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All questions of Unit 6: Gene Expression for Grade 9 Exam

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XO type of sex determination is found in________.
  • a)
    Grasshopper
  • b)
    Elephant
  • c)
    Human beings
  • d)
    Dog
Correct answer is option 'A'. Can you explain this answer?

Ananya Das answered
In grasshopper, sex determination is of XO type, in which the males have only one X-chromosome besides the autosomes whereas females have a pair of X-chromosomes.

The innate tendency of offspring to resemble their parents is called?
  • a)
    Resemblance
  • b)
    Heredity
  • c)
    Variation
  • d)
    Inheritance
Correct answer is option 'B'. Can you explain this answer?

Hansa Sharma answered
The innate tendency of offspring to resemble their parents is called heredity. The offspring resembles to parent due to same genetic combination inherited from parents.

Which of the following is an example of co-dominance?
  • a)
    Skin pigmentation in humans
  • b)
    Sex-linkage in humans
  • c)
    Pink flowers of Snapdragon
  • d)
    The ABO blood groups in human
Correct answer is option 'D'. Can you explain this answer?

Krishna Iyer answered
Co-dominance is the phenomenon that deviates from Mendel’s law of inheritance. Both the alleles appear in offspring instead of one as in Mendel’s experiment. ABO blood grouping in human being is example of co-dominance in which both IA and IB appear simultaneously to form AB blood type.

For ABO system of blood groups, allele IA produces N-acetylgalactosamine transferase enzyme which recognises H- antigen present in RBC membrane and adds N-acetylgalactosamine to sugar parts of H antigens to form A antigen.
The allele IB produces galactosyl transferase enzyme which recognized H antigen to form B antigens. Allele i does not produce any sugar or antigen.
IA  and IB are completely dominant over i, in other words antigens A and B are produced. This is because of co-dominance. These antigens determine the type of blood group. Blood group A has antigens B have antigen, AB has both antigens while blood group. Blood group A have antigen A, group B have antigen B, AB has both antigens while blood group O do not carry any antigens.
Thus, six genotypes and four phenotypes are possible.

Dihybrid cross proves the law of________.
  • a)
    Segregation
  • b)
    Purity of gametes
  • c)
    Law of independent assortment
  • d)
    Dominance
Correct answer is option 'C'. Can you explain this answer?

Deepak Joshi answered
Dihybrid cross proves the law of independent assortment. Mendel found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation. This is known as Law of independent assortment. Dihybrid cross - cross between two parents that differ by two pairs of alleles (AABB X aabb). The formation of gametes is an application of this law.

The term ‘Genetics’ was proposed by
  • a)
    Johannsen
  • b)
    Morgan
  • c)
    Mendel
  • d)
    Bateson
Correct answer is option 'D'. Can you explain this answer?

Rahul Bansal answered
Bateson co-discovered genetic linkage with Reginald Punnett and Edith Saunders, and he and Punnett founded the Journal of Genetics in 1910. Bateson also coined the term "epistasis" to describe the genetic interaction of two independent loci.

A human male produces sperms with the genotypes AB, Ab, aB, ab pertaining to two diallelic characters in equal proportions. What is the corresponding genotype of this person?
  • a)
    AABB
  • b)
    AaBb
  • c)
    AABb
  • d)
    AaBB
Correct answer is option 'B'. Can you explain this answer?

Om Desai answered
If the genotype is AaBb the alleles that will be produced will be AB, Ab, aB, ab, since there are two diallelic characters in the genotypes the person must be heterozygous for both genes. AABB is homozygous. So, the correct answer is "AaBb".

Sex determination in human being is______.
  • a)
    XY type
  • b)
    XX type
  • c)
    XXY type
  • d)
    YY type
Correct answer is option 'A'. Can you explain this answer?

Mohit Rajpoot answered
  • In humans, the males are heterogametic as they have XY sex chromosomes, so they make 50% sperms with X chromosome and 50% sperms with Y chromosome. Females are homogametic. All gametes made by them have X chromosomes. So, humans show XX-XY type of sex determination.
Hence, the correct option is A.
NCERT Reference: Topic SEX DETERMINATION of chapter "Principles of Inheritance and Variation" OF NCERT.

Material used for conducting experiments on genetic traits by Mendel was______.
  • a)
    Lathyrusodaratus
  • b)
    Oryza sativa
  • c)
    Pisumsativum
  • d)
    Mirabilis jalappa
Correct answer is option 'C'. Can you explain this answer?

