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1+2: The diagram shows a gamete. The nucleus contains 16 chromosomes:
A red eyed parent fly RR was crossed with a white eyed parent fly rr. All the offspring had red eyes.
4. The white eyed parent is said to be
5. The heterozygous red eyed offspring were crossed with each other.
6-8: The photograph shows some pea pods on a pea plant.
Mendel investigated the genetics of pea plants. He cross pollinated the flowers of homozygous tall plants with those of homozygous dwarf plants. He planted the seeds that formed and found all the plants grew into tall plants. This is the first generation. He then self-pollinated all these plants and found that the seeds from these plants produced both tall and dwarf plants. This is the second generation.
Rasbak | CC 3.0
9+10: A male brown mouse was mated with a female brown mouse and the coat colour of their offspring is shown in the diagram.
10. The black mouse was mated with the brown parent as shown:
What are the likely offspring?
Question 1:
The correct answer is B. 32.
Explanation: A gamete (sperm or egg) is a haploid cell, meaning it contains half the number of chromosomes of a normal body cell. If the gamete has 16 chromosomes, the diploid number (found in most body cells) is twice that:
A. 16 – This is the haploid number, not the diploid number.
B. 32 – Correct; the diploid number.
C. 8 – Half the haploid number; incorrect.
D. 46 – The human diploid number, but not relevant here.
Thus, B is correct.
*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret. Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.
Question 2:
The correct answer is A. 16.
Explanation: The haploid number (n) is the number of chromosomes in a gamete (sperm or egg cell). The diagram shows a gamete with 16 chromosomes in its nucleus. Therefore, the haploid number is 16.
A. 16 – Correct (haploid number = gamete chromosome count).
B. 32 – This is the diploid number (2n).
D. 46 – The human haploid number is 23, not relevant here.
Thus, A is correct.
Question 3:
The correct answer is B. Rr.
Explanation:
Red is dominant (R), white is recessive (r).
RR (red-eyed) × rr (white-eyed)
Offspring inherit one allele from each parent: R from the red parent and r from the white parent.
All offspring are Rr (heterozygous) and have red eyes (since R is dominant over r).
A. RR – No, the white-eyed parent can only contribute r.
B. Rr – Correct.
C. Red – This is the phenotype, not the genotype.
D. rr – No, the red-eyed parent contributes R.
Question 4:
The correct answer is B. Homozygous recessive.
White eyes are recessive (r).
The white-eyed parent has the genotype rr (two identical copies of the recessive allele).
This is called homozygous recessive.
A. Heterozygous – Incorrect; heterozygous would be Rr (red eyes).
B. Homozygous recessive – Correct.
C. Homozygous dominant – Incorrect; that would be RR (red eyes).
D. Hybrid – Another term for heterozygous; not applicable here.
Question 5:
The correct answer is C. 25%.
Explanation: Crossing two heterozygous red-eyed flies: Rr × Rr
Punnett square:
Offspring genotypes:
RR (red eyes)
Rr (red eyes)
rr (white eyes)
White-eyed offspring (rr) = 1 out of 4 = 25%.
A. 0 – Incorrect; white-eyed offspring are possible.
B. 50% – Incorrect; that would be the chance for a heterozygous Rr.
C. 25% – Correct.
D. 100% – Incorrect.
Thus, C is correct.
Question 6:
The correct answer is A. gene.
Explanation: In Mendel’s experiment, the height of the pea plants (tall vs. dwarf) is determined by genes (specifically, alleles of a gene for plant height). The gene controls the trait, with the tall allele being dominant over the dwarf allele.
A. gene – Correct; the height is controlled by a gene.
B. nucleus – The nucleus contains the genes, but it is not the specific controller of the trait.
C. chromosome – Chromosomes carry genes, but again, the gene itself controls the trait.
D. fertilizer – An environmental factor, not the genetic determinant of height in this experiment (Mendel controlled for environmental conditions).
Question 7:
The correct answer is B. Tall Tt.
Parental cross: Homozygous tall (TT) × Homozygous dwarf (tt)
First generation (F₁): All offspring inherit T from the tall parent and t from the dwarf parent.
Genotype of F₁: Tt (heterozygous)
Since T (tall) is dominant over t (dwarf), the phenotype is tall.
A. Tall TT – Incorrect; offspring would need two T alleles, but the dwarf parent can only give t.
B. Tall Tt – Correct.
C. Dwarf Tt – Incorrect; Tt is tall, not dwarf.
D. Dwarf tt – Incorrect; F₁ plants are all Tt, not tt.
Question 8:
The correct answer is D. 75.
First generation (F₁) plants are all Tt (tall).
Self-pollination of F₁: Tt × Tt
Offspring (F₂) genotypic ratio: 1 TT : 2 Tt : 1 tt
Phenotypic ratio: 3 tall (TT + Tt) : 1 dwarf (tt)
Tall plants = 75% of the offspring.
Thus, D is correct.
Question 9:
Correct answer: A. Both parents are heterozygous for hair colour.
Reasoning:
Two brown parents produced a black offspring → black must be recessive.
For a recessive trait to appear, both parents must carry the hidden allele.
If B = dominant brown, b = recessive black → both parents are Bb (heterozygous).
Question 10:
Correct answer: C. 50% Brown, 50% black.
Black mouse = bb (homozygous recessive).
Brown parent = Bb (heterozygous, from Q9).
Cross: Bb × bb
Result: 50% Brown (Bb), 50% Black (bb).