C HAPTER 14- H UMAN H EREDITY BIG IDEA: How can we use genetics
to study human inheritance?
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14.1 H UMAN C HROMOSOMES The study of any genome begins w/
chromosomes- found in nucleus of eukaryotes o Karyotype shows the
complete diploid set of chromosomes grouped in pairs, from largest
smallest in size
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Human karyotype contains (46 individual) / 23 pairs of
chromosomes
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The last pair of chromosomes (pair 23) are the sex chromosomes,
which determine if youre male or female Female= XX (contributes X
always) Male= XY (50:50 chance of contributing X or Y) Autosomes
are the remaining 44 chromosomes in the human karyotype
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Many human traits follow simple patterns of dominance The
alleles for many human genes display codominant inheritance
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Sex-linked genes are genes located on either the X or Y
chromosomes. Sex-liked genes on: Y: directly father son X: given to
daughter or son, but recessive diseases MUCH more common in
males!!! -Males dont have another X chromosome to mask diseases
located on X chromosome Ex: color blindness, hemophilia, Duchnne
muscular dystrophy
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Females undergo X-inactivation =, where random genes in either
chromosome are switched off (so its on in the other X) -Causes
spots in calico cats A pedigree shows the presence or absence of a
trait according to the relationships between parents, siblings, and
offspring
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14.2 HUMAN G ENETIC D ISORDERS Changes in a genes DNA sequence
can change proteins by altering their amino acid sequences, which
can directly affect phenotype
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Disorders caused by Individual genes: o Sickle cell anemia:
defect in beta-globin (carries oxygen), causing red blood cells to
clump together o Cystic fibrosis: deletion of 3 bases, causing
protein to missfold, problems w/ breathing and digestion o
Huntingtons disease: CAG repeat x40, causing mental and physical
deterioration
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Genetic Advantage: 1/12 people w/ African descendent carry
sickle cell. In Africa the heterozygous form of sickle cell makes
them resistant to malaria, yet no symptoms of disease
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Errors in meiosis Nondisjunction: failure of chromosomes to
separate If nondisjunction occurs gametes w/ an abnormal # of
chromosomes may result Down syndrome: trisomy 21 (mental
retardation) Turner syndrome: female w/ 1 X (sterile) Klinfelter:
XXY male (usually sterile)
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14.3 S TUDYING THE H UMAN G ENOME By using tools that cut,
separate, and then replicate DNA base by base, scientists can now
read the base sequences in DNA from any cell Most DNA is too large
to be analyzed, so it must be cut into smaller pieces by
restriction enzymes.
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After DNA is cut, gel electrophoresis is used to separate and
analyze differently sized fragments. -Mix of DNA is put in well @
top, voltage is applied, DNA is (-) charged, smaller DNA fragments
move quickly to (+) end. Reading DNA: Dye-labeled nucleotides and
DNA polymerase are inserted to produce a color banded complementary
strand
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Human Genome Project: The Human Genome Project was a 13-year
international effort w/ the goal of sequencing all 3 billion base
pairs of human DNA and identifying all human genes Sequencing and
identifying genes: shotgun sequencing=rapid method cutting DNA into
fragments and determining the sequence of those fragments. Linked
together by overlapping frag.s and id-ing promoters
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About 99.9% of genes in humans are the same, but bases that
dont match = single nucleotide polymorphism ( SNPs) Human Genome
Project was completed in 2003, copies of certain human and other
organisms genomes are in databases on the internet. Development
from project: bioinformatics, which combines molecular biology w/
information science. Putting together human genome wouldve been
impossible w/out computer databases Genomics- study of whole
genomes, including genes and functions
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Human Genome Project pinpointed genes and assocaited particular
sequences w/ numerous diseases and disorders. Also id- ed 3 million
diff. locations where single- base DNA differences occur in humans.
-May help us understand, and eventually develop cure for certain
diseases.
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One day your genetic info. may be public to health insurance
companies, doctors, employers, etc. Right now Genetic Information
Nondiscrimination Act (2008) prohibits discrimination based off of
genetic tests.
