• The physical characteristics of an individual are controlled by inherited genes.
• Dominant genetic traits appear if a single dominant allele is inherited; recessive genetic traits require the inheritance of two recessive alleles.

1. What is the difference between genotype and phenotype?
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2. What are three possible genotypes and the two possible phenotypes for a characteristic that is controlled by two alleles, one being dominant and the other recessive?
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Essential Study Partner

• Introduction

• It is possible to determine the chances of an offspring inheriting a particular parental gene, and therefore a particular condition.

1. Why do gametes have only one allele for each pair of alleles being considered?
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2. What phenotypic ratios are expected for all possible crosses involving only one trait?
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3. What is the relationship between the events of meiosis and genetic diversity among the gametes?
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4. What phenotypic ratios are expected for all possible crosses involving two traits?
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Essential Study Partner

• Monohybrid Cross
• Dihybrid Cross

• Certain traits, such as skin color, behavior, and various syndromes, are multifactorial.
• The environment may influence gene expression.
• Blood type is controlled by multiple alleles and exhibit codominance.
• Some traits, like sickle-cell disease, are incompletely dominant.

1. What are some examples of human multifactorial traits?
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2. What type of studies show that human inheritance is influenced by the environment?
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3. What is an example of incomplete dominance in humans?
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4. How is ABO blood type an example of codominance and multiple allele inheritance?
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Essential Study Partner

• Beyond Mendel

• Sex-linked traits are usually carried on the X chromosome. Males, with only one X, are more likely to express X-linked traits.

1. Why are more males than females color blind?
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2. What phenotypic ratios are expected for all possible crosses involving an X-linked recessive allele; involving one X-linked dominant allele?
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3. What is a mixed genetics problem and how would you construct the gametes for individuals in such a problem?
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Essential Study Partner

• Sex Chromosomes