Grade 8 Science Practice Test: Punnett Squares and Inheritance
- Punnett Squares and Inheritance
- 10 questions
- 13 minutes
Ten questions on how traits pass from parents to offspring. Tip: draw a 2 x 2 Punnett square on scrap paper; each box is one quarter, or 25%, of the expected offspring.
Tap an option to mark your answer. You can change your mind, or tap the same option again to leave the question blank. The correct answers and explanations appear when you finish the test.Tap an option to answer; tap it again to leave the question blank.
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Question 1
In pea plants, purple flowers (P) are dominant over white flowers (p). A Pp plant is crossed with a pp plant. What is the chance that an offspring has white flowers?
Correct answer: B
The Punnett square gives Pp, Pp, pp, pp. Two of the four boxes are pp, so the chance of white flowers is 2/4 = 50%.
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Question 2
Two pea plants with genotype Pp are crossed (purple P is dominant over white p). What fraction of the offspring are expected to have white flowers?
Correct answer: C
Pp x Pp gives PP, Pp, Pp and pp. Only pp is white, so 1 of 4 boxes, or 1/4. The other 3/4 are purple.
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Question 3
Purple (P) is dominant over white (p). What is the genotype of a pea plant with white flowers?
Correct answer: A
A recessive trait shows only when there is no dominant allele, so a white-flowered plant must be pp. PP and Pp plants are both purple.
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Question 4
What is an organism called if it has two different alleles for a trait, such as Tt?
Correct answer: D
Hetero means different, so Tt is heterozygous. TT is homozygous dominant and tt is homozygous recessive.
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Question 5
In pea plants, tall (T) is dominant over short (t). What is the phenotype of a Tt plant?
Correct answer: B
The phenotype is the trait you can observe. With one dominant T allele, the plant is tall; "Tt" is its genotype, not its phenotype.
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Question 6
A TT pea plant is crossed with a tt pea plant (tall T is dominant). What will the offspring be like?
Correct answer: D
Each offspring gets a T from one parent and a t from the other, so every one is Tt, and the dominant T makes them all tall.
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Question 7
Where are genes found in a cell?
Correct answer: C
Genes are sections of DNA located on chromosomes in the nucleus. Each gene carries the instructions for making a protein.
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Question 8
For each gene, how many alleles does an offspring receive from each parent?
Correct answer: A
Each parent passes on one allele per gene through the egg or sperm, so the offspring ends up with two alleles, one from each parent.
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Question 9
Which mutation could be passed on to an organism's offspring?
Correct answer: B
Only sex cells pass DNA to the next generation. A mutation in a skin, muscle or liver cell stays in that body and is not inherited.
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Question 10
In rabbits, black fur (B) is dominant over brown fur (b). Two Bb rabbits have 400 offspring over many litters. About how many would you expect to have brown fur?
Correct answer: D
Bb x Bb gives 1/4 bb. One quarter of 400 is 100. 300 is the expected number with black fur.
Questions you leave blank are not counted as wrong.
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