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Beyond Mendel
Despite the importance of Mendel’s work, it would be a mistake to characterize the principles he
discovered as “laws” because there are important exceptions to most of them.
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Incomplete Dominance:
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A form of intermediate inheritance in which
heterozygous alleles are ________expressed,
resulting in a _________________________.
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For example, in cross-pollination experiments
between red and white snapdragon plants the
resulting offspring are pink.
Codominance:
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A number of human traits are the result of 2 types
of alleles that are _____________________. Such traits are said to be
____________________ for that trait.
When an individual is _______________________ for such traits, the
resulting phenotype or expression of these two traits is a
________________, because both traits are ___________________________.
The alleles for curly hair and straight hair are examples of alleles for a trait
that are codominant. Individuals with curly hair are homozygous for curly
hair alleles.
Individuals with straight hair are homozygous for straight hair alleles.
Individuals who are heterozygous, with one of each allele have wavy hair,
which is a blend of the expressions of the curly and straight hair alleles.
Multiple Alleles:
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Diploid organisms naturally have a maximum of ____ alleles for each gene
expressing a particular characteristic, one deriving from each parent.
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In some cases, however, more than two types of allele can code for a particular characteristic, as is
the case of genetic coding for ___________________ in humans or coat color in rabbits.
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______________________________ result from different ___________________ of the same gene.
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Coat color in rabbits is determined by four alleles.
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Human ________ blood types are determined
by alleles A, B, and O.
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A and B are _____________________ which
are both dominant over _____.
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The only possible genotype for a type O person
is _____.
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Type A people have either _______ or
______genotypes.
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Type B people have either ______or______
genotypes.
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Type AB have only the _____ (heterozygous)
genotype.
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The A and B alleles of gene I produce slightly different glycoproteins (_____________) that are on
the surface of each cell.
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Homozygous A individuals have only the ______________, homozygous B individuals have only
the _______________, homozygous O individuals produce __________________, while a fourth
phenotype (AB) produces both ______________________________.
Rh Blood type system:
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When we are told our blood type, it is usually expressed as a letter followed by either a
________________(+) or _______________ (-).
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This + or - refers to the____ system of blood testing and is usually quoted in combination with the
ABO system described earlier in this lecture:
 e.g. ________________________
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The Rh system is actually much more complicated than the ABO system because there are more
than 30 combinations possible when inherited, however for general usage, the Rh ___________ are
grouped into two families:
 either _____________________________________
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As with the ABO system, there is a dominant __________ which happens to be the ___________
family.
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This means that the genetic pairs that can exist in humans are as follows:
Genotype
++
+--
Blood type
Rh +
Rh +
Rh -
Polygenic Traits:
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Traits controlled by ______________________
called ____________________________.
Usually polygenic traits are distinguished by:
1.
2.
3.
Human polygenic traits include
1.
2.
3.
4.
5.
6.
are