Exam Review: Genetics and Heredity

Lecturer: Dr. Davenport

Focus: Chapter 10 (Punnett Squares)

Key Concepts

Carrier

• Definition: An individual carrying a recessive allele that they can pass to offspring but do not exhibit in their phenotype.
• Genotypes:
  • Homozygous Dominant: Two dominant alleles.
  • Homozygous Recessive: Two recessive alleles.
  • Heterozygous (Carrier): One dominant and one recessive allele.

Practice Question Example

• Question: Jane is a carrier for cystic fibrosis (Aa), John is homozygous dominant (AA).
  • Result: 0% chance of having a child with cystic fibrosis because no aa genotype is possible.

Dominance Patterns

Dominant vs. Recessive

• Dominant alleles mask recessive alleles in heterozygous individuals.

Incomplete Dominance

• Example: Curly (CC) + Straight (SS) hair gives Wavy (CS) hair.
• Genotype: A heterozygous individual shows a blend of traits.

Codominance

• Example: Alleles for vertical and horizontal stripes show both traits in full (e.g., vertical and horizontal stripes visible).
• Genotype: Both alleles are fully expressed.

Practice Questions

Incomplete Dominance

• Example Question: Child has wavy hair (CS), determine parents.
  • Not Possible: Both parents having curly hair (CC) or straight hair (SS).

Codominance

• Blood Type Example: Jane has blood type A, John has blood type AB.
  • Child Definitely Not John's: Child with OO genotype (Jeb), as Jane might carry O, but John cannot pass O.

Practice

• Change parental blood types to determine offspring possibilities.

Sex-Linked Genes

Male with X-Linked Gene

• Passage: Males pass X-linked genes only to their daughters (female offspring).

Female Heterozygous for X-Linked Gene

• Passage: Can pass the gene to either male or female offspring (50% chance for each).

Exam Tips

• Pay attention to homozygous vs. heterozygous in genotypes.
• Practice with Punnett squares for different inheritance patterns.
• Understand the differences in inheritance between autosomal and sex-linked genes.

Additional Note:

• Review the example problems discussed and practice with similar questions to solidify understanding.

I hope these notes help in preparing for the exam. Good luck!