AP Biology Quiz: Mendelian Genetics

A genetic counselor is analyzing a pedigree for a rare genetic condition. Two unaffected parents have a child who is affected by the condition.

The inheritance pattern of this condition is most likely which of the following?

In a species of plant, the allele for tall stems ($T$) is dominant to short stems ($t$), and the allele for red flowers ($R$) is dominant to white flowers ($r$). The genes for stem height and flower color are on different chromosomes.

If two plants that are heterozygous for both traits are crossed, what fraction of the offspring is expected to be tall with white flowers?

In tomato plants, red fruit ($R$) is dominant to yellow fruit ($r$), and tall vines ($T$) are dominant to dwarf vines ($t$). The genes are unlinked.

A plant that is heterozygous for both traits is crossed with a plant that has yellow fruit and dwarf vines. What is the expected phenotypic ratio of the offspring?

A pedigree chart traces the inheritance of a particular genetic disorder in a family. Affected individuals are represented by shaded symbols. The disorder appears in every generation and is passed from an affected father to his son.

Based on this information, what is the most likely mode of inheritance for this disorder?

In fruit flies, the allele for long wings ($L$) is dominant to the allele for vestigial wings ($l$). A researcher has a male fruit fly with long wings but an unknown genotype.

To determine the genotype of the long-winged male fly, the researcher should perform a test cross. This involves crossing the male fly with a female of which of the following genotypes?

In snapdragons, the allele for red flowers is completely dominant over the allele for white flowers. A botanist has a large population of red-flowered snapdragons.

Which of the following statements about this population is most accurate?

In a plant species, three genes are unlinked. Tall ($T$) is dominant to short ($t$), purple flowers ($P$) are dominant to white ($p$), and round seeds ($R$) are dominant to wrinkled ($r$).

In a cross between two plants with genotype $TtPpRr$, what is the probability of an offspring being short, having purple flowers, and having wrinkled seeds?

A dominant plant is testcrossed. If it is heterozygous, what is the probability that all 6 offspring are dominant?

In AaBb × AaBb, what fraction of offspring showing both dominant traits are heterozygous at both loci?

Two heterozygotes have two children. What is the probability the children have the same phenotype?

A father has a recessive phenotype; his daughter has the dominant phenotype. What must be true of the mother?

Two carriers of an autosomal recessive disorder have three children. What is the chance exactly one is affected?

In corn, smooth kernels (K) are completely dominant to wrinkled kernels (k). A plant with smooth kernels is self-fertilized, and the offspring show a 3 smooth : 1 wrinkled phenotype ratio. Assume one autosomal gene with complete dominance and no linkage to other genes. Which genotype must the parent plant have had?

Which parental genotype is required to produce a $3:1$ smooth-to-wrinkled ratio by self-crossing?

In snapdragons, tall stems (T) are completely dominant to short stems (t). A tall plant of unknown genotype is crossed with a short plant (tt). In the offspring, 48 plants are tall and 52 plants are short. Assume random fertilization and a single gene with complete dominance. Which genotype is most likely for the tall parent?

In fruit flies, red eyes (R) are completely dominant to sepia eyes (r). Two red-eyed flies are crossed, and both are known to be heterozygous (Rr × Rr). Each fly produces gametes carrying one allele, and fertilization is random. Assume a single gene controls eye color with complete dominance. Which genotype ratio is expected among the offspring?

In rabbits, long ears (L) are completely dominant to short ears (l). A breeder crosses a homozygous dominant rabbit (LL) with a heterozygous rabbit (Ll). Each offspring inherits one allele from each parent, and the gene shows complete dominance. Which proportion of offspring is expected to be heterozygous (Ll)?

In dogs, curly fur (C) is completely dominant to straight fur (c), and black coat color (B) is completely dominant to brown coat color (b). Two dogs with genotypes CcBb are crossed (CcBb × CcBb), and the genes assort independently. Assume complete dominance for both traits. Which proportion of offspring is expected to show straight fur and brown coat?

In corn, smooth kernels (S) are completely dominant to wrinkled kernels (s). A plant with genotype SS is crossed with a plant with genotype ss. Each offspring receives one allele from each parent. Assume a single gene controls kernel texture and inheritance is Mendelian with complete dominance. Which outcome is expected among the offspring?

In a plant, red petals (R) are completely dominant to white petals (r), and round seeds (S) are completely dominant to wrinkled seeds (s). A plant heterozygous for both traits (RrSs) is testcrossed with a plant homozygous recessive for both traits (rrss). Assume independent assortment. Which proportion of offspring is expected to have white petals and wrinkled seeds?

In pea plants, purple flowers (P) are completely dominant to white (p). A plant with purple flowers that is heterozygous (Pp) is crossed with a white-flowered plant (pp). Each offspring receives one allele for flower color from each parent. Assuming Mendelian segregation and no linkage to other traits, the offspring phenotypes depend only on whether they inherit at least one P allele. Which proportion of offspring is expected to have white flowers?​​​