Bio

Genetics Review

Vocabulary Terms

• Alleles

  • Definition: Different forms of a gene that control a specific characteristic.

  • Example: A, a.

• Phenotype

  • Definition: The physical appearance or trait of an organism.

• Genotype

  • Definition: The alleles that control a specific characteristic.

  • Example: AA, Aa, aa.

• Heterozygous

  • Definition: A genotype in which the two alleles are different.

  • Example: Aa.

• Homozygous

  • Definition: A genotype in which the two alleles are the same.

  • Example: AA or aa.

• Dominant Allele

  • Definition: The allele that expresses itself in a heterozygous condition.

  • Presentation: Denoted by a capital letter.

• Recessive Allele

  • Definition: The allele that does not express itself in the presence of a dominant allele in a heterozygous condition.

  • Presentation: Denoted by a lowercase letter.

Examples of Dominant and Recessive Traits

• Axillary Flowers:

  • Dominant form: Allele A (Axillary flowers)

  • Recessive form: Allele a (Terminal flowers)

  • Genotypes and Phenotypes:

  • AA (Homozygous Dominant): Axillary flowers

  • Aa (Heterozygous): Axillary flowers

  • aa (Homozygous Recessive): Terminal flowers

• Stem Height:

  • Dominant form: Allele T (Tall stems)

  • Recessive form: Allele t (Short stems)

  • Genotypes and Phenotypes:

  • TT (Homozygous Dominant): Tall stems

  • Tt (Heterozygous): Tall stems

  • tt (Homozygous Recessive): Short stems

Punnett Squares

a. Chimpanzee Finger Type

• Traits: Straight fingers (S) are dominant to bent fingers (s).

• Cross: Heterozygous straight-fingered chimpanzee (Ss) with a bent-fingered chimpanzee (ss).

• Punnett Square:

  • S s

  • s Ss

  • s ss

• Genotypes and Percentages:

  • Ss: 50% (Straight Fingers)

  • ss: 50% (Bent Fingers)

b. Human Eye Color

• Traits: Brown eyes (B) are dominant over blue eyes (b).

• Cross: Heterozygous brown-eyed male (Bb) marries heterozygous brown-eyed female (Bb).

• Punnett Square:

  • B b

  • B BB

  • b Bb

  • b Bb

  • bb

• Genotypes and Percentages:

  • BB: 25% (1/4) Brown Eyes

  • Bb: 50% (2/4) Brown Eyes

  • bb: 25% (1/4) Blue Eyes

c. Squash Plants

• Traits: Yellow fruit (Y) is dominant to green fruit (y).

• Cross: Plant with genotype (YY) crossed with plant with genotype (Yy).

• Punnett Square:

  • Y Y

  • Y YY

  • y Yy

  • Y YY

  • y Yy

• Genotypes and Percentages:

  • YY: 50% (2/4) Yellow Fruit

  • Yy: 50% (2/4) Yellow Fruit

  • yy: 0% (0/4) Green Fruit

d. Tongue Rolling in Humans

• Traits: Rolling tongue (R) is dominant; the recessive condition cannot roll tongue (r).

• Parental Information: Bob can roll his tongue (Genotype: Rr) and his mother cannot (Genotype: rr). He is married to Sally (Genotype: rr).

• Punnett Square:

  • R r

  • r Rr

  • r rr

• Genotypes and Percentages:

  • Rr: 50% (Tongue Rolling)

  • rr: 50% (No Tongue Rolling)

Principles of Genetics

• Law of Segregation

  • Definition: When gametes are formed, the pair of alleles for each trait separates from each other.

• Law of Independent Assortment

  • Definition: The alleles of two (or more) different genes assort independently into gametes.

  • Implication: The allele a gamete receives for one gene does not influence the allele received for another gene.

Dihybrid Crosses

• Definition: Punnett squares that involve two traits simultaneously.

• Example:

  • Phenotypes of Parents: Yellow Round (YYRR) crossed with Green Wrinkled (yyrr).

  • Gametes for Parents: YR from Yellow Round; yr from Green Wrinkled.

F1 Generation Results

• Genotype of F1: YyRr (Yellow Round)

• Selfing of F1 Generation: YyRr crossed with YyRr.

• Gametes Produced from F1 Offspring:

  • YR, Yr, yR, yr.

F2 Generation Analysis

• Combination of Gametes:

  • YYRR, YYRr, YyRR, YyRr (Yellow Round)

  • YYrr, Yyrr (Yellow Wrinkled)

  • yyRR, yyRr (Green Round)

  • yyrr (Green Wrinkled)

• Phenotypic Distribution:

  • Yellow Round: Dominant trait combination

  • Green Wrinkled: Recessive trait combination