Kadambala Hemalatha answered
Option c is correct.. mendel conducted experiment's on pisumsativum (garden pea)...mirabilus jalapa is also called 4'o clock plant, oryza sativa (rice)...

The physical expression or appearance of a character is called as?  
  • a)
    Phenotype
  • b)
    Morphology
  • c)
    Ecotype   
  • d)
    Genotype
Correct answer is option 'A'. Can you explain this answer?

Dipanjan Chawla answered
The physical appearance of a character is called as phenotype. The genetic make of individual is called genotype. Tallness, round, wrinkled, yellow etc. are physical appearance.

A pure tall and a pure dwarf plant were crossed to produce offspring. Offspring were self-crossed. Find out the ratio between true breeding tall to true breeding dwarf.​
  • a)
    3:1
  • b)
    1:1
  • c)
    2:1
  • d)
    1:2:1
Correct answer is option 'B'. Can you explain this answer?

Rajesh Chatterjee answered
As true tall breeding and true dwarf breeding is seen only a single time in F2 generation, and the remaining are hybtid tall...so the ratio becomes 1:2:2:1.But 1:1 is the ratio for only true tall breeding nd true dwarf breeding in F2 generation.

F2 generation is obtained by______.
  • a)
    Crossing of F1 and F2
  • b)
    Selfing of F1
  • c)
    Selfing of F2
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Sathvika Tadri answered
F2 generation is obtained by selfing of F1 progeny..where F1 generation is obtained by crossing two parents..option B

The gene which controls many characters is called
  • a)
    Pleiotropic gene
  • b)
    Co-dominant gene
  • c)
    Multiple gene
  • d)
    Polygene
Correct answer is option 'A'. Can you explain this answer?

Suresh Iyer answered
A single gene may have two or more phenotypic expressions. The multiple phenotypic effect of a single gene is called pleiotropism. Hence the gene associated with this phenomenon is called Pleiotropic gene.

The crossing of F1 to any one of the parents is called?
  • a)
    Back cross
  • b)
    F1 cross
  • c)
    Test cross
  • d)
    All of these
Correct answer is option 'A'. Can you explain this answer?

Priya Menon answered
The crossing of F1 to any one of the parents is called back cross. It is used to check the purity of individual. When F1 is crossed with recessive parent, it is called test cross.

Down’s syndrome is due to
  • a)
    Linkage
  • b)
    Non-disjunction of chromosome
  • c)
    Crossing over
  • d)
    Sex-linked inheritance
Correct answer is option 'B'. Can you explain this answer?

Lakshmi Pillai answered
Explanation:

Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. This additional genetic material alters the course of development and causes the characteristic features of Down syndrome.

Non-disjunction of chromosome:
The most common cause of Down syndrome is non-disjunction of chromosome 21 during meiosis. Non-disjunction occurs when the chromosomes fail to separate properly during cell division, resulting in an abnormal distribution of chromosomes in the resulting cells. In the case of Down syndrome, non-disjunction of chromosome 21 occurs either during the formation of the egg or sperm, resulting in an extra copy of chromosome 21 in the fertilized egg.

Key Points:
- Non-disjunction of chromosome 21 during meiosis is the most common cause of Down syndrome.
- Non-disjunction can occur during the formation of the egg or sperm.
- Non-disjunction leads to an abnormal distribution of chromosomes in the resulting cells, resulting in an extra copy of chromosome 21.

Other Causes:
While non-disjunction is the primary cause of Down syndrome, there are other rare genetic variations that can also result in the condition. These include translocation, mosaicism, and partial trisomy.

- Translocation: In some cases, a piece of chromosome 21 breaks off and attaches to another chromosome, typically chromosome 14. This is called a translocation. If a person has a translocation involving chromosome 21, they may have a higher risk of having a child with Down syndrome.

- Mosaicism: Mosaicism occurs when there is a mixture of cells with a normal number of chromosomes and cells with an extra copy of chromosome 21. This can result in milder symptoms or features of Down syndrome.

- Partial Trisomy: In rare cases, a person may have only a portion of chromosome 21 duplicated, leading to a condition known as partial trisomy. This can result in a milder form of Down syndrome, as only a subset of genes on chromosome 21 is affected.

Conclusion:
In conclusion, the most common cause of Down syndrome is non-disjunction of chromosome 21 during meiosis. This results in an extra copy of chromosome 21 in the fertilized egg, leading to the characteristic features of Down syndrome. Other rare genetic variations, such as translocation, mosaicism, and partial trisomy, can also result in Down syndrome but are less common.

