Transcript Ppt. 9 (Genetics)

Genetics
DNA & RNA
• DNA (Deoxyribonucleic acid)- named for the sugar deoxyribose.
• RNA (Ribonucleic acid)- name for the sugar ribose.
• Nucleotides- building blocks of nucleic acids that eventually build proteins.
• Adenine
• Thymine
• Guanine
• Cytosine
• A-T
C-G
DNA & RNA
• A,T, C, & G make up the rungs of the ladder of DNA.
• A-T are complementary pairs, as are C-G.
• The two sides of the ladder are held together by hydrogen bonds.
• These nucleotides may also be called Nitrogenous Bases. So the base pairs
are again A-T and C-G.
DNA & RNA
• DNA carries the code for all genes of every organism.
• Genes- pieces of DNA that code for specific proteins. Making genes into
proteins is called Protein Synthesis. Remember: this happens at the
ribosome.
DNA & RNA
• 1. The DNA code of the gene segment must be copied in the nucleus of the
cell.
• 2. The code is then carried from the nucleus into the cytoplasm and finally to
a ribosome.
• 3. The protein is then assembled from the code and released from the
ribosome.
DNA & RNA
• RNA is a molecule used to translate the code from the DNA molecule into a
protein.
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It is single-stranded.
It also has 4 nitrogenous bases. Adenine, Uracil, Cytosine, and Guanine.
Notice that Thymine has been replaced with Uracil.
Base pairs: A-U and C-G.
DNA & RNA
• King’s College Team (1952)
• Rosalind Franklin- used X-ray crystallography to study the physical structure
of the DNA molecule.
• Maurice Wilkins assisted Franklin in this work.
DNA & RNA
• Cambridge Team (1953)
• James Watson and Francis Crick used Franklin’s work to build a model of
DNA.
• Watson and Crick would not have been able to build model without
Franklin’s work.
Protein Synthesis
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Many proteins are within every cell. They make up enzymes and hormones.
Proteins provide structure and act as energy sources.
Proteins also transport other molecules and help fight disease.
Therefore, proteins are essential for survival because almost everything that
happens in the cell involves proteins.
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Transcription
1st step of protein synthesis.
Special kind of RNA called messenger RNA (mRNA) is made.
This copying process is called transcription.
A region of DNA unwinds and separates.
The mRNA is matched with DNA by the enzyme RNA polymerase.
Then the mRNA leaves the nucleus and goes into the cytoplasm to settle on a
ribosome. A ribosome is made of another kind of RNA, ribosomal RNA
(rRNA)
• Then, translation begins.
Transcription
Translation
• This is where the mRNA is decoded or “translated” and a corresponding
polypeptide is formed. (Remember: A polypeptide is a string of amino
acids).
Translation
Translation
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Codon= three nucleotides together code for specific amino acids.
Amino acids build together like blocks to make different proteins.
!st codon is called the start codon.
Here there is a 3rd type of RNA, transfer RNA (tRNA)
tRNA uses a nucleotide segment, called the anticodon.
Anticodon- exact complement of one mRNA codon.
Translation
• The tRNA takes the newly formed amino acid and adds it to the growing
chain of polypeptides.
• This occurs until the mRNA reaches a stop codon, which tells it to stop the
translation.
• Then the ribosome releases the newly formed protein.
Genetic Expression
• Cell Differentiation= means that cells grow to look and function very
differently.
• Cell differentiation can occur during the embryonic stages of development.
It also happens as organisms repair damaged cells.
• During embryonic development, genes are activated or inactivated. This
allows cells to develop different shapes, function, etc.
Cell Differentiation Stages of Zygote
Genetic Expression
• Stem cells have the capability to become any type of cell.
• These cells can still turn on or off specific genes, thus developing in different
ways.
• Cell signaling= when cells receive chemical signals from the environment and
other cells that start the differentiation process.
• Cell differentiation can occur throughout your life. For example, when there is
an injury, new blood, bone, or skin cells are grown from stem cells found in
the body. Adult stem cells can operate the same way as embryonic stem cells.
Coding Dictionary
• Codons with code for specific amino acids. You must be able to figure out
which amino acid is being coded for by using a coding dictionary.
• Some amino acids can be coded for by more than one codon.
• The codon AUG codes for methionine. This is a common “start” codon.
• The codon UGA is one of three “stop” codons.
Mutations
• Mutations= mistakes in the duplication of the chromatin material (DNA).
• They usually occur in the nucleus during the replication process of cell
division.
• Some mutations are harmful, some beneficial, and some have no effect.
• Mutations play a significant role in the diversity of life on Earth today.
Mutations
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2 Types
Gene mutations and chromosomal mutations.
Gene mutations= mistakes that affect individual genes.
Chromosomal mutations= mistakes that affect the whole chromosome.
Example of Gene Mutation
Chromosomal Mutations
Mutations
• Mutations in somatic cells only affect the tissues of the organism.
• Mutations in reproductive cells (sperm & egg) may be transmitted to
offspring.
• This can result in a variety of genetic diseases.
