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Inheritance Patterns
Ch. 11-3
Independent Assortment
• Says that traits are not inherited together
• Color is not inherited with height
• Plants can be
– Green and short
– Green and tall
– Yellow and short
– Yellow and tall
Mendel’s 4 Principles
• Inheritance of biological characteristics is determined
by individual units known as genes. Genes are passed
from parents to their offspring.
• In cases in which two or more forms (alleles) of the
gene for a single trait exist, some forms of the gene
may be dominant and most others may be recessive.
• In most sexually reproducing organisms, each adult has
two copies of a gene – one from each parent. These
genes are segregated from each other when gametes
are formed.
• The alleles for different genes usually segregate
independently of one another.
Beyond Dominant and Recessive
Alleles
• Some alleles are neither dominant nor
recessive, and many traits are controlled by
multiple alleles or multiple genes.
• Incomplete dominance
• Codominance
• Multiple alleles
• Polygenic traits
Incomplete Dominance
• Neither allele is completely dominant – they
mix
• Red flower x white flower = pink flower
• RR x WW = RW
• Practice
– Blue dog x yellow dog = ?
– worksheet
Codominance
• Both alleles contribute to the phenotype –
both show up
• Black chicken x white chicken = black and
white chicken
• BB x WW = BW
• Practice
– Red cow x white cow = ?
– worksheet
Multiple Alleles
• Genes have more than two alleles
• Example
– Blood type
– Alleles
• A, B, AB, O
• Example
– Gene – rabbit coat color
– Alleles
• Full color, chinchilla, himalayan, albino
Polygenic Traits
• “having many genes”
• Many different genes control the phenotype
of a trait
• Example
– Skin
– Multiple genes with multiple alleles control the
variations in skin color
Applying Mendel’s Principles
• This doesn’t only apply to plants
• It also applies to:
– Flies
– Humans
– Animals
Genetics and the Environment
• Nature vs. nurture
• Genes provide the plan
• The plan unfolds depending on the
environment
• Example
– Sunflower’s height and color are determined by
genes
– This can also be determined by amount of
sunlight, food, water, etc.