Mendelian Genetics MCQ Quiz in मल्याळम - Objective Question with Answer for Mendelian Genetics - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept: 

• Mendel studied the inheritance of seven different features in peas, including height, flower color, seed color, and seed shape.

• He established pea lines with two different forms of a feature, such as tall vs. short height.

• He grew these lines for generations until they were pure-breeding (always produced offspring identical to the parent), then bred them to each other and observed how the traits were inherited.

​​Explanation:

Option 1:

• The Law of Dominance states that the offspring always exhibits a dominant trait.
• From the two alleles received from parents, the only dominant allele is expressed.
• Therefore, this is not the correct answer.

Option 2:

• A cross between two pure breeding different varieties of organism taking the alternative traits of one single character is called monohybrid cross or inheritance of one gene.
• Therefore, this is not the correct answer.

​Option 3:

• In codominance, two alleles express themselves independently when present together. Therefore, the offspring resembles both parents.
• Codominance is a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual. That is, instead of one trait being dominant over the other, both traits appear, such as in a plant or animal that has more than one pigment color.
• This can be observed in the ABO blood group.
• In the ABO blood group system, both A and B groups are dominant, hence leading to the AB blood group.
• Therefore, an individual inheriting the A allele from the mother and the B allele from the father has a blood type AB.
• Therefore, this is the correct answer.

​Option 4:

• In the case of incomplete dominance, the phenotype of the F1 is an intermediate of the two alleles from the parents in their homozygous state.
• Therefore, the offspring do not resemble either parent.
• Example- Snapdragon (Antirrhinum sp)
• Therefore, this is not the correct answer.

The correct answer is y and w

Concept:

• In genetics, linkage refers to the tendency of genes that are located close to each other on a chromosome to be inherited together during meiosis.
• Recombination frequency is a measure of the likelihood of two genes being separated during crossing over in meiosis.
• A low recombination frequency indicates strong linkage between the genes, meaning they are likely to be inherited together.
• Thomas Hunt Morgan's experiments with fruit flies (Drosophila melanogaster) were pivotal in understanding genetic linkage and recombination.

Explanation:

• y and w: The genes y (yellow body) and w (white eyes) showed a recombination frequency of only 1.3%, indicating strong linkage. This means that these genes are very close to each other on the same chromosome and are rarely separated by recombination.
• w and m: This pair of genes does not show the same low recombination frequency of 37.2%, indicating they are not as closely linked as y and w.

Key Points

• In a cross between RRyy (round, yellow seeds) and rrYY (wrinkled, green seeds), the F1 generation will all be RrYy, exhibiting the dominant traits (round and green seeds).
• The F2 generation, obtained by self-pollinating the F1 generation, will show a variety of genotypes due to the independent assortment and segregation of alleles during gamete formation.
• When considering two traits controlled by two genes, each with two alleles (Rr and Yy), the Punnett square method predicts that 16 different genotypes can be formed in the F2 generation.
• However, these 16 genotypes will only result in 4 different phenotypes because the traits are independently inherited and express complete dominance (round yellow, round green, wrinkled yellow, wrinkled green).
• Therefore, the number of genotypes is 9 and the number of phenotypes is 4, which aligns with option 3.

Additional Information

• Option 1 (16 genotypes and 4 phenotypes) incorrectly suggests a reversal in the number of genotypes and phenotypes.
• Option 2 (4 genotypes and 16 phenotypes) also incorrectly reverses the numbers, and it is not possible to have more phenotypes than genotypes in this scenario.
• Options 4 and 5 are not applicable as they either present incorrect combinations or are left blank.
• The correct understanding of Mendelian genetics and the principles of dominance, segregation, and independent assortment is crucial for predicting the outcomes of genetic crosses.

CONCEPT:

• Homologous organs have common ancestors or origins, with the same structural plan but their functions and external appearances are different.
• Homology is based on divergent evolution. 
• The same structure developed along different directions due to adaptions to different needs, this is known as divergent evolution.
• These organs are present in related species.

EXPLANATION:

• Carrots and radishes are tap roots.
• As they are anatomically similar structures and both are roots, hence they are considered homologous structures.
• Potato is the stem modification whose function is to store food.
• Tomato is a kind of berry fruit.

Additional Information

• Carrots are modified tap roots and potatoes are modified stems but both store food, hence they are analogous structures.
• Radish and potato also the analogous structure, as their function is similar but not similar in origin.

