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All questions of Principles of Inheritance & Variation for NEET Exam

Match column -I with column-ii and select the correct option from the codes given below
  • a)
    A - (i), B - (iv), C - (iii), D - (v)
  • b)
    A - (i), B - (iv), C - (ii), D - (v)
  • c)
    A - (iii), B - (ii), C - (iv), D - (v)
  • d)
    A - (ii), B - (v), C - (iii), D - (i)
Correct answer is option 'A'. Can you explain this answer?

Lead Academy answered
Dihybrid Cross is a genetic cross or breeding experiment in which two individuals or parent organisms that differ in two specific traits or alleles are crossed to observe the inheritance patterns of these traits in their offspring. 
Law of Segregation, proposed by Gregor Mendel, is one of the fundamental principles of classical genetics. It states that during the formation of gametes (sperm and egg cells), the two alleles (gene variants) for a given trait segregate or separate from each other, with each gamete receiving one allele. This law is also known as 'Law of Purity of Gametes'.
Law of Independent Assortment, also formulated by Gregor Mendel, is another fundamental principle of genetics. It states that genes located on different, non-homologous chromosomes segregate independently during the formation of gametes. In other words, the inheritance of one gene does not affect the inheritance of another gene, assuming they are located on different chromosomes. This law contributes to the genetic diversity of offspring by allowing for the assortment of different combinations of alleles. Dihybrid crosses are used to study the independent assortment of genes located on different chromosomes and help determine the probability of particular combinations of traits occurring in the offspring.
ABO Blood Group in Humans, is a classification system for human blood types based on the presence or absence of specific antigens (A and B) on the surface of red blood cells. This is an example of multiple allelism. This system is one of the most important in blood transfusion and transplantation medicine. There are four main blood types in the ABO system:
  • Type A: Red blood cells have A antigens on their surface.
  • Type B: Red blood cells have B antigens on their surface.
  • Type AB: Red blood cells have both A and B antigens on their surface.
  • Type O: Red blood cells have neither A nor B antigens on their surface.
Clear all your doubts with EduRev

 What can be the blood group of offspring when both parents have AB blood group? 
  • a)
    AB only
  • b)
    A, B and AB
  • c)
    A, B, AB and O
  • d)
    A and B only
Correct answer is option 'B'. Can you explain this answer?

Ananya Das answered
When both parents have blood group AB(IAIB) then offsprings can have blood groups A(IAIA),B(IBIB) or AB(IAIB) but not O as allele i is not present in any of the parents.

The characters which appear in the first filial generation are called
  • a)
    recessive characters
  • b)
    dominant characters
  • c)
    holandric characters
  • d)
    lethal characters
Correct answer is option 'B'. Can you explain this answer?

Meera Singh answered
In heterozygous individuals or hybrids, out of the two factors or alleles representing the alternate traits of a character, one is dominant and expresses itself in the hybrid or F1 generation. The other factor or allele is recessive and does not show its effect in the heterozygous individual (Principle of dominance).

Choose the correct statement about recombination and linkage
  • a)
    Complete linkage results in higher non-parental gene combinations than parental type
  • b)
    Recombination results in the generation of parental gene combinations
  • c)
    Genetic maps are constructed by using the frequency of recombination between gene pairs
  • d)
    T.H. Morgan constructed the first chromosome map
Correct answer is option 'C'. Can you explain this answer?

Prashanth Menon answered
Understanding Genetic Maps and Recombination
Genetic mapping is a fundamental concept in genetics that helps to determine the location of genes on chromosomes. The correct statement among the options given is:

Genetic maps are constructed by using the frequency of recombination between gene pairs.

Explanation of Option C
- **Recombination and Linkage**: Recombination occurs during meiosis when homologous chromosomes exchange genetic material. This process leads to the formation of new allele combinations. The frequency of recombination between two genes is inversely related to their physical distance on a chromosome.
- **Construction of Genetic Maps**: Genetic maps utilize the frequency of recombination to estimate the relative positions of genes. The more frequently two genes recombine, the farther apart they are likely to be. This is quantified as a percentage, known as recombination frequency, which helps in constructing a map.
- **T.H. Morgan's Contribution**: T.H. Morgan was pivotal in demonstrating the principles of linkage and recombination. He used fruit flies (Drosophila) to show how genes are inherited and developed the first chromosome maps based on recombination frequencies.

