Transcript Human Genetics Notes

Pedigrees
Pedigree : a chart that shows how a trait and the
genes that control it are inherited in a
family.
Parts :
male female
Carriers : Heterozygous
for the recessive allele
Affected Affected
male
female
Death
*Roman Numerals = generations
Pedigree
Parents
Offspring
I
II
III
Karyotypes
Karyotype : a photograph that shows an
individual’s chromosomes in
homologous pairs. (23 pairs)
*Can be used to show any chromosome
abnormality that is visible.
http://www.biology.iupui.edu/biocourses/N100/2k2humancsomaldisord
ers.html
http://www.gla.ac.uk/medicalgenetics/nhs/karyotypemovie.htm
I. Autosomal Genetic Disorders
 Disorders found on the chromosome pairs 1-22,
not sex chromosomes
 1. Sickle Cell Disease – codominance
disorder where red blood cells have
abnormal sickle shape. *Makes blood cells
stick in capillaries causing low blood flow,
anemia, and tissue damage.
*occurs in about 1 and every 500
African American births, and 1 out of
12 African Americans are carriers.
Sickle cell is a result of a point mutation
http://www.hhmi.org/biointeractive/media/mala
ria_mosquito-lg.mov
http://www.hhmi.org/biointeractive/media/malaria_humanlg.mov
Autosomal Genetic Disorder
(continued)
 2. Tay-Sachs Disease - incurable disorder
where lipids build up in the brain cells and
destroy them.
http://www.pbs.org/wgbh/nova/genome/program.html#03
 3. Cystic Fibrosis - the most common fatal
inherited disorder among whites in the
United States. Caused by recessive allele
on chromosome 7 which causes excessive
secretion of thick mucus from the pancreas,
lungs, and other organs.
Autosomal Genetic Disorder
(continued)
 4. PKU- (Phenylketonuria) an autosomal
recessive disorder in which the body is unable to
use the essential amino acid phenylalanine
because the enzyme phenylalanine hydroxylase is
deficient.
 Phenylalanine occurs in significant amounts in
milk, eggs, and other common foods. The artificial
sweetener NutraSweet (aspartame) also contains
phenylalanine. If treatment is delayed or the
condition remains untreated, brain damage will
occur
Autosomal Genetic Disorder
(continued)
 5. Huntington’s Disease - inherited
disorder caused by a dominant allele. The
disease causes a progressive breakdown of
muscle coordination and mental
deterioration, leading to death.
Chromosomal Disorders
 Additions or deletions on chromosomes
 1. Down Syndrome - disorder that results from an
extra copy of chromosome #21. This causes mental
retardation and physical abnormalities.
XXX
 http://www.livingwithtrisomy13.org/trisomy-13videos.htm
 2. Turner’s Syndrome - caused by the presence of
only one X chromosome - Resulting female has
underdeveloped sexual characteristics. Genotype is :
XO and individual is sterile.
Chromosomal Disorders (con’t)
 3. Klinefelters syndrome - A person with
two X’s and a Y in each cell, resulting male
has underdeveloped sex organs. Genotype
is: XXY and individual is sterile.
http://www.biology.iupui.edu/biocourses/N100/2k2huma
ncsomaldisorders.html
Sex Linked Disorders
 Found on sex chromosomes
 1. Hemophilia - blood is unable to clot.
Recessive gene is carried on X
chromosome.
 Hemophilia is sometimes referred to as “the royal disease” because
several members of noble families in Europe were affected by it.
Queen Victoria had no ancestors with the condition but soon after the
birth of her eighth child, Leopold, in 1853, it became evident that he
had hemophilia. Queen Victoria was thus an example of how the
condition can arise as a spontaneous mutation. Leopold died at the age
of 31 from an intracerebral haemorrhage after a fall. Two of Queen
Victoria"s own daughters, Alice and Beatrice, were also carriers of
hemophilia. The condition was transmitted through them to several
royal families in Europe, including Spain and Russia. Perhaps the most
famous affected individual was the son of Tsar Nicholas II of Russia,
Tsarevich Alexis, who was born in 1904. There has been speculation
that the illness led to severe strain within the royal family, and enabled
Rasputin to gain influence over the family, ultimately leading to the
downfall of this once powerful dynasty.
British Royal Family
*The allele has been traced back to Queen Victoria, and since royal families tend
to marry into royal families this allele has spread into Russia and Spain
Take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice of
Athlone, had one hemophilic son (Rupert) and two other children—a boy and
a girl—whose status is unknown.
a) What is the probability that her other son was hemophilic?
b) What is the probability that her daughter was a carrier? Hemophilic?
c) What is the probability that both children were normal?
Sex Linked Disorders
2. Duchenne Muscular Dystrophy - muscle
tissue breaks down during childhood and the
recessive gene is carried on the X chromosome.
Individuals usually do not live beyond their
teens.
Dystrophin is crucial to the muscle building and muscle maintaining processes. As
muscles are used they quickly deteriorate due to the lack of dystrophin to repair and
maintain muscle growth. Eventually the chest muscles deteriorate causing breathing
difficulties. These difficulties lead to respiratory infections which continue until the
process takes the life of the child.
Sex linked Disorders (con’t)
 3. Color Blindness - recessive disorder
carried on the X chromosome where an
individual cannot perceive certain colors
(usually red and green).
 * Very few females have these conditions
but they can be carriers of the defective
allele
 *Males with the condition can pass it on to
a daughter, but NOT a son. .
Linkage maps estimate distances
between genes.
 The closer together two genes are, the more
likely they will be inherited together.
 Cross-over frequencies are related to
distances between genes. The further the dist
the higher the percentage of crossover.
 Linkage maps show the relative locations of
genes.
 Cross-over frequencies can be converted into
map units.
– gene A and gene B cross over 6.0
percent of the time
– gene B and gene C
cross over 12.5 percent
of the time
– gene A and gene C cross over 18.5 percent of the
time
Incomplete Dominance when two contrasting alleles contribute to an
individual with a trait not exactly like either
parent.
Example : flower color (snapdragons)
R = red
genotype RR
W = white
genotype WW
*Individuals with red & white flowers are always homozygous
R R
W
W
RW RW
RW RW
*Offspring are heterozygous
for both dominant traits.
RW = pink flowers
*Neither red or white are completely dominant so
when they are crossed we get an intermediate type
….pink flowers!
Codominance - 2 dominant alleles are expressed at
the same time.
Example: Roan Coat in some cattle
Homozygous red
shorthorn cattle
CRCR
x
Homozygous white
shorthorn cattle
CWCW
Offspring Roan Coat
CRCW
*Individual shows both red and white = roan coat
Multiple Alleles - three or more different
alleles for a specific trait.
Human Blood Types
3 Alleles
1. A
2. B
3. O
* O is recessive
* A & B are both dominant over O
but neither are dominant over each
other!
* A & B are codominant and both
alleles are expressed
*Can use the capital I to show a dominant allele and the
lowercase i to show a recessive allele.
A is dominant so ……………IA
B is dominant so ……………IB
O is recessive so …………… i
Genotypes
1. IAIA
2. IBIB
3. IAIB (codominant)
4. IAi
5. IBi
6. ii
Phenotypes
A blood
B blood
AB blood
A blood
B blood
O blood
 Polygenic traits
are produced by
two or more
genes.
Order of dominance:
brown > green > blue.
exps: eye color, skin pigment, hair color