Download GENETICS

GENETICS
THE SCIENCE OF HEREDITY
What do you know about genetics?
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Genes
Chromosomes
Genome: human genome project
Birth defects
Mutations
Inherited traits
Dominant traits
DNA
Genetic diversity
Evolution
Gene therapy
cloning
GENETICS
THE SCIENCE OF HEREDITY
What do you know about genetics?
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•
•
•
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Genes
Chromosomes
Genome: human genome project
Birth defects
Mutations
Inherited traits
Dominant traits
DNA
Genetic diversity
Evolution
Gene therapy
cloning
Genetic Information
• Gene – basic unit of genetic
information. Genes are mostly
the “recipe’s for proteins.
• Genome – the collection of
genetic information. A map of
where your genes are on your
chromosomes
• Chromosomes – storage units of
genes. Made of DNA.
• DNA - is a nucleic acid that
contains the genetic instructions
mostly for the making of proteins
Origins of genetics
• Parents know about inheritance by looking at their
kids
• Farmers know from breeding
• Animal breeders know
• Gregor Mendel
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1800’s
Austrian monk
Studied peas
Discovered the laws of genetics
Did not know about genes or DNA
Gregor Mendel
Understanding Physical Anthropology and Archaeology, 8th ed., p. 53
Why peas: give peas a chance
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7 easily observed traits
Easy to grow
Can be self pollinated or cross pollinated
Tasty
They were growing at the monastery
The 7 traits were simple--no combined
expression (tall or short, no medium)
Mendel’s Peas
Mendel’s experiments
• Raise pure bred strains
– P generation
• Cross breed the pure strains to create
hybrids
– F1 generation
• Cross breed the hybrids
– F2 generation
• Did the experiments thousands of times
• Always saw the same ratios
– 3 dominant to 1 recessive (phenotype
ratio)
– 1 DD:2 Dd:1 dd (genotype ratio)
• Conclusion: some traits are dominant.
They need only one gene to be
expressed. Some traits are recessive.
They need 2 genes to be expressed.
Hybrids look just like the pure
dominants.
MENDELS LAWS
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Mendel guessed traits were carried by
particles he called factors (we call them
genes)--PARTICLE THEORY OF
INHERITANCE
3 laws
1. Law of dominance--two forms of genes:
dominant and recessive alleles. Dominant gene
dominates the recessive genes
2. Law of independent assortment--genes for
different traits don’t affect each other. *only true if
the genes are on separate chromosomes.
3. Law of segregation--two genes for a trait get
separated during meiosis
VOCAB
• Pure bred: breed true, offspring like parents
• Hybrid: don’t breed true, offspring mixed
• Homozygous: genotype with both genes the same (pure bred-DD or dd)
• Heterozygous: genotype with one dominant and one
recessive gene (hybrid--Dd)
• Genotype: gene combo that produces the visible results (PP,
Pp, pp)
• Phenotype: visible traits caused by genes (flower color)
• Cross: breed critters
• Allele: type of gene--dominant (T) OR recessive (t)
• Dominant: genes that dominate. Only need one
• Recessive: passive genes. Need two.
PUNNETT SQUARES
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Prediction tool for genetics--like coin tossing
Sometimes called a checkerboard
Assumes equal chance of alleles in gametes
Female gametes on side, male gametes above
Fill in the boxes below and to the right to find the possible
genotypes of offspring.
• Gives chances of each possibility out of 4.
How to find the unknown
genotype
• Do a test cross
– Breed the dominant offspring to a
recessive. You always know the genotype
of a recessive phenotype.
– If any of the offspring have the recessive
trait, the dominant parent had to be hybrid
– Recessive phenotype only shows up with
two recessive genes--one from each
parent
Probability
• The chances are the same for genetics
when there are two alleles…
• What are the offspring possibilities of a
purple (PP) flower and a white flower
(pp)?
– All offspring are PURPLE!
• P1 crosses always result in 100%
dominant traits in the F1
Patterns of inheritance
• Sex (X) linked traits: found in guys
– Genes on the X chromosome
– Guys only have one X
– They can get recessive traits with one
recessive gene
– Hemophilia, baldness, color blindness
• Co-dominance
– Blood types (marker protein on RBC)
– Multiple phenotypes
– A, B, AB, O (no genes)
• Multiple alleles/polygenic traits
– Determined by more than one pair of
genes
– Height, skin color, race, intelligence,
personality
Genetic counseling
• Genetic tests for some disorders
• Radiological testing (x-rays) for some
disorders
• Prenatal testing: amniocentisis
• Pedigree charts: genetic family tree
Pedigrees
• Squares represent males
and circles represent
females
• Horizontal lines connecting a
male and female represent
mating.
• Vertical lines extending
downward from a couple
represent their children.
Interpreting a Pedigree Chart
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Determine if the pedigree chart shows an
autosomal or X-linked disease.
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If most of the males in the pedigree are
affected the disorder is X-linked (23rd
Chromosome)
If it is a 50/50 ratio between men and women
the disorder is autosomal (any of the #1-22
chromosomes)
Genetic disorders
• Mutations in germ cell (egg or sperm) genes
rather than somatic cell genes.
• Usually caused by recessive genes
• Recessive gene disorders concentrate in
small or isolated populations: inbreeding
• Some disorders are more common in some
ethnic groups: tay sacs, sickle cell, CF.
• Few mutations create dominant gene
disorders--dwarfism
Examples
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PKU: phenylketonuria
– Can’t digest an amino acid
Albinism: don’t make melanin
Tay Sachs: eastern european jews
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Cystic fibrosis: carriers may be protected from cholera
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Fatal for infants
recessive
Lungs get clogged with mucous
Need lung transplant by 30
recessive
Sickle cell anemia: carriers protected from malaria
– Red blood cells are misshapen in homosygous recessives
– African Americans
Huntington’s: don’t get symptoms till late in life
– Fatal
– Dominant
Achondroplasia: common form of dwarfism
– damonant
mutations
• Spot mutations: spontaneous
– Some are common
• Everybody has a couple of mutations! Roughly
1/10,000 genes. You have as many as 30,000 genes.
Most go unnoticed and may be beneficial
• Mutations make adaptation and evolution possible
• Pieces of chromosomes can by lost (deletion),
inverted, translocated, or repeated
• Non-disjunction is when chromosomes don’t separate
during meiosis--may cause trisomy (like trisomy 21-downs syndrome)
Genetic applications
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GENE THERAPY
DNA FINGERPRINT
HUMAN GENOME PROJECT
Genetically targeted treatment
GMO--genetically modified organisms
– Bt corn has a bacteria gene that makes pesticide
– Bacteria have been given human genes for making insulin
– Human genes have been put in pigs to grow transplant
organs
– Genes for drugs can be put in fruit and cows/milk
• Who owns your genes?
• Who controls your genetic information?