Monohybrid Cross Vocabulary Flashcards

Genetics Terminology

• Homozygous: Genotypes composed of identical alleles.
• Alleles: Variants of a gene that determine a specific trait.
• Dominant: A gene that consistently manifests in the phenotype, even in the presence of a different allele.
• Recessive: A gene that is only exhibited in the phenotype when paired with another identical allele (homozygous state).
• Heterozygous: Genotypes made of two distinct alleles.

Genotype Examples

• Dominant Alleles Examples: Represented by uppercase letters (e.g., D, L, N, R, S).
• Recessive Alleles Examples: Represented by lowercase letters (e.g., n, d, r, k).
• Homozygous Dominant Examples: Combinations of identical dominant alleles (e.g., AA, KK, TT).
• Homozygous Recessive Examples: Combinations of identical recessive alleles (e.g., ee, qq, ww).
• Dominant Gene Requirement: Genotypes must include a dominant allele (e.g., AA, Dd, EE, Jj, RR, Ss).
• Recessive Gene Requirement: Genotypes must be homozygous recessive (e.g., aa, rr).

Punnett Square Basics

• Outside Letters: Indicate the alleles contributed by the parents.
• Inside Letters: Show possible combinations of offspring traits resulting from parental alleles.

Practical Genetics Applications

• Horned Cattle Case:

  • Parental Cross: Homozygous hornless bull (HH) x Homozygous horned cow (hh).
  • First Generation Genotype/Phenotype: F1 will be Hh (all offspring hornless).

• Tomato Color Cross:

  • Parental Cross: Homozygous red fruit (RR) x Yellow fruit (rr).
  • First Generation Genotype/Phenotype: F1 will be Rr (all offspring red).

Second Generation Predictions

• Tomato F2 Cross:
  • F1 Cross: Rr x Rr.
  • F2 Genotypes and Phenotypes: 1:2:1 genotype ratio; 3:1 phenotype ratio (three red: one yellow).

Human Trait Example

• Tongue Rolling:
  • Father’s Phenotype: Non-roller; Genotype: rr.
  • Mother’s Phenotype: Roller; Genotype: Rr.
  • Probability of having a tongue-rolling child: 50% (1/2 chance).

Eye Color Genetics

• Brown vs. Blue Eyes:
  • Brown-eyed father (genotype Bb, blue-eyed mother bb).
  • Probability of blue-eyed child: 25%.