Download Human Chromosomes Mr. Alvarez March 15, 2013

Human Chromosomes
Mr. Alvarez
March 15, 2013
DNA
• Each diploid cell contains 6 billion base pairs
• An Average Human Gene is 3,000 base pairs
• Largest gene in human genome has more than
2 million base pairs
Lou Gehrig’s Disease
• Amyotrophic Lateral Sclerosis (ALS)- Causes a
progressive loss of muscle control due to the
destruction of nerves in the brain and spinal
cord.
– Caused by a mutation on Chromosome 21
Sex-Linked Genes
Sex-Linked Genes- Genes found
on either the X or Y chromosome
Color-Blindness
• Human genes associated with color vision are
located on the X chromosome
• Most common type of color blindness is RedGreen color blindness
– Effects 1 in 10 males
– Effects 1 in 100 females
Sex-Linked Disorders
KEY: C =Normal Vision
c = Color Blind
Normal Female
Carrier Female
Affected Female
Normal Male
Affected Male
Why Can’t Males Be Carriers?
• Males have just one X chromosome
• All X-linked alleles are expressed in males,
even if they are recessive
In humans, normal vision (XC) is dominant to
colorblindness (Xc) and is sex-linked. A
normal-visioned man marries a colorblind
woman. What are the chances that a son will
be colorblind. A daughter?
A normal male (not colorblind) marries a
female carrier. What are the offspring
genotypes and phenotypes?
Hemophilia is due to a sex-linked recessive
gene (Xh) and the normal condition to the
gene (XH). A hemophiliac man marries a
woman who is not. Their first son has
hemophilia. What are the chances that their
daughter, if they had one, will be hemophilic?
Hemophilia
Hemophilia- Sex-linked heredity disorder in
which the blood fails to clot properly, resulting
in excessive bleeding
Duchene Muscular Dystrophy
Duchene Muscular Dystrophy- Sex-linked
disorders that results in the progressive
weakening and loss of skeletal muscle
Pedigree