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Introduction to Genetics. What is genetics?. The second-most interesting subject in the world. Second to what?! Microbiology That ’ s next semester…something to look forward to. Genetics. Is the study of inherited traits and their variation

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what is genetics
What is genetics?
  • The second-most interesting subject in the world.
  • Second to what?!
  • Microbiology
  • That’s next semester…something to look forward to.
  • Is the study of inherited traits and their variation
  • Is a life science that should not be confused with genealogy

Figure 1.1

Is also an informational science that is having a huge societal impact

topics to consider
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.
  • 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

the genome
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
deoxyribonucleic acid dna
DeoxyribonucleicAcid (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

Box, Figure 1

Reading1.1, Figure 1

ribonucleic acid rna
RibonucleicAcid (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

Box, Figure 2

Reading 1.1, Figure 2

the human genome
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
let s go from big to small
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! Woohoo!
  • Genes are the units of heredity and are sequences of DNA.
  • 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
  • Polymorphisms are variations in the DNA sequence that occur in at least 1% of the population
  • Single nucleotide polymorphisms (SNPs) are single base sites that differ among individuals
  • - Can cause disease or act as genomic markers
  • Genome-wide association studies track SNP patterns among individuals who share a particular trait or disorder
  • Gene expression profiling measures which genes are more or less active in particular cell types
  • 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


A chart displaying the chromosome pairs from largest to smallest

Figure 1.2

Figure 1.2

  • 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

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

the family
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

gene pool and population
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.
mendelian vs multifactorial traits
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

connecting structure to function
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.
genes and disease risk
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
applications of genetics
Applications of Genetics

Genetics impacts many areas of our lives

DNA profiling (DNA fingerprinting) looks at SNPs and short repeated DNA sequences

- It has applications in:

- Forensics

- History and ancestry

health care
Health Care

Diseases are increasingly being described in terms of gene expression patterns

Tracking gene expression can reveal new information about diseases and show how diseases are related to each other

- This is not obvious via traditional medicine

the diseasome
The Diseasome

Figure 1.7

genetic testing and treatment
Genetic Testing and Treatment

Tests to identify about 1,200 single-gene disorders have been available for years

- Direct-to-consumer (DTC) genetic testing

The Genetic Information Non-discrimination (GINA) act was passed in the US in 2008

Genome information is useful for developing treatment to genetic and infectious diseases


Traditional agriculture is the controlled breeding of plants and animals

Biotechnology is the use of organisms or their parts to produce goods and services

Genetically-modified (GM) organisms have new genes or over- or under-express their own genes

an example of gene function pku
An example of gene function--PKU
  • 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?
  • PKU results in mental retardation if untreated.
  • The gene for PAH is located on chromosome 12.

Chromosome 12

  • 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.
  • As long as one normal copy is inherited, a person will be fine.
  • This is an autosomal recessive disorder.