Genetics 2019
1.) Answer any ten questions from the following:
a) State the law of segregation.
Ans→ Law of Segregation states that during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
b) What is incomplete dominance?
Ans→ Incomplete dominance is a form of gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype.
c) What do you mean by Epistasis?
Ans→ Epistasis describes the phenomenon when one gene affeels the phenotype of another gene. Where the expression of one gene is masked / inhibited suppressed) by the expression of another gene.
d) What do you mean is sex linked inheritance?
Ans→ Sex linked inheritance is the transmission of traits from parents to offspring through genes on the sex-chromosomes.
Examples: Red-green colorblindness; Hemophilia A
e) What do you mean by test cross?
Ans→ Test cross is a cross between an individual with an unknown genotype with a homozygous recessive gene.
Example: When a tall plant (TT) is crossed with a dwarf plant (tt).”
f) State what is pleiotropic effect.
Ans→ Pleiotropic effect is a genetic phenomenon where a single gene affects the expression of multiple traits.
Example: Sickle cell anaemia, Phenylketonuria.
g) Define map unit.
Ans→ Map unit (mu) is the distance between genes based on the average number of crossover frequencies between them. Map unit (m.u.) is a unit of measurement for genetic linkage on chromosomes.
It is also known as centimorgan (cM).
h) State the function of Kappa particle.
Ans→ Kappa particles produce poisonous substances (paramecin) used for self defence.
i) What is gynandromorph?
Ans→ Gynandromorphs are individuals that contain both male (XO) character in one part and female (XX) character in another part, but have external characters of only one gender.
Example: It occurs in species such as insects, crustaceans & birds.
j) What is Holliday Junction?
Ans→ Holiday Junction is a four way junction in DNA that connects two duplex DNA structures which is a key intermediate in the homologous recombination.
It is required for repair of double strand breaks in DNA.
k) State the function of SRY.
Ans→ SRY gene encodes a protein, TDF, which triggers the development of male characteristics by promoting the formation of testes in the early embryonic stage.
l) Enumerate the role of sox gene
Ans→ Sox gene function as transcription factors, helps in regulating gene expression during development and cell differentiation.
m) What do you mean by frameshift mutation?
Ans→ A frameshift mutation is a genetic alteration that shifts the reading frame of a gene, resulting in changes to the amino acid sequences.
n) What is pericentric inversion?
Ans→ The segment of a chromosome including centromere is rearranged inversely then it is called pericentric inversion.
o) What do you mean by transposons?
Ans→ Transposons on ‘jumping gene’ is a DNA sequence that can move or jump to different positions within a genome.
- Answer any five questions from the following:
a) Distinguish between Transition and Transversion.
Ans→
| Transition | Transversion |
| A point mutation in which one base is replaced by another of the same class (Purine and Pyrimidine). | A point mutation in which a purine is replaced by Pyramid or vice versa. |
| Base change occurs within the same class. | Best change occurs from one class to another. |
| There are 8 possible types. | There are 4 possible types |
| A particular base can undergo a single type of transition. | A base undergoes two types of transversion. |
b) Differentiated between sex limited, and sex influenced character.
Ans→
| Sex limited | Sex Influenced |
| 1.) Sex limited characters are traits that are observed exclusively in one sex. | 1.) Sex influence characters are traits that are influenced by the sex of the individual expressed differently in male and female. |
| 2.) Traits are typically controlled by jeans present on sex chromosome. | 2.) Some genetic variant express differently best on the sex of the individual. |
| 3.) Example: Antlers in male deer (only males poses and antlers) | 3.) Example: Male pattern baldness gene associated with baldness may have differently expression pattern in male and female. |
c) What is Tautomerism?
Ans→ Tautomerism is a phenomenon where single chemical compound differ from one another based on the position of proton and double bond.
Example: Keto-enol and amino-imino tautomerism are spontaneous mutations of DNA.
d) What is thymine dimer and state its function.
