Inheritance Questions Practice Questions with Answers

1. Concept Explanation

Inheritance is the biological process through which genetic information is passed from parents to their offspring, determining the physical and functional traits of the next generation. This fundamental concept in biology relies on genes, which are segments of DNA located on chromosomes. Gregor Mendel, often called the father of genetics, established the foundational laws of inheritance through his work with pea plants. These laws include the Law of Segregation, which states that alleles separate during gamete formation, and the Law of Independent Assortment, which explains how different genes separate independently of one another. Understanding inheritance involves mastering concepts like genotypes (the genetic makeup), phenotypes (the observable traits), and the interaction between dominant and recessive alleles. In more complex scenarios, inheritance may follow patterns such as incomplete dominance, codominance, or sex-linked traits. Mastery of these patterns is as essential for biology students as understanding Easy Probability Practice Questions is for statistics students, as both fields rely heavily on predicting outcomes based on set ratios.

2. Solved Examples

Reviewing worked solutions helps clarify how to apply Mendelian principles to specific Inheritance Questions.

1. Single Trait (Monohybrid) Cross: In pea plants, purple flowers (P) are dominant over white flowers (p). If a heterozygous purple plant is crossed with a white-flowered plant, what are the expected phenotypic ratios?
   1. Identify parental genotypes: Heterozygous is Pp; white-flowered (recessive) is pp.
   2. Set up a Punnett square: The gametes for Pp are P and p. The gametes for pp are p and p.
   3. Fill the squares: Pp, Pp, pp, pp.
   4. Analyze results: 50% of offspring are Pp (purple) and 50% are pp (white). The ratio is 1:1.
2. Incomplete Dominance: In snapdragons, red flower color (R) is incompletely dominant over white (r). The heterozygous (Rr) phenotype is pink. If two pink flowers are crossed, what is the probability of producing a red flower?
   1. Identify parental genotypes: Both are Rr.
   2. Set up Punnett square: R and r crossed with R and r.
   3. Fill the squares: RR (red), Rr (pink), Rr (pink), rr (white).
   4. Calculate probability: 1 out of 4 offspring is RR. The probability is 25%.
3. Sex-Linked Inheritance: Hemophilia is an X-linked recessive disorder. A carrier mother (X^HX^h) has children with a healthy father (X^HY). What is the chance their son will have hemophilia?
   1. Identify maternal gametes: X^H and X^h. Identify paternal gametes: X^H and Y.
   2. Construct the square: X^HX^H (healthy girl), X^HX^h (carrier girl), X^HY (healthy boy), X^hY (hemophilic boy).
   3. Focus on the sons: Out of the two possible male genotypes (X^HY and X^hY), one has the disorder.
   4. Result: There is a 50% chance that any son born to this couple will have hemophilia.

3. Practice Questions

Test your knowledge with these Inheritance Questions ranging from basic Mendelian crosses to complex pedigree analysis.

1. A homozygous dominant tall plant (TT) is crossed with a homozygous recessive short plant (tt). What percentage of the F1 generation will be tall?
2. In humans, brown eyes (B) are generally dominant over blue eyes (b). If two brown-eyed parents have a blue-eyed child, what must the genotypes of the parents be?
3. In a dihybrid cross between two individuals heterozygous for two traits (AaBb x AaBb), what is the expected phenotypic ratio?

4. A person with Type A blood (genotype AO) marries someone with Type B blood (genotype BO). List all possible blood types for their children.
5. Explain the concept of codominance using the example of Roan cattle, where both red and white hairs are expressed.
6. If a trait skips generations and affects males and females equally, is it more likely to be autosomal dominant or autosomal recessive?
7. Color blindness is an X-linked recessive trait. If a color-blind man marries a woman who is homozygous for normal vision, what is the probability that their daughters will be color-blind?
8. In a certain species of bird, feather color is determined by a gene with two alleles: Blue (B) and Yellow (Y). The heterozygote (BY) appears Green. What type of inheritance does this represent?
9. Using the Law of Segregation, explain why a recessive trait can reappear in the F2 generation after disappearing in the F1 generation.
10. A pedigree shows a trait appearing in every generation, and every affected child has at least one affected parent. What is the most likely mode of inheritance?

4. Answers & Explanations

1. 100%: All offspring in the F1 generation will have the genotype Tt. Since T (tall) is dominant, every plant will be phenotypically tall.
2. Bb and Bb: For a child to have blue eyes (bb), they must receive a recessive allele from each parent. Since the parents have brown eyes, they must each carry one dominant allele (B), making them both heterozygous (Bb).
3. 9:3:3:1: This is the classic Mendelian dihybrid ratio for two heterozygous parents: 9 (dominant for both), 3 (dominant for first, recessive for second), 3 (recessive for first, dominant for second), and 1 (recessive for both).
4. A, B, AB, and O: The cross AO x BO produces four genotypes: AB (Type AB), BO (Type B), AO (Type A), and OO (Type O). Each has a 25% chance of occurring.
5. Codominance: In codominance, both alleles are fully expressed in the phenotype. In Roan cattle, the offspring of a red cow and a white cow have both red and white hairs distinct from one another, rather than a blend.
6. Autosomal Recessive: Recessive traits can be hidden in carriers and only appear when two carriers produce offspring, causing the trait to "skip" generations. Because it affects both sexes equally, it is autosomal rather than sex-linked.
7. 0%: The daughters receive one X chromosome from their father (X^b) and one from their mother (X^B). All daughters will be carriers (X^BX^b) but will have normal vision because the normal allele is dominant.
8. Incomplete Dominance: Since the heterozygote (Green) is a blend of the two parental phenotypes (Blue and Yellow), it characterizes incomplete dominance rather than codominance.
9. Explanation: During gamete formation, the two alleles for a trait separate. In the F1 generation (Tt), the recessive allele (t) is masked. In the F2 generation (Tt x Tt), the alleles segregate again, allowing the 'tt' combination to form in 25% of offspring.
10. Autosomal Dominant: Dominant traits typically do not skip generations because an individual only needs one copy of the allele to express the trait. If a child has it, at least one parent must also have it.

5. Quick Quiz

6. Frequently Asked Questions

What is the difference between genotype and phenotype?

The genotype refers to the actual genetic makeup or set of alleles an organism carries, such as BB or Bb. The phenotype is the physical expression or observable trait resulting from that genotype, such as brown eyes.

What is a carrier in genetics?

A carrier is an individual who has inherited a recessive allele for a genetic trait or mutation but does not display that trait or show symptoms of the disease. They can, however, pass the allele on to their offspring.

How does codominance differ from incomplete dominance?

In codominance, both alleles are expressed equally and distinctly in the phenotype, like the ABO blood group. In incomplete dominance, the heterozygous phenotype is a blend or intermediate of the two homozygous phenotypes, like pink flowers from red and white parents.

Why are males more likely to express X-linked recessive traits?

Males have only one X chromosome (XY), so a single recessive allele on that chromosome will be expressed. Females have two X chromosomes (XX) and would need two copies of the recessive allele to express the trait.

What is a Punnett square used for?

A Punnett square is a graphical tool used to predict the probability of offspring inheriting specific genotypes and phenotypes from a cross between two parents. It visualizes all possible combinations of parental gametes.

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