Why Other Options Are Incorrect
- **Option A**: Complete linkage results in only parental types, not higher non-parental combinations.
- **Option B**: Recombination generates non-parental combinations rather than parental ones.
- **Option D**: While Morgan constructed the first chromosome map, the statement does not directly relate to the role of recombination frequency, making option C the most accurate.

Conclusion
Understanding the role of recombination in genetic mapping is crucial for grasping how traits are inherited and how genetic diversity arises in populations.

In Mendelian dihybrid cross, when heterozygous Round Yellow are self crossed, Round Green offsprings are represented by the genotype
  • a)
    RrYy, RrYY, RRYy
  • b)
    Rryy, Rryy, rryy
  • c)
    rrYy, rrYY
  • d)
    Rryy, RRyy
Correct answer is option 'D'. Can you explain this answer?

Vivek Patel answered
A typical Mendelian dihybrid cross between yellow round (dominant) and green wrinkled (recessive plants) can be represented as follows:
Thus, round green (green round) offsprings are represented by genotypes yyRR and yyRr (or RRyy and Rryy).

In Antirrhinum (dog flower), phenotypic ratio in F2 generation for the inheritance of flower colour would be
  • a)
    3:1
  • b)
    1:2:1
  • c)
    1:1
  • d)
    2:1
Correct answer is option 'B'. Can you explain this answer?

Lavanya Menon answered
The inheritance of flower colour in the Antirrhinum majus (snapdragon or dog flower) is an example of incomplete or partial dominance. Incomplete dominance is the phenomenon in which neither of the two alleles of a gene is completely dominant over the other. In a cross between true-breeding redflowered (RR) and true-breeding white-flowered plants (rr), the F1 plants obtained were pink (Rr) coloured. When the F1 plants were self-pollinated, the F2 generation resulted in the ratio, 1(RR) Red : 2(Rr) Pink : 1(rr) White. The phenotypic ratios had changed from the normal 3:1 dominant : recessive ratio to 1:2:1. R was not completely dominant over r and this made it possible to distinguish Rr (pink) from RR (red) and rr (white).

Law of independent assortment can be explained with the help of
  • a)
    dihybrid cross
  • b)
    test cross
  • c)
    back cross
  • d)
    monohybrid cross
Correct answer is option 'A'. Can you explain this answer?

Bhavya Pillai answered
Explanation of Law of Independent Assortment with Dihybrid Cross:

Dihybrid Cross:
In a dihybrid cross, two different traits are studied simultaneously. For example, if we consider pea plants, we can study the inheritance of seed color (yellow or green) and seed shape (round or wrinkled) at the same time.

Law of Independent Assortment:
According to the law of independent assortment, alleles of different genes assort independently of each other during gamete formation. This means that the inheritance of one trait does not influence the inheritance of another trait.

Illustration with Dihybrid Cross:
When we perform a dihybrid cross between two heterozygous pea plants (YyRr x YyRr), where Y stands for yellow seed color, y stands for green seed color, R stands for round seed shape and r stands for wrinkled seed shape, we can observe the law of independent assortment in action.

Outcome of Dihybrid Cross:
The offspring of the dihybrid cross will exhibit a 9:3:3:1 phenotypic ratio, which means that 9 individuals will have both dominant traits, 3 individuals will have one dominant and one recessive trait, 3 individuals will have the other pair of dominant and recessive traits, and 1 individual will have both recessive traits.

Conclusion:
By observing the phenotypic ratio in the offspring of a dihybrid cross, we can understand how the law of independent assortment works. This phenomenon demonstrates how genes located on different chromosomes are inherited independently of each other, following Mendel's principles of inheritance.

Read the given statements and select the correct option
Statement 1: The law of segregation is one of the most important contributions to the biology
Statement 2: It introduced the concept of heredity factors as discrete physical entities which do not become blended.
  • a)
    Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1
  • b)
    Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1
  • c)
    Statement 1 is correct and statement 2 is incorrect
  • d)
    Both statement 1 and 2 are incorrect
Correct answer is option 'A'. Can you explain this answer?