Which of the following is not a Mendelian disorder?
  • a)
    Haemophilia
  • b)
    Turner’s syndrome
  • c)
    Cystic fibrosis
  • d)
    Colour blindness
Correct answer is option 'B'. Can you explain this answer?

Devanshi Mehta answered
All humans have 46 chromosomes, which determine who and what we are genetically. Boys have an X and Y chromosome. Girls have 2 X chromosomes. Turner Syndrome is a chromosomal disorder in girls in which part or all of one of the X-chromosomes is missing.
This loss of genetic material causes 2 primary features: namely, short stature and underdeveloped ovaries causing delayed or absent puberty. It is usually diagnosed when a girl is noted to be very short and a chromosome blood test is obtained. It should also be suspected if a girl has not developed breasts by 13-14 years of age or had her menstrual period by 15-16 years of age.  Effective hormonal treatment is available for both the short stature and to stimulate normal pubertal changes.

In a given plant, red colour (R) of fruits is dominant over white fruit (r); and tallness (T) is dominant over dwarfness (t). If a plant with genotype RrTt is crossed with a plant of genotype rrtt, what will be the percentage of tall plants with red fruits in the next generation?
  • a)
    20%
  • b)
    40%
  • c)
    50%
  • d)
    60%
Correct answer is option 'C'. Can you explain this answer?

Universal Academy answered
According to question, tallness (T) is dominant over dwarfism (t) and red colour (R) is dominant over white (r) fruit colour.
Parent Generation; P1 : RRTt  x  rrtt
F1 generation :

Phenotypic ratio = 1  (tall plant, red fruit)         
: 1 (dwarf plant, red fruit)
; thus, percent of tall plant with red fruit is 50%.

What will be expected blood groups in the off spring when there is a cross between AB blood group mother and heterozygous B blood group father?
  • a)
    25% AB, 25% A, 50%B
  • b)
    50% AB, 25% A, 25%B
  • c)
    25% AB, 50% O, 25%A
  • d)
    25% O, 25% A, 50%B
Correct answer is option 'A'. Can you explain this answer?

Suresh Kumar answered
Given; Mother is with "AB" blood group....i.e. it means the genotypes are 'IAIB' .. For "B" blood group genotypes are:-'IBIB'(homozygous condition);'IBIO'(Heterozygous condition).. In question it is said that Father is with "B" heterozygous blood group...So;the genotypes are 'IBIO' ... When cross is done between Mother with 'IAIB' & father with 'IBIO'.. the possible genotypes of the progeny are :- 'IAIB'(i.e."AB" blood group);'IAIO'(i.e."A" blood group);'IBIB'(i.e."B" blood group);'IBIO'(i.e."B" blood group).. % of "AB" blood group=>1×100/4 =>25% of progeny with "AB" blood group.. % of "A" blood group=>1×100/4 =>25% of progeny with "A" blood group.. % of "B" blood group =>2×100/4 =>50% of progeny with "B" blood group.... Hence;option _'A'_holds true here...

Mutations which arise suddenly in nature are called
  • a)
    Spontaneous mutations
  • b)
    Gene mutations
  • c)
    Induced mutations
  • d)
    Chromosomal mutations
Correct answer is option 'A'. Can you explain this answer?

Pooja Mehta answered
Gene mutation is defined as a sudden discrete change in the genetic material of gene which is heritable. Mutations when they arise suddenly in nature are called spontaneous mutations.

The test cross is used to determine the________.
  • a)
    Genotype of the plant
  • b)
    Phenotype of the plant
  • c)
    Both a and b
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Arpita Tiwari answered
The test cross is used to determine the genotype of the plant in which F1 plant is crossed with homozygous recessive plants. If the ratio is 1:1 the plant is homozygous.

Monohybrid ratio is_____.
  • a)
    9:3:1
  • b)
    3:1
  • c)
    9:3:3:1
  • d)
    9:1
Correct answer is option 'B'. Can you explain this answer?

Dipika Das answered
Monohybrid ratio is the ratio of different phenotypic traits obtained on hybridizing single pair of trait. It is 3:1. When tall pea plant is crossed with dwarf, the offspring obtained are in ¾ tall and ¼ dwarf.

Turner syndrome is
  • a)
    XYY
  • b)
    XO
  • c)
    XXX
  • d)
    XXY
Correct answer is option 'B'. Can you explain this answer?

