6.What is heredity? Define the terms: (a) Gene, (b) Allele, (c) Locus, and (d) Genome.
7.Why did Gregor Mendel select the garden pea plant (Pisum sativum) for his genetic hybridization experiments? List four distinct advantages of this plant.
8.List the seven pairs of contrasting traits in garden pea plants studied by Mendel, identifying which allele was dominant and which was recessive in each pair.
9.Define a monohybrid cross. Illustrate Mendel's monohybrid cross between a pure tall pea plant (TT) and a pure dwarf pea plant (tt) using a Punnett square. Find the phenotypic and genotypic ratios of the $F_2$ generation.
10.State Mendel's Law of Dominance based on his monohybrid cross observations. How does this law explain why dwarfism is hidden in the $F_1$ generation?
11.Explain Mendel's Law of Segregation (Law of Purity of Gametes). Why does a gamete always contain only one allele for a given gene?
12.What is a test cross? How did Mendel use a test cross to determine whether a tall pea plant in the $F_2$ generation had a homozygous (TT) or heterozygous (Tt) genotype?
13.Define a dihybrid cross. Illustrate Mendel's dihybrid cross between a pure round-yellow seeded plant (RRYY) and a pure wrinkled-green seeded plant (rryy) using a Punnett square showing the $F_2$ generation.
14.State the phenotypic ratio obtained in the $F_2$ generation of a Mendel's dihybrid cross. Identify the new phenotypic combinations obtained and discuss how they arise.
15.State Mendel's Law of Independent Assortment based on his dihybrid cross observations. Explain why genes for two different traits do not influence each other's distribution during gamete formation.
16.Differentiate between homozygous and heterozygous genotypes, giving one genetic example of each.
17.Differentiate between phenotype and genotype of an organism. Can two organisms have the same phenotype but different genotypes? Explain.
18.How are traits expressed in an organism? Explain the biochemical pathway: Gene → Protein (Enzyme) → Metabolic Action → Trait Expression using stem height as an example.
19.How do eukaryotic cells maintain a complete set of genes on discrete chromosomes rather than on a single long DNA molecule? Explain the importance of pairing of chromosomes.
20.Explain the chromosomal theory of inheritance in brief. How does the union of sperm and egg during fertilisation restore the diploid chromosome number in the zygote?
21.What is sex determination? Explain the two primary mechanisms (environmental and genetic) of sex determination, giving examples of organisms for each.
22.How is the sex of a human child determined genetically? Draw a neat genetic cross diagram showing the inheritance of sex chromosomes from parents to offspring.
23.Why is the probability of a human couple having a boy or a girl always exactly 50% (1:1 ratio)? Explain based on male heterogamety.
24.In some societies, women are blamed and mistreated for giving birth only to female children. Evaluate this practice scientifically and explain why the male parent is genetically responsible for the sex of the child.
25.How does sex determination in reptiles (like turtles and lizards) differ from that in humans? Explain how ambient incubation temperature affects the sex ratio.
26.Explain how snails show flexibility in sex determination. What does this indicate about the nature of sex determination in some lower animals?
27.What are autosomes and sex chromosomes? How many pairs of each are present in a normal human somatic cell?
28.Why does a human male have a mismatched pair of sex chromosomes? Compare the physical size and gene content of the X and Y chromosomes.
A botanist crosses a homozygous violet-flowered pea plant (VV) with a homozygous white-flowered pea plant (vv). All F1 plants produce only violet flowers. She self-pollinates these F1 plants to obtain the F2 generation. The total number of F2 plants produced is 400.
29.Based on Case Study 1, answer the following:
- What will be the genotype of the F1 generation? Why do they produce only violet flowers?
- Calculate the expected number of violet-flowered plants and white-flowered plants in the F2 generation of 400 plants.
- State the genotypic ratio of the F2 generation.
In a school lab, students cross a pea plant with round-yellow seeds (RrYy) with a plant showing wrinkled-green seeds (rryy). This is a test cross for two traits. They count the resulting offspring and observe that they do not get a standard 9:3:3:1 ratio. Instead, they get approximately equal numbers of four different phenotypes.
30.Based on Case Study 2, answer the following:
- What are the four different phenotypes obtained in the offspring of this cross?
- Draw the Punnett square for this specific cross (RrYy x rryy) and state the genotypic and phenotypic ratio.
- Does this cross support Mendel's Law of Independent Assortment? Explain.
A child has blood group O. The mother of the child has blood group A, and the father has blood group B. The maternal grandparents are shocked, claiming that the child must have been swapped in the hospital. The doctor uses Mendelian genetics to explain that this is biologically expected.
31.Based on Case Study 3, answer the following:
- What must be the genotypes of the mother and the father to yield a child with blood group O? (Use alleles $I^A$, $I^B$, and $i$).
- Draw a genetic cross showing how a couple with blood groups A and B can have a child with blood group O. What is the probability of this happening?
- Name the genetic phenomenon shown by the AB blood group in humans, where both alleles express themselves fully.
Ecologists studying a crocodile nesting site in a tropical swamp notice that due to a heatwave, the average nest incubation temperature has risen to 34 °C. Over the next three breeding seasons, they record that nearly 98% of the hatched crocodile hatchlings are male, creating a severe sex imbalance.
32.Based on Case Study 4, answer the following:
- What mode of sex determination is exhibited by crocodiles? How does it differ from humans?
