Download Biology Heritable information provides for continuity of life. (3.A.4

The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
Big Idea 3: Genetics and
Information Transfer
Heritable information provides for
continuity of life. (3.A.4)
Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Pearson Education, Inc., publishing as Person Benjamin Cummings
College Board, AP Biology Curriculum Framework 2012-2013
14.3, 15.1-15.5
Copyright © Rebecca Rehder Wingerden
a. Many traits are the product
of multiple genes and/or
physiological processes.
1. Patterns of inheritance of
many traits do not follow
ratios predicted by Mendel’s
laws and can be identified by
quantitative analysis, where
observed phenotypic
ratios statistically differ
from the predicted ratios.
Incomplete dominance in snapdragon color.
When red snapdragons are crossed with white
ones, the F1 hybrids have pink flowers.
Segregation of alleles into gametes of the F1
plants results in an F2 generation with a 1:2:1
ration for both genotypes and phenotypes. The
letter C with a superscript indicates an allele for
flower color: CR for red and CW for white.
Copyright © 2012 Rebecca Rehder Wingerden
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
Multiple Alleles- Only two alleles existed for
the pea characters that Mendel studied, but
most genes exist in more than two allelic forms.
The ABO blood groups in humans, are
determined by three alleles of a single gene: IA,
IB, and i. A person’s blood group (phenotype)
may be one of four types: A, B, AB, or O. These
letters refer to two carbohydrates -A and B- that
may be found on the surface of red blood cells.
A person’s blood cells may have carbohydrate A
(type A blood), carbohydrate B (type B), both
(type AB), or neither (Type A Blood).
AB), or neither (Type A Blood).
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
AB), or ne
Epistasis- a gene at one locus which alters the phenotypic expression
of a gene at a second locus.
Labrador Retriever Coat Color. Black (B) coat color is dominant to
chocolate (b) coat color and the pigmentation gene (E/e) is epistasis
to the coat color locus.
(co dominance)
Multiple alleles for the ABO blood groups. The four
blood groups result from different combinations of three
alleles.
Copyright © 2012 Rebecca Rehder Wingerden
Copyright © 2012 Rebecca Rehder Wingerden
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
Quantitative characters are those characteristics which occur in a
population along a continuum (in gradations). Quantitative variation
usually indicates polygenic inheritance, an additive effect of two
or more genes on a single phenotypic characteristic.
NOTE:
Polygenic
inheritance is
the converse
of pleiotropy,
where a
single gene
affects several
phenotypic
characters.
Bar graph of the results.
A simplified model for polygenic inheritance of skin color- According to this model, three separately inherited
genes affect the darkness of skin. The Punnett square shows all the possible genetic combination in gametes
and in offspring of a large number of hypothetical mating between these heterozygous.
Copyright © 2012 Rebecca Rehder Wingerden
Jet,
Sawyer,
and Abbie
Blood Types and the Population- O positive is the most
common blood type. Not all ethnic groups have the same mix
of these blood types. The mix of the different blood types in the
U.S. population is shown above.
Example of epistasis. This Punnett square
illustrates the genotypes and phenotypes
predicted for offspring of mating between two
black mice of genotype BbCc. The C/c gene,
which is epistatic to the B/b gene codling for the
hair pigment, controls whether or not pigment of
any color will be deposited in the hair.
AB), or neither (Type A Blood).
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
Environmental Impact of Phenotype- Phenotypic range is called
the norm of reaction. Generally, norms of reaction are broadest for
polygenic characters. Environment contributes to the quantitative
nature of these characteristics. Geneticists refer to such characters a
multifactorial, meaning the many factors, both genetic and
environment, collectively influence phenotype.
For humans, nutrition
influence height, exercise
alters build, sun-tanning
darkens the skin and
experience improves
performance on intelligence
test. Even identical twins,
who are genetical equals,
accumulate phenotypic
differences as a result of
their unique experiences.
The effect of environment on phenotype- The outcome of a genotype lies within its norm or reaction, a phenotypic
range that depends on the environment in which the genotype is expressed. For example, hydrangea flowers of the
same genetic variety range in color from blue-violet to pink, with the shade and intensity of color depending on the
acidity and aluminum content of the soil. (Pink: no aluminum, pH 6.0-6.4, Blue: aluminum present in soil, pH 5.0).
