9.2: Procedure

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Analysis of several single gene characteristic in humans

If individuals are homozygous dominant (e.g., AA) or heterozygous (e.g., Aa), their phenotype will show the dominant characteristic. Dominant phenotype could be encoded as “A–”. If individuals are homozygous recessive (aa), their phenotype will show the recessive characteristic.

Work with a partner to determine your phenotype for the traits listed in the table below.
Record your phenotype and possible genotypes (circle the letters on the appropriate line).
After the totals for class are tallied, calculate the percentage of the class with each characteristic.

Human genetics and pedigree analysis

An important and useful tool provided by Mendel is that one’s genotype can often be inferred by knowing the phenotype of the individual’s parents, grandparents, children, etc. Furthermore, one can also infer whether the alleles are dominant or recessive.

Genetic counselors are sometimes able to identify parents who are likely to produce children with genetic disorders. Fetal cells can then be tested to determine if the newborn does indeed have the disorder. This is called prenatal analysis.

Another type of genetic counseling uses pedigree analysis. Pedigree charts show the inheritance of a genetic disorder within a family and make it possible to determine whether any particular individual has an allele for that disorder.

In pedigree charts, symbols are used to indicate:

normal (clear) and affected (filled-in),
males (squares) and females (circles),
reproductive partners (linked at midline), and
siblings (linked from above).

For the below practice pedigrees, determine how the characteristic is passed. Is it dominant or recessive (attempt to use both)? Determine as many genotypes as possible: