Genetics and Heritability: Principles, Laws, and Inheritance Types

1. What principle states that alleles for a gene separate during gamete formation?

Principle of Segregation.

2. Which law describes how alleles of different genes segregate independently during gamete formation?

Principle of Independent Assortment.

3. In pea plants, tall (Le) is dominant to short (le). What is the phenotype ratio in a cross of two heterozygotes?

3 tall : 1 short.

4. What is it called when one gene masks or modifies the effect of another gene?

Epistasis.

5. When both alleles are equally expressed, this is known as what type of inheritance?

Co-dominance.

6. In incomplete dominance, how does the heterozygote's phenotype compare to the homozygotes?

Intermediate phenotype.

7. What violates Mendel's law of independent assortment?

Linkage.

8. If two carriers of a lethal recessive gene mate, what proportion of offspring are expected to die?

25%.

9. Which type of inheritance is controlled by genes located on the X chromosome?

Sex-linked inheritance.

10. A male has genotype XoY for coat color. What color will he express?

Orange.

11. Define a quantitative trait.

A trait influenced by many genes and environmental factors.

12. What equation represents phenotype as a function of genetics and environment?

P = G + E.

13. What does BV stand for, and what does it represent?

Breeding Value; additive genetic merit.

14. What is the dominance deviation (d)?

Deviation of heterozygote from midpoint of homozygotes.

15. What is the additive effect (a)?

Half the difference between homozygotes.

16. What is the Expected Progeny Difference (EPD)?

Expected genetic difference in progeny.

17. What does G×E stand for, and what does it represent?

Genotype × Environment interaction; how genotypes perform differently in environments.

18. Which genetic effect can be passed to offspring: BV or GCV?

BV.

19. What is the relationship between PTA and BV?

PTA = ½ BV.

20. In cattle, what does STA = +1 mean?

One standard deviation above average.

21. Define the Gene Combination Value (GCV).

Value derived from dominance and epistasis effects unique to an individual.

22. Which type of gene interaction describes when one genotype performs better in one environment, but worse in another?

G×E crossover interaction.

23. Give an example of a major gene affecting a livestock trait.

Estrogen receptor in pigs; DGAT1 in cows.

24. What is the sum of additive effects across all loci called?

Genome-wide breeding value.

25. What is the difference between additive and dominance effects?

Additive effects are inherited; dominance effects are not.

26. Define narrow-sense heritability.

Proportion of phenotypic variance due to additive genetic effects.

27. Define broad-sense heritability.

Proportion of phenotypic variance due to all genetic effects.

28. What does repeatability measure?

Consistency of performance over time.

29. What is the equation for heritability (h²)?

h² = σ²A / σ²P.

30. How is EBV calculated using heritability?

EBV = h² × (Performance - Average).

31. What statistical method is used to predict breeding values in livestock?

BLUP (Best Linear Unbiased Prediction).

32. If h² = 0.25 and a pig's performance is +100 above average, what is its EBV?

+25.

33. What does it mean if a trait has h² = 0?

There is no additive genetic variance for that trait.

34. Why is heritability a population measure and not an individual one?

Because heritability measures variance within a population, not between individuals.

35. What is the correlation between true BV and EBV called?

Accuracy.

36. What is the Hardy-Weinberg equilibrium formula?

p² + 2pq + q² = 1.

37. List the five assumptions of Hardy-Weinberg equilibrium.

No mutation, no migration, no selection, random mating, large population (no drift).

38. If p = 0.8, what is q?

q = 0.2.

39. Calculate the expected frequency of homozygous recessive individuals when q = 0.3.

q² = 0.09 or 9%.

40. What factor causes random changes in allele frequencies, especially in small populations?

Genetic drift.

41. What type of mating occurs when individuals choose mates with similar phenotypes?

Assortative mating.

42. Which evolutionary force introduces new alleles into a population?

Mutation.

43. Give an example of a mutation that changes phenotype in animals.

SLC45A2 mutation (white tiger).

44. What is migration in genetic terms?

Movement of alleles between populations.

45. What effect does inbreeding have on heterozygosity?

It reduces heterozygosity.

46. Why might a trait be genetically determined but not heritable?

If there's no genetic variation in that trait.

47. What is pleiotropy?

When one gene affects multiple traits.

48. In a dihybrid cross (YyRr × YyRr), what is the probability of Yy rr offspring?

2/16 or 12.5%.

49. Which component of variance is affected by early-life management?

Permanent environment (Ep).

50. Which component of variance changes daily?

Temporary environment (Et).

51. How does genotype-environment interaction affect selection outcomes?

It changes how genotypes perform under different conditions, affecting selection success.

52. If heritability of milk yield is high, how will selection affect genetic progress?

Selection will result in faster genetic improvement.

53. Why can't dominance and epistatic effects be directly passed to offspring?

They depend on allele combinations, not individual alleles.

54. What is an example of a threshold trait in livestock?

Mastitis or calving difficulty.

55. What type of distribution do quantitative traits usually follow?

Normal (bell-shaped) distribution.

56. How do additive and environmental effects combine to shape phenotype?

They add together to form total phenotype (P = G + E).

57. What is the equation that includes BV, GCV, and environmental components?

P = BV + GCV + Ep + Et + G×E.

58. In population genetics, what happens if selection favors a recessive allele?

The allele increases slowly since it is hidden in heterozygotes.

59. What is linkage and how does it affect inheritance patterns?

Genes on the same chromosome are inherited together, violating independent assortment.

60. What is the main difference between simple and quantitative traits?

Simple traits involve few genes; quantitative traits involve many genes plus environmental effects.