SvS Biology 2000 - Year 10:
Some trial questions on genetics.
1. A condition known as Microsoftia is inherited by a single pair of alleles, this means that BOTH males and females have TWO alleles for that trait. Having Microsoftia is a recessive condition, and requires the affected individual to be HOMOZYGOUS for the trait. Use a test cross to explain how a Headmaster can have Microsoftia even if his parents do not have the trait. (show all of your working, set out correctly to indicate Parents, Gametes and F1)
Don’t forget to use a Key!
| Phenotype | Genotype |
2. Blood groups are controlled by Codominance where blood group A and B are both dominant over O, and A and B are CODOMINANT to each other. For example, AA or AO = blood group A, BB or BO = blood group B, AB = blood group AB, and OO = blood group O.
If your dad is blood group O, and your mum is blood group AB, what possible bloodgroups might their kids have? (show all of your working, set out correctly to indicate Parents, Gametes and F1)
3. Colourblindness is a sex-linked recessive condition. This means that the characteristic is carried only on the X chromosome. Females therefore have two alleles for the trait, and males have only ONE.
(a) Draw a key to show the genotypes and phenotypes for this
trait (like the example in question 1)
(b) If a colourblind female were to mate with a normal male, what would
the chance be that they produced a colourblind daughter? (show all of your working, set
out correctly to indicate Parents, Gametes and F1)
4. A student with red hair wanted to map the inheritance of red hair colour. His paternal grandparents did not have red hair. They had 3 children. Two girls and a boy. Only the second girl had red hair. The student's mother did not have red hair, but her mother did. His maternal grandfather did not, and neither does his mother's only brother. The student has an older sister, who doesn't have red hair. She married a man who doesn't have red hair, and they produced two daughters, the first of whom has red hair.
(a) Construct a pedigree chart for the inheritance of red
hair in this boy's family.
(b) According to this chart, is red hair a dominant or recessive
condition? (How can you tell?)
(c) Is it possible that red hair is a sex linked trait? (How can you
tell?)
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S. van Strien