Hence, the correct option is 3) Radish and carrot.

Key Points

• The blood group O is recessive, meaning that a child needs to inherit the O allele from both parents to have this blood group.
• Since the father has the AB blood group, he cannot pass on an O allele.
• The mother with blood group B can pass either B or O alleles to the child.
• Therefore, it is genetically impossible for a child of an AB father and a B mother to have an O blood group.

The correct answer is Tyrosine

Concept:

• Phenylketonuria (PKU) is a metabolic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase, which is necessary to convert phenylalanine into tyrosine. When this enzyme is deficient, phenylalanine accumulates in the blood and can cause severe intellectual disabilities and other neurological problems if not managed through diet.
• Phenylketonuria is an inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives. Accumulation of these in brain results in mental retardation. These are also excreted through urine because of its poor absorption by kidney.

Explanation of each option:

• Option 1: tryptophan – Tryptophan is an essential amino acid that serves as a precursor for serotonin and melatonin. However, it is not a product of phenylalanine hydroxylase activity. Therefore, this option is incorrect.
• Option 2: alanine – Alanine is a non-essential amino acid commonly involved in glucose metabolism but is not produced from phenylalanine by phenylalanine hydroxylase. This option is also incorrect.
• Option 3: tyrosine – Tyrosine is the correct answer. Phenylalanine hydroxylase catalyzes the hydroxylation of phenylalanine to produce tyrosine, which is essential for synthesizing neurotransmitters like dopamine and norepinephrine.
• Option 4: threonine – Threonine is an essential amino acid involved in protein synthesis, but it is not synthesized from phenylalanine by the action of phenylalanine hydroxylase. This makes this option incorrect as well.

Concept:

• Genetics is the study of inheritance and the cause of variations in living organisms.
• It involves the study of genes and heredity. 
• It helps to explain how certain traits are passed down from one generation to another.
• Gregor Mendel is regarded as the father of genetics.
• Mendel carried out experiments on garden pea plants to determine the hereditary characteristics of living organisms.
• Mendel studied specific characteristics in pea plants which included stem height, flower color, flower position, pod shape, pod color, seed shape, and seed color. Each of these characters had two contrasting traits i.e. two alleles of a gene.

Explanation:

• A dihybrid cross is a cross between two organisms in the parental generation that differ in two traits.
• A dominant trait is a character that is expressed in both homozygous and heterozygous states.
• A recessive trait is a character that is expressed only in the homozygous state.
• In the given question,
  • Round seed (R) is dominant over wrinkled seed (r).
  • Yellow cotyledon (Y) is dominant over green cotyledon (y).
  • The cross between a plant with RRYY genotype and a plant with rryy genotype is as follows:

• From the above cross, it can be determined that in a cross between RRYY × rryy, the progeny so obtained in the F₂ generation will have phenotypes in the order: Plant with round seed and yellow cotyledon - 9, Plant with round seed and green cotyledon - 3, Plant with wrinkled seed and yellow cotyledon - 3, and Plant with wrinkled seed and green cotyledon - 1. 
• Thus the phenotypic ratio of F₂ generation in the above cross will be 9:3:3:1.
• Hence, the expected phenotypes in the F2 generation of the cross RRYY × rryy are Round seeds with yellow cotyledons and wrinkled seeds with green cotyledons.

So the correct answer is option 4 (Round seeds with yellow cotyledons and wrinkled seeds with yellow cotyledons).

Concept:

• Inheritance can be defined as the passing down of genetic traits from parents to offspring.
• The traits are passed down from parents to offspring through genes.
• A gene comprises two forms called alleles.
• The alleles of a gene can be either dominant or recessive for a trait. For e.g.: The gene coding for the height of a pea plant has two alleles - tall and dwarf. Here tall (T) is dominant over dwarf (t), hence in the heterozygous state (Tt), the phenotype of the plant will be tall (T).