• Mutagens= environmental factors that can cause mutations. Ex. X-rays, UV
light, radioactivity, pollutants, chemicals, etc.
Genetic Disorders & Diseases
• 1. Sickle cell anemia
• Result of 2 recessive genes
• Causes the red blood cells to take on a sickle, or crescent, shape
• These distorted RBC’s cannot get through tiny blood vessels, preventing oxygen and
nutrients from getting to organs.
• Leads to frequent and severe infections, damage to major organs and episodes of
intense pain in the back, chest, abdomen, and extremities.
Genetic Disorders & Disease
• 2. Hemophilia
• Sex-linked, recessive condition
• Involves failure of blood to clot properly.
• The X chromosome carries the trait.
Genetic Disorders & Diseases
• 3. Down’s syndrome
• Inherited an extra copy of chromosome 21
• Result of nondisjunction during meiosis.
• The extra genetic material interferes with normal growth and development and results in mild
to severe learning disabilities, a small skull, extra folds of skin under the eyes, a flattened nose
bridge and low muscle tone throughout the body.
• Can also lead to medical conditions that include heart abnormalities and thyroid problems.
• Women over the age of 35 have an increased risk of having children with Down’s syndrome
Genetic Disorders & Diseases
• 4. Cystic fibrosis
• Genetic disorder passed on to children from parents.
• CF is caused by a mutation in the CFTR gene.
• To develop CF, an individual must have both recessive forms of the CFTR gene.
• Causes increased mucus in the lungs, lung infection, lung disease, poor growth rate, clubbing
of fingers, decreased life span, and infertility.
• No treatment for CF, but the symptoms can be lessened with antibiotics, breathing
treatments, and exercise.
Genetic Disorders & Disease
• 5. Tay-Sachs Disease
• Genetic disorder inherited by children from their parents.
• Recessive genetic disorder.
• Caused by any mutations to the HEXA gene found on chromosome 15.
• Results in the buildup of fatty acids in the nerve tissues.
• Symptoms include blindness, deafness, difficulty swallowing and eventual death.
• Infants born with this disease usually do not live past the age of 3.
• Individuals with juvenile TSD have a life expectancy of 5-15 yrs.
• Individuals with adult-onset TSD can manage the disease with drugs.
Genetic Disorders & Diseases
• 6. Color blindness
• Recessive condition.
• Individual cannot distinguish certain colors.
Genetic Disorders & Diseases
• 7. Turner’s Syndrome
• Chromosomal condition affecting approximately 1 in 2,500 females.
• Only have 1 X chromosome. Normal females have 2 X chromosomes.
• Sex-linked condition.
• Results in short physical stature, low hairline along the back of the neck, low set ears, and
an increased number of moles.
• Women with TS also commonly lack ovaries and thereby experience problems with
puberty and fertility.
Genetic Disorders & Disease
• 8. Phenylketonuria (PKU)
• Rare genetic disorder where the patient has a mutation in the gene that codes for a
particular metabolic enzyme.
• The mutated enzyme cannon convert phenylalanine found in food into the amino acid
tyrosine.
• This autosomal recessive mutation causes phenylalanine to accumulate in tissues. If left
untreated, the buildup of phenylalanine causes seizures, mental retardation, and death.
• No cure, but medical advancements have allowed patients to control symptoms and lead
normal lives.
Meiosis
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Cell division that creates the sex cells sperm and egg. (AKA gametes)
Produces 4 gametes with only 1 set of chromosomes each (haploid).
Two phases of cell division, meiosis I and meiosis II.
Resting phase is known as Interphase
Meiosis
• During meiosis I, each set of replicated chromosomes line up with its
homologous pair.
• Homologous chromosomes= matched pairs of chromosomes. Similar in size,
shape, and carry the same kinds of genes.
• These homologous pairs exchange pieces during the crossing over process.
This results in genetic variation.
• Interkinesis is the resting period before meiosis II begins.
Meiosis
• During meiosis II, the 2 daughter cells divide again.
• This results in 4 gametes, each having half the number of chromosomes of the
mother cell.
• In human males, all 4 gametes each produce long whip-like tails, now called
sperm.
• In human females, 1 gamete forms an egg cell. The other 3 gametes, called polar
bodies, disintegrate.
• Meiosis is vital to maintaining the correct number of chromosomes. If extra or
not enough chromosomes are passed on, diseases can result.
Asexual vs. Sexual Reproduction
• Asexual Reproduction by mitosis is a careful copying mechanism. Some
unicellular organisms, like amoeba, produce asexually.
• However, these offspring are always genetically identical to the parent.
• Sexual Reproduction by meiosis bring genetic variability of offspring.
• The number of possible chromosome combinations is 2n. Therefore, humans
have 23 chromosomes, so 223 = 8,388,608 genetic possibilities.
DNA Experiments
• In 1928, Frederick Griffith done an experiment with bacteria on mice.
DNA Experiments
• 2 Important Things to Notice:
• 1. Mice injected with heat-killed bacterial solution lived.
