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Human Heredity

+Karyotypes

Genome= the full set of genetic information that an organism carries in its DNA

To see human chromosome, biologists photograph cells in mitosis (when chromosomes are fully condensed). They then cut them out and arrange them in a karyotype a karyotype shows the complete diploid set of

chromosomes grouped in pairs and arranged in order of decreasing size

+Sex Chromosomes

First 44 chromosomes = autosomes 2 of 46 chromosomes- sex chromosomes

Females: XX Males: XY

X chromosome contains more than 1200 genes Y chromosome contains about 140

Most are associated with male sex determination and sperm development

+Dominant and Recessive Alleles

MC1R helps determine skin and hair color some of MC1R’s recessive alleles produce red hair An individual with red hair usually has two of these

recessive alleles (one from each parent) Dominant alleles produce darker hair colors

Rh blood group- Rh+ and Rh- Rh+ is dominant

+Codominant and Multiple Alleles ABO blood group determined by a gene with three

alleles: IA, IB, and i IA and IB are codominant—individuals with both alleles

produce both antigens and therefore have the blood type AB

Homozygous recessive individuals (ii) produce no antigens and have blood type O

+Sex Linked Inheritance

Hemophilia Colorblindness

+X- Chromosome Inactivation

In female cells, most of the genes in one of the X chromosomes are randomly switched off forming a dense region in the nucleus called a Barr body

Cats: the color of spots on their fur is controlled by a gene on the X chromosome. Spots are either orange or black depending on which X chromosome is inactivated in different patches of their skin. Male cats can have spots of only one color Tricolor must be female

+Human Pedigrees

A chart used to trace traits over several generations Can be used for any species Shows the presence or absence of a trait according to

the relationships between parents, siblings, and offspring

= FEMALE

= MALE

= FEMALE WITH TRAIT

= MALE WITH TRAIT

OR = DECEASED

+More pedigree symbols…

= MARRIAGE LINE

= CHILD LINE

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1 2

1 2 3 4

1

Generation #

Individual #

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When describing a person you write the generation # a dash (-) then the individual number

Example: II-2 shows the trait

Example: II-1 is the oldest child of the original parents

1 2

1 2 3 4

1

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What is the genotype of I-2? What is the genotype of I-1? Can II-1 be homozygous

dominant?

1 2

1 2 3 4

1

EarlobesE = Free earlobes

e = attached earlobes

This pedigree shows the

occurrence of attached earlobes

(shaded in).

+Human Genetic Disorders to know: Sickle Cell Disease Huntington’s Disease- caused by a dominant allele for a

protein found in brain cells symptoms: mental deterioration, uncontrollable movements Appear in middle age

Cystic fibrosis (CF) Most common in people of European ancestry Deletion of 3 bases in the gene for a protein called CFTR removes

phenylalanine from CFTR protein, causing protein to fold improperly

Cell membranes are unable to transport Cl- ions CF allele is recessive Children with CF have serious digestive problems and produce

thick, heavy mucus that clogs their lungs and breathing passages

+Genetic Disorders to know…

Tay-Sachs disease Deadly disease of the nervous system Autosomal recessive disorder Common among Ashkenazi Jewish population Symptoms appear between 3-6 months; child usually dies

by age 4 or 5 Symptoms:

Deafness, blindness Loss of muscle strength, loss of motor skills Increased startle reaction seizures

+Studying the Human Genome

For a long time, reading the DNA sequences in the human genome seemed impossible (the smallest chromosome contains nearly 50 million base pairs!)

1960’s- scientists found that they could use natural enzymes in DNA analysis

By using tools that cut, separate, and then replicate DNA base by base, scientists can now read the base sequences in DNA from any cell

+Cutting DNA

DNA is much too large to analyzed, so it must first be cut into pieces

Restriction enzymes= high specific substances produced by bacteria that can cut even the largest DNA molecule into precise pieces that are several hundred bases long called restriction fragments Hundreds of known restriction enzymes

A restriction enzyme is like a key that fits only one lock

+Cutting DNA

The EcoRI restriction enzyme only recognizes the base sequence GAATTC. Cuts each strand between G and A, leaving single-stranded

overhangs with the sequence AATT Overhangs called “sticky ends” because they can bond, or

“stick” to a DNA fragment with the complementary base sequence

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+Separating DNA

Gel electrophoresis= a technique used to separate and analyze DNA fragments

DNA fragments are put into wells on a gel that is similar to a slice of gelatin

Electric voltage moves them across the gel (gel is positively charged on the end; fragments are negatively charged) Shorter fragments move faster than longer fragments