Ans→ Thymine dimer is a covalently bonded complex of two adjacent thymines on a single strand of DNA [ [They are also called cyclobutane pyrimidine dimers (CPDs)]
Function: Thymine dimers inhibit DNA replication, may lead to mutation and subsequent cancer development.
e) State the correlation that exists between interference and coincidence.
Ans→ Interference and coincidence are inversely related in genetic recombination. High interference reduces the likelihood of double crossovers, resulting in low coincidence, while low interference allows more double crossovers, leading to high coincidence.
f) Mention the role of TDF in determination of sex in human.
Ans→ TDF (Testis-Determining Factor), encoded by the SRY gene on the Y chromosome, triggers the development of testes in humans, leading to male sexual differentiation.
g) Explain secondary non-disjunction with suitable examples.
Ans→ Secondary non-disjunction occurs during the second meiotic division (meiosis II) when sister chromatids fail to separate properly. This results in abnormal gametes with an incorrect number of chromosomes.
Example:In humans, secondary nondisjunction can lead to conditions like trisomy 21 (Down syndrome) if the gamete with an extra chromosome 21, fertilizes a normal gamete.
h) Differentiate between complete and incomplete linkage.
Ans→
| Complete Linkage | Incomplete Linkage | |
| 1.) Definition | Genes are very close on the same chromosome and do not undergo crossing over. | Genes are on the same chromosome but can undergo crossing over. |
| 2.) Recombination | No recombination occurs between linked genes. | Partial recombination occurs due to crossing over. |
| 3.) Gamete Types | Produces only parental gametes | Produces both parental and recombinant gametes. |
| 4.) Proportion of Gametes | 100% parental. | Parental gametes are more frequent than recombinant gametes. |
| 5.) Example | Found in Drosophila males. | Found in Drosophila females. |
Genetics 2020
1.) a) Define allele.
Ans→ Allele is a variant form of a gene that occupies a specific position (locus) on a chromosome.
b) State the law of segregation.
Ans→ Law of Segregation states that during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
c) Define back cross.
Ans→ Back cross is cross between hybrid individual with one of its parent or individuals genetically similar to its parent.
d) What do you mean by ‘Epistasis’?
Ans→ Epistasis describes the phenomenon when one gene affeels the phenotype of another gene. Where the expression of one gene is masked / inhibited suppressed) by the expression of another gene.
e) What are LINES?
Ans→ Long interspersed nuclear elements are a group of non-TLR retrotransposone have the ability to replicate themselves and move to different position within the genome.
f) What are epigenetic modifications?
Ans→ Epigenetic modification are changes to DNA or associated proteins that influence gene expression without altering the DNA sequence.
g) State the function of kappa particle.
Ans→ Kappa particles produce poisonous substances (paramecin) used for self defence.
h) Name two Y linked characters in human.
Ans→ Hypertrichosis of the ear, webbed toes
i) State the function of SRY.
Ans→ SRY gene encodes a protein, TDF, which triggers the development of male characteristics by promoting the formation of testes in the early embryonic stage.
j) What is paracentric inversion?
Ans→ The segment of chromosome without centromere rearranged inversely then it is called paracentric inversion.
k) What do you mean by transposon?
Ans→ Transposons on ‘jumping gene’ is a DNA sequence that can move or jump to different positions within a genome.
l) What is the role of photolyase in DNA repair?
Ans→ DNA photolyase converts the light energy to chemical energy to break the pyrimidine dimers in DNA during DNA repairing.
m) Give an example of polygenic inheritance.
Ans→ Skin colour, hair colour, height are some examples of polygenic inheritance.
n) What is ‘Alu’ element?
Ans→ Elements are non-autommonus, short transposable elements (type of SINEs) found in human genome rely on other elements for their transposition.
o) State the function of synaptonemal complex.
