Principles of Inheritance and Variation | Unit Test - 4 Sets of PDF QPs in one page with answer key I Class 12

➡️ Unit Test - 4 Sets of PDF QPs Download

CODE A (Max. score: 15)

1. A cross between two parents differing in two pairs of contrasting characters is called ………………. (1)
2. Mention the karyotype of Down’s syndrome. (1)
3. Gopalan argues that If father is ‘A’ blood group, mother is ‘B’ group, their children can only be A, B or AB groups. Do you agree with Gopalan’s argument? Why? (2)
4. Drosophila is a better material for genetic study. Why? (Any 4 reasons) (2)
5. Sex of the baby is determined by the father, not by the mother. Substantiate. (2)
6. Distinguish between α Thalassemia & β Thalassemia. (2)
7. Complete the table. (2)

   Symbols	Meanings
   ☐	a. ……………….
   b. ……………….	Female
   ⃟	c. ……………….
   d. ……………….	Affected male

8. Briefly explain Mendel’s Laws of Inheritance. (3)

Code A: ANSWER KEY

1. Dihybrid cross.
2. 45A + XX or 45A + XY
3. No, I do not agree.
   Reason: If both parents are heterozygous (Father: I^Ai and Mother: I^Bi), there is a 25% chance for the child to inherit 'O' blood group (genotype ii).
4. ● Can be grown on simple synthetic medium.
   ● Short life cycle (about 2 weeks).
   ● Single mating produces a large number of progeny flies.
   ● Clear differentiation of male and female sexes (sexual dimorphism).
   ● Many types of hereditary variations that can be seen under a low power microscope. (Any 4 points)
5. Females produce only one type of ovum carrying 'X' chromosome (homogametic). Males produce two types of sperms (heterogametic)—50% with 'X' chromosome and 50% with 'Y' chromosome. Fertilization of an ovum by an X-bearing sperm results in a female child (XX), and by a Y-bearing sperm results in a male child (XY). Hence, the father determines the sex of the baby.
6. α Thalassemia: Production of α globin chain is affected. Controlled by two closely linked genes HBA1 and HBA2 on chromosome 16.
   β Thalassemia: Production of β globin chain is affected. Controlled by a single gene HBB on chromosome 11.
7. a. Male
   b. ◯
   c. Sex unspecified
   d. ⬛
8. 1. Law of Dominance: Characters are controlled by discrete units called factors (genes) which occur in pairs. In a dissimilar pair of factors, one member dominates (dominant) the other (recessive).
   2. Law of Segregation: Alleles of a pair segregate from each other during gamete formation such that a gamete receives only one of the two factors.
   3. Law of Independent Assortment: When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters.

CODE B (Max. score: 15)

1. The crossing of an organism with dominant phenotype to a recessive individual is called ………………. (1)
2. Mention the karyotype of Turner’s syndrome. (1)
3. What is meant by pleiotropy? Give 2 examples. (2)
4. Distinguish between linkage and recombination. (2)
5. Match column I with column II. (2)

   Column I	Column II
   (a) XX-XO mechanism	i. Honeybee
   (b) XX-XY mechanism	ii. Birds
   (c) ZZ-ZW mechanism	iii. Grasshopper
   (d) Haplodiploid sex determination	iv. Human & Drosophila

6. Analyse the diagram of pedigree analysis and answer the following questions. (2)

   

   1. Mention the number of male and female offspring.
   2. How many individuals are affected? Mention the ratio of affected male and female offspring.
7. Write down the possible gametes from the genotype TtYy (heterozygous tall yellow). (2)
8. What is meant by Mendelian disorders? Briefly explain any two blood related Mendelian disorders. (3)

Code B: ANSWER KEY

1. Test cross.
2. 45 (44A + X0).
3. Pleiotropy is the phenomenon where a single gene exhibits multiple phenotypic expressions.
   Examples: Phenylketonuria, Sickle-cell anaemia.
4. Linkage: Physical association of two or more genes on the same chromosome.
   Recombination: Generation of non-parental gene combinations due to crossing over during meiosis.

5. Column I	Column II
   (a) XX-XO mechanism	iii. Grasshopper
   (b) XX-XY mechanism	iv. Human & Drosophila
   (c) ZZ-ZW mechanism	ii. Birds
   (d) Haplodiploid sex determination	i. Honeybee

6. 1. Number of male offspring: 2
      Number of female offspring: 3
   2. 2 individuals are affected.
      Ratio of affected male and female offspring = 1 : 1.
7. TY, Ty, tY, ty.
8. Mendelian disorders: Genetic disorders mainly caused by alteration or mutation in a single gene.
   1. Haemophilia: Sex-linked recessive disease. A single protein involved in blood clotting is affected, leading to non-stop bleeding from simple cuts.
   2. Sickle-cell anaemia: Autosomal recessive disorder caused by substitution of Glutamic acid by Valine at 6th position of β-globin chain, causing RBCs to become sickle-shaped under low oxygen tension.

