Warm-up: 12/9
• With Pea Plants which is dominant, purple
flower or white flower?
• What does P1 generation mean?
– What does purebred mean
• For flower color what does the F1 generation
look like in terms of dominant vs recessive
trait?
Mendel Cont.
pp. 177-181
Mendel’s Experiment Review:
• Grew plants for pure traits (i.e. purple always
produces purple) via self-pollination to make a
pure strain (P1 generation)
• Cross-pollination of pure strains (P cross)
PFP with WFP
Counted the offspring (F1 generation)
• Self-pollination of the F1 generation to create
the F2 generation
Mendel’s results
• One trait was masked by a dominant factor
and the trait that did not appear (in F1 but did
in F2) was recessive
• Trait controlled by a recessive factor is
masked when paired with a dominant
Chromosomes and genes
• Gene (located on a chromosome) codes for a
characteristic (ie flower color)
• Different forms of a gene = allele (purple or
white)
• Letters used to represent alleles
dominant trait capitalized (purple = P)
recessive lower case (white = p)
Genotypes and Phenotypes
• Genotype: alleles an organism inherits
EX: PP Pp pp
• Phenotypes: appearance due to the genotype
EX: PP (purple) Pp (purple) pp (white)
• Homozygous: both alleles are alike (PP or pp)
• Heterozygous: alleles are different
Rules
• Law of segregation: paired factors separate
during meiosis (formation of gametes)
• Law of independent assortment: alleles sort
independently of one another (not all dominant
appeared together)
Punnett Squares
pp. 180-183
• Monohybrid cross: cross between individuals
that looks at one trait
• Punnett square: diagram to predict the
probability of inheritance of certain traits
Parent I
Parent II
B
B
b
b
• Place the parent genotypes in:
Bb x Bb
• Match letters and fill in squares
Parent I
Parent II
B
B
b
BB
Bb
Bb
bb
b
Mendel’s Ratios from his experiments
What are the
Genotypes?
What is the genotype
ratio?
What are the
Phenotypes?
What is the
Phenotype ratio?
Mendel’s Ratios from his experiments
Genotype ratio 1:2:1
Phenotype ratio 3:1
Mendel’s Ratios from his experiments
Genotype ratio 1:2:1
Phenotype ratio 3:1
Genotype ratio ?
1: 1
Phenotype ratio ?
All black