- Explain how high incubation temperatures affect the active enzymes responsible for sex hormone synthesis in reptile eggs.
- Discuss the long-term threat of climate change and rising global temperatures on the survival of species with environmental sex determination.
A student grows tall pea plants (Tt) and self-pollinates them. She wants to select only the homozygous tall (TT) plants from the progeny for a future breeding program, but she cannot distinguish them by their physical appearance since both TT and Tt plants look identical.
33.Based on the Stem Challenge, answer the following:
- Explain why the student cannot identify homozygous tall plants by physical inspection alone.
- Describe a genetic breeding method (cross) that the student can perform to verify the genotype of any selected tall plant.
- Draw the two possible genetic crosses and describe the expected phenotypic ratios in the offspring that will confirm the genotype.
A farmer has a sack of round-yellow seeds. He knows that round (R) is dominant over wrinkled (r) and yellow (Y) is dominant over green (y). The seeds could have any of four genotypes: RRYY, RrYY, RRYy, or RrYy. The farmer needs to identify the exact genotype of a specific seed 'S' from the sack.
34.Based on the puzzle description, answer the following:
- If the farmer crosses the plant grown from seed 'S' with a wrinkled-green seeded plant (rryy) and gets only round-yellow seeded plants in the progeny, what is the genotype of 'S'?
- If the progeny of the cross contains 50% round-yellow and 50% wrinkled-yellow seeds, identify the genotype of 'S'.
- If the progeny contains 25% round-yellow, 25% round-green, 25% wrinkled-yellow, and 25% wrinkled-green seeds, what is the genotype of 'S'?
35.Why is variation in a population beneficial for the species but not necessarily for the individual? Explain with an example of an individual carrying a mutation that makes it highly sensitive to cold water.
36.What is the difference between a dominant trait and a recessive trait? State Mendel's findings that prove traits can be inherited but may not be expressed in an individual.
37.Describe how Mendel's experiment shows that traits are inherited independently. Construct a dihybrid phenotypic matrix to support your answer.
38.Explain why a homozygous tall pea plant (TT) crossed with a homozygous dwarf pea plant (tt) produces only tall plants in the F1 generation, but dwarf plants reappear in the F2 generation. Construct the genetic cross.
39.Explain the genetic mechanism of sex determination in humans. Why are all human eggs chemically identical in terms of sex chromosomes, whereas sperms are of two types?
40.Why did Mendel obtain exactly a 3:1 ratio in the F2 generation of his monohybrid crosses? Discuss in terms of probability and independent alignment of gametes.
41.Explain how the genotype of an organism is represented by letters, using a homozygous recessive dwarf plant as an example. Why do we write alleles in pairs?
42.What is co-dominance? How does human blood group inheritance demonstrate both co-dominance and multiple allelism?
43.How do genes control the biochemical characteristics of an organism? Explain the role of DNA as an information source for making proteins.
44.A heterozygous tall pea plant (Tt) is crossed with a homozygous tall plant (TT). What will be the phenotypic and genotypic ratios of the offspring? Draw the Punnett square.
45.A pure round-green seeded pea plant (RRyy) is crossed with a pure wrinkled-yellow seeded plant (rrYY). What will be the phenotype of the F1 generation? If the F1 generation is self-pollinated, list the phenotypes in F2.
46.Explain why acquired traits (like muscles built in a gym or a cut tail of a mouse) cannot be inherited by the progeny. Discuss in terms of somatic vs germ cells.
47.State the contribution of Gregor Mendel to the field of genetics. Why is he universally referred to as the "Father of Genetics"?
48.A man with blood group A marries a woman with blood group O. Their daughter has blood group O. What does this tell you about the dominance of alleles $I^A$ and $i$? Explain.
49.What is genetic drift? Discuss how genetic drift can alter allele frequencies in a small population due to random accidents rather than natural selection.
50.How does the cellular mechanism of inheritance work during gamete formation? Why does each gamete receive only one chromosome from each homologous pair?
51.Explain the difference between a self-cross and a back-cross. How does a back-cross help plant breeders?
52.Why is sex determination in humans genetic, whereas in turtles it is temperature-dependent? Discuss the evolutionary origin of both systems.
53.What would be the effect of a mutation that inactivates the SRY gene on the Y chromosome of a human zygote? What sex would the child develop into?
54.Explain how Mendel ensured that his parental pea plants were true-breeding before commencing his crosses.
55.A student crosses a pink-flowered plant with another pink-flowered plant of the same species and gets 25% red, 50% pink, and 25% white-flowered offspring. Name and explain this genetic phenomenon.
56.Why is the ratio of males to females in a large human population generally very close to 1:1? Show mathematically using sperm types.
57.Explain how the law of segregation ensures that alleles are not blended or lost in the F1 generation, even though the recessive trait is not physically visible.
58.If you cross a homozygous tall plant with round seeds (TTRR) with a dwarf plant with wrinkled seeds (ttrr), what will be the genotype of the F1 offspring? Write the gametes produced by the F1 generation.
59.A researcher exposes fruit flies to X-rays to induce mutations in their somatic cells. Will these mutations be inherited by their offspring? Explain.
60.How does sexual reproduction restore the diploid number of chromosomes in a zygote without increasing it indefinitely over subsequent generations?
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