Download NOTES Ch. 11 Inheritance Patterns

NOTES Complex Inheritance and Human Heredity
PEDIGREE – graphic representation of genetic inheritance.
- female
- male
- w/trait
- w/trait
-heterozygous for trait (carrier)
-heterozygous for trait (carrier)
 Recessive alleles cause most genetic diseases, so the
individual with the disease must inherit one allele for the
disease from each parent (must be homozygous) – thus
making these diseases rare.
(i.e. cystic fibrosis, Tay-Sachs, albinism)
 If an individual has just one dominant allele, the trait will not be
expressed.
Carrier – someone who is heterozygous for a recessive disorder
Dominant Genetic Disorders – caused by dominant alleles. Those
who do not have the disorder are homozygous recessive for the trait.
(Huntington’s, achondroplasia)
Autosomes – chromosomes #1 – 22
Sex Chromosomes – 23rd pair of chromosomes in humans
determine the individuals sex. If 23rd pair of chromosomes is:
 XX = female
 Females can only produce gametes with X chromosomes
 XY = male
 Males can produce gametes with either X or Y
chromosomes.
1:1 ratio of males to females:
PATTERNS OF INHERITANCE:
Type of
Definition
Inheritance
Inheritance
Simple
pattern based on
Mendelian
Mendel’s Laws.
Dominant traits
mask recessive
traits.
Where the
phenotype of a
(R and R’ used heterozygote is
intermediate
instead of
between those of
R and r)
the two
homozygotes
Where the
Codominance phenotype of
both parent’s
(two different
uppercase letters alleles are
expressed
are used)
equally in the
phenotype of
heterozygous
offspring
Incomplete
Dominance
Examples
Other Information
Pea Plants –
crossing Tall
(TT) x Short (tt)
yields all Tall (Tt)
offspring.
Attached
earlobes (ff) are
recessive.
Recessive: TaySachs, cystic
fibrosis
In snapdragons,
crossing Red
(RR) with White
(R’R’) yields all
Pink (RR’)
offspring.
Huntington’s Disease –
Dominant disease is rare.
Those without Huntington’s
are homozygous for the
trait.
In chickens,
crossing Black
(BB) with White
(WW) yields all
checkered (BW)
offspring.
In humans, sickle anemia
is an example.
R’ indicates incomplete
dominance.
Neither allele is dominant.
Type of
Inheritance
Multiple
Alleles
Definition
More than one
allele controls the
trait.
Examples
Other Information
Blood types
IA IA or IAi = type A
Coat color in
rabbits.
IB IB or IBi = type B
IA IB = type AB
ii = type O
Epistasis
Dosage
Compensation
Polygenic
Sex-linked
(written as
superscripts of
the X or Y
chromosome –
XB)
One allele hides
the effect of
another.
Since females get
2X
chromosomes, to
compensate, one
stops working in
each of the
female’s body
cells. Which one
stops working is
completely
random
Inheritance
pattern of a trait
controlled by two
or more genes.
May be on same
or different
chromosomes
Phenotypes show
a continuous
range of
variability.
Traits controlled
by genes located
on the X
chromosome.
Fur color in dogs.
Calico cats
(this is why all
calico cats are
female)
Humans:
skin color
eye color
height
Plant stem height
In fruit flies – eye
color
XX – female
XY – male
Humans:
red/green
colorblindness
(X-linked),
hemophilia (Xlinked)
Since the Y chromosome
has no other corresponding
allele, many males have
recessive linked diseases.
In females, the recessive
trait can be masked by a
dominant trait on the other
X chromosome.
Abnormal
number of
chromosomes
Trisomy – has an
extra
chromosome (47
instead of 46)
Down Syndrome
Environmental Influences
 Sunlight and water
 Temperature
Twin studies
 Researchers study identical twins to help them separate
genetic contributions from environmental contributions.
Karyotype
 Images of chromosomes stained during metaphase
 Consists of 2 sister chromatids
 Arranged in decreasing size
Female karyotype
Telomeres
 protective end caps for chromosomes
 might be involved in aging and cancer
Nondisjunction
 sister chromatids do not separate correctly
 resulting in one gamete with an extra chromosome after fertilization
(trisomy = 47 chromosomes, i.e. Down’s syndrome = trisomy 21)
 and one missing a chromosome (monosomy - usually do not survive, i.e.
Turner syndrome is not lethal)
Fetal Testing
 amniocentesis
 chorionic villus sampling
 fetal blood sampling