Q.Study the genetic traits like rolling of tongue or widow's peak in your class and write your own observations.

Tongue rolling (the ability to roll the tongue into a U-shape) and widow's peak (a V-shaped hairline) are easily observed human traits usually taught as autosomal dominant characters, so a class survey lets you see dominant and recessive phenotypes in real people and compare their frequencies. Record each student's phenotype, tally the two classes, work out the proportion showing each form, and note that a dominant phenotype can hide either the homozygous or the heterozygous genotype. …

Aim. To observe the distribution of a simple human genetic trait, tongue rolling or widow's peak, among the students of your class.

Materials. A notebook or a printed table, a mirror (for widow's peak), and the class list.

Procedure.

1. Choose one trait. Tongue rolling: ask each student to try to curl the sides of the tongue upward into a U-shape. Widow's peak: ask each student to push the hair back and look at the hairline in the middle of the forehead, a downward V is a widow's peak, a level line is a straight hairline.
2. Record each student's name, sex and phenotype (roller / non-roller; widow's peak / no widow's peak) in a table.
3. Count the students in each class and calculate the percentage of each phenotype for the whole class and separately for boys and girls.
4. If students are willing, ask whether either parent shows the trait and note it beside the student's entry.

Observation table (sample layout).

Points to discuss in your write-up.

• Which phenotype is commoner in your class? Widow's peak is described in section 3.9 as an autosomal dominant trait (WW or Ww) and a straight hairline as recessive (ww); tongue rolling is usually described the same way.
• Both sexes should show the trait in similar proportions, because these are autosomal, not sex-linked, traits. Check whether your boys-versus-girls percentages agree.
• A student showing the dominant phenotype may be homozygous or heterozygous; you cannot tell the genotype from the phenotype alone. A student showing the recessive phenotype must be homozygous recessive. …