• 2. Mice injected with the mixed solution (heat-killed virulent + live nonvirulent) died.
• The result indicates that some type of biomolecule survived the heat killing
treatment to later be taken up be the living bacteria. (DNA)
DNA Experiments
• In 1953, Alfred Hershey and Martha Chase tagged bacteriophages (viruses
that attack bacteria) with 2 different radioactive elements.
DNA Experiments
• Hershey and Chase’s results showed the phosphorous with the bacterial cells.
• Scientists agreed that DNA was the molecule responsible for heredity in
organisms.
Genetic Expression
• Genes= specific portions of DNA that determine hereditary characteristics.
• Genes carry traits from one generation to the next.
• Alleles= different forms of a gene. (Dominant and recessive alleles)
Genetic Expression
• Genotype= the combination of alleles inherited from the parents.
• Dominant Gene= the trait that will most likely express itself.
• Recessive Gene= both alleles must be recessive ones for the gene to be expressed.
Ex. bb
• Homozygous= inherits two of the same alleles. Ex. BB or bb.
• Heterozygous= inherits one dominant allele and one recessive allele. Ex. Bb
• Phenotype= the physical expression of the trait. Ex. Blue eyes. (What you see)
Genetic Expression
• Punnett Square= scientists use these to show possible combinations
offspring may inherit from their parents.
• A monohybrid cross focuses on only one trait.
Mendel
• Gregor Mendel (1822-1884)= father of genetics. He did experimental crosses
with pea plants to see how traits are passed from one generation to another.
• Cross-pollinate means the pea plant has 2 different parents.
• Self-pollinate means the pea plant has only 1 parent.
• True breeders= have a known genetic history and will self-pollinate to produce
offspring identical to themselves.
Principle of Dominance
• Principle of Dominance states that some forms of a gene or trait are
dominant over other traits, which are called recessive.
• Parental (P) Generation= 1st generation
• F1 Generation= 2nd generation, children of the P generation.
• F2 Generation= 3rd generation, children of the F2 generation.
Principle of Segregation
• Principle of Segregation was developed by Mendel. It states that when
forming sex cells, the paired alleles separate so that each egg or sperm cell
only carries one form of the allele.
Principle of Independent Assortment
• This principle states that each pair of alleles segregates independently during
the formation of the egg or sperm. For example, the allele for green seed
color may be accompanied by the allele for round texture in some gametes and
by wrinkled texture in others. The alleles for seed color are inherited
independently of those for seed texture.
• Dihybrid Crosses= involve 2 traits.
Pedigree Charts
• Pedigree= a chart used to identify the lineage of individuals. These are
useful when the genotypes are unknown.
Sex-linked Traits
• Sex chromosomes= the chromosomes responsible for determining the sex
of an organism.
• Females= XX
Males= XY
• Genetic carrier= a female with a recessive gene on one X chromosome.
• A carrier is usually NOT affected with the condition themselves.
Incomplete Dominance
• Incomplete dominance is when traits blend together.
• Ex. A red and white flower produce pink offspring.
• BLEND
Codominance
• Codominance is when both traits show up.
• Ex. A chicken with black feathers and a chicken with white feathers have
offspring that have a checkerboard look to their feathers.
• Ex. Blood types. AB
• BOTH SHOW UP
Multiple Alleles & Polygenic Traits
• Several alleles or genes contribute to a trait.
• This will create a range of possibilities for the trait.
• Ex. Skin color, hair color, and height.
• RANGE
Biotechnology
• Biotechnology= the commercial application of biological products and has
been in existence for thousands of years.
• It includes the production of wine, beer, cheese, and antibiotics. Today, it
also refers to manipulating DNA to benefit humans. Ex. Agriculture, crime
scenes, finding family members.
Biotechnology
• Tissue Culturing= allows bioengineers to grow human tissues and organs in
the laboratory.
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Recombinant DNA= helps produce vaccines or cancer-fighting medications.
Gene Therapy= used in the medical community to help cure diseases.
Drug Development= used to treat diseases.
Bacterial transformation= uses bacteria to create beneficial products.
Ethical Issues in Biotechnology
• Many products of biotechnology have been genetically altered.
• Ex. Transgenic crops and terminator seeds.
• Genome= an organism’s complete set of DNA.
• Human Genome Project= launched in 1990, sought to identify all human
genes and determine all of the base pair sequences in all human chromosomes.
• Human have 46 chromosomes that contain 30,000 genes made up of
approximately 3 billion base pairs.
Stem Cell Research
• Stem Cells= are found in the human body. They have yet to become a
specialized type of cell. “Pre cell”
• Ex. A stem cell could develop into a nerve cell, skin cell, or a liver cell.
• 3 Sources of Stem Cells
• 1. Adult bone marrow
• 2. Umbilical cord blood
• 3. Embryos
Cloning
• Cloning= the creation of genetically identical organisms.
• In 1996, the cloning of Dolly the sheep from a somatic cell of an adult
sheep happened.
• Dolly was the 277th attempt in cloning a mammal.
• Cloning raises ethical and scientific questions that are still debated today.