AP Biology: Heredity — Practice Questions & Answers
How meiosis generates genetic diversity, how traits pass from parents to offspring through Mendelian and non-Mendelian patterns, and how chromosomal behavior and chi-square analysis explain inheritance.
713 practice questions available for this unit — here are 10 with full answers and explanations.
During which phase of meiosis do homologous chromosomes separate and move to opposite poles of the cell?
Anaphase I
Anaphase II
Metaphase I
Telophase II
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WhyHomologous chromosomes (each still composed of two sister chromatids) are separated during anaphase I. This reduces the chromosome number from diploid to haploid. Sister chromatids do not separate until anaphase II.
2Multiple choice · Easy
A diploid cell with 2n = 8 undergoes meiosis. How many chromosomes are present in each resulting gamete?
2
4
8
16
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WhyMeiosis is a reduction division that halves the chromosome number. A cell with 2n = 8 produces haploid gametes with n = 4 chromosomes each.
3Multiple choice · Easy
Which process during meiosis I exchanges segments of DNA between homologous chromosomes, increasing genetic variation?
Independent assortment
Crossing over
Nondisjunction
Cytokinesis
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WhyCrossing over occurs during prophase I when homologous chromosomes pair (synapsis) and exchange segments at chiasmata. This recombines alleles and increases genetic diversity among gametes.
4Multiple choice · Easy
In a cross between two heterozygous individuals (Aa x Aa) for a trait showing complete dominance, what is the expected phenotypic ratio of the offspring?
1:1
9:3:3:1
3:1
1:2:1
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WhyA monohybrid cross of Aa x Aa yields genotypes 1 AA : 2 Aa : 1 aa. With complete dominance, AA and Aa both show the dominant phenotype, giving a 3 dominant : 1 recessive phenotypic ratio.
5Multiple choice · Easy
Mendel's law of segregation states that:
Alleles for different genes assort independently
The two alleles of a gene separate during gamete formation so each gamete receives one allele
Dominant alleles are always more common in a population
Genes on the same chromosome are always inherited together
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WhyThe law of segregation holds that the two alleles for a gene separate during gamete formation, so each gamete carries only one allele for each gene. This reflects the separation of homologous chromosomes in meiosis I.
6Multiple choice · Easy
In snapdragons, crossing a red-flowered plant (RR) with a white-flowered plant (rr) produces all pink-flowered offspring (Rr). This inheritance pattern is an example of:
Codominance
Incomplete dominance
Multiple alleles
Epistasis
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WhyIncomplete dominance produces a heterozygous phenotype that is an intermediate blend of the two homozygous phenotypes. Pink is intermediate between red and white, so neither allele is fully dominant.
7Multiple choice · Easy
In the human ABO blood group system, an individual with type AB blood expresses both A and B antigens. This is an example of:
Incomplete dominance
Polygenic inheritance
Codominance
Pleiotropy
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WhyIn codominance, both alleles are fully and simultaneously expressed in the heterozygote. The IA and IB alleles are codominant, so type AB individuals display both A and B antigens rather than a blend.
8Multiple choice · Medium
A dihybrid cross (AaBb x AaBb) involving two genes that assort independently produces offspring. What fraction of the offspring is expected to be homozygous recessive for both traits (aabb)?
9/16
3/16
1/16
1/4
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WhyFor each gene, the chance of an offspring being homozygous recessive from an Aa x Aa cross is 1/4. Because the genes assort independently, multiply the probabilities: 1/4 x 1/4 = 1/16.
9Multiple choice · Medium
A color-blind man (X^c Y) marries a woman who is a carrier (X^C X^c) for red-green color blindness, an X-linked recessive trait. What is the probability that a son will be color-blind?
0
1/4
1/2
All sons
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WhySons receive Y from the father and X from the mother. The carrier mother passes X^C or X^c with equal probability. Therefore 1/2 of sons receive X^c and are color-blind. Considering only sons, the probability is 1/2.
10Multiple choice · Medium
Independent assortment of chromosomes during meiosis occurs because:
Sister chromatids separate at random in anaphase II
Homologous chromosome pairs orient randomly and independently at the metaphase plate in metaphase I
Crossing over shuffles whole chromosomes between cells
DNA replication produces random mutations before meiosis
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WhyDuring metaphase I, each pair of homologous chromosomes orients randomly and independently of other pairs at the metaphase plate. This random orientation means maternal and paternal chromosomes can be distributed in any combination to the gametes.
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