Questions: Principles of Inheritance and Variation

Q1. State Mendel's law of dominance and the law of segregation.

Answer (English): The law of dominance says that in a pair of contrasting characters, the character that expresses itself in the heterozygote is dominant and the other is recessive. The law of segregation says that the two factors of a pair separate during gamete formation, so each gamete carries only one factor of the pair. Segregation is universal, while dominance depends on the trait.

Hinglish: Law of dominance kehta hai ki heterozygote mein jo character dikhta hai woh dominant hai aur doosra recessive. Law of segregation kehta hai ki gamete banne waqt do factors alag ho jate hain, isliye har gamete mein ek hi factor jata hai. Segregation universal hai, dominance trait par depend karti hai.

Q2. Why did Mendel choose pea plants, and which seven traits did he study?

Answer (English): Mendel chose the garden pea because it grows quickly, can be self pollinated to keep pure lines, and can also be cross pollinated by hand. It has clear pairs of contrasting traits, so the offspring can be put into distinct classes. The seven traits were flower colour, flower position, seed colour, seed shape, pod colour, pod shape and stem height.

Hinglish: Pea plant tez ugti hai, self pollination se pure lines banti hain, aur haath se cross bhi kiya ja sakta hai. Iske traits clear contrasting pairs mein hote hain. Saat traits: flower colour, flower position, seed colour, seed shape, pod colour, pod shape aur stem height.

Q3. What is a test cross and when is it used?

Answer (English): A test cross is a cross between an individual whose genotype is unknown and a homozygous recessive individual. It is used to find out whether the unknown individual is homozygous or heterozygous for a dominant trait. If the unknown plant is homozygous tall, all offspring are tall; if it is heterozygous, half the offspring are dwarf. The appearance of any dwarf offspring proves the parent was heterozygous.

Hinglish: Test cross mein unknown genotype wale individual ko homozygous recessive se cross karte hain, taaki pata chale woh homozygous hai ya heterozygous. Agar tall plant TT hai to sab offspring tall; agar Tt hai to aadhe dwarf. Ek bhi dwarf offspring milna prove karta hai ki parent heterozygous tha.

Q4. Explain incomplete dominance with the snapdragon example.

Answer (English): In incomplete dominance the heterozygote shows a phenotype that is between the two homozygotes. In snapdragon, red flowered plants crossed with white flowered plants give pink F1 plants. When the F1 plants are self pollinated, the F2 generation has red, pink and white plants in the ratio 1 : 2 : 1, which is also the genotypic ratio. The allele for red pigment is not completely dominant, so a single dose gives a diluted colour.

Hinglish: Incomplete dominance mein heterozygote ka phenotype dono homozygotes ke beech ka hota hai. Snapdragon mein red aur white ko cross karne par pink F1 aata hai; selfing se F2 mein red, pink aur white 1 : 2 : 1 mein aate hain, jo genotypic ratio bhi hai. Red allele complete dominant nahi hai isliye ek dose se halka rang aata hai.

Q5. State the law of independent assortment and explain the 9 : 3 : 3 : 1 ratio.

Answer (English): The law says that when two pairs of traits are considered together, the segregation of one pair is independent of the segregation of the other. In a dihybrid cross between two heterozygotes, each pair separately gives a 3 : 1 ratio, and multiplying the two gives 9 : 3 : 3 : 1. The new combinations, round green and wrinkled yellow, appear because the two gene pairs assort independently during gamete formation.

Hinglish: Independent assortment ka matlab do trait pairs ek saath lete waqt ek pair ka segregation doosre se independent rehta hai. Dihybrid cross mein har pair alag 3 : 1 deta hai; dono ko multiply karo to 9 : 3 : 3 : 1 milta hai. Round green aur wrinkled yellow jaise naye combinations independent assortment ki wajah se bante hain.

Q6. What is linkage? How did Morgan demonstrate it?

Answer (English): Linkage is the tendency of genes located on the same chromosome to be inherited together. Morgan crossed Drosophila flies and followed two genes at a time. He found that parental combinations appeared much more often than new recombinant combinations, whereas independent assortment predicts equal parental and recombinant classes. He concluded that genes on the same chromosome are linked, and that the closer two genes are, the fewer recombinants they produce. The white eye and yellow body genes were tightly linked.

