Mendelian Inheritance

• Inheritance of Mendle is the topic.
• Johann Gregor Mendel is considered "the father of genetics".

Homologous Chromosomes

• Homologous chromosomes share the same length.
• The centromeres must be in the same location.
• Contain genes for the same traits.
• Genotype: The alleles an individual possesses, for example BB, or Bb for brown eyes.
• Phenotype: The physical appearance of an individual, for example, brown eyes.

Dominant Alleles

• A dominant allele is expressed in the phenotype.
• B = brown eyes, b = blue eyes

Recessive Alleles

• Recessive alleles are masked in the presence of dominant alleles.
• Bb = brown eyes, phenotype.
• Bb = genotype.

Heterozygous Alleles

• If the two alleles of an inherited pair are different, they are recognized as heterozygous.
• Homozygous dominant: BB = brown eyes
• Homozygous recessive: bb = blue eyes.

Hybrids

• Monohybrid: hybrid for one trait, example, Bb = brown and blue eyed allele
• Dihybrid: hybrid for two traits, example, Bb Cc = eye color and hair straightness

Mendel's Laws of Inheritance

Law of Segregation

• During gamete formation, alleles for each gene segregate, so each gamete carries only one allele for each gene.

Law of Independent Assortment

• Genes for different traits can segregate independently during the formation of gametes.

Law of Dominance

• Some alleles are dominant while others are recessive.
• If an organism has at least one dominant allele, it will display the effect of that dominant allele.

Phenotype Examples

• YY, RR = yellow, round
• YY, Rr = yellow, round
• Yy, RR = yellow, round
• Yy, Rr = yellow, round
• YY, rr = yellow, wrinkled
• Yy, rr = yellow, wrinkled
• Yy, RR = yellow, round

F1 Progeny Example

• Tt x Tt (selfing)
• Gametes: T, t, T, t
• Possible combinations: TT, Tt, Tt, tt

Expected Ratio

• Mendel's total expected ratio was 9:3:3:1, which can also be described as :
• 9 yellow, round
• 3 yellow, wrinkled
• 3 green, round
• 1 green wrinkled.
• 9/16 of the offspring were round-yellow.
• 3/16 were round-green.
• 3/16 were wrinkled-yellow.
• 1/16 were wrinkled-green.