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Genetics: Human Heredity & Genetic Engineering
Transcript of Genetics: Human Heredity & Genetic Engineering
Transmission of Human Traits
Human Pedigrees Genetics Genetic Engineering Transmission of Human
Traits Human Pedigrees Chromosomal Disorders II. Human Genetic Disorders
From Molecular to Phenotype
Chromosomal Disorders III. The Human Genome
The Human Genome Project Karyotype: Genome: Sex Chromosome: Autosomal Chromosomes: The full set of genetic information that an organism carries in its DNA. A picture that Shows the complete diploid set of chromosomes
Pictures taken during mitosis
Grouped in pairs & arranged from largest to smallest. Two of the 46 chromosomes in the human genome that determine an individuals sex.
Females have two copies of the X Chromosome
Males have one X chromosome and one Y chromosome.
All egg cells carry a single X chromosome. Half of all sperm cells carry an X chromosome and half carry a Y chromosome. The remaining 44 chromosomes are autosomal chromosomes.
These chromosomes contain most of the genetic information in the cell. Chapter 14 & 15 Human Genes follow Mendelian patterns
of inheritance FOR EXAMPLE Dominant and Recessive Alleles Trait Dominant Recessive Eye Color Brown Blue - Green Hair Color Dark Blonde - Light - Red Chin Cleft No Cleft Hairline Widows Peak Straight Eye Brow
Shape Separated Unibrow * It should be noted that hair and eye color are polygenic Co-dominant & Multiple Alleles Blood Type Sex-Linked Inheritance X & Y chromosomes determine sex; therefore, the genes located on them show a pattern of inheritance.
Only Males have genes on the Y chromosome.
This can cause Problems
Color Blindness Humans have 3 genes for color vision
on the X chromosome. A defective allele
in any of the 3 genes results in color
blindness. Inherited from Father Why are more males color
blind than Females? X-Chromosome Inactivity Because females have two X chromosomes, many of the genes on the X chromosome are inactive.
A cell only needs one active X chromosome to function normally.
Cat spots and alleles for colored spots. (Orange & Black) What is a Pedigree? A pedigree is a chart that shows the pattern of inheritance and whether or not the trait is autosomal or sex-linked Pedigrees can be used to find out the genotypes of family members A pedigree shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring. Exercise http://wps.prenhall.com/wps/media/objects/1143/1170603/3_4.html Genes are made from DNA
They interact with environment to make individual characteristics or phenotype.
Genotype and Phenotype are directly connected.
Changes in DNA sequence can change proteins
Therefore, can change one's phenotype In other words, there is a molecular basis for genetic disorders Examples 1. Sickle-Cell Disease 2. Huntington's Disease 3. Cystic Fibrosis Caused by flawed allele for a polypeptide in hemoglobin Hemoglobin is the oxygen-carrying protein in red blood cells
Makes the polypeptide molecules stick together at times
The shape the red blood cell makes is like that of a sickle
Normal red blood cells are flexible & able to fit through capillaries; whereas, sickle shaped cells are more ridged & get stuck in capillaries.
This can lead damage cells, tissue, and even organs. Cause: A dominant allele for a protein found in brain cells
Has a long string of bases
The codon CAG repeats over more than 40 times
This produces the amino acid glutamine
No one knows why this long string of glutamine cause this disease Effect: Decreasing mental abilities
Symptoms do not appear until middle age.
The greater number of CAG repeats, the earlier the disease appears and more sever its symptoms are. Cause: Deletion of three bases in one gene
This gene codes for a protein called CFTR
The loss of these bases removes one amino acid from CFTR
This causes the protein to fold incorrectly, so it cannot do its job Effect: The CF allele is recessive so two copies of the defective allele are needed.
Children have trouble digesting food
Thick, heavy mucus blocks their lungs and airways Genetic Advantages A parasite that lives in red blood cells causes Malaria; however, the parasite cannot live in sickled blood cells People with only one copy of the sickle cell allele are more resistant to the parasite People with a single CF allele are less likely to die from typhoid fever. The protein made by the CF allele helps block this bacterium from entering the cells Nondisjunction When homologous chromosomes do not separate during meiosis
Each sex cell receives 23 chromosomes
Nondisjunction results in the wrong number of chromosomes
This can lead to disorders Example: If two copies of a chromosome fail to separate during meiosis, an individual may be born with three copies of that chromosome.
