Transcript Human Genetics

Introduction to Genetics
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What is genetics?
The second-most interesting subject in the
world.
Second to what?!
Microbiology
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Genetics
Is the study of inherited
traits and their variation
Figure 1.1
Is also an informational science that is
having a huge societal impact
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Topics to consider
An understanding of genetics undergirds an
understanding of the world.
More diseases are now being understood in
terms of gene expression.
As our knowledge of and technology in this
field increase, bioethical issues arise that
preceding generations could not have
imagined.
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Genes
Contain the instructions within the cells for
protein production
Genes are composed of deoxyribonucleic
acid (DNA)
Traits are produced by an interaction
between the genes and their environment
Figure 1.1
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The Genome
Is the complete set of genetic information
for an organism
It includes all of the genes present in an
organism
- It also includes DNA sequences that do
not encode genes
Genomics is a field that analyzes and
compares genomes of different species
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Levels of Genetics
Figure 1.2
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How DNA is organized
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Deoxyribonucleic Acid (DNA)
A double-stranded polymer consisting of a chain
of nucleotides
Deoxyribonucleotide components:
- Phosphate
- Sugar: Deoxyribose
- Base: Adenine A
Guanine G
Thymine T
Cytosine C
The sequence of the bases code for the amino
acid sequence in a protein
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Box, Figure 1
Reading1.1, Figure 1
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Ribonucleic Acid (RNA)
A single stranded polymer of ribonucleotides
Ribonucleotide components:
- Phosphate
- Sugar: Ribose
- Base: Adenine A
Guanine G
Uracil
U
Cytosine C
Exists in several types
Uses information on DNA to construct proteins
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Box, Figure 2
Reading 1.1, Figure 2
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The Central Dogma of Molecular
Biology
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The Human Genome
Only 1.5% of our DNA encodes protein
- About 20,325 protein-encoding genes in all
Rest of the human genome includes highly
repeated sequences with unknown functions
Genes known to cause disorders or traits are
cataloged in a database
- Online Mendelian Inheritance in Man (OMIM)
Proteomics is a field that studies the proteins
made in a cell
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Let’s go from big to small…
All of our cells have a nucleus (except red blood
cells).
The nucleus consists of ______ pairs of
chromosomes.
That’s _______ total chromosomes
That means we have 2 copies of every
chromosome!
Genes are the units of heredity and are
sequences of DNA.
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Continued…
Therefore, we have two copies of every gene.
These copies are called alleles.
The changes in DNA sequence that
distinguish alleles arise through mutation.
Mutations in sperm or egg cells are passed on
to the next generation
Mutations may be positive, negative, or
neutral
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Chromosomes
Composed of DNA and protein
Found in the nucleus of the cell
Human somatic cells have 46 chromosomes
- 22 pairs of autosomes
- A pair of sex chromosomes
- Females have two X chromosomes
- Males have one X and a Y
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Karyotype
A chart displaying the chromosome pairs from
largest to smallest
Figure 1.2
Figure 1.2
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Cells
A human body contains approximately 50-100
trillion cells
- All cells except RBCs contain the same genome
Differentiation causes cells to differ in appearance
and function
- Controlled by variation in gene expression
Stem cells are less specialized and can become
many different cell types
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Individual
The genotype of an individual refers to the
alleles they carry
The phenotype is the visible trait
A dominant allele is expressed if the
individual carries just one copy
A recessive allele is only expressed if the
individual carries two copies
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The Family
Individuals are genetically connected into
families
A pedigree is a diagram used to study traits
in families
- Can be used to trace multiple genes or
genes with large environmental component
- Will be discussed in detail in Chapter 4
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Gene Pool and population
Gene pool—all of the alleles in a population.
A population is a group of interbreeding
individuals.
An individual does not have a gene pool.
Depending on environmental conditions,
certain alleles may be more prevalent in
certain populations.
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Mendelian vs. Multifactorial Traits
Mendelian traits are determined by a single gene
- Their recurrence is predicted based on Mendel’s
laws
Multifactorial traits are determined by one or more
genes and the environment
- Predicting their recurrence is much more difficult
Most traits are multifactorial
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Mendelian vs. Multifactorial Traits
Figure 1.5
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Connecting Structure to Function
Genesprotein products
MutationsDisorders
Enzymes are proteins, so if there is a mutation
in a gene coding for an enzyme, the cells
may not be able to process a certain food or
build a certain macromolecule.
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Genes and Disease Risk
Genetic determinism is the idea that the
expression of an inherited trait is inevitable
(ignores environmental influences).
This may be harmful or helpful, depending on
its application
- As part of a social policy, it is disastrous
- Knowing genetic risks can help us make
good choices
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An example of gene function-PKU
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Stands for phenolketonuria
Caused by deficiency in an enzyme called
PAH (phenylalanine hydroxylase).
PAH helps break down phenylalanine, an
amino acid.
What do you think happens if phenylalanine
can’t break down?
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PKU
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PKU results in mental
retardation if
untreated.
The gene for PAH is
located on
chromosome 12.
Chromosome 12
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PKU
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A mutation in PAH could cause the protein
to misfold and not produce functional PAH
enzyme.
This is ok because we have two copies of
chromosome 12, and therefore two copies
of PAH, so one will work.
However, if both copies of the gene are
mutated, a person will have PKU.
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PKU
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As long as one normal copy is inherited, a
person will be fine.
This is an autosomal recessive disorder.
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