Complete the Punnett square below to show the cross between a male with genotype BB for brown eyes and a female with genotype bb for blue eyes. Analyse your results in terms of percentages.

• Male genotype: BB (produces B gametes)
• Female genotype: bb (produces b gametes)

The female alleles (b, b) are placed in the top row.
The male alleles (B, B) are placed in the left-hand column.

• All offspring have the genotype Bb.

• Since B (brown eyes) is dominant over b (blue eyes), all offspring will have brown eyes.

• Genotypic percentages:

  • Bb: $\frac{4}{4} \times 100\% = \boxed{\text{100\% Bb}}$

• Phenotypic percentages:

  • Brown eyes: $\frac{4}{4} \times 100\% = \boxed{\text{100\% Brown eyes}}$
  • Blue eyes: $\frac{0}{4} \times 100\% = \boxed{\text{0\% Blue eyes}}$

b) An allele W, for white wool, is dominant over allele w, for black wool. In a sample of 900 sheep, 891 are white and 9 are black. Calculate the allelic frequencies within this population, assuming that the population is in H-W equilibrium.

• Total number of sheep = 900
• Number of black sheep (ww) = 9
• Frequency of black sheep ($q^2$) = $\frac{\text{Number of black sheep}}{\text{Total number of sheep}} = \frac{9}{900} = 0.01$

• $q = \sqrt{q^2} = \sqrt{0.01} = 0.1$

• Using the Hardy-Weinberg equation $p + q = 1$:

• $p = 1 - q = 1 - 0.1 = 0.9$

• Allelic frequencies:

  • Frequency of allele W ($p$) = $\boxed{\text{0.9}}$
  • Frequency of allele w ($q$) = $\boxed{\text{0.1}}$

c) Explain why children born by the same parents show different attitude at home.

Children born by the same parents can show different attitudes at home due to a combination of genetic and environmental factors. While they share genes from their parents, each child inherits a unique combination of alleles, leading to individual differences in temperament and personality predispositions. Furthermore, environmental factors such as birth order, unique experiences, different peer groups, and even subtle variations in parental treatment or expectations can significantly shape each child's attitude and behavior. These unique interactions and experiences contribute to distinct individual development.

Question 2

a) A heterozygous male for tongue rolling marries a homozygous recessive female. Complete a Punnett square to show their possible offspring. Analyse your results as percentages and proportions. In this Punnett square female alleles should be shown in the top row and male alleles should be placed in the left-hand column.

• Let R = allele for tongue rolling (dominant)
• Let r = allele for non-tongue rolling (recessive)
• Male genotype: Rr (heterozygous)
• Female genotype: rr (homozygous recessive)

The female alleles (r, r) are placed in the top row.
The male alleles (R, r) are placed in the left-hand column.

• Genotypes: Rr, rr

• Phenotypes: Tongue rolling (Rr), Non-tongue rolling (rr)

• Genotypic proportions and percentages:

  • Rr: $\frac{2}{4} = \boxed{\text{1:1 proportion, 50\%}}$
  • rr: $\frac{2}{4} = \boxed{\text{1:1 proportion, 50\%}}$

• Phenotypic proportions and percentages:

  • Tongue rolling (Rr): $\frac{2}{4} = \boxed{\text{1:1 proportion, 50\%}}$
  • Non-tongue rolling (rr): $\frac{2}{4} = \boxed{\text{1:1 proportion, 50\%}}$

b) In a population that is in Hardy-Weinberg equilibrium, the frequency of the recessive homozygote genotype of a certain trait is 0.09. Calculate the percentage of individuals homozygous for the dominant allele.

• Frequency of recessive homozygote ($q^2$) = 0.09

• $q = \sqrt{q^2} = \sqrt{0.09} = 0.3$

• Using the Hardy-Weinberg equation $p + q = 1$:
• $p = 1 - q = 1 - 0.3 = 0.7$

• $p^2 = (0.7)^2 = 0.49$

• Percentage of individuals homozygous for the dominant allele = $0.49 \times 100\% = \boxed{\text{49\%}}$

c) Name the types of genetic variations in nature and outline the clear cut differences between them.

There are several types of genetic variations in nature, each contributing to the diversity within populations:

• Mutation: This is the ultimate source of all new genetic variation. It involves a permanent change in the DNA sequence of an organism. Mutations can introduce entirely new alleles into a population.
• Genetic Recombination (during sexual reproduction): This process shuffles existing alleles into new combinations. It occurs primarily through crossing over (exchange of genetic material between homologous chromosomes) and independent assortment (random alignment of homologous chromosomes) during meiosis. Recombination does not create new alleles but creates new combinations of them.
• Gene Flow (Migration): This refers to the transfer of genetic material from one population to another. It involves the movement of individuals or gametes, which can introduce new alleles into a population or change the frequencies of existing alleles.
• Genetic Drift: This is the random fluctuation of allele frequencies in a population due to chance events, particularly significant in small populations. It does not introduce new alleles or create new combinations, but rather randomly alters the proportions of existing alleles.