Transcript You Light Up My Life - Lakefield District Secondary School

Patterns of Inheritance
Complete Dominance
Incomplete Dominance
Co-dominance
Co-dominance with Multiple Alleles
Sex Linked
Impact of Mendel’s Work

Mendel published his results in 1866
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Paper received little notice
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Mendel discontinued his experiments in
1871
Paper rediscovered in 1900
Mendel’s Law of Segregation
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An individual inherits ONE “unit” of
information (allele) about a trait from each
parent
During gamete formation, the alleles
separate from each other (Tt
T or t )
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Mendel’s Law of
Independent Assortment
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Mendel concluded that one gene did not
affect another gene
Alleles for these genes separated random
from each other
TtRr
T or t
R or r
so TR Tr tR tr
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Complete
Dominance
Inheritance

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2 alleles; one dominant
or the other
if dominant allele
present, it will be
expressed
True-breeding
homozygous recessive
parent plant
aa
True-breeding
homozygous dominant
a a
parent plant
2 distinct phenotypes;
3:1 ratio
Aa
Aa
Aa
Aa
A Aa Aa
AA
A Aa Aa
An F1 plant
self-fertilizes
and produces
gametes:
F2
PHENOTYPE
S
Aa
A

F1
PHENOTYPE
S
AA
Aa
Aa
aa
a
A AA Aa
a Aa aa
Genetics After Mendel
1. Incomplete Dominance
2. Co-dominance
3. Co-dominance with Multiple Alleles
4. Sex Linked
1. Incomplete
Dominance
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neither allele is
completely
dominant over
the other
X
Incomplete
Homozygous
Homozygous
parent R R
parent
Dominance r r
All F1 are
Rr
heterozygous
3 phenotypes
heterozygous is
a “intermediate
or “blend”
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Rr
rr
Rr
X
Rr
Rr
RR
F2 shows three phenotypes in 1 : 2 : 1 ratio
2.Co-dominance


both alleles are
expressed at the same
time in the
heterozygous (roan)
3 phenotypes;
1 : 2 : 1 ratio
page
3. Co-dominance
with Multiple
Alleles:
ABO Blood types

Genotype
Phenotype
IAIA or IAi
Type A
IBIB or IBi
Type B
IAIB
Type AB
ii
Type O
3 alleles; two that are co-dominant and
one recessive
IA , I B , i
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ABO Blood Types

type of blood determined by antigen on surface (flag)
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type of blood make antibodies against other antigens
Blood Transfusions
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During transfusions recipient’s antibodies in plasma will
attack blood cells that have an unfamiliar surface antigen
(agglutination – clumping of blood)

Type AB is universal recipient since it does not have any
antibodies because it has both antigens – any blood can be
donated to them!

Type O is universal donor since it has neither type A nor
type B antigen for antibodies to attack – give to anyone
Transfusions
Antibodies
Can Receive
Blood From
A or O
Type A
B
Type B
A
B or O
none
A, B, AB, O
Type AB
Type O
A and B
only O
Rh Factor
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another protein marker on red blood cells
independent of type of blood
inheritance works according to complete
dominance
either Rh+ or Rh- ; Rh+ is dominant
special problem during pregnancy of
second child if mom is Rh- and first was
baby Rh+
4. Sex Linked
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genes on the sex
chromosomes
have different
probabilities in
females and males
examples of
recessive X linked
traits
– hemophilia
– red/green colour
blindness
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Other types of Inheritance
5. Multifactorial/Multiple Genes/Polygenic
6. Sex Limited
7. Sex Influenced
8. Gene Linkage
5. Multifactorial/Multiple Genes/Polygenic
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Traits show wide range of phenotypic
expression; continuous distribution
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Controlled by more than one gene
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Traits maybe influenced by other factors

Examples human hair colour, height, eye
colour, skin colour
Describing Continuous Distribution
Number of individuals with
some value of the trait
(line of bell-shaped curve indicates continuous
variation in population)
Range of values for the trait
6. Sex Limited Traits
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Expression of the trait is limited by sex of
the individual
Traits NOT on sex chromosome
Thought to be influenced by hormones
Example: heavy beards – phenotype in
males only but females inherit but don’t
express it but can pass trait to sons
7. Sex Influenced Traits
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Idea of how genes are influenced by
internal environments
Genes may be dominant in one sex but
recessive in other; genotype interpreted
differently
Baldness – dominant trait in males; in
females recessive trait and don’t see
“bald” but rather thin
Nature verse Nurture
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Expression of traits are not fully under control of
just what your genotype is (NATURE)
An organism’s internal environment and external
environmental factors influence how genes may
be expressed (NURTURE)
Example – height – may have genetics to be tall
but if there is hormonal imbalance or nutritional
deficiency than won’t reach genetic potential
Temperature Effects
on Phenotype
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Rabbit is homozygous for
an allele that specifies a
heat-sensitive version of an
enzyme in melaninproducing pathway
Melanin is produced in
cooler areas of body
Environmental Effects on Plant
Phenotype
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Hydrangea macrophylla
Action of gene responsible for floral
color is influenced by soil acidity
Flower color ranges from pink to blue