Ch 3.1 Monohybrid and Dihybrid Crosses Flashcards

Mendelian Genetics Practice

• Practice exercises related to monohybrid and dihybrid crosses

Some Important Terms

• Gene: Basic unit of heredity in living organisms.

• Allele: Different forms of a gene.

• Genotype: The genetic constitution of an organism.

• Phenotype: The observable physical or biochemical characteristics of an organism.

• Homozygous: Having two identical alleles for a particular gene.

• Heterozygous: Having two different alleles for a particular gene.

• Dominant: An allele that expresses its phenotype even in the presence of a recessive allele.

• Recessive: An allele that only expresses its phenotype if the organism has two copies of it.

Mendel’s 1st Deductions

• Concept of Dominant vs Recessive Variants: Explains how traits are inherited based on dominant and recessive alleles.

• Particulate Theory of Inheritance: Traits are inherited as discrete units (genes) that remain unchanged as they are passed from parent to offspring.

• Law of Segregation (Mendel’s 1st Law):

  • Each organism carries two alleles for each gene.

  • The alleles segregate from each other during gamete formation, ensuring that each gamete carries only one allele for each trait.

Probability Questions

• Probability of Albinism in Heterozygous Parents:

  • Assessing the likelihood that two heterozygous parents for albinism will have an offspring with the trait.

• Probability of Two Offspring with Albinism:

  • Evaluating the chances that two offspring will express the recessive trait of albinism from the same heterozygous parents.

Mendel’s 2nd Deductions

• Data from Dihybrid Crosses:

  • Results contradict the linkage model, supporting the independent assortment model.

• Law of Independent Assortment (Mendel’s 2nd Law):

  • Different genes independently segregate their alleles when gametes are formed, leading to genetic variation.

Phenotypic Ratios in Dihybrid Cross

• Expected Phenotype Ratios in BbGg x Bbgg Cross:

  • Determine the ratio of phenotypes in the offspring when two genes assort independently.

Dog Coat Color Genetics Problem

• Coat Color in Dogs:

  • The solid coat color allele (S) is dominant to the spotted allele (s).

  • The black coat color allele (B) is dominant to the tan coat allele (b).

  • Cross between a solid tan female and a solid black male results in pups with various phenotypes (2 solid tan, 2 solid black, 1 spotted tan, 1 spotted black).

  • Analyze to deduce the genotypes of the parents based on phenotypes.

Tetrahybrid Gamete Probability Questions

• Probability of a Specific Gamete from Tetrahybrid Individual:

  • Calculate probability for tetrahybrid individual (AaBbCcdd) producing a specific gamete genotype (aBCd).

• Tetrahybrid Cross Probability:

  • Assess the likelihood of producing individuals homozygous for dominant A and B alleles and recessive C and D alleles from a tetrahybrid cross (AaBbCcdd x AaBb ccDd).

Expected Ratios of Pea Plants Cross

• Pp Pea Plant Cross Outcomes:

  • Crossing two Pp plants (purple dominant over white) leads to expected ratios of phenotypes:

    • 3 purple : 1 white

    • 1 PP : 2 Pp : 1 pp

• Gamete Types from rrYy Plant:

  • Identifying different gametes produced by genotype rrYy and the possible proportions including combinations of alleles.

  • Types: 1 rY : 1 ry.

• Predicted Outcome of RrYy and rrYy Cross:

  • Expected phenotype ratios from crossing RrYy with rrYy.

  • Typical outcomes include ratios like 9 round yellow, 3 round green, 3 wrinkled yellow, and 1 wrinkled green, depending on allele pairings.