Hinglish: Linkage matlab ek hi chromosome par wale genes ka saath inherit hona. Morgan ne Drosophila mein do genes ek saath follow kiye aur dekha ki parental combinations zyada aate hain aur recombinants kam, jabki independent assortment barabar classes deta. Isse pata chala ki same chromosome ke genes linked hain, aur paas ke genes mein recombination kam hota hai. White eye aur yellow body tightly linked the.

Q7. Write any two differences between Mendelian and chromosomal disorders.

Answer (English): Mendelian disorders are caused by a defect in a single gene, are inherited according to Mendel's laws, and include haemophilia, sickle cell anaemia and phenylketonuria. Chromosomal disorders are caused by an extra or missing chromosome or by a change in chromosome structure, are detected by karyotyping, and include Down syndrome, Klinefelter syndrome and Turner syndrome. Mendelian disorders do not usually show a chromosome number change, while chromosomal disorders do.

Hinglish: Mendelian disorders ek gene ke defect se hote hain aur Mendel ke laws follow karte hain, jaise haemophilia, sickle cell aur PKU. Chromosomal disorders chromosome ke extra ya missing hone se hote hain aur karyotyping se pakde jate hain, jaise Down, Klinefelter aur Turner. Mendelian mein chromosome number same rehta hai, chromosomal mein badalta hai.

Q8. Explain the inheritance of haemophilia.

Answer (English): Haemophilia is an X linked recessive disorder in which a clotting protein is missing. A female is affected only if both her X chromosomes carry the allele, because the normal allele on one X is enough to produce the protein. A male has only one X, so a single recessive allele makes him affected. An unaffected carrier mother can therefore have an affected son, and this is exactly the pedigree pattern asked in the paper.

Hinglish: Haemophilia X linked recessive hai, ismein clotting protein nahi banta. Female ko disease tab hoti hai jab uske dono X par allele ho, kyunki ek normal X kaafi hota hai. Male ke paas ek hi X hota hai, isliye ek recessive allele se woh affected ho jata hai. Isliye carrier mother se affected son ho sakta hai.

Q9. Distinguish between Down syndrome and Turner syndrome.

Answer (English): Down syndrome is caused by an extra chromosome 21, so the karyotype is 47 with trisomy 21; the affected child has a furrowed tongue, a single palmar crease and delayed development. Turner syndrome is caused by the absence of one X chromosome in a female, giving a karyotype of 45 X0; the affected female has rudimentary ovaries and is usually sterile. Down syndrome is autosomal, while Turner syndrome is a sex chromosome disorder.

Hinglish: Down syndrome mein chromosome 21 ki extra copy hoti hai, karyotype 47, aur furrowed tongue, palm crease aur delayed development dikhte hain. Turner syndrome mein ek X missing hota hai, karyotype 45 X0, aur ovaries rudimentary hote hain aur female aksar sterile hoti hai. Down autosomal disorder hai, Turner sex chromosome disorder hai.

Q10. What is a point mutation? Give one example and its effect.

Answer (English): A point mutation means that one base pair in the DNA is altered, as in a substitution. In sickle cell anaemia a single base change in the beta globin gene replaces glutamic acid with valine at the sixth position of the chain. The altered haemoglobin sticks together at low oxygen, so the red blood cells become sickle shaped and carry less oxygen. The mutation is autosomal recessive, so only a homozygous child has the disease.

Hinglish: Point mutation DNA ke ek base pair ka badalna hai, jaise substitution. Sickle cell anaemia mein beta globin gene mein ek base badalne se sixth position par glutamic acid ki jagah valine aa jata hai. Kam oxygen par badla hua haemoglobin chipak jata hai, RBC sickle shape le leti hain aur oxygen kam le jati hain. Yeh autosomal recessive hai, isliye homozygous child ko hi disease hoti hai.

Quiz: the five question check for this chapter covers Mendelian ratios, blood groups, linkage, sex determination and genetic disorders. Attempt it after the questions above, then revise the topic page where you lost a mark.