Genetics Practice Questions
IB (International Baccalaureate) · IB Biology HL · 147 free MCQs with instant results and detailed explanations.
147
Total
46
Easy
74
Medium
27
Hard
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Sample Questions from Genetics
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Q1
Easy
What is the genotype of an organism with a dominant phenotype for a trait controlled by a single gene?
A.
Homozygous dominant
B.
Heterozygous
C.
Homozygous recessive
D.
Cannot be determined
Show Answer & Explanation
Correct Answer: D
An organism with a dominant phenotype could either be homozygous dominant (AA) or heterozygous (Aa). Therefore, without further information, we cannot determine the exact genotype.
Q2
Easy
In a dihybrid cross between two pea plants (RrYy x RrYy), what is the probability of obtaining a plant with the genotype RRYY?
A.
1/16
B.
1/4
C.
1/8
D.
3/16
Show Answer & Explanation
Correct Answer: A
The probability of obtaining RRYY from RrYy x RrYy is calculated by finding the probability of RR (1/4) and YY (1/4) and multiplying them: 1/4 * 1/4 = 1/16.
Q3
Easy
Which of the following statements best describes the role of histones in DNA packaging?
A.
Histones degrade DNA.
B.
Histones help in the unwinding of DNA.
C.
Histones facilitate the condensation of DNA into chromatin.
D.
Histones are only found in prokaryotic cells.
Show Answer & Explanation
Correct Answer: C
Histones are proteins that bind to DNA and help package it into a compact form called chromatin, allowing for efficient storage in the nucleus.
Q4
Medium
Which of the following best describes the role of a promoter in gene expression?
A.
It binds RNA polymerase to initiate transcription.
B.
It synthesizes mRNA from a DNA template.
C.
It prevents the binding of transcription factors.
D.
It modifies histones to activate gene expression.
Show Answer & Explanation
Correct Answer: A
A promoter is a DNA sequence that provides a location for RNA polymerase to bind and initiate transcription. This is essential for the expression of the gene.
Q5
Medium
In a dihybrid cross between two heterozygous individuals (AaBb x AaBb), what is the probability of obtaining the genotype AABb?
A.
1/16
B.
3/16
C.
1/4
D.
1/8
Show Answer & Explanation
Correct Answer: A
The probability of obtaining the genotype AABb can be calculated using a Punnett square. The specific combination of alleles leads to a probability of 1 out of 16 possible combinations.
Q6
Medium
What type of inheritance pattern is illustrated by a trait that is expressed in every generation and affects both sexes equally?
A.
Autosomal dominant
B.
Autosomal recessive
C.
X-linked dominant
D.
Y-linked recessive
Show Answer & Explanation
Correct Answer: A
An autosomal dominant pattern means that only one copy of the dominant allele is needed for the trait to be expressed, leading to it appearing in every generation with equal frequency in both sexes.
Q7
Medium
In terms of genetic variation, what is the significance of crossing over during meiosis?
A.
It ensures the production of identical gametes.
B.
It increases genetic diversity among offspring.
C.
It prevents mutations from occurring.
D.
It duplicates chromosomes prior to division.
Show Answer & Explanation
Correct Answer: B
Crossing over during meiosis involves the exchange of genetic material between homologous chromosomes, leading to new combinations of alleles and increasing genetic diversity among offspring.
Q8
Hard
In a certain species of plant, flower color is determined by a single gene with two alleles: R (red) and r (white). If a red-flowered plant (homozygous) is crossed with a white-flowered plant (homozygous), what will be the genotypic ratio of the offspring?
A.
1:0
B.
1:1
C.
3:1
D.
0:1
Show Answer & Explanation
Correct Answer: A
All offspring will inherit the R allele from the red-flowered parent and the r allele from the white-flowered parent, resulting in all Rr genotype (red flowers). Thus, the genotypic ratio is 1:0.
Q9
Hard
A genetic disorder is caused by a recessive allele on the X chromosome. If a carrier female (X^HX^h) mates with a normal male (X^HY), what is the probability that their son will express the disorder?
A.
0%
B.
25%
C.
50%
D.
100%
Show Answer & Explanation
Correct Answer: C
The son can inherit either X^H or X^h from the mother and Y from the father. The probability of inheriting X^h (the allele for the disorder) is 50%. Thus, there is a 50% chance the son will express the disorder.
Q10
Hard
In a certain plant species, flower color is controlled by two alleles: R (red) is dominant over r (white). If a plant that is heterozygous for flower color is crossed with a plant that is homozygous recessive, what is the ratio of red to white flowers among the offspring?
A.
1:1
B.
3:1
C.
2:1
D.
1:2
Show Answer & Explanation
Correct Answer: A
The cross between a heterozygous plant (Rr) and a homozygous recessive plant (rr) produces two types of offspring: Rr (red) and rr (white). The ratio of red to white flowers is thus 1:1.
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Genetics — IB (International Baccalaureate) IB Biology HL Practice Questions Online
This page contains 147 practice MCQs for the chapter Genetics in IB (International Baccalaureate) IB Biology HL. The questions are organized by difficulty — 46 easy, 74 medium, 27 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.