- Alternative gene forms
- A protein type
- DNA sequence
- Chromosomal arm
Explanation: Alleles are slightly different forms of the same gene that code for a pair of contrasting traits.
Who among the following was NOT involved in the rediscovery of Mendel’s laws in 1900?
- Hugo de Vries
- Thomas Hunt Morgan
- Carl Correns
- Erich von Tschermak
Explanation: De Vries, Correns, and Tschermak independently rediscovered Mendel’s work. Morgan later provided experimental evidence through his work on Drosophila.
What is the genotypic ratio of a monohybrid cross in the F2 generation?
Explanation: While the phenotypic ratio is 3:1, the genotypic ratio is 1 (TT) : 2 (Tt) : 1 (tt).
Which of the following represents a dihybrid genotype?
Explanation: A dihybrid is an individual that is heterozygous for two different genes.
In sex-linked inheritance, the 'carrier' female is one who:
- Expresses the trait
- Lacks X chromosomes
- Is homozygous dominant
- Has one allele
Explanation: A carrier has one recessive allele for the trait but does not express it because she has a dominant normal allele.
In birds, the mechanism of sex determination is defined as:
- Haplo-diploid system
- ZZ male / ZW female
- XX male / XO female
- XY male / XX female
Explanation: In birds, the female is heterogametic (ZW) and the male is homogametic (ZZ), which is the opposite of the human system.
Statement I: Queen Victoria was a carrier of Hemophilia.
Statement II: Hemophilia is a Y-linked disorder passed to her sons.
- Statement II correct
- Statement I correct
- Both are correct
- Both are incorrect
Explanation: Statement I is correct. Statement II is incorrect because Hemophilia is an X-linked recessive disorder, not Y-linked.
Which of the following conditions is an 'inborn error of metabolism' that follows Mendelian inheritance?
- Scurvy
- Night blindness
- Beri-beri
- Phenylketonuria
Explanation: PKU is an autosomal recessive disorder where the individual lacks an enzyme to convert phenylalanine into tyrosine.
In humans, the sex of a child is determined by the gamete contributed by:
- The environment
- The father
- The mother
- Both parents equally
Explanation: The mother always contributes an X chromosome. The father contributes either an X or a Y, determining the sex (XX or XY).
In a test cross of an $F_1$ dihybrid ($AaBb imes aabb$), what is the expected phenotypic ratio?
- 3:1
- 9:3:3:1
- 1:2:1
- 1:1:1:1
Explanation: A dihybrid test cross yields four phenotypic classes in equal proportions if the genes assort independently.
In Mendelian genetics, a cross between $F_1$ hybrids ($Tt imes Tt$) results in what percentage of tall plants?
- 25 percent
- 100 percent
- 50 percent
- 75 percent
Explanation: The phenotypic ratio is 3:1 (75% dominant tall, 25% recessive dwarf).
A 'true-breeding' plant is one that:
- Requires cross pollination
- Produces diverse offspring
- Is always heterozygous
- Produces identical offspring
Explanation: True-breeding lines have undergone continuous self-pollination and show stable trait inheritance for several generations (homozygous).
Which of the following is NOT a trait studied by Mendel in pea plants?
- Seed texture
- Pod shape
- Flower color
- Leaf size
Explanation: Mendel studied 7 traits: Stem height, Flower color, Flower position, Pod shape, Pod color, Seed shape, and Seed color.
A recessive trait is only expressed in an organism when it is in which state?
- Hemizygous only
- Homozygous
- Heterozygous
- None of above
Explanation: A recessive allele is masked by a dominant one and only appears phenotypically when two copies are present ($aa$).
Which chromosome is responsible for determining the male sex in humans through the SRY gene?
- Y chromosome
- Chromosome 21
- Mitochondrial DNA
- X chromosome
Explanation: The Y chromosome contains the SRY (Sex-determining Region Y) gene, which triggers male developmental pathways.
