DAT DAT - Dental Admission Biology: Genetics and Heredity 2 — Questions and Answers
Question 1: In a testcross, an organism of unknown genotype is crossed with which individual?
- A heterozygote
- A homozygous dominant individual
- A homozygous recessive individual (Correct answer)
- A sibling
Correct answer: A homozygous recessive individual
A testcross uses a homozygous recessive individual to reveal the genotype of an organism expressing a dominant phenotype.
Question 2: For an X-linked recessive trait, which parent passes the allele to an affected son?
- Father only
- Mother only (Correct answer)
- Either parent equally
- Neither parent
Correct answer: Mother only
Sons inherit their single X chromosome from their mother, so an X-linked recessive trait is passed from a carrier mother to affected sons.
Question 3: A standard dihybrid cross (AaBb × AaBb) produces which classic phenotypic ratio?
- 9:3:3:1 (Correct answer)
- 1:2:1
- 3:1
- 1:1:1:1
Correct answer: 9:3:3:1
The dihybrid cross produces a 9:3:3:1 phenotypic ratio when both genes show complete dominance and independent assortment.
Question 4: Genes that are physically located on the same chromosome are described as:
- Pleiotropic
- Linked (Correct answer)
- Codominant
- Epistatic
Correct answer: Linked
Linked genes reside on the same chromosome and tend to be inherited together unless separated by crossing over during meiosis.
Question 5: The recombination frequency between two genes is used to estimate:
- Gene expression levels
- The physical distance between genes on a chromosome (Correct answer)
- The number of alleles present
- The mutation rate
Correct answer: The physical distance between genes on a chromosome
Higher recombination frequency indicates greater physical distance between genes, measured in centimorgans (cM), forming the basis of genetic maps.
Question 6: Human skin color is determined by multiple genes contributing to a continuous range of phenotypes — this is an example of:
- Pleiotropy
- Codominance
- Polygenic inheritance (Correct answer)
- Epistasis
Correct answer: Polygenic inheritance
Polygenic inheritance involves multiple genes each contributing to a trait, producing a continuous bell-curve distribution of phenotypes in a population.
DAT DAT - Dental Admission Biology: Genetics and Heredity 2
In a testcross, an organism of unknown genotype is crossed with which individual?