Transcript Patterns of Heredity and Human Genetics

Patterns of Heredity and
Human Genetics
When Heredity Follows Different
Rules
Incomplete Dominance

The phenotype of the
heterozygous is
intermediate between
those of the two
homozygous
individuals.
 Neither allele is
completely dominant.
Incomplete dominance
Incomplete Dominance

In humans, curly hair (HH) is incompletely
dominant to straight hair (H’H’). The
heterozygous individual has wavy hair
(HH’). Cross a person with curly hair with a
person who has wavy hair.
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__________ X _________
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Codominance

The phenotypes of
both homozygous
individuals are
visible in
heterozygous
individuals.
 Both alleles are
expressed equally.
 EX: Red horse (RR)
crossed with a white
horse (WW) results
in roan (RW)
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In chickens, black feather color (BB) is
codominant to white feather color (WW). Both
feather colors show up in a checkered pattern
in the heterozygous individual (BW). Cross a
checkered chicken with a checkered chicken.
__________
X
________
Codominance
Codominance in Humans
Sickle cell carriers

Heterozygous individuals have normal and
sickle shaped cells.
 Carry sickle cell trait and can pass on to
offspring.
Multiple Allelic
 Traits
controlled
by more than two
alleles

EX: blood type (A-B-O)
GENOTY
PES
I AI A
IAi
I BI B
IBi
IAIB
ii
RESULTING
PHENOTYPES
Type A
Type A
Type B
Type B
Type AB
Type O
1. A woman with Type O blood and a man who is
Type AB have are expecting a child. What are
the possible blood types of the kid?
So our cross is: ii x IAIB. The proper p-square would look like this:
on to #2 As you can see, our
results are as follows:
50% of kids will be
heterozygous with
blood Type A
50% will be
heterozygous with
blood Type B
2. What are the possible blood types of a child
who's parents are both heterozygous for "B"
blood type?
There is a 75% (3 of 4)
chance that the child
will be Type B,
and a 25% (1 of 4)
chance that the child
will inherit Type O (ii).
Jill is blood Type O. She has two older
brothers (who tease her like crazy) with blood
types A & B. What are the genotypes of her
parents with respect to this trait?
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With some careful thinking we don't even need to do the psquare thing. Jill is Type O, meaning her genotype is
"ii". This means that her parents each have at least one "i"
in their genotype (since she inherited one from each
parent).
Since one brother is Type B, one of the parents must have
the IB allele, making that parent IBi.
And since the other brother is Type A, the other parent
must have the IA allele & have a genotype of IAi.
There you have it. Jill's parents are IAi & IB , and her
brothers shouldn't be so mean. on to #6
Multiple Alleles in Humans
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Blood type
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Importance:
– Mixing incompatible blood causes clumping
resulting in death.
– Determining parentage
Sex-Linked Inheritance

Traits controlled by genes located on sex
chromosomes are sex-linked traits.
– The alleles for sex-linked traits are written as
superscripts (XRY, XRXr)
– Traits carried on Y chromosomes are only
passed from a father to his son.
– X-linked traits can be passed to a son or
daughter.
X-linked traits
EXAMPLE: Drosophilia
In males fruit flies, eye color is carried on the X chromosome.
Red eyes (R) is dominant to white (r).
If a male inherits a single recessive allele (r ) he will have
white eyes. If a female inherits a single recessive allele (r )
she will have red eyes.
Male XrY white eyes
Male XRY red eyes
Female XRXr –red
Female XRXR - red
Female XrXr -white
Sex-linked traits in Humans
Red/green color blindness
 X-linked disorder.

Can’t differentiate b/w
red and green.

Trouble identify red
and green traffic lights.
Hemophilia
 X-linked disorder
 Inability to clot.
 Males inherit from carrier
mothers.
 Females need two
recessive alleles.
 Treated with transfusions,
injecting blood clotting
enzyme.
Polygenic Inheritance

The inheritance of a trait that is controlled
by two or more genes that may or may not
be on the same gene.
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All heterozygous individuals have an
intermediate phenotype.
Polygenic Inheritance in
Humans

Skin color
– When a light and dark-
skinned person mate,
children are
intermediate color.

Eye color
 Height
 stature, hair color, and
body shape
Environmental Influences
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The genetic makeup (GENOTYPE)
determines an organisms potential to
develop and function.
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Many factors can influence how a gene is
expressed.
– External influences
– Internal Influences
Environmental Influences
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External
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Internal
– Temperature
– Hormones
– Nutrition
– Structural differences
– Light
– Age
– Chemicals
– Infectious agents
Human gender differences in facial hair
Pictures and examples are taken
from various websites.