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6.5 Quantitative Genetics & Heritability — Test 2
Q1. When the progeny of diverse parental varieties show greater vigour, size and fertility than either parent, the phenomenon is called:✓ Heterosis (hybrid vigour)
Q2. A 1-pound apple variety is crossed with a 2-pound variety; F1 are 1.5 pounds. If weight is controlled by two unlinked additive genes, the F2 ratio of phenotypic classes is:✓ 1:4:6:4:1
Q3. Quantitative (polygenic) traits still obey Mendelian inheritance because:✓ Each contributing gene segregates and assorts in the normal Mendelian way
Q4. Polygenic (quantitative) trait loci in crops are commonly identified by:✓ QTL mapping
Q5. Variation in a quantitative trait is generally due to:✓ Variation in both genotype and environment
Q6. A new trait that is highly variable, shows a bell-shaped (normal) distribution and is influenced by the environment is most likely:✓ A polygenic trait
Q7. Clones of a single plant grown in a field show a range of heights forming a bell-shaped curve. This variation is due to:✓ Environmental effects
Q8. Heritability of a quantitative character measures:✓ The proportion of phenotypic variation due to genetic factors
Q9. Broad-sense heritability (H²) is calculated as:✓ VG / (VG + VE)
Q10. Two maize varieties averaging 48 and 72 inches are crossed; the F1 are uniform at 60 inches. Of 500 F2 plants, the two shortest are 48 inches and the two tallest 72 inches. The approximate number of contributing gene pairs is:✓ Four
Q11. Two pure lines of corn have mean cob lengths of 9 cm and 3 cm. With purely additive polygenes, the F1 mean cob length is expected to be:✓ 6.0 cm
Q12. Rabbit body weight is set by additive alleles at two loci. Genotype a⁻a⁻b⁻b⁻ averages 1 kg and a⁺a⁺b⁺b⁺ averages 3.4 kg. The F1 (a⁺a⁻b⁺b⁻) is expected to average:✓ 2.2 kg
Q13. Two inbred bean lines are crossed. The F1 has a variance of 2.0 and the F2 a variance of 7.0. The broad-sense heritability of bean length in the F2 is:✓ 0.71
Q14. Interacting genes that contribute to continuous variation in a quantitative phenotype are known as:✓ Quantitative trait loci (QTLs)
Q15. In a wheat cross, white × dark-red gives red F1, and the F2 is 1 dark-red : 4 : 6 : 4 : 1 white. This pattern indicates:✓ Two genes, each with two alleles, acting additively
Q16. Which statement about quantitative traits is INCORRECT?✓ Their genes do not segregate or assort independently
Q17. A disease-resistant plant is crossed with a susceptible one; the F1 is resistant and the F2 segregates 3 resistant : 1 susceptible. This resistance is best described as:✓ Qualitative (monogenic, dominant) resistance
Q18. Narrow-sense heritability (h²) differs from broad-sense heritability (H²) in that h² considers only the:✓ Additive genetic variance (VA)
Q19. Marker-assisted selection (MAS) for a quantitative agronomic trait works best with a molecular marker that is:✓ Tightly linked to the QTL of interest
Q20. Match each term with its description and select the correct option.✓ A-iii, B-i, C-ii, D-iv