Transcript Human Genetics

Human Genetics
Biology 40S
Summer Session 2013
Outline
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Human Traits – Focus on Disorders.
Chromosome Theory
Human Inheritance Patterns
Pedigree Analysis
Why Focus on Disorders?
• Humans have thousands of traits that are
common to all individuals.
– List some examples
• There are more rare “traits” that show up
in some individuals – genetic
abnormalities that result in a genetic
disorder.
– Why would we want to understand the
mechanism of inheritance of disorders?
Chromosome Theory
• Our traits are
controlled by gene
sequences of DNA
that are located in
various structures
called
chromosomes.
Chromosome Number
• Every species has a unique
number of chromosomes.
• Chromosomes are paired up in
diploid organisms.
• Chromosomes pair up
according to similarities in size
and structure.
• Chromosome pairs are known
as homologous pairs.
Humans
46
Chromosome
Number
Pig
38
African
Hedgehog
90
Human Genome
• Males and females
contain 22 pairs of
similar chromosomes –
autosomes.
• The 23rd pair is unique
to males and females
and are called the sex
chromosomes.
Human Inheritance Patterns
Pattern
Autosomal
Dominant
Autosomal
Recessive
X-Linked
Dominant
X-Linked
Recessive
Autosomal Dominant Pattern
• The gene is on one of the autosomes and the
trait is dominant.
• Homozygotes and heterozygotes both express
the trait.
• Males and females affected equally.
• Examples: Marfan syndrome, sickle cell anemia,
achrondoplasia.
Autosomal Recessive Pattern
• The gene is on one of the autosomes and is in
the recessive form to show the trait.
• Heterozygous individuals never show the trait,
but do carry the recessive allele.
• The trait may skip a generation in a family.
• Males and females affected equally.
• Examples: cystic fibrosis, tay-sachs disease,
albinism, phenylketonuria
X-Linked Dominant Pattern
• The gene is on the X chromosome.
• Males always express the dominant gene if
received, females express if heterozygous or
homozygous.
• Males affected more severely – usually lethal.
• More common for females to be affected in a
population. WHY??
• Rare disorders: Coffin-Lowry syndrome,
incontentia pigmenti
X-Linked Recessive Pattern
• The gene is located on an X chromosome
and is recessive to express the trait.
• Males affected if the recessive allele is
received.
• Females affected only if both recessive
alleles received. Heterozygous females
are carriers.
• Examples: colour blindness, muscular
dystrophy, hemophilia, androgen
insensitivity syndrome
Pedigrees
• A pedigree is a specialized chart used to
track a specific trait within a family.
• Pedigree analysis allows us to
– Determine the pattern of inheritance
– Predict the chance of passing on the trait
http://www.ndsu.edu/pubweb/~mcclean/pls
c431/mendel/mendel9.htm