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Dihybrid Cross Worksheet

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Table of Contents

A dihybrid cross is a genetic experiment or breeding technique in which the inheritance of two different traits or characteristics is simultaneously studied in offspring. It involves the crossing of two individuals, often with known genotypes for both traits, to predict the possible combinations of alleles in their offspring.

Key points about dihybrid crosses:

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  1. Two Traits: Dihybrid crosses focus on the inheritance of two distinct genetic traits or characteristics. These traits can be controlled by different genes located on separate chromosomes.
  2. Alleles: Each trait under consideration has different versions or alleles. These alleles can be dominant or recessive, determining the expression of the trait in an individual.
  3. Genotype: In a dihybrid cross, the genotype of each parent is known, typically represented by letters. For example, “AaBb” represents an individual heterozygous for both traits.
  4. Punnett Square: Dihybrid crosses often use Punnett squares, a visual tool, to predict the possible combinations of alleles in offspring. The rows and columns of the square represent the alleles from each parent, and the boxes within the square show the possible combinations of alleles in the offspring.
  5. Independent Assortment: Dihybrid crosses illustrate Gregor Mendel’s Law of Independent Assortment, which states that alleles for different traits segregate independently during gamete formation, assuming the genes are located on different chromosomes. This means that the inheritance of one trait does not influence the inheritance of the other trait.
  6. Phenotypic Ratios: The outcome of a dihybrid cross provides phenotypic ratios, indicating the expected proportions of different traits or characteristics in the offspring.

Dihybrid crosses are an important tool in genetics to understand how multiple genes with different alleles interact and segregate during reproduction. They are used to predict the genetic diversity and phenotypic variations that can occur in a population when individuals with known genotypes are bred together.

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Problems With Answers

Problem 1: Seed Color and Seed Shape in Pea Plants

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In pea plants, seed color is determined by two genes: one controls color (C) with yellow (C) as dominant and green (c) as recessive, and the other controls seed shape (S) with round (S) as dominant and wrinkled (s) as recessive.

a. Perform a dihybrid cross between two pea plants: one with genotype CCss and the other with genotype ccSS. Show the Punnett square and determine the genotypic and phenotypic ratios of their offspring.

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b. What are the possible genotypes of the F1 offspring in this cross?

Problem 2: Fur Color and Tail Length in Cats

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In cats, fur color is controlled by one gene (B) where black (B) is dominant over brown (b), and tail length is controlled by another gene (T) where long tail (T) is dominant over short tail (t).

a. Cross a heterozygous black cat with a heterozygous long-tailed cat. Create a Punnett square and determine the genotypic and phenotypic ratios of their kittens.

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b. What are the possible genotypes for a brown cat with a long tail from the F2 generation in this cross?

Problem 3: Eye Color and Hair Type in Humans

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In humans, eye color is influenced by multiple genes, but for simplicity, let’s consider two genes: one controls eye color (E) with brown (E) as dominant and blue (e) as recessive, and the other controls hair type (H) with straight hair (H) as dominant and curly hair (h) as recessive.

a. A person with heterozygous brown eyes (Ee) and straight hair (HH) has a child with someone who has blue eyes (ee) and curly hair (hh). What are the possible genotypes and phenotypes of their offspring? Use a Punnett square to show your work.

b. If the F1 generation in this cross has a child with someone with the same genotype as the parent with brown eyes and straight hair, what is the probability that their child will have blue eyes and curly hair?

Problem 4: Flower Color and Flower Shape in Snapdragons

In snapdragons, flower color is determined by one gene (P) with red (P) as dominant over white (p), and flower shape is controlled by another gene (F) with normal shape (F) as dominant over fused petals (f).

a. Cross two heterozygous snapdragons: one with genotype PpFf and the other with genotype PpFf. Create a Punnett square and determine the genotypic and phenotypic ratios of their offspring.

b. What is the probability of obtaining a snapdragon with red flowers and fused petals in the F2 generation from this cross?

Problem 5: Coat Color and Ear Shape in Rabbits

In rabbits, coat color is determined by one gene (C) where black (C) is dominant over albino (c), and ear shape is controlled by another gene (E) with upright ears (E) as dominant over floppy ears (e).

a. Cross a rabbit with genotype CCEE (black coat, upright ears) with a rabbit with genotype ccee (albino coat, floppy ears). Use a Punnett square to find the genotypic and phenotypic ratios of their offspring.

b. If the F1 generation from this cross has a child with a rabbit that is heterozygous for coat color (Cc) and homozygous for ear shape (EE), what is the likelihood that their offspring will have black fur and floppy ears?

