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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.