Genetics Notes: Incomplete Dominance & Codominance — Page-by-Page

Page 1

• Opening prayer; context only. No scientific content.

Page 2

• Non-Mendelian patterns of inheritance introduced; contrast with Mendel’s laws. Key non-Mendelian patterns covered: incomplete dominance and codominance.

Page 3

• Lesson objectives:
  • a) Explain incomplete pattern of inheritance.
  • b) Determine offspring phenotypes/genotypes using a Punnett square.
  • c) Understand importance of incomplete pattern of inheritance.

Page 4

• Key genetic terms:
  • $\text{GENE}$ – basic unit of heredity; made of DNA.
  • $\text{GENETICS}$ – study of genes, variation, and heredity.
  • $\text{HEREDITY}$ – passage of traits from generation to generation.
  • $\text{PHENOTYPE}$ – observable traits (e.g., height, eye color).

Page 5

• Additional terms:
  • $\text{GENOTYPE}$ – genetic constitution.
  • $\text{ALLELE}$ – alternative form of a gene.
  • $\text{MULTIPLE ALLELES}$ – more than two alleles control a trait.
  • $\text{GAMETE}$ – reproductive cell; unites to form zygote.
  • $\text{PUNNETT SQUARE}$ – method to determine possible genotypes/phenotypes from a cross.

Page 6

• Additional terms:
  • $\text{DOMINANT}$ – trait that masks the recessive.
  • $\text{RECESSIVE}$ – trait hidden by dominant.
  • $\text{HOMOZYGOUS}$ – two identical alleles.
  • $\text{HETEROZYGOUS}$ – two different alleles.

Page 7

• Recall: test crosses and Punnett squares to predict offspring.

Page 8

• Example setup:
  • Red (R) is dominant to Yellow (r).
  • Test cross: homozygous red plant crossed with yellow plant.
  • Genotype of offspring: $RR \times rr \rightarrow Rr$; Phenotype: red.

Page 9-10

• Punnett square example:
  • Yellow plant: $rr\,\;\text{left side}$
  • Red plant: $RR\,\;\text{top}$
  • Offspring all have genotype $Rr$ and phenotype red.

Page 11-12

• Prompt-style questions illustrating simple dominance (fur/feather color) to apply dominance concepts.

Page 13-15

• INCOMPLETE DOMINANCE: Red (RR) x White (WW) cross:
  • Cross: $RR \times WW \rightarrow RW$
  • Phenotype of offspring: pink (RW).
  • Genotype of offspring: all $RW$.

Page 16-17

• Incomplete dominance example (two pink parents):
  • Cross: $RW \times RW$
  • Offspring genotypes: $RR, RW, WW$ in a 1:2:1 ratio.
  • Phenotypes: red, pink, white respectively.

Page 18-20

• Another incomplete dominance example: curliness vs straightness
  • Cross: $CC \times SS \rightarrow CS$
  • Phenotype: intermediate (e.g., wavy hair).
  • Note: Incomplete dominance yields a third phenotype that is a blend of the two parental traits.

Page 21-22

• Activity on incomplete dominance (eggplant color):
  • Key: Purple (EE), Violet (Ee), White (ee).
  • Cross: often Ee x Ee to produce 1:2:1 genotype ratio:
  • Genotypes: $EE,\; Ee,\; ee$
  • Phenotypes: purple, violet, white with ratio $1:2:1$ (25%, 50%, 25%).

Page 23-28

• CODOMINANCE:
  • Definition: heterozygote expresses both traits simultaneously; not blended.
  • Example context: ABO blood types in humans.

Page 24-25

• Codominance in biology: a clear case where both alleles in the heterozygote are fully expressed.

Page 27-28

• ABO blood types summary:
  • Alleles: $I^A,\; I^B,\; i$ (notations used for A, B, O).
  • Genotypes and phenotypes:
  • Type A: $I^A I^A$ or $I^A i$ → phenotype A.
  • Type B: $I^B I^B$ or $I^B i$ → phenotype B.
  • Type AB: $I^A I^B$ → phenotype AB (codominant expression).
  • Type O: $i i$ → phenotype O.
  • Other notes:
  • Codominance: heterozygotes express both A and B antigens (AB).
  • Blood type compatibility: universal donor/recipient concepts (e.g., O is universal donor; AB is universal recipient).

Page 29-31

• Activity: Who's My Family?
  • Use Punnett squares to infer possible baby genotypes/phenotypes from parental ABO types.
  • Steps:
    1) Determine parental genotypes from their blood types.
    2) Construct Punnett square with ABO alleles.
    3) Compare babies’ phenotypes/genotypes to identify parental matches.
  • Guiding questions focus on matching babies to Cruz, Fernandez, and Lopez families.