Ananya Das answered
The principlem of segregation is the most fundamental principle of heredity that has universal application with no exception. Some workers like Bateson call the principal of segregation as the principle of purity of gametes because segregation of the two Mendelian factors of a trait result result in ametes receiving only one factor out of a pair. As a result gametes are always pure for a character. It is also known as law of non-mixing of alleles and can be demostrated through a monohybrid cross.

What is the probability of production of dwarf offsprings in a cross between two heterozygous tall pea plants?
  • a)
    Zero
  • b)
    50%
  • c)
    25%
  • d)
    100%
Correct answer is option 'C'. Can you explain this answer?

Moumita Datta answered
The probability of production of dwarf offspring in a cross between two heterozygous tall pea plants can be determined using the principles of Mendelian genetics and Punnett squares.

Mendelian Genetics and Punnett Squares:
Mendelian genetics is the study of how traits are inherited from one generation to the next. It is based on the principles proposed by Gregor Mendel, who performed experiments with pea plants in the 19th century. Mendel's laws state that traits are determined by genes, and these genes are inherited in predictable patterns.

A Punnett square is a tool used to determine the possible combinations of alleles (alternative forms of a gene) that can be produced from a cross between two individuals. It allows us to determine the genotypes and phenotypes of the offspring.

Cross Between Two Heterozygous Tall Pea Plants:
In this case, both pea plants are heterozygous for the tall trait. The tall trait is dominant over the dwarf trait, where T represents the allele for tall and t represents the allele for dwarf.

The genotypes of the two parents can be represented as follows:
Parent 1: Tt
Parent 2: Tt

Creating a Punnett Square:
To determine the possible genotypes and phenotypes of the offspring, we can create a Punnett square.

T t
T TT Tt
t Tt tt

Possible Combinations:
From the Punnett square, we can see that there are four possible combinations of alleles in the offspring:

- 1 TT (tall)
- 2 Tt (tall)
- 1 tt (dwarf)

Probability of Dwarf Offspring:
Out of the four possible combinations, only one combination (tt) represents the dwarf phenotype. Therefore, the probability of producing a dwarf offspring is 1 out of 4 possible combinations, which is 1/4 or 25%.

Conclusion:
The probability of production of dwarf offspring in a cross between two heterozygous tall pea plants is 25%. This is because the dwarf trait is recessive, and both parents carry one copy of the recessive allele.

Mendel law of independent assortment does not hold true for the genes that are located closely on
  • a)
    same chromosome
  • b)
    non-homologous chromosomes
  • c)
    X - chromosome
  • d)
    autosomes
Correct answer is option 'A'. Can you explain this answer?

Lavanya Menon answered
As per linkage experiments carried out by Morgan, the two linked genes do not always segregate independently of each other and F2 ratio deviated very significantly from 9:3:3:1 ratio (expected when two genes are independent). Hence, if linkage was known at the time of Mendel, he would riot have been able to explain law of independent assortment.

What will be the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus?
  • a)
    3:1
  • b)
    1:2:1
  • c)
    1:1
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
F1 or first filial or progeny is the generation of hybrids produced from a cross between the genetically different individuals called parents. A cross between homozygous and heterozygous parents for a single locus will produce 1:1 ratio of phenotypic features in F1 generation.

In mice, Y is the dominant allele for yellow fur and y is the recessive allele for grey fur. Since Y is lethal when homozygous, the result of cross Yy x Yy will be
  • a)
    3 yellow : 1 grey
  • b)
    2 yellow : 1 grey
  • c)
    1 yellow : 1 grey
  • d)
    1 yellow : 2 grey
Correct answer is option 'B'. Can you explain this answer?

Priya Menon answered
Given, that Y is dominant for yellow fur and y is recessive for grey fur, the cross between Yy and Yy will produce ratio of 1YY:2Yy:1yy. But as Y is lethal in homozygous condition, hence phenotypic ratio would be 2 yellow (Yy):1 grey (yy).