Within an hour or two, the fragments separate, each appearing as a band on the gel

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+Reading DNA

After the DNA fragments have been separated, they are placed in a test tube containing DNA polymerase, along with all four nucleotide bases

DNA polymerase makes new strands of DNA using the templates

The researchers also add a small number of bases that have a chemical dye attached

Each time a dye-labeled nucleotide is added, DNA replication stops

The result is a series of color-coded DNA fragments of different lengths

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Researchers can then separate these fragments, often by gel electrophoresis

The order of the colored bands on the gel tells the exact sequences of bases in the DNA

The entire process can be automated and controlled by computers so that thousands of bases can be read in a matter of seconds.

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Genetic Engineering

+Selective Breeding

Humans use selective breeding, which takes advantage of naturally occurring genetic variation, to pass wanted traits on to the next generation of organisms. New varieties of plants (teosinte corn!!!) Over 150 dog breeds Horses, cats, and cows

+Hybridization

Two common methods of selective breeding: Hybridization Inbreeding

Hybridization- crossing dissimilar individuals to bring together the best of both organisms Hybrids- individuals produced by such crosses; tend to be

hardier Luther Burbank- developed over 800 varieties of plants

Combined disease resistance with food-producing capacity

+Inbreeding

Inbreeding= the continued breeding of individuals with similar characteristics Maintains desirable characteristics Dogs

Can be risky—most of the members of the breed are genetically similar Increases the chance that a cross between two individuals

will bring together two recessive alleles for a genetic defect Human example: Amish (Pennsylvania Dutch)—high

incidence of genetic disorders since almost all descend from about 200 18th century founders

+Increasing Variation

Breeders can increase genetic variation in a population by introducing mutations, which are the ultimate source of biological diversity.

Biotechnology= the application of a technological process, invention or method to living organisms Manipulating the genetic makeup of an organism

Can increase mutations by exposure to radiation or chemicals Can produce a few mutants w/ useful characteristics

+ Bacterial mutations Millions of bacteria can be treated at one time increases

chances of being successful Allowed scientists to produce hundreds of useful bacterial

strains Oil-digesting bacteria for cleaning oil spills Working on bacteria that can clean up radioactive

substances and metal pollution

Polyploid plants Use drugs that prevent that separation of chromosomes

Plant Probable Ancestral Haploid #

Chromosome Number

Ploidy Level

Domestic oat 7 42 6Npeanut 10 40 4N

Sugar cane 10 80 8NBanana 11 22, 33 2N, 3NCotton 13 52 4N

+Copying DNA

Extracting DNA- easy. Finding a specific gene among millions of fragments-

not so easy. Southern blot analysis= a technique for finding

specific DNA sequences, among dozens Polymerase chain reaction (PCR)= a technique that

allows biologists to make copies of a specific gene once it is found

+PCR

1. A short piece of DNA that complements a portion of the sequence is added (called a primer)

2. DNA is heated to separate strands3. As the DNA cools, primers bind to the single strands4. DNA polymerase starts copying the region between

the primers5. These copies can sere as templates to make more

copies

+PCR

+Recombinant DNA

A DNA sequence can be synthesized and incorporated into the DNA of an organism using DNA ligase or other enzymes

A gene from one organism can also be attached to the DNA of another organism…called recombinant DNA

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+Transgenic Organisms

Contain genes from other species Produced by the insertion of recombinant DNA into the

genome of a host organism Can be done in plants and animals Cloning

+Genetically Modified (GM) organisms GM crops- resistance to insects, herbicides, viral

infections Rot and spoilage???

GM animals- 30% of milk in US comes from cows that have been injected with hormones that increase milk production Pigs—more lean meat, high levels of omega-3 acids Salmon– growth hormones Spider genes in lactating goats—silk Antibacterial goat milk

+Recombinant DNA technology in health and medicine Preventing disease Medical research- simulate human disease in studies Treating disease

HGH Insulin Blood clotting factors Cancer fighting molecules (interleukin-2 and interferon)

+Gene therapy

The process of changing a gene to treat

a medical disease or disorder An absent or faulty gene is replaced by a normal,

working gene Engineer a virus that cannot reproduce or cause

harmful effects (just delivers the gene to the target cells)

Very high risk (Jessie Gelsinger)

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