Transcript Inheritance

Complex Inheritance
and Human Heredity
Chapter 11
Basic Patterns of Human
Inheritance
Chapter 11.1
Recessive Genetic Disorders
• A recessive trait is expressed when the
individual is homozygous recessive for
that trait.
• An individual who is heterozygous for a
recessive disorder is called a carrier.
• Ex) Cystic Fibrosis, Albinism, TaySachs Disease, Galactosemia
Dominant Genetic Disorders
• Individuals with a dominant disorder will
have at least one dominant allele.
• Ex) Huntington’s Disease,
Achondroplasia
Pedigrees
• A diagram that traces the inheritance of
a particular trait through several
generations.
• A pedigree uses symbols to illustrate
inheritance of the trait.
Pedigrees
http://www.sciencecases.org/sickness_and_health/sickness_and_health_notes.asp
Pedigrees
Affected Male
Female
Carrier Female
Affected Male
http://www.214bio.com/TOPICS/DNA/new214bio/simple_pedigree.gif
Analyzing Pedigrees
• Pedigrees are used to infer genotypes
from the observation of phenotypes.
• If good records are kept within families,
disorders in future offspring can be
predicted.
Complex Patterns of
Inheritance
Chapter 11.2
Incomplete Dominance
• The heterozygous
phenotype is an
intermediate phenotype
between the two
homozygous phenotypes.
• Ex) Snapdragons (Flower)
• RR (red) x rr (white)
• 100% Rr (pink)
Codominance
• Both alleles are
expressed in the
heterozygous condition.
• Ex) Sickle-cell disease
• Individuals will have
normal and sickleshaped cells.
AA = normal
Aa = sickle cell trait (few symptoms)
aa = sickle cell anemia
Multiple Alleles
•
Some forms of inheritance are determined by multiple alleles.
•
Ex) Blood Types
•
ABO blood groups have 3 forms of alleles.
•
IA is blood type A, IB is blood type B, and i is blood type O.
•
i is recessive to IA and IB.
•
IA and IB are codominant resulting in the AB blood type.
•
Rh factors are either positive or negative. Rh+ is dominant.
Multiple Alleles
Epistasis
• Epistasis is an
interaction where one
allele hides the effects
of another allele.
• Ex) Coat color in
Labrador retrievers
http://faculty.southwest.tn.edu/rburkett/GB%20Genetics.htm
Sex Determination
• Sex chromosomes: determine an
individual’s gender
• Autosomes: the other 22 pairs of
chromosomes
• Females have 22 pairs of autosomes and
one pair of X chromosomes (XX).
• Males have 22 pairs of autosomes and one
X and one Y chromosome (XY).
Sex Determination
• The X chromosomes is larger than the
Y chromosome because it carriers
genes that are necessary for the
development of both male and females.
• To balance the “dose” of X-related
genes, one of the X chromosomes in
females is inactivated (X-inactivation).
Sex-Linked Traits
• Traits controlled by genes located on the X
chromosome are called sex-linked or X-linked
traits.
• Because males only have one X chromosome
they are affected by recessive X-linked traits
more than females.
• In females the other X-chromosome will often
mask the effect of the recessive trait.
Sex-Linked Traits
• Red-green color
blindness is a
recessive X-linked
trait.
• 8% of males in the
US are red-green
color blind.
http://www.colblindor.com/2010/03/02/what-is-color-blindness/
Color Blindness
Hemophilia
The Royal Family
Hemophilia
Polygenic Traits
• Many phenotypic traits arise from the
interaction of multiple pairs of genes
and are called polygenic traits.
• Ex) Skin color, height, eye color, and
fingerprint pattern.
Environmental Influences
• The environment also has an effect on
phenotype.
• Ex) Heart disease is inherited but diet
and exercise play an important role in
the occurrence and seriousness of the
disease.
Twin Studies
• By studying identical twins, geneticists
can separate genetic contributions from
environmental conditions.
Chromosomes and Human
Heredity
Chapter 11.3
Karyotypes
• Scientists study whole chromosomes by using
images of chromosomes stained during
metaphase.
• The staining bands identify or mark identical
places on homologous chromosomes.
• The homologous chromosomes are arranged
in decreasing size to produce a micrograph
called a karyotype.
Karyotype
http://www.cancerquest.org/cell-cycle-mitosis.html
Telomeres
• Chromosomes end in protective caps
called telomeres.
• The cap serves as a protective structure
for the chromosome.
• Scientists believe that telomeres may
play a role in both aging and cancer.
Telomeres
http://www.immortalhumans.com/telomeres-is-it-an-accurate-biological-measurement-for-aging/
Nondisjunction
• When sister chromatids fail to separate
properly during cell division it is called
nondisjunction.
• If this occurs during meiosis I or meiosis
II the resulting gametes will not have the
correct number of chromosomes.
Nondisjunction
• Nondisjunction can result in extra copies of a
chromosome or only one copy of a
chromosome.
• Trisomy: having a set of three chromosomes of
one kind.
• Monosomy: having only one of a particular
type of chromosome.
Down Syndrome
• Disorder resulting from an extra
chromosome 21.
• Often called trisomy 21.
• Characteristics include distinctive facial
features, short stature, heart defects,
and mental disability.
Down Syndrome
http://geneticdisorderinfo.wikispaces.com/Down+Syndrome
Fetal Testing
• Amniocentesis: diagnosis of chromosome
abnormalities and other defects
• Chorionic villus sampling: diagnosis of
chromosome abnormalities and certain genetic
defects
• Fetal blood sampling: diagnosis of genetic or
chromosome abnormalities, checks for fell
blood problems and oxygen levels