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

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.

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 11

Explanation:

• Thalassemia is an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous).
• The defect could be due to either mutation or deletion, which ultimately results in a reduced rate of synthesis of one of the globin chains (α and β chains) that make up haemoglobin.
• This causes the formation of abnormal haemoglobin molecules, resulting in anaemia, which is characteristic of the disease.
• Thalassemia can be classified according to which chain of the haemoglobin molecule is affected.
• In α Thalassemia, production of α globin chain is affected, while in β Thalassemia, production of β globin chain is affected.
• α Thalassemia is controlled by two closely linked genes, HBA1 and HBA2 on chromosome 16 of each parent
• β Thalassemia is controlled by a single gene, HBB on chromosome 11 of each parent and occurs due to a mutation of one or both the genes.

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:

• The ABO blood groups in humans have three alleles that affect the expression of antigens on the surface of red blood cells: alleles A, B, and O. This is due to autosomal codominance.
• The inheritance of two alleles of an autosomal gene where each allele contributes to the phenotypic characteristics is known as the autosomal codominant.
• ABO blood typing is controlled by gene I.
• There are three alleles of the gene (I)- I ^A, I ^B, and i.
• The plasma membrane of the red blood cells is made up of carbohydrate sugar polymers.
• The alleles I^A and I^B produce sugar such as N-acetylgalactosamine and D-galactose respectively. While allele 'i 'does not produce any sugar.
  • I^A allele: Encodes an enzyme that adds N-acetylgalactosamine to the H antigen, resulting in the A antigen.
  • I^B allele: Encodes an enzyme that adds D-galactose to the H antigen, resulting in the B antigen.
  • i allele: Does not encode any functional enzyme, thus the H antigen remains unchanged (no additional sugar is added).
• Humans are diploid organisms and each person possesses any two of the three I gene alleles.
• I^A and I^B are dominant over gene 'i'. 'i' is recessive as it does not produce any sugar.
• If I^A and I^B are present together they will both express their own types of sugars. The phenomenon of expressing the both trait is due to co-dominance.

Explanation:

Option  1)  A person will have only two of the 3 alleles. - CORRECT

• ABO blood typing is controlled by gene I.
• There are three alleles of the gene (I)- I ^A, I ^B, and i.
• A person can have any of the two alleles that are inherited from their parents.
• So, this option is correct

Option  2)  When I^A and I^B are present together, they express the same type of sugar. -INCORRECT

• I^A and I^B both produce different kinds of sugars.
• So, this option is incorrect

 Option  3)  Allele ‘i’ does not produce any sugar. – CORRECT

• Allele ‘i’ does not produce any sugar and therefore it is recessive.
• So, this option is correct.

Option  4)  The gene (I) has three alleles – CORRECT

• There are three alleles of the gene (I)- I^A, I^B, and i.
• So, this option is correct.

So, the incorrect option is Option  2)  When I^A and I^B are present together, they express the same type of sugar

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).