human heredity. human chromosomes a chromosome is a threadlike structure within the nucleus...
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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 circle represents female
A square represents male
A half shaded circle or square indicates that a person is a carrier of the trait
A completely shaded circle or square indicates that a person express that trait
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)
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