Honor Bio 11.1 Flashcards
(14 cards)
What is a genotype?
The genetic makeup of an organism; the combination of alleles
What does homozygous mean?
Having two identical alleles for a trait
What does heterozygous mean?
Having two different alleles for a trait
What is a phenotype?
The observable physical or biochemical characteristics of an organism, determined by its genotype.
What is a genotypic ratio?
The ratio of different genetic combinations in offspring
What is a phenotypic ratio?
The ratio of observable traits in offspring
What is the difference between dominant and recessive alleles?
Dominant alleles mask recessive ones. A trait shows if at least one dominant allele is present.
What is codominance?
A situation where both alleles are fully expressed in a heterozygote
How did Mendel set up his genetic experiments?
He used pea plants, controlling their mating to study traits one at a time.
What were the generations in Mendel’s experiments, and what did he observe?
P (parental): pure-breeding
F1: all dominant phenotype (100%)
F2: 3:1 phenotypic ratio, 1:2:1 genotypic ratio
Contrast genotype and phenotype ratios in dominant/recessive vs. codominant traits.
Dominant/recessive traits often show a 3:1 phenotypic ratio (F2), hiding the recessive genotype in heterozygotes. Codominant traits show a 1:2:1 phenotypic ratio because both alleles are expressed in heterozygotes.
How does a test cross work?
Cross an individual with an unknown genotype (showing dominant phenotype) with a homozygous recessive individual. If any offspring show the recessive trait, the unknown genotype is heterozygous.
Predict genotypic and phenotypic ratios for a dominant/recessive trait (Aa x Aa).
Genotypic: 1 AA : 2 Aa : 1 aa
Phenotypic: 3 dominant : 1 recessive
Predict genotypic and phenotypic ratios for a codominant trait (e.g., R¹R¹ x R¹R²).
Genotypic: 1 R¹R¹ : 1 R¹R²
Phenotypic: 1 full R¹ : 1 mix of R¹ and R² (both traits expressed)
