Human Heredity
Human Chromosomes
• A chromosome is a threadlike structure within
the nucleus containing DNA:
• To analyze chromosomes,
- biologists photograph cells in mitosis, when the
chromosomes are fully condensed and easy to
see
- The biologist then cut out the chromosomes from
the photographs and group them together in
pairs
- A picture of chromosomes arranged in this is
known as karyotype
Human Chromosomes
• A typical human body cell
contains _______
chromosomes:
- 2 of those 46 chromosomes
are known as sex
chromosomes: X and Y
chromosome
- The remaining 44
chromosomes are known as
autosomal chromosomes, or
autosomes
- Male: 46 XY
- Female: 46 XX
Pedigree Chart
• A pedigree chart shows the distribution of
particular traits within a specific family group
A half shaded
circle or square
indicates that a
person is a
carrier of the
trait
A circle
represents
female
A completely shaded circle or square indicates
that a person express that trait
A square
represents male
A completely un-shaded circle or
square indicates that a person
neither express nor carry the trait
Human Traits
• Some human traits are almost impossible to
associate with single genes:
- Some traits are polygenic, meaning they are
controlled by many genes:
e.g. shape of your eyes or ears
- Many traits are strongly influenced by
environmental factors including nutrition and
exercise:
e.g. height
Genetic Disorders
• Many human genes have become known
through the study of genetic disorders:
-Disorders caused by recessive alleles:
You need to inherit 2 copies of the recessive
alleles to have these disorders
- Disorders caused by dominant alleles:
You only need to inherit 1 copy of the dominant
alleles to have these disorders
Recessive alleles disorder
• Albinism: lack of pigment in skin, hair, and eyes (video)
• Cystic fibrosis: Excess mucus in lungs, digestive tract
and liver (video)
• Galactosemia : Accumulation of galactose in tissues;
mental retardation, eye and liver damage
• Phenylketonuria (PKU): Accumulation of phenylalanine
(an amino acid); lack of normal skin pigment, mental
retardation (video)
• Tay-Sachs disease: Lipid accumulation in brain cells;
mental deficiency, blindness, death in early childhood
(video)
Dominant alleles Disorder
• Achondroplasia: a form of
dwarfism
• Huntington's disease:
Mental deterioration and
uncontrollable
movements, appears in
middle age (video)