Today ________ are extensively used as a _______ point in the sequencing of whole genome
  • a)
    Pedigree charts, conclusive
  • b)
    Genetic maps, starting
  • c)
    Pedigree charts, starting
  • d)
    Genetic maps, conclusive
Correct answer is option 'B'. Can you explain this answer?

Amar Mehra answered
Understanding Genetic Maps
Genetic maps are crucial tools in the field of genomics, especially when it comes to sequencing whole genomes.
Definition of Genetic Maps
- Genetic maps represent the arrangement of genes and genetic markers on chromosomes.
- They are based on the frequency of recombination between genetic markers during gamete formation.
Role as a Starting Point
- Genetic maps serve as a foundational resource in genome sequencing projects.
- They help researchers identify the locations of genes and other important sequences, guiding the sequencing process.
Importance in Whole Genome Sequencing
- By providing a reference framework, genetic maps simplify the complex task of sequencing entire genomes.
- They enable the alignment of sequenced data to known genetic locations, enhancing accuracy.
Comparison with Pedigree Charts
- Pedigree charts illustrate family relationships and inheritance patterns but do not provide the genomic context necessary for sequencing.
- They are more useful in genetic counseling and tracing inheritance rather than in the technical aspects of genome sequencing.
Conclusion
- The statement's correct answer is "Genetic maps, starting" because genetic maps are indeed the essential tools that provide a starting point in the sequencing of whole genomes.
- Their utility in mapping genetic information makes them indispensable in modern genetics research.
Overall, understanding the role of genetic maps not only clarifies their significance in sequencing but also highlights their foundational importance in genomic studies.

Inheritance of roan coat in cattle is an example of
  • a)
    incomplete dominance
  • b)
    codominance
  • c)
    multiple allelism
  • d)
    none of these
Correct answer is option 'B'. Can you explain this answer?

Geetika Shah answered
Coat colour in short-horned cattle is an exampl of co-dominance. If a cattle with black coat is crossed with a cattle with white coat, the F1 hybrids possess neither black nor white coat colour, but have roan coat colour, where black and white patches appear separately. The effect is produced due to juxtaposition of small patches of red and white colour. Hence the alleles which are able to express themselves independently when present together are called codominant alleles and the inheritance pattern is called co-dominance. On inbreeding, the roan hybrids produce three types of cattle — red, roan and white in the ratio of 1:2:1.

What proportion of the offsprings obtained from cross AABBCC x AaBbCc will be completely heterozygous for all the genes segregated independently?
  • a)
    1/8
  • b)
    1/4
  • c)
    1/2
  • d)
    1/16
Correct answer is option 'A'. Can you explain this answer?

Preeti Iyer answered
Since one parent is homozygous AABBCC  the genotype formed will be only 1 type i.e. ABC. The other parent is heterozygous for all genes. About 1/8th or 12.5% of total offspring will be heterozygous at all three-locus.

Depending upon the distance between any two genes which is inversely proportional to the strength of linkage, cross overs will vary from
  • a)
    50−100%
  • b)
    0−50%
  • c)
    75−100%
  • d)
    100−150%
Correct answer is option 'B'. Can you explain this answer?

Isha Khanna answered
It is not possible to determine the exact number of crossovers based solely on the distance between two genes. The frequency of crossovers is influenced by several factors, including the specific genetic loci involved, the presence of recombination hotspots, and other genetic and environmental factors.

A couple has six daughters. What is the possibility of their having a girl next time?
  • a)
    10%
  • b)
    50%
  • c)
    90%
  • d)
    100%
Correct answer is option 'B'. Can you explain this answer?

Rohit Jain answered
The possibility of having a girl or boy child is equal i.e., 50% as 50% male gametes are Y type and 50% are X type. Fusion of egg with X type sperm will produce a girl child.

Morgan coined the term recombination to describe
  • a)
    Physical association of genes on a chromosome
  • b)
    Generation of new traits by mutation
  • c)
    Linkage of two genes on different chromosomes
  • d)
    Generation of non-parental gene combinations
Correct answer is option 'D'. Can you explain this answer?

