In mice, the allele for brown fur is dominant to the allele for white fur. The diagram shows the inheritance of fur colour in a family of mice.
Which two individuals are heterozygous for fur colour?
A) 1 and 4
B) 2 and 8
C) 6 and 7
D) 7 and 10
▶️ Answer/Explanation
Ans: B
Let B represent the dominant brown allele and b the recessive white allele. Heterozygous individuals have the genotype Bb.
From the pedigree:
- Individual 2 must be Bb (since it has a white offspring, individual 5, genotype bb).
- Individual 8 must be Bb (since it has a white offspring, individual 10, genotype bb).
Other options are incorrect because:
- 1 and 4 could be homozygous (BB).
- 6 and 7 are both brown but could be BB or Bb with no evidence of being heterozygous.
- 10 is white (bb), so cannot be heterozygous.
Thus, the correct answer is B (2 and 8).
The graph shows how the mass of DNA per cell changes before, during and after a nuclear division in a diploid cell.
Which row describes the type of nuclear division and the chromosome number of the daughter cells shown in the graph?
▶️ Answer/Explanation
Ans: C
The graph shows DNA mass doubling (S-phase) before division and returning to the original mass after division, characteristic of mitosis. In mitosis, diploid cells produce diploid daughter cells (2n → 2n). Meiosis (A/B) would halve chromosome number (2n → n), while option D incorrectly suggests haploid daughter cells from mitosis. Thus, C (mitosis, 2n) is correct.