Copyright © 2012 Rebecca Rehder Wingerden
AB), or ne
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
Sex-link Inheritance in Drosophila
Experiment- Tomas Hunt Morgan wanted to
analyze the behavior of two alleles of a fruit fly
eye-color gene. In crosses similar to those done
by Mendel with pea plants, Morgan and his
colleges mated a wild-type (red-eyed) female
with a mutant white-eyed male.
Morgan then bred an F1 red-eyed female to an
F1 red-eyed male to produce the F2 generation.
b. Some traits are determined by genes on sex
chromosomes.
• Sex-linked genes reside on sex
chromosomes (X in humans).
• In mammals and flies, the Y
Results- The F2 generation showed a typical
Mendelian ration of 3 red-eyed flies: 1 whiteeyed fly. However, no females displayed the
white-eyed trait; all white-eyed flies were males.
chromosome is very small and
carries few genes.
• In mammals and flies, females
XX and males are XY; as such,
X-linked recessive traits are
always expressed in males.
• Human sex-linked disorders:
- Color blindness (3A3)
- Duchenne muscular
dystrophy (p. 291)
- Hemophilia (p. 291)
Human sex chromosomes. Hemizygote
an individual, organism, or cell that has
only one allele for a specific
characteristic. The trait specified by the
allele is expressed regardless of whether
the allele is dominant or recessive. Such
alleles include those on the single X
chromosome in males, which have no
corresponding alleles on the Y
chromosome.
Copyright © 2012 Rebecca Rehder Wingerden
Copyright © 2012 Rebecca Rehder Wingerden
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
•
Some traits are sex limited, and expression depends
on the sex of the individual, such as milk production in
female mammals and pattern baldness in males.
Male Pattern Baldness (androgenic alopecia) is the most common type of hair loss in
men and is related to an individual’s genes and the production of male sex hormones.
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
c. Some traits result from nonnuclear inheritance.
1. Chloroplasts and mitochondria are randomly assorted to gametes
and daughter cells; thus, traits determined by chloroplast and
mitochondrial DNA do not follow simple Mendelian rules.
Mitochondrial InheritanceIn most multicellular
organisms mitochondrial
DNA (mtDNA) is inherited
exclusively from the mother,
therefore mtDNA can be
used to trace maternal
lineages far back in time.
• The androgen receptor responds to signals from male hormones and is
encoded by the AR gene, which is located on the X chromosome. If a
man has the baldness-promoting version of the androgen receptor, then
he must have received this variant of the gene from this mother.
• A second gene region
associated with MPB has
been found on chromosome
20. It is still unclear as to
what these genes are
influencing, but research
shows they act
independently of the
androgen receptor variant
on the X chromosome.
Mitochondrial Eve Theory states that
the mitochondrial DNA in all human is
inherited from one common female
ancestor in Africa ~ 200,000 years ago.
Male Pattern Baldness:
Chromosome 20 and X chromosome
https://www.youtube.com/watch?v=yuT4IC1KXoc
http://www.mhrc.net/mitochondrialEve.htm
http://biol1020-2011-2.blogspot.com/2011/09/combing-through-genetics-of-male.html
Copyright © 2012 Rebecca Rehder Wingerden
Copyright © 2012 Rebecca Rehder Wingerden
The inheritance pattern of many traits cannot be explained by
simple Mendelian genetics. (3.A.4)
Bozeman Biology: Advanced Genetics (13:00 min.)
http://www.bozemanscience.com/030-advanced-genetic
Bozeman Biology: Linked Genes (18:00 min.)
https://paul-andersen.squarespace.com/linked-genes
Bozeman Biology: Blood Types (11:00 min.)
http://www.bozemanscience.com/blood-types
Bozeman Biology: Genotype Expression (9:00 min.)
http://www.bozemanscience.com/053-genotype-expression
Copyright © 2012 Rebecca Rehder Wingerden
Conclusion- All F2
offspring had red
eyes, so the mutant
white-eye trait (w)
must be recessive to
the wild-type red-eye
trait (w+). Since the
recessive trait -white
eyes- was expressed only in the male in the F2
generation, Morgan deduced that this eye-color
gene is located on the X chromosome and that
there is no corresponding locus on the Y
chromosome.