Ans→ The synaptonemal complex plays a crucial role during meiosis, facilitating the pairing of homologous chromosomes and promoting genetic recombination.
- a) Mention two differences between lytic and lysogenic cycle in bacteria.
Ans→
| Lytic Cycle | Lysogenic Cycle |
| The virus immediately replicates within the host, leading to the destruction of the host cell. | The viral genome integrates into the host’s DNA and remains dormant (provirus) for a period. |
| Results in the release of new viral particles. | The host cell divides normally, passing on the viral DNA to daughter cells. |
| Quick and results in cell death. | The virus may enter the lytic cycle later under certain conditions. |
b) What are mutagens and name a chemical mutagen?
Ans→ Mutagens are agents, such as chemicals, radiation, or biological factors, that cause changes (mutations) in the DNA sequence of an organism.
Example: Ethyl methanesulfonate (EMS), alcohol.
c) What do you mean by reciprocal crossing over?
Ans→ Reciprocal crossing over is the exchange of equal segments of genetic material between homologous chromosomes during meiosis, leading to genetic variation.
d) Distinguish between transition and transversion.
Ans→
| Transition | Transversion |
| A point mutation in which one base is replaced by another of the same class (Purine and Pyrimidine). | A point mutation in which a purine is replaced by Pyramid or vice versa. |
| Base change occurs within the same class. | Best change occurs from one class to another. |
| There are 8 possible types. | There are 4 possible types |
| A particular base can undergo a single type of transition. | A base undergoes two types of transversion. |
e) What is ‘Tautomerism’?
Ans→ Tautomerism is a phenomenon where single chemical compound differ from one another based on the position of proton and double bond.
Example: Keto-enol and amino-imino tautomerism are spontaneous mutations of DNA.
f) Explain secondary nondisjunction with suitable example.
Ans→ Secondary nondisjunction occurs during the second meiotic division (meiosis II) when sister chromatids fail to separate properly. This results in abnormal gametes with an incorrect number of chromosomes.
Example:In humans, secondary nondisjunction can lead to conditions like trisomy 21 (Down syndrome) if the gamete with an extra chromosome 21 fertilizes a normal gamete.
g) Differentiate between complete and incomplete linkage.
Ans→
| Complete Linkage | Incomplete Linkage | |
| 1.) Definition | Genes are very close on the same chromosome and do not undergo crossing over. | Genes are on the same chromosome but can undergo crossing over. |
| 2.) Recombination | No recombination occurs between linked genes. | Partial recombination occurs due to crossing over. |
| 3.) Gamete Types | Produces only parental gametes | Produces both parental and recombinant gametes. |
| 4.) Proportion of Gametes | 100% parental. | Parental gametes are more frequent than recombinant gametes. |
| 5.) Example | Found in Drosophila males. | Found in Drosophila females. |
h) What do you mean by nucleocytoplasmic inheritance?
Ans→ Nucleocytoplasmic inheritance refers to the transmission of genetic material from both the nucleus and cytoplasmic organelles (like mitochondria or chloroplasts) to offspring, influencing traits.
Genetics 2021
a) What is Chiasma?
Ans→ A chiasma is a point of contact of crossover or exchange of genetic material between homologous chromosomes during Meiosis occurring at the site where chromatids overlap.
b) Define test cross.
Ans→ Test cross is a cross between an individual with an unknown genotype with a homozygous recessive gene.
Example: When a tall plant (TT) is crossed with a dwarf plant (tt).”
c) State the role of Sox gene.
Ans→ Sox gene function as transcription factors, helps in regulating gene expression during development and cell differentiation.
d) Why is the genetic code a triplet code?
Ans→ The genetic code is a triplet code because three nucleotide bases (a codon) are required to specify one amino acid. This ensures enough combinations (64 codons) to code for all 20 amino acids.
e) Define frameshift mutation.
Ans→ A frameshift mutation is a genetic alteration that shifts the reading frame of a gene, resulting in changes to the amino acid sequences.
f) Define Gynandromorph.
