Transcript Genetic Disorders, Disease, and Karyotypes

*
14.1 and 14.2
* Disease determined by inheritance of an allele
* There are three possibilities for genetic
disease:
* Recessive: disorder caused by having 2 recessive
alleles
* Dominant: disorder caused by having at least one
copy of the dominant allele
* Co-dominant: heterozygous genotype gives a
different phenotype
*
*A.Cystic fibrosis: Homozygous recessives
(cc) have cystic fibrosis - body cannot make
needed chloride channel, high
concentrations of extracellular chloride
causes mucous to build up, infections,
pneumonia. Diet, antibiotics and treatment
can extend life to 25 years or more.
*B.Tay-Sachs: Enzyme that breaks down
brain lipids is non-functional in homozygous
recessives (tt). Buildup of lipids causes
death by age 2-3
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*Achondroplasia (dwarfism): AA =
Homozygous dominant is lethal –
usually fatal before or shortly after
birth. Aa = dwarfism. aa = no dwarfism.
99.96% of all people in the world are
homozygous recessive (aa)
*Sporadic mutation can occur from
paternal gene during spermatogenesis
and then be passed on
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*Polydactyly (extra fingers or toes): PP or Pp = extra
digits, pp = 5 digits. 98% of all people in the world are
homozygous recessive (pp)
* Manifests in many ways including:
-a small extra bump on the side of the hand,
-a finger which widens to end in two fingertips,
-an extra finger which dangles by a thin cord from the
hand
-a hand which looks normal except that it has a thumb and
five fingers
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*Sickle Cell Anemia
* SS= sickle cell anemia (misshapen Sickle Cell: many
believe sickle cell anemia co evolved with malaria cells
lead to death) life expectancy approx: 43 yrs
* AA= normal red cells, healthy
* AS= not enough sickle cells to kill and resistant to
malaria! (body destroys the sickle cells and the
parasite)
*
*Mistakes can happen in Meiosis
*Most common = Non-Disjunction
*Results in wrong chromosome
number in gametes
*Examples include:
*Trisomy 21 (Down’s Syndrome) with
an extra # 21
*Klinefelter’s Syndrome (XXY)
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*During puberty, the physical traits of the
syndrome become more evident; because
these boys do not produce as much
testosterone as other boys, they have a less
muscular body, less facial and body hair,
and broader hips. As teens, XXY males may
develop breast tissue and also have weaker
bones, and a lower energy level than other
males.
*Occurs in 1/500 to 1/1000 live births
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*Humans have 46 chromosomes
*Occurs in 23 pairs (most autosomes)
*2 of the 46 are sex-determining
chromosomes (X and Y)
*XX=Female, XY=Male
*Picture of chromosomes=karyotype
*Doctors use to determine sex of baby and
genetic abnormalities
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