Ishani Nambiar answered
Turner syndrome (TS), also known 45,X, or 45,X0, is a genetic condition in which a female is partly or completely missing an X chromosome. Signs and symptoms vary among those affected.

Mating of an organism to a double recessive in order to determine whether it is homozygous or heterozygous for a character under consideration is called
  • a)
    Back cross
  • b)
    Dihybrid cross
  • c)
    Reciprocal cross
  • d)
    Test cross
Correct answer is option 'D'. Can you explain this answer?

Ayush Joshi answered
Test cross is the cross of the individuals with its homozygous recessive parent. In other words, we can say that it is a specialized back cross of F1 hybrid with it's homozygous recessive parent in order to determine whether it is homozygous or heterozygous for a character. Reciprocal cross is the cross that could be made either way or independent of the sex of the parents. Dihybrid cross is the cross of the hybrids of F1 generations with either of its parents. 

The phenotypic ratio in the F2 generation of a dihybrid cross is​
  • a)
    1:2:2:4:1:2:1:2:1
  • b)
    9:3:3:1
  • c)
    7:1:1:7
  • d)
    12:3:4
Correct answer is option 'B'. Can you explain this answer?

Neha Sharma answered
Because it produces produced nine plants with round, yellow seeds, three plants with round, green seeds, three plants with wrinkled, yellow seeds and one plant with wrinkled, green seeds.therefore the ratio is 9 : 3 : 3 : 1

Can you explain the answer of this question below:

The phenotypic ratio in the F2 generation of a dihybrid cross is​

  • A:

    1:2:2:4:1:2:1:2:1

  • B:

    9:3:3:1

  • C:

    7:1:1:7

  • D:

    12:3:4

The answer is b.

Ashish Dasgupta answered
Explanation:

In a dihybrid cross, two traits are considered simultaneously. The F1 generation produced after crossing two pure breeding lines will all be heterozygous for both traits.

For example, if two pure breeding plants with yellow round seeds (YYRR) are crossed with plants with green wrinkled seeds (yyrr), the F1 generation will all be heterozygous for both traits (YyRr).

When the F1 generation is crossed with itself or another F1 individual, the resulting F2 generation will exhibit all possible combinations of the two traits.

The phenotypic ratio in the F2 generation of a dihybrid cross is determined by the number of possible combinations of the two traits.

The possible combinations of the two traits can be determined using a Punnett square or the FOIL method.

For example, using the FOIL method:

(YyRr) x (YyRr)
YYRr YyRR YyRr yyRR
YYRr YyRR YyRr yyRR
YyRr yyRR YyRr yyrr
yyRR yyRR yyrr yyrr

In this example, there are 9 individuals with both dominant traits (yellow and round seeds), 3 individuals with one dominant and one recessive trait (yellow and wrinkled seeds, green and round seeds), and 1 individual with both recessive traits (green and wrinkled seeds).

Therefore, the phenotypic ratio in the F2 generation of this dihybrid cross is 9:3:3:1, which is option B.

With green pods as a dominant trait over yellow, which of the following crosses will result in all progeny having yellow pods?
  • a)
    Homozygous green and homozygous yellow
  • b)
    Heterozygous green and heterozygous green
  • c)
    Homozygous yellow and homozygous yellow
  • d)
    Homozygous green and homozygous green
Correct answer is option 'C'. Can you explain this answer?

Anjali Sharma answered
Yellow being recessive will express only when both alleles are present. That occurs only when both parents can contribute an allele encoding for the yellow pod. For all progeny to have yellow pods, both parents have to be homozygous for yellow pods.

Which of the following statements is true regarding the “law of independent assortment”?
  • a)
    Independent assortment leads to variation.
  • b)
    Independent assortment leads to formation of new combinations of characters.
  • c)
    Factors assort independent of each other when more than one pair of characters are present together.
  • d)
    All of these
Correct answer is option 'D'. Can you explain this answer?

Meera Singh answered
Independent Assortment describes how different genes independently separate from one another when reproductive cells develop. Independent assortment of genes and their corresponding traits was first observed by Gregor Mendel. Recombination occurs during meiosis and is a process that breaks and recombines pieces of DNA to produce new  combinations of genes. Recombination scrambles pieces of maternal and paternal genes, which ensures that genes assort independently from one another.