Lead Academy answered
Morgan coined the term "recombination" to describe the generation of new, non-parental gene combinations due to crossing over during meiosis.

question 3 question is incomplete
ChatGPT
Apologies for the incomplete question. Here is the revised and complete version of

Which of the following statements accurately describes linked genes?
  • a)
    Linked genes are located near each other on the same chromosome, violate the law of independent assortment, and segregate together during meiosis.
  • b)
    Linked genes are located on different chromosomes, violate the law of independent assortment, and segregate independently.
  • c)
    Linked genes are located near each other on the same chromosome, do not violate the law of independent assortment, and segregate independently.
  • d)
    Linked genes are located on different chromosomes, do not violate the law of independent assortment, and segregate together during meiosis.
Correct answer is option 'A'. Can you explain this answer?

EduRev NEET answered
Linked genes are those located near each other on the same chromosome. This proximity means that they do not assort independently and tend to segregate together during meiosis, which violates the law of independent assortment. Thus, Option A accurately describes linked genes.

Linkage was described by Morgan in Drosophila. Which of the following combinations are correct?
  • a)
    (ii), (iv), (v)
  • b)
    (i), (iii)
  • c)
    (i), (iii), (v)
  • d)
    (i) and (iv)
Correct answer is option 'B'. Can you explain this answer?

Mohit Rajpoot answered
Morgan observed that in his experiments with Drosophila, the F2 generation did not exhibit the expected 9:3:3:1 ratio due to linkage, with parental combinations being more frequent than recombinants. He attributed linkage to the physical association of genes on the same chromosome, not their chemical association. Thus, options (i) and (iii) are correct.

"When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters is independent of the other pair of characters." The statement is independent of the other pair of characters. The statement explains which of the following laws/principles of Mendel?
  • a)
    Principle of paired factors
  • b)
    Principle of dominance
  • c)
    Law of segregation
  • d)
    Law of independent assortment
Correct answer is option 'D'. Can you explain this answer?

Gaurav Kumar answered
Cross involving two contrasting character is called dihybrid cross or a two factor cross. The two factors of each trait assort at random and independent of the factors of other traits at the time of meiosis (gametogenesis) and get randomly as well as independently rearranged in the offspring producing both parental and new combinations of traits. This forms the basis of the law of independent assortment given by Mendel.

Genes which code for a pair of contrasting traits are known as
  • a)
    dominant genes
  • b)
    alleles
  • c)
    linked genes
  • d)
    none of these
Correct answer is option 'B'. Can you explain this answer?

Lavanya Menon answered
Genes are the units of inheritance and contain the information that is required to express a particular trait in an organism. Alternating form if a single gene which code for pair of contrasting traits are known as alleles, i.e, tall and drawf are alleles determining the height of pea plant.

A tobacco plant heterozygous for a recessive character is self-pollinated and 1200 seeds are subsequently germinated. Flow many seedlings would have the parental genotype?
  • a)
    1250
  • b)
    600
  • c)
    300
  • d)
    2250
Correct answer is option 'B'. Can you explain this answer?

Anshika Ahuja answered
Given information:
- A tobacco plant is heterozygous for a recessive character.
- The plant is self-pollinated.
- 1200 seeds are germinated.

To solve the problem, we need to use the principles of Mendelian genetics and Punnett squares.

Step-by-step solution:

1. Write down the genotype of the parent plant:
- Let's use A to represent the dominant allele and a to represent the recessive allele. The parent plant is heterozygous, so its genotype is Aa.

2. Create a Punnett square to show the possible gametes and offspring:

| | A | a |
|----|---|---|
| A | AA | Aa |
| a | aA | aa |

- Each box represents a possible offspring genotype that can result from the combination of the parent's gametes.
- The probability of each genotype occurring can be calculated by multiplying the probabilities of the corresponding gametes.

3. Determine the probability of each genotype:
- In this case, we want to know the probability of the parental genotype (Aa) occurring.
- We can see from the Punnett square that there are two Aa offspring genotypes out of four possible genotypes, so the probability is 2/4 or 1/2.

4. Calculate the number of offspring with the parental genotype:
- We know that there are 1200 seeds germinated, so we can use the probability we calculated in step 3 to find the expected number of Aa offspring.
- Expected number of Aa offspring = probability of Aa genotype x total number of offspring
- Expected number of Aa offspring = 1/2 x 1200 = 600

5. Choose the correct answer:
- The question asks how many seedlings would have the parental genotype, which is Aa.
- From step 4, we know that the expected number of Aa offspring is 600. Therefore, the correct answer is B, 600.