CODE C (Max. score: 15)

1. An inheritance in which heterozygous offspring shows intermediate character between two parental characteristics is called ………………. (1)
2. Note the relationship between first two words and fill up the fourth place.
   45A + XX: Down’s syndrome
   44A + X0: …………… (1)
3. Distinguish between the sex determination mechanisms in Drosophila and Grasshopper. (2)
4. Match the following: (2)

   A	B
   a) Monohybrid phenotypic ratio	9:3:3:1
   b) Monohybrid genotypic ratio	3:1
   c) Monohybrid test cross ratio	1:2:1
   d) Dihybrid phenotypic ratio	1:1

5. What is polygenic inheritance? Explain with suitable example. (2)
6. Differentiate point mutation & frameshift mutation. (2)
7. Briefly explain Phenylketonuria. (2)
8. 1. Distinguish between Aneuploidy and Polyploidy.
   2. Mention any 2 features of Klinefelter’s syndrome. (3)

Code C: ANSWER KEY

1. Incomplete dominance.
2. Turner’s syndrome.
3. Drosophila: XX-XY type. Males have one X and one Y chromosome (XY), females have two X chromosomes (XX).
   Grasshopper: XX-XO type. Males have only one X chromosome (XO), females have two X chromosomes (XX).

4. A	B
   a) Monohybrid phenotypic ratio	3:1
   b) Monohybrid genotypic ratio	1:2:1
   c) Monohybrid test cross ratio	1:1
   d) Dihybrid phenotypic ratio	9:3:3:1

5. Polygenic inheritance: Inheritance controlled by multiple genes (polygenes) where the phenotype reflects the contribution of each allele.
   Example: Human skin colour (controlled by three genes A, B, C). The dominant alleles A, B & C responsible for dark skin colour and recessive alleles a, b & c for light skin colour.
6. Point mutation: Mutation that arises due to change in a single base pair of DNA. E.g., Sickle-cell anaemia.
   Frameshift mutation: Mutation caused by insertion or deletion of one or two base pairs in DNA, altering the reading frame.
7. Inborn error of metabolism, inherited as an autosomal recessive trait. Affected individual lacks the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. Accumulation of phenylalanine converts it into phenylpyruvic acid, causing mental retardation and poor absorption by kidneys.
8. 1. Aneuploidy: Gain or loss of a chromosome(s) due to failure of segregation of chromatids during cell division.
      Polyploidy: Increase in a whole set of chromosomes due to failure of cytokinesis after telophase stage.
   2. ● Overall masculine development with feminine development (e.g., Gynecomastia / development of breast).
      ● Individuals are sterile.

CODE D (Max. score: 15)

1. A cross involving 2 plants differing in one character pair is called ………………. (1)
2. Note the relationship between first two words and fill up the fourth place.
   Mendel: Pisum sativum
   Morgan: …………… (1)
3. Mention the karyotype of Klinefelter’s syndrome. Write any 3 symptoms. (2)
4. What is multiple allelism? Explain with an example. (2)
5. Distinguish between incomplete dominance and codominance. (2)
6. Briefly explain Chromosomal theory of inheritance. Name the scientists who proposed this theory. (2)
7. Observe the β globin chains of two persons. (2)

   

   1. Which person has abnormal β globin chain?
   2. Name the disorder affected him.
   3. What will be the effect of this change?
8. 1. What is pedigree analysis?
   2. What is its importance in human genetics?
   3. Draw the symbols for:
      1. Affected female
      2. Consanguineous mating (3)

Code D: ANSWER KEY

1. Monohybrid cross.
2. Drosophila melanogaster.
3. Karyotype: 47 (44A + XXY).
   Symptoms: Overall masculine development, development of breasts (Gynecomastia), sterile individual, tall stature. (Any 3)
4. Multiple allelism: Presence of more than two alleles governing the same character in a population.
   Example: ABO blood grouping in humans controlled by three alleles I^A, I^B, and i.
5. Incomplete dominance: F1 phenotype does not resemble either of the two parents and is in between the two (intermediate). E.g., Flower colour in Snapdragon (Antirrhinum).
   Codominance: F1 phenotype resembles both parents, as both alleles express themselves fully. E.g., AB blood group in humans.
6. It states that chromosomes are the carriers of Mendelian factors (genes) and chromosomes segregate and assort independently during meiosis just like genes.
   Proposed by: Walter Sutton and Theodore Boveri (1902).
7. 1. Person A.
   2. Sickle-cell Anaemia.
   3. The mutant haemoglobin undergoes polymerisation under low oxygen tension, changing the shape of RBC from biconcave disc to elongated sickle-like structure.
8. 1. Analysis of genetic traits in several generations of a family is called pedigree analysis.
   2. It helps to trace the inheritance of specific traits, genetic abnormalities, or hereditary diseases in human families.
   3. i. Affected female: ●
      ii. Consanguineous mating: □=○