Ans→ Gynandromorphs are individuals that contain both male (XO) character in one part and female (XX) character in another part, but have external characters of only one gender.
Example: It occurs in species such as insects, crustaceans & birds.
g) Define map unit.
Ans→ Map unit (mu) is the distance between genes based on the average number of crossover frequencies between them. Map unit (m.u.) is a unit of measurement for genetic linkage on chromosomes.
It is also known as centimorgan (cM).
h) What is pleiotropic effect?
Ans→ Pleiotropic effect is a genetic phenomenon where a single gene affects the expression of multiple traits.
Example: Sickle cell anaemia, Phenylketonuria.
i) State the function of kappa particle.
Ans→ Kappa particles produce poisonous substances (paramecin) used for self defence.
j) What is Holliday Junction?
Ans→ Holiday Junction is a four way junction in DNA that connects two duplex DNA structures which is a key intermediate in the homologous recombination.
It is required for repair of double strand breaks in DNA.
k) What is thymine dimer?
Ans→ A thymine dimer is a DNA lesion formed when two adjacent thymine bases bond covalently due to UV radiation, disrupting DNA structure and replication.
l) State the role of synaptonemal complex.
Ans→ The synaptonemal complex plays a crucial role during meiosis, facilitating the pairing of homologous chromosomes and promoting genetic recombination.
m) What are SINEs?
Ans→ SINEs are small non-autonomous transposable elements that rely on the enzymatic machinery of LINEs for their transposition present in the human genome.
n) What do you mean by lethal alleles?
Ans→ Lethal alleles are genetic variants that when present in certain combinations, result in the death of the organism carrying those alleles.
o) Indicate the number of Barr bodies in interphase cells of the individuals with – Turner syndrome.
Ans→ Individuals with Turner syndrome (45, X) have only one X chromosome, so there are no Barr bodies in their interphase cells.
2.) a) Differentiate between sex-linked and sex- influenced characters.
Ans→
| Sex-Linked Characters | Sex-Influenced Characters | |
| Location | Genes are located on the sex chromosomes (X or Y chromosome). | Genes are located on autosomes (non-sex chromosomes). |
| Inheritance | Traits are inherited differently in males and females due to differences in sex chromosomes (e.g., X-linked traits are expressed more in males). | Expression is influenced by the hormonal environment and differs between males and females, even with the same genotype. |
| Gender Bias | Traits often show a specific gender bias, e.g., males are more affected in X-linked traits due to having one X chromosome. | Both genders can express the trait, but the severity or pattern may differ between sexes. |
| Examples | Hemophilia, color blindness (X-linked); hypertrichosis (Y-linked). | Baldness (dominant in males, recessive in females). |
b) What is retroposons?
Ans→ Retroposons are a type of transposable element that move within the genome by reverse transcription of an RNA intermediate into DNA, which is then inserted into a new location in the genome.
c) Distinguish between missense and non-sense mutation.
Ans→
| Missense Mutation | Nonsense Mutation |
| A single nucleotide change results in the substitution of one amino acid for another in the protein. | A single nucleotide change converts a codon into a stop codon, prematurely terminating protein synthesis. |
| Can affect the protein’s function depending on the nature of the substitution. | Often leads to a truncated, nonfunctional protein. |
d) What is polygenic inheritance?
Ans→ Polygenic inheritance is the genetic phenomenon where multiple genes contribute to the determination of a single trait, resulting in continuous variation, such as in height or skin colour.
e) Differentiate between incomplete dominance and codominance.
Ans→
| Incomplete Dominance | Co-dominance | |
| Definition | Both alleles contribute to a blending of traits in the offspring. | Both alleles are equally expressed in the offspring |
| Phenotype | The heterozygote exhibits an intermediate phenotype between the two homozygotes. | The heterozygote exhibits both parental phenotypes simultaneously. |
| Expression | Only one dominant allele is partially expressed. | Both alleles are fully expressed in the phenotype. |
| Example | Red and white flowers produce pink flowers (e.g., snapdragon). | Blood type AB, where both A and B alleles are equally expressed. |
f) “Drosophila flies that are XXY are fertile females” – Explain.