The phenomenon where a single gene can exhibit multiple phenotypic expressions is called:
- Codominance
- Pleiotropy
- Incomplete dominance
- Polygenic inheritance
Explanation: In pleiotropy, one gene influences multiple, seemingly unrelated phenotypic traits (e.g., Phenylketonuria).
According to the Law of Segregation, how many alleles for a specific gene does a single gamete contain?
Explanation: During meiosis, the two alleles of a gene pair segregate such that each gamete receives only one allele.
What was the primary reason Mendel chose the garden pea (Pisum sativum) for his experiments?
- Complex genome
- Distinct contrasting traits
- Requirement of cross-pollination
- Long lifespan
Explanation: Pea plants had easily observable, binary traits (e.g., tall vs dwarf, round vs wrinkled) and a short life cycle.
In Mendelian genetics, when an $F_1$ heterozygous tall plant ($Tt$) is self-pollinated, the reappearance of the dwarf phenotype in the $F_2$ generation definitively proves the biological law of:
- Segregation of alleles
- Blending of inheritance
- Independent assortment
- Chromosomal linkage
Explanation: The self-pollination of the $F_1$ hybrid ($Tt$) allows the recessive $t$ allele to segregate unblended from the $T$ allele and pair with another $t$, resulting in the reappearance of the dwarf phenotype in the $F_2$ generation.
The 'Factors' (Genes) in Mendel’s experiments are physically located on which cellular structures?
- Ribosomes
- Chromosomes
- Mitochondria
- Lysosomes
Explanation: As established by the chromosomal theory, genes are linear sequences of DNA located at specific loci on chromosomes.
Which scientist is credited with the 'Mutation Theory' based on work with Oenothera lamarckiana?
- Gregor Mendel
- Charles Darwin
- Hugo de Vries
- Thomas Morgan
Explanation: De Vries proposed that mutations are large, random, and directionless changes that lead to the formation of new species.
Which graphical representation is commonly used to calculate the probability of all possible genotypes of offspring in a genetic cross?
- Punnett square
- Pie chart
- Pedigree chart
- Histogram
Explanation: Developed by Reginald C. Punnett, it is a square diagram used to predict the genotypes of a particular cross or breeding experiment.
The transmission of a trait from a father to his grandson through his daughter is known as:
- Linear inheritance
- Y-linked inheritance
- Direct inheritance
- Criss-cross inheritance
Explanation: X-linked traits follow a criss-cross pattern where a father passes the gene to his daughter (carrier), who then passes it to her son.
In ABO blood grouping, the $I^A$ and $I^B$ alleles show which type of inheritance when present together?
- Codominance
- Incomplete dominance
- Epistasis
- Recessiveness
Explanation: In AB blood type, both A and B antigens are fully expressed on the surface of red blood cells.
A woman with normal vision, whose father was color-blind, is a genetic carrier. If she marries a man with normal vision, what is the statistical probability that their son will be color-blind?
- Exactly 0 percent
- Exactly 25 percent
- Exactly 50 percent
- Exactly 100 percent
Explanation: The woman inherited the mutated $X^c$ chromosome from her color-blind father, making her a carrier ($X^C X^c$). Since sons inherit their $Y$ chromosome from their father, the son has a 50% chance of receiving the $X^c$ chromosome from his mother, resulting in color blindness.
Which Mendelian law is also known as the 'Law of Purity of Gametes'?
- Law of Dominance
- Law of Segregation
- Independent Assortment
- Linkage Law
Explanation: It is called so because gametes carry only one allele for each gene, remaining 'pure' for that specific trait.
Mendel observed that the $F_1$ generation always resembled:
- The recessive parent
- A new intermediate
- The dominant parent
- Both parents equally
Explanation: In a cross between two contrasting true-breeding parents, the $F_1$ offspring only express the dominant trait.
