Transcript CP: Chapter 14

HUMAN HEREDITY
A look at Several Genetic Disorders
Human Chromosomes
• Humans have 46 chromosomes-
23 pairs
•23 from mom’s egg + 23 from dad’s sperm
• Autosomes are the first 22 pairs
• Sex Chromosomes are the last pair
•Genotype of Female is XX
•Genotype of Male is XY
Karyotype: picture of chromosomes
Most genetic disorders are caused by
RECESSIVE alleles.
• Cystic fibrosis- large accumulation of
muscus due to lack of protein.
• Phenylketonuria (PKU)- lack enzyme
that converts phenylalanine to
tyrosine.
• Tay-Sachs- lack of enzyme that breaks
down fat in the CNS
• Albinism- lack of pigment in skin.
Cystic Fibrosis
• Caused by a defect in a protein that
results in an overproduction of muscus.
• Favors bacterial infections.
• 1 in 20 white Americans are carriers.
• 1 in every 2000 children born to white
americans has this disorder.
• Without treatments, most children die
before age 5.
• With treatments, can live into 20’s+
Tay-Sachs
• Lack enzyme that breaks down fat in the
CNS- fat collects on the brain.
• No treatment or cure. Most will die before
the age of 6.
• http://www.pbs.org/wgbh/nova/genome/me
dia/2809_q056_03.html
Albinism
Disorders caused by dominant
alleles:
• Huntington’s Disease: neurodegenerative
genetic disorder that affects muscle coordination
and leads to cognitive decline and psychiatric
problems, typically becomes noticeable in midadult life.
• Dwarfism: adult height of less than 4 feet 10
inches
• Polydactylism
Huntington’s Disease
http://www.youtube.com/watch?v=u9XzqreToII&feature=
related
Dwarfism
• http://www.youtube.com/watch?v=iC5B3zU0Iv0
Polydactyl- more than 5 digits on hand or
foot
Caused by changes in DNA
(mutations):
• Sickle-cell Anemia: amino acid is
changed in hemoglobin to give cells
a sickle shape. Blocks the flow of
red blood cells.
Sickle Cell Anemia
• http://www.youtube.com/watch?v=ujf72mjy0Bg
Some genetic disorders are
Sex-Linked
• Most commonly found in males
• Mostly on X chromosome (recessive) and
since males have only one X chromosome
they will express the disorder more often.
• Examples:
• Colorblindness
• Hemophilia: blood cannot clot
• Muscular Dystrophy: affects muscle
development
Colorblindness (write what is red)
• Some genes are located on the X chromosome.
Females receive two alleles for these genes, but
males only receive one.
• If the parent is a male, the genotype is
automatically known. A colorblind male has to be
b, since he only has one allele and colorblindness
is recessive. A normal male must then be B
• Females can be heterozygous for the
colorblindness trait - they are called carriers. A
female can be BB - normal, Bb - carrier, or bb colorblind
The following shows a cross between a normal man
and a woman who is a carrier (COPY THIS)
colorblindess test
Hemophilia
• http://www.youtube.com/watch?v=FS64UXi74lY
Chromosomal Disorders
• Nondisjunction: chromosomes fail to
separate properly during meiosis
(formation of gametes)
• Down Syndrome- extra chromosome
on #21 (results in total of 47 chrom)
• Turner’s
• Klinefelter’s
Down Syndrome- Extra
chromosome on #21.
Total of 47 chromosomes
Down Syndrome Karyotype
Klinefelter’s Karyotype - XXY
Klinefelter’s
• XXY…….Only affects Males
• Lower Muscle mass
• Lower testosterone
• Less Muscle, less facial hair, broader hips
• Often Taller
• Increase in Breast Tissue
• Low Fertility
Turner’s Karyotype – Missing one Sex
Chromosome
Turner’s Syndrome
• X………Only affects Females
• Shorter in Stature
• Broader Chest
• Lower Hairline
• Webbed Neck
• No Menstrual Cycle
• Sterile
Pedigree: graphic representation of genetic inheritance.
- Male = square
- Female = circle
- Shaded = has the disorder or trait
- Half shaded = carrier of disorder or trait (heterozygous)
- Unshaded = neither affected nor a carrier