Ans→ In Drosophila (fruit flies), females typically have XX sex chromosomes, and males have XY. XXY flies have an extra X chromosome, which is usually associated with sterility in many species, but in Drosophila, the presence of two X chromosomes and one Y chromosome still allows normal female development. These XXY flies are considered fertile females because the extra X chromosome does not prevent the proper functioning of female traits
g) Distinguish between composite and non- composite transposons.
Ans→
| Composite Transposons | Non-Composite Transposons | |
| Structure | Consist of two inverted repeat sequences at the ends, with a central region containing antibiotic resistance genes. | Composed of only inverted repeats at both ends, with no additional surrounding genes. |
| Genetic Material | Can carry additional genes, such as those for antibiotic resistance. | Generally contain only genes required for transposition (e.g., transposase gene). |
| Transposition Mechanism | Transposition occurs via cut-and-paste mechanism. | Can follow both cut-and-paste or replicative transposition mechanisms. |
| Movement | Often move as a unit; the two IS sequences at either end help mediate the transposition process. | Can transpose independently without the need for additional elements. |
h) Explain Holandric sex linkage.
Ans→ Holandric sex linkage refers to the inheritance of genes located on the Y chromosome, which are passed from father to son only. These genes do not affect females, as they do not possess a Y chromosome. Holandric traits are inherited exclusively through the male lineage.
Genetics 2022
a) Define back cross.
Ans→ Back cross is cross between hybrid individual with one of its parent or individuals genetically similar to its parent.
b) What do you mean by Epistasis?
Ans→ Epistasis describes the phenomenon when one gene affeels the phenotype of another gene. Where the expression of one gene is masked / inhibited suppressed) by the expression of another gene.
c) State the function of synaptonemal complex.
Ans→ The synaptonemal complex plays a crucial role during meiosis, facilitating the pairing of homologous chromosomes and promoting genetic recombination.
d) What do you mean by Aneuploidy?
Ans→ Aneuploidy is the genetic condition where an organism has an abnormal number of chromosomes in their genome.
Examples: Monosomy- (Turner’s Syndrome); Trisomy (Down Syndrome)
e) What is specialized transduction?
Ans→ Transduction is the transfer of genetic material between bacteria through a virus (bacteriophage) as a vector, integrating foreign DNA into the bacterial genome.
f) What do you mean by sex-limited genes?
Ans→ Sex limited genes that are present in both success but only functional or expressed in one sex due to hormonal or developmental factors.
g) Define suppressor mutation.
Ans→ A suppressor mutation is a genetic change that compensates for the effects of another mutation, restoring the original phenotype or reducing the severity of the mutation’s effect.
h) State the function of SRY.
Ans→ SRY gene encodes a protein, TDF, which triggers the development of male characteristics by promoting the formation of testes in the early embryonic stage.
i) Define multiple allele.
Ans→ Multiple alleles refer to the presence of more than two alternative forms of a gene within a population, although an individual can carry only two alleles for that gene.
Example: ABO blood group
j) What is the relationship between linkage and distance?
Ans→ In genetics, linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together. Distance between genes is inversely proportional to their likelihood of being linked:
- Shorter distance = Higher linkage (less likely to recombine).
- Longer distance = Lower linkage (more likely to recombine due to crossing over).
Or… Linkage ∝ 1/Distance
k) What is holandric trait?
Ans→ A holandric trait is a characteristic determined by genes located on the Y chromosome and is passed only from father to son.
l) What are bacteriocins?
Ans→ Bacteriocins are proteins produced by bacteria that inhibit or kill other closely related bacterial strains.
m) Define Law of Independent Assortment.
