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Mendelian Heredity
(Fundamentals of Genetics)
CH9 pg 173
Sexual Reproduction
• Combining of a sperm cell and an egg cell
from two individuals
• The offspring of this "cross" will have
characteristics from both "parents“
– hybrid
Self – Pollination
Contrasting traits, easy to grow and reproduce
Heterozygous 3:1 Ratio
Characters vs Traits
Mendel’s Laws of Heredity
• Law of Dominance - One factor (trait) in a pair
may mask the effect of the other. Pg 177
Mendel’s Laws of Heredity
• Law of Segregation - The two traits for a
characteristic separate during the formation of
eggs and sperm. Pg 177
Mendel’s Laws of Heredity
• Law of Independent Assortment - The traits
for different characteristics are distributed to
reproductive cells independently. pg177
Using Punnett Squares
• Punnett Square
– Model that predicts the likely outcomes of a
genetic cross with the alleles taken from the
parents
– Shows all the genotypes that could result from a
given cross
How to for Punnett Square
• Capital letter
– Dominant trait
– Letter represents trait (B for brown)
– Dominant always written first in sequence (Bb)
• Lower case letter
– recessive trait
– same letter as dominant trait (b for blond)
Monohybrid Cross
• Contrasting traits (purple vs white flower)
• Homozygous Cross (PP or pp)
• Heterozygous Cross (Pp)
– Paternal alleles across the top
– Maternal alleles down the left side
Monohybrid Cross
• Phenotype
• Genotype
Using Probability
• Likelihood that a specific event will occur
• Probability = # of one kind of possible outcomes
total # of all possible outcomes
• Probability of a specific allele in a gamete
• Represented as a fraction or ratio
Probability in a Heterozygous Cross
• Flipping a coin/ possible alleles
• Both parents have Pp, How do you know?
P
P
p
p
Using a Pedigree
• Several generations
• Determine genetic disorders or diseases that
can be inherited
• Pedigrees can help answers questions about
the three factors of inheritance
– Sex-linked Genes
– Dominant or Recessive
– Heterozygous or Homozygous
Many Genes, Many Alleles
• Polygenic Inheritance
– Several genes affect characteristic
– Relative greenness or brownness, blue eyes are
recessive
Many Genes, Many Alleles
• Incomplete Dominance
– Intermediate between traits
– Snapdragon (red and white = pink)
Many Genes, Many Alleles
• Multiple Alleles
– 3 or more possible alleles, only to alleles for a
gene can be present
– Complex dominance
– Blood types and Labrador coat color
ABO blood groups
Many Genes, Many Alleles
• Codominance
– Both Alleles for the same gene are fully expressed
Genes affected by the Environment
• Nutrients and temperature
• Personality and behavior
Genes Linked Within Chromosome
• Genes that are close together are less likely to
be separated than genes that are far apart