Biology Practice Test: Genetics and Heredity
- Genetics and Heredity
- 15 questions
- 20 minutes
This test covers Mendelian inheritance with Punnett squares, other inheritance patterns, DNA structure and protein synthesis. Tip: write each parent's possible gametes first, then fill in the Punnett square; most mistakes happen in that first step.
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, tall (T) is dominant over short (t). Two heterozygous tall plants (Tt × Tt) are crossed. What fraction of the offspring is expected to be tall?
Correct answer: B
The Punnett square gives TT, Tt, Tt and tt. Three of the four boxes contain at least one T, so 3/4 of the offspring are tall. The fraction 1/2 is the share of heterozygous (Tt) offspring, not of tall ones.
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Question 2
A guinea pig with black fur (dominant, B) is crossed with a white guinea pig (bb). Of their 10 offspring, 5 are black and 5 are white. What is the most likely genotype of the black parent?
Correct answer: A
This is a test cross. A white offspring must get b from each parent, so the black parent carries b and is Bb; Bb × bb predicts a 1 : 1 ratio, which matches the result. A BB parent would give only black offspring.
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Question 3
In a plant, purple flowers (A) are dominant over white (a), and smooth seeds (B) are dominant over wrinkled (b). The genes are on different chromosomes. Two plants with genotype AaBb are crossed. What fraction of the offspring is expected to have purple flowers and wrinkled seeds?
Correct answer: D
Treat each gene separately: purple (A_) has probability 3/4 and wrinkled (bb) has 1/4, so 3/4 × 1/4 = 3/16. This is the "3" group of the classic 9 : 3 : 3 : 1 ratio; 9/16 is the share with both dominant traits.
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Question 4
In snapdragons, a cross between a red-flowered plant (RR) and a white-flowered plant (WW) gives only pink-flowered plants (RW). If two pink plants are crossed, what percent of the offspring is expected to be pink?
Correct answer: C
This is incomplete dominance. RW × RW gives RR, RW, RW and WW, so 1 red : 2 pink : 1 white, and 2 of 4 boxes (50%) are pink. The 75% answer comes from treating red as fully dominant.
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Question 5
A mother has blood type A with genotype IAi, and a father has blood type B with genotype IBi. What is the probability that their child has blood type O?
Correct answer: B
Each parent passes on i with probability 1/2, so ii (type O) has probability 1/2 × 1/2 = 1/4. The other children would be IAIB (AB), IAi (A) or IBi (B), each also 1/4. Two parents who are not type O can have a type O child if both carry i.
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Question 6
Red-green color blindness is an X-linked recessive trait. A woman with normal vision whose father was color-blind (XBXb) has children with a man with normal vision (XBY). If they have a son, what is the probability that he is color-blind?
Correct answer: A
A son gets his Y from his father and one X from his mother, who passes Xb half the time, so the chance is 1/2. The value 1/4 is the chance that any child (son or daughter) is a color-blind son.
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Question 7
One strand of a DNA molecule has the base sequence 5'-ATGCCA-3'. What is the sequence of the complementary strand?
Correct answer: C
In DNA, A pairs with T and G pairs with C, and the two strands run in opposite directions. So ATGCCA pairs with TACGGT. Uracil (U) occurs in RNA, not in DNA.
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Question 8
A sample of double-stranded DNA is 30% adenine. What percent of the sample is cytosine?
Correct answer: D
Adenine pairs with thymine, so T is also 30%, and A + T = 60%. The remaining 40% is split equally between G and C, so cytosine is 20%. The 40% answer is G and C together.
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Question 9
A section of a DNA template strand reads TAC GGA TTC. Which mRNA sequence is transcribed from it?
Correct answer: B
RNA polymerase pairs each DNA base with its RNA partner: T → A, A → U, C → G, G → C. TAC GGA TTC becomes AUG CCU AAG. The sequence ATG CCT AAG has the right pairing but uses thymine, which RNA does not contain.
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Question 10
Use the codons below.
Codon Amino acid AUG Methionine (start) UUU, UUC Phenylalanine GGU, GGC Glycine AAA Lysine UAA, UAG Stop Which chain of amino acids is made from the mRNA AUG UUC GGU AAA UAG?
Correct answer: A
Reading three bases at a time: AUG = methionine, UUC = phenylalanine, GGU = glycine, AAA = lysine, and UAG is a stop codon. A stop codon ends translation; it does not code for any amino acid.
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Question 11
Where in a eukaryotic cell does translation take place?
Correct answer: C
Transcription makes mRNA in the nucleus; the mRNA then leaves the nucleus, and ribosomes read it to build the protein. Ribosomes are free in the cytoplasm or attached to the rough ER.
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Question 12
Which mutation in the coding part of a gene is most likely to change every amino acid after the point of the mutation?
Correct answer: D
Adding one base shifts the reading frame, so every codon after it is read differently (a frameshift mutation). Changing UUU to UUC is silent, since both code for phenylalanine, and deleting a whole codon removes just one amino acid without shifting the frame.
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Question 13
Human body cells have 46 chromosomes. Which statement correctly describes the cells produced by meiosis in humans?
Correct answer: B
Meiosis has two divisions and produces four haploid cells, each with 23 chromosomes, which is half the body-cell number. Two cells with 46 chromosomes each is the result of mitosis.
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Question 14
During meiosis I, homologous chromosomes exchange segments of DNA. What is this process called, and what is its effect?
Correct answer: C
In crossing over, homologous chromosomes swap pieces in prophase I, so gametes carry new mixes of alleles. This increases genetic variation. Nondisjunction is a failure of chromosomes to separate, not an exchange of segments.
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Question 15
Two parents who do not have a certain disorder have a child who has it. The disorder is controlled by a single autosomal gene. What is the probability that their next child will also have the disorder?
Correct answer: A
Unaffected parents can only have an affected child if the disorder is recessive and both parents are carriers (Aa). Aa × Aa gives aa with probability 1/4, and each child is an independent event, so the chance is again 1/4.
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