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)