Download Antigens

The Human Genome
Chapter 14 –
Human Heredity
Human Chromosomes
Sex Chromosomes and Autosomes
• Two of the 46 chromosomes in humans
are known as the sex chromosomes.
X Chromosome
Y Chromosome
• The remaining 44 chromosomes (22 pairs)
are known as autosomes.
X and Y chromosomes
Factors to Consider in Pedigrees
• Is the trait located on a sex chromosome
or an autosome?
– Autosomal – not on a sex chromosome
– Sex Linkage – located on one of the sex
chromosomes
• Y-linked - only males carry the trait.
• X-linked (recessive) - sons inherit the disease from
normal parents
Factors to Consider in Pedigrees
• How is the trait expressed?
– Dominant - the trait is expressed in every
generation.
– Recessive - expression of the trait may skip
generations.
Pedigree
•A pedigree is a chart which shows
the relationships within a family,
often highlighting the inheritance
of a particular trait (such as heart
disease or a widow’s peak
hairline).
Pedigree Diagrams: I
• Basic Symbols
Pedigree Diagrams: II
• Basic Symbols for offspring and the
expression of a trait.
– The offspring are depicted below the
parents.
– Filling the symbol with black indicates the
expression of the studied trait.
Pedigrees
• Draw the pedigree for a family in which:
– A man with unattached earlobes (the trait of
interest) and a woman with attached earlobes
have three children; first a boy, then a girl,
then another boy.
– The two boys have attached earlobes, the
daughter has unattached earlobes.
Blood types
• Antibodies – are protective proteins
in the blood that identify “invaders”,
(things that don’t belong) and attack
them. The antibody name identifies
what it will attack.
• Antigens – are chemical signals that
identify “self” from “non-self”. Think of
as a “flag” on the surface of the cell.
Antibodies will attack any cell that has
the “wrong” antigen (“wrong flag”).
ABO blood types
antigens
ABO blood types
antigens
CLOTTING!!
YOU’RE
DEAD!!
ABO blood types
antigens
ABO blood types
antigens
CLOTTING!!
YOU’RE
DEAD!!
ABO blood types
antigens
ABO blood types
antigens
NO
CLOTTING!!
YOU’RE FINE!!
ABO blood types
antigens
ABO blood types
antigens
CLOTTING!!
YOU’RE
DEAD!!
Summary of Blood types
A
B
•I i X I i
–What blood types are these?
–What blood types might their
offspring have?
Summary of Blood types
•Type O blood (neither A nor B
antigens) can donate to any
blood type (universal donor).
•Type AB (no A or B antibodies)
can receive blood from any
donor (universal recipient).
Types of Genetic Disorders
•
•
•
•
Autosomal Recessive
Autosomal Dominant
Autosomal Codominant
Sex-Linked (X-linked)
Recessive
• Chromosomal Disorders
Autosomal Recessive Genetic
disorders
• Trait revealed only in homozygous
recessive individuals.
• In equal numbers of males and females.
• Two unaffected heterozygous parents can
have affected children.
Autosomal Recessive Genetic
disorders
• Examples:
– Albinism – lack of pigment in skin, hair, eyes
– Cystic fibrosis – excess mucus in lungs
– Phenylketonuria (PKU) – accumulation of
phenylalanine in tissues, mental retardation
– Tay-Sachs disease – lipid accumulation in brain
cells, early death
Autosomal Dominant Genetic
disorders
• Trait is revealed in every individual with a
dominant gene.
• In equal numbers of males and females.
• Every affected individual has at least one
affected parent.
Autosomal Dominant Genetic
disorders
• Examples
– Achondroplasia – dwarfism (one form)
– Huntington’s disease – causes mental
deterioration and uncontrolled movements.
– Hypercholesterolemia – excess cholesterol in
blood.
Autosomal Codominant Genetic
disorders
• Trait caused by both alleles (neither allele
is masked).
• Most important autosomal codominant
genetic disorder is Sickle Cell Disease.
– Bent and twisted (sickle-shaped) red blood
cells tend to get stuck in capillaries. This
damages tissues (brain, heart, spleen) and may
be fatal.
– Homozygotes and heterozygotes are affected
to differing degrees.
Sex-Linked (X-linked) Recessive
Genetic disorders
• Trait caused by genes found on the Xchromosome (entirely absent from the y
chromosome).
• Because males have only one X
chromosome, a single recessive allele (Xa)
will cause the disorder.
• Females must have 2 copies of the disease
allele (homozygous recessive) to have the
disorder.
Sex-Linked (X-linked) Recessive
Genetic disorders
• Examples of sex-linked recessive
disorders
– Colorblindness
– Hemophilia
– Duchenne Muscular Dystrophy
Sex-Linked (X-linked) Recessive
Trait example
• Because the gene is found on the X chromosome
and not the Y chromosome, you write the
possible genotypes in the following way:
• Males
– XAY (dominant phenotype)
– XaY (recessive phenotype) – note it only takes
one recessive allele for males to have the
recessive phenotype because there is nothing
on the Y chromosome to influence the trait.
Sex-Linked (X-linked) Recessive
Trait example
• Females
– XAXA (dominant phenotype)
– XAXa (dominant phenotype)
– XaXa (recessive phenotype)
• Females (XX) must have two copies of the
recessive allele to have the recessive
phenotype (heterozygotes have dominant
phenotype).
Sex-Linked (X-linked) Recessive
Trait example
• XRXr x XRY cross
Chromosomal Disorders
•In normal meiosis, homologous
chromosomes separate from one
another.
•In nondisjunction, the
homologues fail to separate,
resulting in gametes with too
many or too few chromosomes.
Chromosomal Disorders
•Down Syndrome, also known as
Trisomy 21, is a chromosomal
disorder resulting from the
nondisjuction of chromosome 21
in humans (the person has an
extra chromosome 21)