BIO 235 Exam 2 Study Guide | Questions with 100%
Verified Answers | Latest Update 2026/2027
Question: Complete dominance
Answer: A heterozygote has the same phenotype as one of the homozygotes—ex: Red or
white
flower
Question: Incomplete dominance
Answer: The phenotype of the heterozygote falls in between the phenotypes of the two
homozygotes ex: Red, pink and white flowers
Question: Codominance
Answer: Heterozygotes express both phenotypes together.
Phenotypic ratio = genotypic ratio ex: A, B, AB, and O blood types
Question: Dominance does not impact how alleles are inherited
Answer: It influences how alleles are expressed as a phenotype
Question: The type of dominance depends on
Answer: the level at which you examine the phenotype
Question: Incomplete Penetrance
Answer: Some people with the allele don't express the trait
The genotype does not always produce the expected phenotype.
Question: Expressivity
Answer: The degree to which a trait is expressed.
Question: Variable expressivity
Answer: expression ranges from a skin tag to fully functional additional fingers or toes
Question: Penetrance and Expressivity are both due to
Answer: effects of other genes and environmental factors that can alter or completely
suppress
the effect of a particular gene
Question: Truly dominant lethal alleles cannot be transmitted unless
Answer: expressed after affected individuals reach reproductive maturity
, Question: The Ay allele has differing (variable) effects depending on the level of phenotype
considered
Answer: fur color - dominant
survival (lethality)—recessive (because it takes two alleles)
Question: Pleiotropy
Answer: one gene affects multiple, seemingly unrelated traits
Question: The agouti gene is pleiotropic -
Answer: 1. Lethal in homozygous individuals.
2. Yellow fur color in heterozygous individuals
Question: Ay is dominant to wild-type A
Answer: for the trait of fur color
Question: Ay is recessive to wild-type A
Answer: for the trait of lethality
Question: Some loci have more than two alleles within a group or population, but diploid
individuals will
Answer: each still only have two alleles in their own genome
Question: Multiple alleles, also called
Answer: allelic series
Question: Compound heterozygotes
Answer: (at least) Two different alleles at a locus that result in a recessive phenotype
- Different alleles produce the same phenotype.
Question: Compound Heterozygote example: CFTR locus
Answer: Cystic fibrosis is an example of a compound heterozygous phenotype.
• Autosomal recessive - must inherit two non-functional alleles; they can be identical
or
different
Question: Lethal Alleles
Answer: can be dominant but are typically recessive otherwise they wouldn't be heritable
Verified Answers | Latest Update 2026/2027
Question: Complete dominance
Answer: A heterozygote has the same phenotype as one of the homozygotes—ex: Red or
white
flower
Question: Incomplete dominance
Answer: The phenotype of the heterozygote falls in between the phenotypes of the two
homozygotes ex: Red, pink and white flowers
Question: Codominance
Answer: Heterozygotes express both phenotypes together.
Phenotypic ratio = genotypic ratio ex: A, B, AB, and O blood types
Question: Dominance does not impact how alleles are inherited
Answer: It influences how alleles are expressed as a phenotype
Question: The type of dominance depends on
Answer: the level at which you examine the phenotype
Question: Incomplete Penetrance
Answer: Some people with the allele don't express the trait
The genotype does not always produce the expected phenotype.
Question: Expressivity
Answer: The degree to which a trait is expressed.
Question: Variable expressivity
Answer: expression ranges from a skin tag to fully functional additional fingers or toes
Question: Penetrance and Expressivity are both due to
Answer: effects of other genes and environmental factors that can alter or completely
suppress
the effect of a particular gene
Question: Truly dominant lethal alleles cannot be transmitted unless
Answer: expressed after affected individuals reach reproductive maturity
, Question: The Ay allele has differing (variable) effects depending on the level of phenotype
considered
Answer: fur color - dominant
survival (lethality)—recessive (because it takes two alleles)
Question: Pleiotropy
Answer: one gene affects multiple, seemingly unrelated traits
Question: The agouti gene is pleiotropic -
Answer: 1. Lethal in homozygous individuals.
2. Yellow fur color in heterozygous individuals
Question: Ay is dominant to wild-type A
Answer: for the trait of fur color
Question: Ay is recessive to wild-type A
Answer: for the trait of lethality
Question: Some loci have more than two alleles within a group or population, but diploid
individuals will
Answer: each still only have two alleles in their own genome
Question: Multiple alleles, also called
Answer: allelic series
Question: Compound heterozygotes
Answer: (at least) Two different alleles at a locus that result in a recessive phenotype
- Different alleles produce the same phenotype.
Question: Compound Heterozygote example: CFTR locus
Answer: Cystic fibrosis is an example of a compound heterozygous phenotype.
• Autosomal recessive - must inherit two non-functional alleles; they can be identical
or
different
Question: Lethal Alleles
Answer: can be dominant but are typically recessive otherwise they wouldn't be heritable
