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Year 10 Biology Quiz: Mendelian Genetics

Instructions:

Answer each question in detail. Good luck!

Questions:

  1. Define and explain the concepts of incomplete dominance and codominance. Provide one example for each.

  2. Summarize Gregor Mendel's experiments that led to the foundation of Mendelian genetics. What were the three laws of inheritance he formulated?

  3. Create a monohybrid cross example. Write out a sample problem, including the parents' genotypes, and demonstrate how to solve a Punnett square to determine the genotypic and phenotypic ratios.

  4. Explain the difference between homozygous and heterozygous genotypes. Provide examples of each.

  5. In a dihybrid cross, traits for seed shape (round vs. wrinkled) and seed color (yellow vs. green) are analyzed. Define the genotypes of the parents if one parent is homozygous round and homozygous yellow and the other parent is heterozygous for both traits. Then create a Punnett square and calculate the ratios.

  6. Given the parental genotypes AaBb x AABb, list all possible gametes produced by each parent.

  7. Identify and differentiate between dominant and recessive alleles with examples. What role do they play in determining phenotypes?

  8. What is a Punnett square, and how is it used in genetics? Create an example of how a Punnett square can help predict offspring phenotypes in a monohybrid cross.

  9. Explain why Mendel's laws of segregation and independent assortment are important for understanding genetic variation.

  10. How do homologous chromosomes differ from sister chromatids? Discuss their roles during meiosis.

  11. Provide a detailed explanation of phenotypes and genotypes. How can environmental factors influence an organism's phenotype?

Correct Answers:

  1. Incomplete dominance occurs when the phenotype of a heterozygote is an intermediate of the two homozygous phenotypes (e.g., red and white flowers producing pink flowers). Codominance occurs when both alleles in a heterozygote are expressed fully and independently (e.g., a red and a white flower producing a flower with both red and white patches).

  2. Mendel carried out experiments on pea plants, leading to the formulation of three laws: the Law of Segregation, stating that allele pairs separate during gamete formation; the Law of Independent Assortment, stating that genes for different traits assort independently of one another during gamete formation; and the Law of Dominance, indicating that some alleles are dominant over others.

  3. Example: Parent genotypes: Tt (tall) x tt (short). Punnett Square:

           T        t
    -----------------
 t |   Tt     |   tt  |
    -----------------
 t |   Tt     |   tt  |

    Genotypic ratio: 2 Tt : 2 tt (or 1:1). Phenotypic ratio: 2 tall: 2 short (or 1:1).

  4. Homozygous genotypes have two identical alleles (e.g., AA, aa), while heterozygous genotypes have two different alleles (e.g., Aa).

  5. Parent genotypes: One parent is AARR (homozygous round yellow) and the other is AaBb (heterozygous for both traits). Create a Punnett square for the dihybrid cross:

        AB      Ab      aB      ab
  ---------------------------------
AR | AABb | AABb | AABb | AABb |
  ---------------------------------
Ar | AABb | AABb | AABb | AABb |
  ---------------------------------
aR | AaBb | AaBb | AaBb | AaBb |
  ---------------------------------
ar | AaBb | AaBb | AaBb | AaBb |

    Calculate ratios from the completed Punnett square.

  6. Possible gametes for AaBb: AB, Ab, aB, ab; for AABb: AB, Ab.

  7. Dominant alleles mask the effects of recessive alleles in heterozygotes (e.g., A is dominant over a). Dominant alleles express the phenotype despite the presence of a recessive allele.

  8. A Punnett square is a diagram that predicts the result of a genetic cross. Example: For Tt x Tt, the Punnett Square shows 1 TT, 2 Tt, and 1 tt, indicating expected offspring phenotypes.

  9. Mendel's laws explain genetic variation because they show how alleles segregate and assort independently, leading to diverse possible combinations in offspring.

  10. Homologous chromosomes are pairs of chromosomes that have the same genes but may carry different alleles; sister chromatids are identical copies of a single chromosome joined at the centromere. During meiosis, homologous chromosomes separate, leading to genetic variation.

  11. Genotype refers to the genetic makeup (e.g., AA, Aa, aa), while phenotype refers to the observable traits. Environmental factors such as nutrition or climate can significantly influence the expression of certain phenotypes.