This is called a trisomy Down Syndrome is a trisomy of chromosome 21 Article Nondisjunction of sex chromosomes also cause problems A female who only inherits one X chromosome usually has Turner's Syndrome. Her sex organs do not develop at puberty - so she cannot have offspring. Why would you want a pedigree? The Human Genome Project Technology Just over a decade ago, the human genome was unknown
Now, with the aid of technology, we can find the human genome online.
Working with DNA is very technical and so advance tools are needed to cut, separate, and replicate DNA. Cutting DNA To Study DNA, scientists first cut it into smaller pieces
They use bacterial enzymes called restriction enzymes.
Restriction enzymes cut DNA into exact pieces called restriction fragments.
Different enzymes cut DNA in different places, and into pieces of different sizes.
This allows scientists to study specific genes. Example: The EcoRI enzyme functions as a key that only fits into one lock. The EcoRI restriction enzyme can only recognize the base sequence GAATTC.
It cuts each strand of DNA between the G and A bases This cut leaves single-stranded DNA overhangs with the sequence AATT.
Overhangs are called "sticky ends." Activity Separating DNA After DNA is cut, scientists use a technique called gel electrophoresis.
This technique is use to separate DNA fragments
Then fragments are placed into wells on a gel
An electric current is applied which makes the DNA move toward one end of the gel.
Smaller fragments move faster than larger fragments.
The result is a pattern of bands on the gel. The pattern is based on the size of the DNA fragments. Why is this process used? DNA fingerprinting for forensic purposes
To get a DNA fingerprint for paternity testing
To get a DNA fingerprint so that you can look for evolutionary relationships among organisms
To check a PCR reaction.
To test for genes associated with a particular disease. http://www.sumanasinc.com/webcontent/animations/content/gelelectrophoresis.html Article Article on DNA Forensics Activity on DNA testing for parents Handout DNA Processing Virtual Lab Cutting Lab Reading DNA DNA polymerase uses the bases to make many new DNA strands.
Some of the bases are labeled with a chemical dye.
When the synthesis is finished, the result is a series of color-coded DNA strands.
Researchers can then separate these strands on a gel.
The order of the color bands on the gel tells the exact sequence of bases in the DNA.
This is called your DNA fingerprint - unique to only you. Article DNA Screening DNA Drug Testing Lab Worksheet The Project In 1990 the US and other countries began the 13-year Human Genome Project.
The Project had 2 main goals:
1. To sequence all 3 billion base pairs of human DNA
2. To identify all human genes Sequencing & Identifying Genes Once DNA strands are marked they are cut into random fragments.
Then they determine the base sequence of each fragment.
Computers put the fragments in order using the markers
This method is called, "Shotgun Sequencing"
Scientists break up the whole genome into smaller pieces
Next, they determine the base sequences in regions of a DNA strand that are far apart.
These regions act as markers that researchers can find and come back to. Comparing Sequences Most people have identical genomes. On average, only one base in 1200 will not match between two people.
The single base differences are called SNPs (Single Nucleotide polymorphism).
Some sets of closely linked SNPs occur together often
Scientists hope to use these SNPs to identify various diseases and conditions Sharing Data The Human Genome Project was completed in 2003
You can access copies of the Genome project online.
A new field of research was created called bioinformatics. Using computer tools to collect, organize, and interpret biological data is a big part of this field.
Bioinformatics began another field of study called genomics - the study of whole genomes What we have learned Human genome contains 3 billion nucleotide bases
Only 2 percent of out genome has codes for making proteins.
Identified genes linked to various diseases
Found 3 million locations where single base pairs are different in humans (SNPs) Activity on Forensics Worksheet IV. Selective Breeding
Increasing Variation V. Recombinant DNA
Transgenic Organisms Selective Breeding Recombinant DNA Selective Breeding Increasing Variation Copying DNA Changing DNA Transgenic Organisms Selective Breeding Much of what we eat today has been improved for our own benefit - Such as corn
Humans have bred many organisms for our own benefits
What are some examples of this?
Humans are always looking to make animals that are better hunters, better retrievers, better companions etc
Letting only those animals with the desired characteristics produce the next generation is called selective breeding Crossing organisms that have different traits to bring together the best of both organisms.