Explanation:

• Option A: Dominance
  • ​Dominance refers to the trait that is expressed in a heterozygous state. 
  • A gene comprises two alleles - dominant and recessive. The dominant allele gets expressed in the heterozygous state.
  • E.g.: In a pea plant, round seed shape (R) is dominant over wrinkled seed shape (r). Therefore in the heterozygous state (Rr), the phenotype of the plant will be a round seed shape (R).
• Option B: Co-dominance
  • ​In the heterozygous state if both alleles express themselves it is referred to as co-dominance.
  • Both genes are equally dominant and do not interfere with the expression of each other.
  • E.g.: In the human ABO blood group system, the genes I^A and I^B are co-dominant and the blood group of an individual with genotype I^A and I^B will be AB blood group.
• Option 3: Pleiotropy
  • Pleiotropy refers to the ability of a gene to have multiple phenotypic effects. This is due to the influence of a single gene on several characters simultaneously.
  • A pleiotropic gene can cause several related changes that together are referred to as a syndrome.
  • E.g.:  Phenylketonuria is caused due to a single gene mutation in the gene coding for the enzyme phenylalanine hydroxylase. This single gene mutation in turn results in a series of different phenotypic expressions such as mental retardation, slow growth, etc. Thus a mutation in a single gene gives rise to a series of phenotypic expressions which indicates pleiotropy.
• Option 4: Polygenic inheritance
  • ​Polygenic inheritance refers to the quantitative traits that are inherited by an individual showing varying degrees of character.
  • These varying characteristics are due to the combined action of several genes. 
  • The net effect of a trait will depend on the number of genes involved.
  • Since the effect increases with the increase in the number of genes, the action is regarded as a cumulative effect.
  • E.g.: Skin color in humans is an example of polygenic inheritance. In humans, skin color can be either white, light, medium (mulatto), dark or black. This varying coloration is due to varying amounts of melanin in their skin. This in turn is determined by the effect of the number of genes that are involved.

• From the above-given information,
  • Dominance (A) matches with In heterozygous organisms only one of the alleles expresses itself (2).
  • Co-dominance (B) matches with In a heterozygous organism, both alleles express themselves fully (3).
  • Pleiotropy (C) matches with Only one gene influences many characters (4).
  • Polygenic inheritance (D) matches with Many govern a single character (1).
• This co-relation matches with option 1.

So the correct answer is option 1 (A - 2, B - 3, C - 4, D - 1).

The correct answer is Down’s syndrome

Concept:

• A chromosomal disorder is a condition caused by an abnormality in the number or structure of chromosomes.
• Humans typically have 23 pairs of chromosomes, totaling 46.
• Chromosomal disorders can result from an extra chromosome, a missing chromosome, or structural changes in chromosomes.
• These disorders can lead to developmental and physical abnormalities.

• Most common Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle- cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc.

Explanation:

• Down’s syndrome: This is a chromosomal disorder caused by the presence of an extra copy of chromosome 21 (trisomy 21).  This disorder was first described by Langdon Down (1866). The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded

Other Options:

• Phenylketonuria: This is a genetic disorder, not a chromosomal disorder. It is caused by a mutation in the gene that helps produce the enzyme needed to break down the amino acid phenylalanine. It is caused by a mutation in a single gene that affects multiple systems in the body, including brain development and skin pigmentation, illustrating pleiotropy.
• Sickle-cell anemia: This is a genetic disorder caused by a mutation in the hemoglobin-Beta gene found on chromosome 11. It leads to the production of abnormal hemoglobin, resulting in misshapen red blood cells that can cause various health complications.
• Cystic fibrosis: It is a Mendelian disorder. It is caused by mutations in the CFTR gene on chromosome 7. It affects the respiratory and digestive systems, leading to severe chronic illness and reduced life expectancy.

The correct answer is Birds

Explanation:

• Sex determination mechanisms vary among different species and are genetically controlled.
• Common sex determination systems include the XY system, the XO system, and the ZW system.
• In the ZW system, females have two different sex chromosomes (ZW), while males have two of the same sex chromosomes (ZZ).

Explanation:

• Birds:
  • Birds exhibit female heterogamety.
  • Female birds have ZW sex chromosomes, and males have ZZ sex chromosomes.
• Grasshoppers:
  • Grasshoppers are examples of XO type of sex determination
  • Males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.
• Drosophila:
  • Drosophila (fruit flies) do not exhibit female heterogamety. Instead, they exhibit male heterogamety, where males have XY chromosomes and females have XX chromosomes.
• Humans:
  • Humans use the XY system of sex determination, where females are XX and males are XY. Therefore, they do not use the ZW system.
• Honeybees:
  • Honeybees use a haplodiploid system of sex determination.
  • Males are haploid (having one set of chromosomes), while females are diploid (having two sets of chromosomes).