Problem 6: Pod Color and Pod Length in Pea Plants

In pea plants, pod color is determined by one gene (G) where green (G) is dominant over yellow (g), and pod length is controlled by another gene (L) with long pods (L) as dominant over short pods (l).

a. Cross two pea plants: one with genotype GGLL (green pods, long pods) and the other with genotype ggll (yellow pods, short pods). Construct a Punnett square and find the genotypic and phenotypic ratios of their offspring.

b. What is the probability of obtaining a pea plant with yellow pods and long pods in the F2 generation from this cross?

MCQ With Answers

  1. In a dihybrid cross, how many traits are simultaneously studied?
    a) One
    b) Two
    c) Three
    d) Four
    (Answer: b)
  2. What principle of genetics do dihybrid crosses confirm?
    a) Law of Dominance
    b) Law of Segregation
    c) Law of Independent Assortment
    d) Law of Recombination
    (Answer: c)
  3. In a dihybrid cross, how many alleles are considered for each trait?
    a) One
    b) Two
    c) Three
    d) Four
    (Answer: b)
  4. What is the genotype of a dihybrid organism with alleles RrYy?
    a) Homozygous dominant
    b) Heterozygous
    c) Homozygous recessive
    d) Homozygous for one trait and heterozygous for the other
    (Answer: b)
  5. In a dihybrid cross, how many different combinations of alleles can gametes produce?
    a) Two
    b) Three
    c) Four
    d) Six
    (Answer: c)
  6. What is the phenotypic ratio expected in the F2 generation of a dihybrid cross following Mendel’s principles?
    a) 3:1
    b) 9:3:3:1
    c) 1:2:1
    d) 2:1
    (Answer: b)
  7. In a dihybrid cross, what is the probability of obtaining offspring with the same genotype as one of the parents?
    a) 1/4
    b) 1/8
    c) 1/16
    d) 1/32
    (Answer: c)
  8. In a dihybrid cross involving two heterozygous parents (RrYy x RrYy), what is the probability of obtaining an offspring with the genotype RRYy?
    a) 1/4
    b) 1/8
    c) 1/16
    d) 1/32
    (Answer: b)
  9. What does a dihybrid Punnett square illustrate?
    a) Genotype frequencies of the parents
    b) Genotype frequencies of the F1 generation
    c) Possible allele combinations in the F2 generation
    d) Phenotypic ratios in the F2 generation
    (Answer: c)
  10. If two genes are located on different chromosomes, how do they segregate during meiosis?
    a) Independently
    b) Dependently
    c) Not at all
    d) Sequentially
    (Answer: a)
  11. What is the expected phenotypic ratio in the F2 generation of a dihybrid cross if genes are linked and do not assort independently?
    a) 9:3:3:1
    b) 1:1:1:1
    c) 3:1
    d) 1:2:1
    (Answer: b)
  12. In a dihybrid cross, what is the probability of obtaining a homozygous recessive individual for both traits in the F2 generation?
    a) 1/16
    b) 1/8
    c) 1/4
    d) 1/32
    (Answer: a)
  13. When performing a dihybrid cross, what is used to determine the possible genotypes of the offspring?
    a) Punnett square
    b) Pedigree analysis
    c) Gel electrophoresis
    d) Polymerase chain reaction
    (Answer: a)
  14. What is the purpose of conducting dihybrid crosses in genetics?
    a) To study a single trait in depth
    b) To determine if genes are linked
    c) To examine the inheritance of two or more traits simultaneously
    d) To study genetic mutations
    (Answer: c)
  15. In a dihybrid cross involving two heterozygous parents, how many different genotypic combinations are possible in the F2 generation?
    a) 2
    b) 3
    c) 4
    d) 9
    (Answer: d)
  16. If a dihybrid organism has the genotype RrYy, how many different types of gametes can it produce?
    a) 2
    b) 3
    c) 4
    d) 6
    (Answer: d)
  17. What is the genetic basis for the phenotypic variations observed in the offspring of a dihybrid cross?
    a) Multiple genes interacting
    b) Complete dominance of one gene
    c) Gene linkage
    d) Gene mutation
    (Answer: a)
  18. In a dihybrid cross, if the genotype of one parent is RrYy and the other is Rryy, what is the probability of obtaining an offspring with the genotype RrYy?
    a) 1/2
    b) 1/4
    c) 1/8
    d) 1/16
    (Answer: b)
  19. What is the primary outcome of performing a dihybrid cross?
    a) To determine the dominant allele
    b) To calculate the allele frequency
    c) To predict the phenotypic ratios of offspring
    d) To identify the genotype of the parents
    (Answer: c)
  20. In a dihybrid cross, if the genotype of one parent is RrYy and the other is rrYY, what is the probability of obtaining an offspring with the genotype RrYY?
    a) 1/2
    b) 1/4
    c) 1/8
    d) 1/16
    (Answer: c)

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