The offspring of such crosses are called hybrids - think hybrid cars.
Hybrids (plants) are often hardier than their parents
Example: Crossing a plant that was resistant to a particular disease with a plant that produced a lot of food.
Much of what you buy from the store are hybrids. Activity Web Karyotyping Hybridization Activity Observation lab Inbreeding is used by breeders to keep a certain characteristic in a line of organisms.
Many breeds of dogs are inbred
Inbreeding can cause harmful effects since inbred organisms are genetically very similar - it increases the probability that organisms may inherit alleles that lead to genetic disorders Inbreeding Increasing Variation Sometimes breeders want more variation than they find in the wild so they add to the genetic variation in a population by introducing mutations.
When scientists change the genetic makeup of an organism, they are using biotechnology
Selective breeding is one form of biotechnology important in farming and medicine. Bacterial Mutations Mutations are changes in DNA that parents can pass to offspring.
Mutations often happen on their own; however, breeders can also make mutations happen.
Some mutations are harmful while others are beneficial
Making mutations in bacteria is very useful because they are so small - millions of them can be treated with radiation or chemicals at the same time
This technique has let scientists develop hundreds of useful kinds of bacteria.
For example, scientists are working to make bacteria that can clean up radioactive substances and metal pollution. Polyploid Plants Scientists use drugs that keep chromosomes from separating during meiosis - very helpful to plant breeders
These drugs can make cells with many times the normal number of chromosomes
Plants grown from these cells are called polyploid
Does not work so well with animals.
Polyploid plants are often stronger and larger than their diploid relatives Copying DNA Example of computer programming
In the past, plant and animal breeders had to work with variations that already existed in nature.
Now, scientists can transfer genes for particular traits from one organism to another - eg. Char in strawberries.
How does this happen?
DNA is cut into fragments using restriction enzymes. However, when DNA is cut there are millions of pieces of DNA - How do we find the a sing gene among all these pieces? Finding Genes Scientists first study the amino acid sequence for a particular protein - eg. jellyfish (GFP protein absorbs energy from light and makes parts of the jellyfish glow)
Then, they figure out the mRNA sequence that would make that protein.
That mRNA sequence allows us to see understand the DNA sequence of the gene.
By making a piece of RNA that would match that DNA, scientists essentially make a DNA "magnet" to find the specific gene. PCR Method of Copying DNA PCR - Polymerase Chain Reaction
Once scientists find a gene, they need to make copies of it.
There is four steps to this process. Step 1: DNA is heated to separate strands Step 2: DNA is cooled and primers are added Primers are short pieces of DNA added to the original piece of DNA to prepare, or prime, a place for DNA polymerase to start working. Step 3: DNA polymerase adds nucleotides to strands, producing two complementary strands DNA Polymerase copies the DNA between the primers.
New strands become templates to make more copies. Step 4: The procedure is repeated starting at step 1 Cycle 2 All 4 Stages 1. Heat & separate DNA 2. Prime DNA 3. DNA polymerase
copies DNA between
primers 4. Steps 1-3 repeated Changing DNA Scientists can make the DNA for any gene whose sequence they know.
They can put those genes into living cells
Changing genes for a practical purpose is called genetic engineering.
How do they do this? First, scientists build a DNA sequence with the gene or genes they want to put into a cell.
Machines known as DNA synthesizers can make short pieces of DNA.
These pieces are then joined to natural pieces of DNA using enzymes (eg. DNA ligase).
So a gene from one organism and attach it to to the DNA of another organism - this is called recombinant DNA Example Transgenic Organisms Most living things have the same genetic code
So, scientists can make organisms that are transgenic - organisms having genes from another organism.
Scientists can make transgenic plants, animals, and microorganisms. Article "Fluorescent Mice Herald Gene-Transfer Breakthrough" Cloning A clone is a member of a group of identical cells made from a single cell.
Cloning uses a single cell from an adult organism to grow a new individual - who is genetically identical to the organism from which the cell was taken. Worksheet Pedigree groups of 2 Movie: "Men and Women, the Difference is in the Genes" "Extra chromosome 21 removed from Down syndrome cell line" 4 Cases "Rare Genetic Disorders"