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AP Biology 5.3 Mendelian Genetics

Practise AP Biology 5.3 questions by applying Mendelian laws, probability and genetic crosses to interpret inheritance patterns and offspring outcomes.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • apply segregation and independent assortment to predict gamete and offspring genotypes
  • use monohybrid, dihybrid, testcross and pedigree data to infer modes of inheritance
  • calculate genotype and phenotype probabilities from parental allele combinations
  • compare observed and expected inheritance data using ratios, linkage evidence and chi-square tests

Covered syllabus points

5.3.A—Explain the inheritance of genes and traits as described by Mendel’s laws

5.3 Mendelian Genetics question 1

[Maximum number: 3]

Drosophila melanogaster (D. melanogaster) is a species of fruit fly frequently used by researchers in genetic studies. Members of this species have two of each of four different chromosomes: the sex chromosome (flies have X and Y) and three autosomes (chromosomes 2, 3, and 4). Researchers studying D. melanogaster conducted genetic crosses to investigate a particular X-linked recessive trait encoded by a single gene (Table 1). Affected flies have the trait.

TABLE 1. CROSSES PERFORMED AND THE PHENOTYPES OF THE RESULTING OFFSPRING

TABLE 1. CROSSES PERFORMED AND THE PHENOTYPES OF THE RESULTING OFFSPRING

Question (a)

(a)

Identify the genotypes of the male and female flies used in cross 2.

[ 1 ]

Question (b)

(b)

Identify the cross in which the female parent was most likely heterozygous.

[ 1 ]

Question (c)

(c)

The researchers hypothesize that crossing any unaffected female and an affected male will result in a 0\% chance of producing an affected male offspring. Evaluate the validity of the hypothesis.

[ 1 ]
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