Patterns of Inheritance

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Chapter 8

• Patterns of Inheritance

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Inheritance
Offspring bear witness to the genetic make-up
of the parents and their parents
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Gregor Mendel and the Garden Pea
Mendel experimented with the garden pea in an
effort to understand inheritance. He did
intentional crosses to determine patterns of
inheritance.
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Garden Pea Traits
Mendel worked with several traits in his
experiments related to colors, shapes,
positions, and plant height
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Monohybrid Cross
The Principle of Segregation indicates that pairs
of alleles separate during gamete formation, and
refuse at fertilization to form pairs.
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Dihybrid Cross
The Principle of Independent Assortment indicates
that each pair of alleles separates independently
from the other pairs of alleles
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Chance
Segregation of alleles and fertilization patterns
all occur as chance events One can never be
certain of the outcome, especially in small
numbers
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Pedigrees
It is possible to trace lineages and keep track
of when traits appear in a family lineage
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Recessive Disorder Inheritance
Recessive disorders can appear if both parents
are carriers of the recessive gene
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Autosomes are chromosomes that are not
responsible for sex determination
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Incomplete Dominance
One modification of the Principles that Mendel
determined is Incomplete Dominance In this case
both the dominant and recessive alleles are
displayed in the phenotype
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Multiple Alleles More than Two Alleles
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Pleiotropy
When one gene codes for multiple characteristics,
the condition is called Pleiotropy An example is
sickle-cell anemia
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Polygenic Inheritance
When multiple genes code for one trait, the
condition is known as Polygenic Inheritance An
example is skin color
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Chromosomal Basis of Inheritance
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Linked Genes Chromosomal Connection
Not all genes sort independently. Genes on the
same chromosome travel together into the gametes
and then into the offspring
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Linked Genes
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Linked Genes
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Sex-Linked Genes
Linked genes that appear on the sex chromosomes
are called sex-linked In humans, these are the X
and Y chromosomes XX is female, XY is
male Color blindness is an example
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Summary

• Principle of Segregation
• Principle of Independent Assortment
• Probability
• Pedigrees

• Incomplete Dominance
• Multiple Alleles
• Pleiotropy
• Polygenic Inheritance
• Gene Linkage
• Sex-linkage