Ch 14- Human Genome How many chromosomes does a human cell have? Karyotype- photograph of...
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Ch 14- Human Genome How many chromosomes does a human cell have? Karyotype- photograph of chromosomes grouped in order in pairs Sex chromosomes- 2 chromosomes
Ch 14- Human Genome How many chromosomes does a human cell
have? Karyotype- photograph of chromosomes grouped in order in
pairs Sex chromosomes- 2 chromosomes that determine the sex of the
individual Females have two copies of a large X chromosome Males
have one X and one small Y chromosome Autosomes- the other 44
chromosomes Males and females are born 50:50 ratio because sex
chromosomes segregate during meiosis Half of sperm cells carry X
chromosome and other half carry Y chromosome
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Human Traits Biologists must identify if an inherited trait is
controlled by a single gene Pedigree- chart that shows the
relationships within a family that can be used to help identify
inherited traits Genetic counselors analyze pedigrees So can you
look at a pedigree and figure out which family the good looks came
from? Shape of eyes and ears are actually polygenic traits Many
traits influenced by environmental factors such as nutrition and
exercise
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Human Genes Human genome- complete set of genetic information-
includes tens of thousands of genes DNA sequences on these genes
carry information for specifying many characteristics- eye color,
protein structure in cells Scientists spent years studying the
genetics of our species- able to identify genes that directly
control a single human trait Some of first genes identified were
those that control blood type
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Blood Types Number of genes responsible for human blood groups-
ABO and Rh blood groups Rh blood group determined by a single gene
with alleles- positive and negative Positive allele is dominant ABO
blood group has three alleles for this gene, I^A, I^B, and I A and
B are codominant, blood type AB I allele is recessive, I^AI^A and
I^Ai is blood type A I^BI^B and I^Bi is blood type B People who are
homozygous for I allele (ii) are blood type O Why is knowing the
blood type important?
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Autosomal Disorders in Humans Human genes have become known
through study of genetic disorders Phenylketonuria (PKU)- recessive
allele, people lack the enzyme that is needed to break down
phenylalanine, may build up in tissues during childs first year and
cause mental retardation Tay- Sachs- recessive allele, lipid
accumulation in brain cells, blindness, death early in childhood
Achondroplasia- dominant allele disorder, dwarfism Huntingtons
disease- dominant allele, mental deterioration and uncontrollable
movements, symptoms appear in middle age
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How do the actual DNA sequences in genes affect phenotype so
profoundly? Many genetic disorders are still being worked on, but
in both cystic fibrosis and sickle cell disease there is a small
change in the DNA of a single gene that affects the structure of a
protein, causing the disorder Cystic fibrosis- recessive allele
disorder, excess mucus in lungs, digestive tract, liver. More
likely to get infections Sickle cell disease- characterized by bent
and twisted shape of red blood cells, tend to get stuck in
capillaries and cause damage to cells, tissues, organs Hemoglobin
in person has different amino acid sequence- just one DNA base is
changed Common among African Americans
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Sec 2- Human Chromosomes Chromosomes 21 and 22- smallest human
autosomes First chromosomes whose sequences were determined Long
stretches of repetitive DNA are unstable sites where rearrangements
occur Form of leukemia and neurofibromatosis found on chromosome 22
Gene associated with Lou Gehrigs disease found on chromosome 21
Genes located together on same chromosome tend to be inherited
together Is there a special pattern of inheritance for genes
located on the X chromosome or the Y chromosome?
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Sex Linked Genes Sex linked genes- gene located on the X or Y
chromosome Many sex linked genes found on X chromosome Y chromosome
is much smaller than X, contains only a few genes Colorblindness-
an inability to distinguish certain colors, most common is
red-green, more common in males Sex linked disorders are more
common in men X-linked alleles are always expressed in males,
because males have only one X chromosome
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Hemophillia- another sex linked disorder, a protein necessary
for normal blood clotting is missing Duchenne Muscular Dystrophy-
sex linked disorder, results in progressive weakening and loss of
skeletal muscle X-Chromosome Inactivation Females have 2 X
chromosomes, one X chromosome is enough How does the cell adjust to
the extra X chromosome in female cells? In female cells, one X
chromosome is randomly switched off-this forms a Barr body Female
cats
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Chromosomal Disorders Nondisjunction- homologous chromosomes
fail to separate during meisois May involve autosomes, sex
chromosomes, homologous chromosomes If nondisjunction occurs,
abnormal numbers of chromosomes may find their way into gametes,
and a disorder of chromosome numbers may result Trisomy- when two
copies of autosomal chromosomes fail to separate during meiosis,
individual is born with three copies of chromosomes Down snydrome-
most common form of trisomy, involves three copies of chromosome 21
Produces mild to severe mental retardation, and higher frequency of
some birth defects
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Sex Chromosome Disorders Turners syndrome- females only inherit
one X chromosome Are sterile- unable to reproduce Sex organs do not
develop at puberty Klinefelters syndrome- males inherit an extra X
chromosome Prevent individuals from reproducing No reported
instances of babies born without an X chromosome Contains genes
vital for survival and development of embryo
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Sec 3- Human Molecular Genetics Roughly 6 billion base pairs in
your DNA Genetic tests are now available for hundreds of disorders
DNA fingerprinting- form of DNA analysis that analyzes sections of
DNA that have little or no known function that vary widely from
individual to individual Used to identify individuals Used since
1980s in United States How has DNA fingerprinting been
beneficial?
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Human Genome Project Human Genome Project is the ongoing effort
in analyze the human DNA sequence Scientists have analyzed smaller
genomes, such as those of viruses and bacteria Why is this an
important breakthrough? Provides useful clues to some of basic
properties of life May be useful in developing new drugs and
treatments for diseases
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Gene Therapy The process of changing the gene that causes a
genetic disorder In gene therapy, an absent or faulty gene is
replaced by a normal, working gene Both positive and negative
results What potential ethical problems might occur if humans gain
the opportunity to design our bodies? High School Biology
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