Human Heredity

Human Chromosomes A karyotype is a picture of matching pairs of chromosomes. Two of the 46 chromosomes are sex chromosomes The other 44 chromosomes are called autosomes. Females are XX, and males are XY

Human Traits A pedigree is a chart that shows relationships within a family (family tree) We can use a pedigree to trace genetic disorders through generations of families

Blood Group types Rh blood group is determined by a single gene with 2 alleles Rh stands for “rhesus monkey” the animal in which the factor was discovered (Rh+) is dominant (DD,Dd) (Rh-) is recessive (dd) ABO blood group has 3 alleles A,B, are codominant, O is recessive

Autosomal Disorders in Humans Recessive disorders: Albinism: lack of pigment Cystic fibrosis: excess mucus (infections, early death) Galactosemia: accumulation of sugar in tissues (mental retardation) PKU: accumulation of phenylalanine in tissues (mental retardation) Tay-sachs disease: lipid accumulation in brain cells( mental deficiency, early death)

Autosomal Disorders in Humans Disorders caused by dominant alleles: Achondroplasia (dwarfism) Huntingtons disease: mental deterioration Hypercholesterolemia: excess cholesterol Disorders caused by codominant alleles: Sickle cell anemia: sickle shaped red blood cells, causes damage to many tissues

Sex-linked Genes A sex-linked gene is a gene located on the X or Y chromosome A sex chromosome is one of 2 chromosomes that determine an individuals sex Males have only one X chromosome. All X-linked genes are expressed in males, even if they are recessive

Examples of Sex-linked Disorders Colorblindness- recessive sex-linked disorder (1 in 10 males affected) rarer in females Hemophilia- recessive disorder that affect s the blood’s ability to clot (1 in 10,000 males) Duchenne Muscular Dystrophy- a sex-linked disorder that results in the progressive weakening and loss of skeletal muscle (1 0f 3000 males)

Chromosomal Disorders Disorders caused by abnormal separation of chromosomes during meiosis Nondisjunction- the most common error in meiosis, chromosomes fail to separate, the word means “not coming apart” If nondisjunction occurs abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may occur

Examples of Nondisjunction Down syndrome occurs when an individual is born with 3 copies of a chromosome This is known as “trisomy” (3 bodies) The most common form of trisomy involves 3 copies of chromosome 21 1 of 800 babies is born with Down syndrome

Sex chromosome disorders Turners syndrome- Female only inherits one X chromosome ( women are usually unable to have children) Klinefelters syndrome- males born with an extra X, usually prevents males from reproducing (nondisjunction is the cause) Interesting fact: There have been no reported instances of babies being born without an X chromosome