XO type of sex determination and XY type of sex determination are the examples of
  • a)
    male heterogamety
  • b)
    female heterogamety
  • c)
    male homogamety
  • d)
    both (b) and (c)
Correct answer is option 'A'. Can you explain this answer?

Jyoti Sengupta answered
In XO type and XY type sex determining mechanisms, males produce two different types of gametes, (a) either with or without X-chromosome (XO type), (b) some gametes with X-chromosome and some with Y-chromosome (XY type). Such type of sex determination mechanism is designated to be the example of male heterogamety. In both, females are homogametic and produce X type of gametes in both the cases and have XX genotype.

If both parents are carriers for thalassaemia, which is an autosomal recessive disorder, what are the chances of pregnancy resulting in an affected child?
  • a)
    25%
  • b)
    100%
  • c)
    No chance
  • d)
    50%
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
Thalassemia-autosomal-linked recessive
AA-Normal
Aa-Carrier
aa-Disease
Affected = 1/4 ​= 25%
An autosomal recessive disorder like thalassemia is caused by abnormalities in both members of a pair of genes. Both parents may carry a single dose of the gene on one chromosome but have a normal gene on the other chromosome, which prevents the appearance of the disease in the carrier parent. A child must get one abnormal gene from each parent in order to be affected by the disease. Parents who are both carriers of an autosomal recessive disorder have a 25% risk of producing an offspring affected by the disease and a 50% risk of producing normal-appearing carriers.

Which of the following is incorrect regarding ZW-ZZ type of sex determination?
  • a)
    It occurs in birds and some reptiles
  • b)
    Females are homogametic and males are heterogametic
  • c)
    1:1 sex ratio is produced in the offsprings
  • d)
    All of these
Correct answer is option 'B'. Can you explain this answer?

Vivek Patel answered
In ZW - ZZ type of sex determination, the male has two homomorphic sex chromosomes (ZZ) and is homogametic, and the female has two heteromorphic sex chromosomes (ZW) and is heterogametic. There are, thus, two types of eggs : with Z and with W, and only one type of sperms, i.e., each with Z. Fertilisation of an egg with Z chromosome by a sperm with Z chromosome gives a zygote with ZZ chromosomes (male). Fertilisation of an egg with W chromosome by a sperm with Z chromosome yields a zygote with ZW chromosomes (female). This mechanism operates in some vertebrates (fishes, reptiles and birds).

An allele is said to be recessive, when it is expressed in
  • a)
    heterozygous condition only
  • b)
    homozygous condition only
  • c)
    F3 generation
  • d)
    both homozygous and heterozygous conditions
Correct answer is option 'B'. Can you explain this answer?

Nilanjan Kapoor answered
Understanding Recessive Alleles
Recessive alleles are a fundamental concept in genetics. They play a crucial role in determining phenotypes, or observable traits, of an organism.
Definition of Recessive Alleles
- An allele is termed "recessive" when its effects are masked by the presence of a dominant allele in a heterozygous condition.
- For a recessive allele to manifest its traits, it must be present in a homozygous condition, meaning two copies of the recessive allele are required.
Homozygous vs. Heterozygous Conditions
- Homozygous Condition:
- An organism possesses two identical alleles for a particular gene (e.g., aa).
- The recessive trait is expressed when both alleles are recessive.
- Heterozygous Condition:
- An organism carries one dominant and one recessive allele (e.g., Aa).
- The dominant allele will overshadow the recessive allele, preventing its expression.
Expression of Recessive Traits
- A recessive trait is only observable in the homozygous condition.
- Therefore, the correct answer to the original question is option 'B', as recessive alleles are expressed only when an individual has two copies of that allele.
Conclusion
Understanding the interaction between dominant and recessive alleles is essential for predicting inheritance patterns in genetics. Recessive traits require a specific genetic configuration (homozygous) to be expressed, distinguishing them from dominant traits, which can manifest even in a single copy.