A cross used to determine the unknown genotype of a dominant-phenotype individual is called a:
- Test cross
- Out cross
- Dihybrid cross
- Self cross
Explanation: A test cross involves crossing the unknown individual with a homozygous recessive individual to reveal the unknown genotype.
A human female with Turner syndrome has which chromosomal constitution?
- 44 + XO
- 44 + XXY
- 44 + XXX
- 44 + XYY
Explanation: Turner syndrome is caused by the absence of one of the X chromosomes, resulting in a 45-chromosome karyotype ($44+XO$).
Statement I: Sex-linked traits are only found on the Y chromosome.
Statement II: Most sex-linked traits in humans are associated with the X chromosome.
- Statement I correct
- Statement II correct
- Both are correct
- Both are incorrect
Explanation: Statement I is false; sex-linked can be X or Y. Statement II is correct because the X chromosome is much larger and carries more genes.
In a dihybrid cross involving two heterozygous parents (RrYy), what fraction of the offspring will show both recessive traits?
Explanation: In the 9:3:3:1 ratio, only 1 out of 16 individuals (rryy) expresses both recessive phenotypes.
In a cross between a red-flowered plant and a white-flowered plant, if all offspring are pink, this is an example of:
- Incomplete dominance
- Complete dominance
- Independent assortment
- Codominance
Explanation: Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the two homozygotes.
Traits that are exclusively passed from father to son are associated with which chromosome?
- Chromosome 21
- X chromosome
- Autosomes
- Y chromosome
Explanation: Y-linked traits (holandric traits) are passed directly from father to son as females do not possess a Y chromosome.
The 'Chromosomal Theory of Inheritance', which aligned Mendelian factors with chromosomes, was proposed by:
- Sutton and Boveri
- Hugo de Vries
- Morgan and Sturtevant
- Watson and Crick
Explanation: Walter Sutton and Theodore Boveri noted that the behavior of chromosomes was parallel to the behavior of genes used to explain Mendel’s laws.
Which Mendelian law is violated when two genes are physically linked together on the same chromosome?
- Independent Assortment
- Law of Dominance
- Law of Segregation
- Purity of Gametes
Explanation: Linked genes do not assort independently because they are inherited as a single unit, unless separated by crossing over.
Statement I: Mendel’s laws are universally applicable to all eukaryotic organisms without exception.
Statement II: Phenomena like linkage and incomplete dominance represent deviations from Mendelian patterns.
- Statement I correct
- Statement II correct
- Both are correct
- Both are incorrect
Explanation: Statement I is incorrect because linkage and polygenic inheritance deviate from Mendel's laws. Statement II is correct regarding these exceptions.
In a dihybrid cross, the 9:3:3:1 ratio represents the distribution of:
- Chromosomes
- Genotypes
- Alleles
- Phenotypes
Explanation: The 9:3:3:1 ratio refers to the phenotypic combinations in the F2 generation of a dihybrid cross.
The frequency of recombination between gene pairs on the same chromosome is a measure of:
- Mutation rate
- Chromosome length
- Distance between genes
- Gene size
Explanation: Alfred Sturtevant used the frequency of recombination to map the relative positions and distances of genes on a chromosome.
Which Mendelian law explains why a person with the genotype 'Tt' for height appears tall?
- Purity of Gametes
- Independent Assortment
- Law of Segregation
- Law of Dominance
Explanation: The Law of Dominance states that in a heterozygote, one trait (dominant) will conceal the presence of another trait (recessive).
Which of the following is a result of 'Criss-cross inheritance' in humans?
- Pattern baldness
- Hairy pinna
- Color blindness
- Down syndrome
Explanation: X-linked recessive traits show criss-cross inheritance, moving from father to daughter (carrier) to grandson.
Which of the following is a classic example of a sex-linked recessive disorder in humans?
- Down syndrome
- Hemophilia
- Sickle anemia
- Cystic fibrosis
Explanation: Hemophilia is an X-linked recessive disorder, meaning the gene is located on the X chromosome. It is more common in males.