Principles OF Inheritance AND Variation` flash cards

1. 1.Who is regarded as the 'Father of Genetics' and on which plant did he work?

   Gregor Johann Mendel; he worked on the garden pea, Pisum sativum (1856-1863).

   Hint: Austrian monk, pea plant.

2. 2.Why was Pisum sativum an ideal choice for Mendel's hybridisation experiments?

   It has many distinct contrasting characters, is normally self-pollinating (pure lines), has a short life cycle, produces many offspring, and can be easily cross-pollinated artificially.

   Hint: Pure lines + easy to cross.

3. 3.How many pairs of contrasting characters of the pea plant did Mendel select for study?

   Seven pairs of contrasting traits (e.g., seed shape, seed colour, flower colour, pod shape, pod colour, flower position, plant height).

   Hint: Same as number of chromosomes... coincidentally 7.

4. 4.List the seven contrasting characters studied by Mendel with dominant traits.

   Seed shape (round dominant), seed colour (yellow), flower colour (violet/purple), pod shape (inflated/full), pod colour (green), flower position (axial), stem height (tall).

   Hint: Round, yellow, violet, inflated, green, axial, tall.

5. 5.Define the term 'allele'.

   Alleles are slightly different (alternative) forms of the same gene occupying the same locus on homologous chromosomes and controlling a particular character (e.g., T and t).

   Hint: Alternative forms of a gene.

6. 6.Distinguish between genotype and phenotype.

   Genotype is the genetic constitution of an organism (e.g., Tt); phenotype is the observable/expressed characteristic (e.g., tall).

   Hint: Genes written vs trait seen.

7. 7.Distinguish between homozygous and heterozygous.

   Homozygous = both alleles identical (TT or tt), breeds true; heterozygous = two different alleles (Tt), a hybrid.

   Hint: Same pair vs different pair.

8. 8.What is a monohybrid cross?

   A cross between two parents differing in a single pair of contrasting characters (e.g., tall TT x dwarf tt).

   Hint: Mono = one character.

9. 9.QUESTION (ratio): In a monohybrid cross (Tt x Tt), what is the phenotypic ratio in the F2 generation?

   $3:1$ (3 tall : 1 dwarf).

   Hint: Classic monohybrid F2.

10. 10.QUESTION (ratio): What is the genotypic ratio of a monohybrid F2 (Tt x Tt)?

    $1:2:1$ (1 TT : 2 Tt : 1 tt).

    Hint: Homozygous dom : hetero : homozygous rec.

11. 11.In Mendel's monohybrid cross, what were all F1 plants and why?

    All F1 were tall because tall (T) is completely dominant over dwarf (t); the dwarf trait was masked.

    Hint: F1 shows only the dominant trait.

12. 12.State Mendel's Law of Dominance.

    Characters are controlled by discrete units called factors; factors occur in pairs; in a dissimilar pair one member (dominant) expresses itself while the other (recessive) is masked.

    Hint: One factor of a pair dominates.

13. 13.State Mendel's Law of Segregation (Law of Purity of Gametes).

    The two alleles of a character segregate (separate) during gamete formation so that each gamete receives only one allele; alleles do not blend and are pure.

    Hint: Gametes are always pure for one allele.

14. 14.Why is the Law of Segregation also called the Law of Purity of Gametes?

    Because the alleles separate without mixing, so each gamete carries only one pure allele of the pair (never both, never a blend).

    Hint: Gamete carries only one factor.

15. 15.What is a Punnett square?

    A checkerboard/graphical device (devised by R.C. Punnett) used to calculate the probability of all possible genotypes of offspring by combining gametes of both parents.

    Hint: Checkerboard of gametes.

16. 16.What is a test cross? Why is it performed?

    Crossing an organism showing a dominant phenotype (unknown genotype) with the homozygous recessive parent, to determine whether the dominant individual is homozygous or heterozygous.

    Hint: Cross with the recessive parent.

17. 17.QUESTION (ratio): In a test cross of a heterozygous tall plant (Tt x tt), what is the phenotypic ratio of offspring?

    $1:1$ (1 tall : 1 dwarf).

    Hint: Hetero x recessive = 1:1.

18. 18.QUESTION (ratio): In a test cross, if a dominant individual is homozygous (TT x tt), what offspring result?

    All offspring show the dominant phenotype (all tall); ratio is uniform, no recessives appear.

    Hint: Homozygous dominant = 100% dominant.

19. 19.How does a test cross differ from a back cross?

    A back cross is a cross of F1 with either parent; a test cross is specifically a cross of F1 (or any dominant phenotype) with the homozygous recessive parent to reveal genotype.

    Hint: Test cross = back cross with recessive parent.

20. 20.What is a dihybrid cross?

    A cross between two parents differing in two pairs of contrasting characters simultaneously (e.g., round yellow RRYY x wrinkled green rryy).

    Hint: Two characters together.

21. 21.QUESTION (ratio): What is the F2 phenotypic ratio of a dihybrid cross (RrYy x RrYy)?

    $9:3:3:1$ (9 round-yellow : 3 round-green : 3 wrinkled-yellow : 1 wrinkled-green).

    Hint: Classic dihybrid ratio.

22. 22.QUESTION (ratio): How many genotypes and phenotypes appear in a dihybrid F2?

    9 different genotypes and 4 different phenotypes.

    Hint: 9 genotypes, 4 phenotypes.

23. 23.QUESTION (ratio): What is the genotypic ratio of a dihybrid F2?

    $1:2:1:2:4:2:1:2:1$ (the 9-genotype distribution among 16).

    Hint: Nine boxes, 1:2:1 pattern squared.

24. 24.State Mendel's Law of Independent Assortment.

    When two pairs of contrasting characters are considered together, the alleles of one pair segregate (assort) independently of the alleles of the other pair during gamete formation.

    Hint: Each trait pair assorts independently.

25. 25.QUESTION (ratio): How many types of gametes does a dihybrid RrYy produce, and in what proportion?

    Four types — RY, Ry, rY, ry — in equal proportion $1:1:1:1$.

    Hint: 2^2 = 4 gamete types.

26. 26.QUESTION (ratio): In a dihybrid F2, what fraction shows both recessive traits (wrinkled green)?

    $1/16$ (rryy).

    Hint: The '1' of 9:3:3:1.

27. 27.QUESTION (ratio): In the dihybrid F2, what is the ratio when you consider each character separately?

    Each character independently gives $3:1$ (3 round : 1 wrinkled, and 3 yellow : 1 green), confirming independent assortment.

    Hint: 9:3:3:1 breaks into two 3:1s.

28. 28.What is incomplete dominance? Give an example.

    A condition where neither allele is completely dominant, so the heterozygote shows an intermediate (blended) phenotype — e.g., pink flowers in Mirabilis jalapa (4 o'clock plant) / snapdragon from red x white.

    Hint: F1 is intermediate (pink).

29. 29.QUESTION (ratio): In incomplete dominance (red RR x white rr → pink Rr), what are the F2 phenotypic and genotypic ratios?

    Both are the same: $1:2:1$ (1 red : 2 pink : 1 white).

    Hint: Phenotype = genotype ratio here.

30. 30.What is co-dominance? Give an example.

    When both alleles of a pair express themselves fully and simultaneously in the heterozygote (neither is dominant nor recessive) — e.g., AB blood group where both A and B antigens appear; also roan coat in cattle.

    Hint: Both alleles shown together (AB).

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