Which of the following cross will give tall and dwarf pea plants in same proportions?
  • a)
    TT x tt
  • b)
    Tt x tt
  • c)
    TT x Tt
  • d)
    tt x tt
Correct answer is option 'B'. Can you explain this answer?

Raghav Bansal answered
This is an example of a test cross in which a cross is made between heterozygous tall and homozygous dwarf individuals, tall and dwarf plants are obtained in the same proportions.

Inheritance of which of the following traits is shown in the given cross?
  • a)
    X-linked dominant trait
  • b)
    X-linked recessive trait
  • c)
    Autosomal recessive trait
  • d)
    Autosomal dominant trait
Correct answer is option 'B'. Can you explain this answer?

Suresh Iyer answered
  • In the given cross, passing of disease is from carrier female to male progeny (criss-cross inheritance). Any trait that shows criss-cross inheritance is located on the sex chromosome.
  • Presence of a single recessive gene i.e. Xc in carrier individuals (XXC) does not cause the disease, thus the trait is recessive.

Complete the given table showing different possililities of genotypes and their corresponding blood group, by selecting the correct option
  • a)
    (i) - IAIA,  (ii) - IBIB,  (iii) - IAIB,  (iv) - ii
  • b)
    (i) - IAIA,  (ii) - IBIB,  (iii) - IAIB,  (iv) - IAi
  • c)
    (i) - IAi,  (ii) - IBi,  (iii) - IAIB,  (iv) - ii
  • d)
    (i) - IAi,  (ii) - IBi,  (iii) - IAIB,  (iv) - IBi
Correct answer is option 'C'. Can you explain this answer?

Ananya Das answered
  • This case where three alleles are present in one gene is called co-dominance, The gene I has three forms and when either A or B is expressed in the gene then either A or B blood group is expressed respectively.
  • When both A and B are present then it results in the AB blood group. The i allele represents the recessive form and codes for O blood group and will be expressed only in the dominant recessive genotype expression.

In the following pedigree chart, the mutant trait is shaded black. The gene responsible for the trait is 
  • a)
    dominant and sex linked
  • b)
    dominant and autosomal
  • c)
    recessive and sex linked
  • d)
    recessive and autosomal
Correct answer is option 'D'. Can you explain this answer?

Anjali Sharma answered
The given trait cannot be sex-linked as sex-linked traits follow criss-cross inheritance and in the given pedigree, no criss-cross inheritance is being followed. The trait exhibited in pedigree chart is autosomal recessive. An autosomal recessive trait appears in case of marriage between two heterozygous individuals (Aa x Aa=3Aa+1aa), a recessive individual with hybrid (Aa x aa=2Aa+2aa) and two recessives (aa x aa= all aa). It expresses its effect only in pure or homozygous state.
If the trait had been controlled by dominant gene, then one of the parent must have possessed the dominant gene and hence the disease.

question 1:

Select the correct statement from the ones given below with respect to dihybrid cross.
  • a)
    Tightly linked genes on the same chromosome show higher recombinations
  • b)
    Genes far apart on the same chromosome show very few recombinations
  • c)
    Genes loosely linked on the same chromosome show similar recombinations as the tightly linked ones
  • d)
    Tightly linked genes on the same chromosome show very few recombinations.
Correct answer is option 'D'. Can you explain this answer?

Mohit Rajpoot answered
In a dihybrid cross, tightly linked genes on the same chromosome show very few recombinations because they are so close together that they tend to be inherited as a unit. This is consistent with Option D, which accurately describes the nature of tightly linked genes. Options A, B, and C do not correctly describe the behavior of linked genes.

When a cross is made between a tall plant with yellow seeds (Tt Yy) and a tall plant with green seeds (Tt yy), what is true regarding the proportions of phenotypes of the offsprings in F1 generation?
  • a)
    a
  • b)
    b
  • c)
    c
  • d)
    d
Correct answer is option 'A'. Can you explain this answer?

Mira Joshi answered
A cross between a tall plant with yellow seeds (TtYy) and a tall plant with green seeds (Ttyy) will be:
Pnenotypic ratio is
Tall and yellow : Tall and green : Dwarf and yellow : Dwarf and green :: 3 : 3: 1: 1 or 3/8, 3/8,1/8,1/8.

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