Ans→ The Law of Independent Assortment states that alleles of different genes assort independently of each other during the formation of gametes, provided the genes are located on different chromosomes.
n) What do you mean by transposons?
Ans→ Transposons on ‘jumping gene’ is a DNA sequence that can move or jump to different positions within a genome.
o) What is point mutation?
Ans→ A point mutation is a genetic change where a single nucleotide in DNA or RNA is altered, inserted, or deleted.
- a) Distinguish between transition and transversion.
Ans→
| Transition | Transversion |
| A point mutation in which one base is replaced by another of the same class (Purine and Pyrimidine). | A point mutation in which a purine is replaced by Pyramid or vice versa. |
| Base change occurs within the same class. | Best change occurs from one class to another. |
| There are 8 possible types. | There are 4 possible types |
| A particular base can undergo a single type of transition. | A base undergoes two types of transversion. |
b) What is “Tautomerism”?
Ans→ Tautomerism is a phenomenon where single chemical compound differ from one another based on the position of proton and double bond.
Example: Keto-enol and amino-imino tautomerism are spontaneous mutations of DNA.
c) Why are haemophilic women are rare to find?
Ans→ Haemophilic women are rare because haemophilia is an X-linked recessive disorder. Women have two X chromosomes, so they would need mutations on both copies to have the condition, which is uncommon. Most women with one affected X chromosome are just carriers.
d) If you cross a white eyed female Drosophila with a red eyed male Drosophila, what will be the colour of the eyes for their male and female offspring?
Ans→ Here is the genetic cross for a white-eyed female (XʷXʷ) and a red-eyed male (XᴿY):
| Xʷ (from mother) | Xʷ (from mother) | |
| Xᴿ (from father) | XᴿXʷ | XᴿXʷ |
| Y (from father) | XʷY | XʷY |
Offspring Phenotypes:
- Females: 100% red-eyed (XᴿXʷ).
- Males: 100% white-eyed (XʷY).
e) Mention two differences between lytic and lysogenic cycle in bacteria.
Ans→
| Lytic Cycle | Lysogenic Cycle |
| The virus immediately replicates within the host, leading to the destruction of the host cell. | The viral genome integrates into the host’s DNA and remains dormant (provirus) for a period. |
| Results in the release of new viral particles. | The host cell divides normally, passing on the viral DNA to daughter cells. |
| Quick and results in cell death. | The virus may enter the lytic cycle later under certain conditions. |
f) Mention two criteria for extra chromosomal inheritance.
Ans→(i) Maternal Inheritance: Traits are inherited exclusively from the mother, as the cytoplasmic organelles (like mitochondria and chloroplasts) are passed through the egg.
(ii) Non-Mendelian Segregation: Inheritance patterns do not follow Mendel’s laws due to genes being located outside the nucleus.
g) What is difference between interference and coincidence?
Ans→ Interference:
- Definition: The phenomenon where the occurrence of one crossover reduces the likelihood of another crossover in the same region.
- Measurement: Calculated as 1 – coefficient of coincidence.
- Value: Ranges from 0 (no interference) to 1 (complete interference).
- Purpose: Explains why double crossovers are less frequent than expected.
Coincidence:
- Definition: The actual frequency of observed double crossovers relative to the expected frequency.
- Measurement: Calculated as (observed double crossovers) ÷ (expected double crossovers).
- Value: Ranges from 0 (no coincidence, no double crossovers occur) to 1 (expected double crossovers occur exactly).
- Purpose: Helps assess the accuracy of genetic distance predictions.
h) Write the problems related to frameshift mutation.
Ans→ Frameshift mutations cause:
- Altered protein structure: By shifting the reading frame, they produce nonfunctional or truncated proteins.
- Genetic disorders: Linked to diseases like cystic fibrosis and Tay-Sachs.
- Severe functional disruption: May affect essential cellular processes.