The pure line round-seeded pea plant was crossed with a wrinkled-seeded pea plant. The F1 generation is ____ and it can be explained by _____.
  • a)
    Wrinkled : Law of segregation
  • b)
    Round : Law of dominance
  • c)
    Round : Co-dominance
  • d)
    Wrinkled : Law of dominance
Correct answer is option 'B'. Can you explain this answer?

Infinity Academy answered
The F1 generation from crossing a pure line round-seeded pea plant with a wrinkled-seeded pea plant will be round-seeded. This can be explained by the Law of Dominance, where round seeds are dominant over wrinkled seeds.

Indentify the incorrect statement:
  • a)
    Tall plant produce gametes by meiosis and the dwarf plants by mitosis.
  • b)
    Only one allele is transmitted to a gamete.
  • c)
    The segregation of alleles is a random process.
  • d)
    Gametes will always be pure for the trait.
Correct answer is option 'A'. Can you explain this answer?

Ajay Yadav answered
Both tall and dwarf plants produce gametes by mitosis. Plants use meiosis only to produce spores that develop into multicellular haploid gametophytes which produce gametes by mitosis.
Therefore, gamete formation in both tall and dwarf plants is by mitosis.

Match the items of Column - I with Column - II:

Column-I                                                                                           Column-II

(a) XX-XO method of sex determination                                        (i) Turner's syndrome  

(b) XX-XY method of sex determination                                       (ii) Female heterogametic

(c) Karyotype-45                                                                           (iii) Grasshopper

(d) ZW-ZZ method of sex determination                                       (iv) Female homogametic

Select the correct option from the following:
  • a)
    (a) - (ii), (b) - (iv), (c) - (i), (d) - (iii)
  • b)
    (a) - (i), (b) - (iv), (c) - (ii), (d) - (iii)
  • c)
    (a) - (iii), (b) - (iv), (c) - (i), (d) - (ii)
  • d)
    (a) - (iv), (b) - (ii), (c) - (i), (d) - (iii)
Correct answer is option 'C'. Can you explain this answer?

Ritika Sain answered
(c) is correct option

Gene for colour blindness is located on​
  • a)
    13th chromosome
  • b)
    Y chromosome
  • c)
    21st chromosome
  • d)
    X chromosome
Correct answer is option 'D'. Can you explain this answer?

Asha Chauhan answered
Introduction:
Color blindness is a genetic disorder that impairs a person's ability to perceive certain colors, usually red and green. It is caused by a genetic mutation that affects the cones in the retina of the eye, which are responsible for color vision. This mutation is located on the X chromosome.

Explanation:
1. Genetic Basis of Color Blindness:
Color blindness is an X-linked recessive genetic disorder. This means that the gene responsible for color blindness is located on the X chromosome. The X chromosome is one of the two sex chromosomes, with females having two X chromosomes (XX) and males having one X and one Y chromosome (XY). Since the gene for color blindness is located on the X chromosome, it primarily affects males.

2. X Chromosome and Inheritance:
The X chromosome carries many genes that are responsible for various traits and characteristics. In males, the Y chromosome does not have a corresponding allele for the genes on the X chromosome. Therefore, if a male inherits a mutated gene on the X chromosome, he will express the trait associated with that gene, as there is no second copy of the gene to mask its effects.

3. Inheritance Pattern of Color Blindness:
When a female carries a mutated gene on one of her X chromosomes, she is considered a carrier. As carriers have a normal copy of the gene on their other X chromosome, they do not exhibit color blindness themselves but can pass the mutated gene to their offspring. If a carrier female has a son, there is a 50% chance that he will inherit the mutated gene and be color blind.

4. Higher Prevalence in Males:
Since males have only one X chromosome, they are more susceptible to color blindness. If a male inherits the mutated gene on his X chromosome, he will be color blind. On the other hand, females need to inherit the mutated gene on both of their X chromosomes to be color blind. This is why color blindness is more commonly seen in males.

Conclusion:
The gene for color blindness is located on the X chromosome. This genetic disorder primarily affects males due to the inheritance pattern of the X chromosome. Understanding the genetic basis of color blindness helps in diagnosing and managing the condition effectively.

A plant that exhibits two alleles for only one trait is called ________
  • a)
    monohybrid
  • b)
    dihybrid
  • c)
    monogamous
  • d)
    digamous
Correct answer is option 'A'. Can you explain this answer?

Riya Banerjee answered
Monohybrid refers to a hybrid that differs at only one gene. Thus, a plant that exhibits two alleles for one trait is a monohybrid.

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