
10/14
History of Genetics
A. Blended Theory of Heredity
a. Pre- Mendelian theory of heredity
b. Proposed that hereditary material from each parent mixes in the offspring
c. Offspring are some intermediate of the parents
d. According to this theory
i. Individuals of a population should reach a uniform appearance after many generations (like mixing several colors of paint together)
ii. Once the traits are blended, they can no longer be separated out to appear in later generations
B. Particulate Theory of Heredity
a. Theory that parents transmit to their offspring discreet inheritable factors (genes) that remain separate factors from one generation to the next
b. Developed by Gregor Mendel 1860s
i. Discovered the fundamental principals of heredity
ii. Used a quantitative approach to his experiments
iii. Used pea plants to control self and cross pollination
iv. Started with true breeding plant varieties Mendel’s Laws
A. Law of Segregation
a. Alternative forms of genes are responsible for variations inherited characters
i. For example, the gene for flower color in pea plants exists in two alternative forms called alleles
b. For each character, an organism inherits two genes, one from each parent
i. Each parent contributes one allele through meiosis
c. The two genes for each character segregate during gamete production
i. Sperm and egg cells carry only one allele for each inherited characteristic
ii. Gametes of true- breeding parents will carry the same allele. If different alleles, there is a 50% chance of getting the dominant or recessive allele
iii. This sorting of alleles into separate gametes is called the Law of Segregation
B. Law of Independent Assortment
a. Each allele pair segregates independently of the other gene pairs during gamete formation
b. Determined by performing crosses that looked at two traits (dihybrid)
c. Ratios for crossing heterozygous parents were now 9:3:3:1 versus monohybrid 3:1
d. Law of Segregation was determined by looking at only one trait in a cross (monohybrid)
C. (11/4/03) Extending Mendel’s Laws
a. Incomplete Dominance
i. Neither allele is fully expressed
ii. Resulting offspring is “intermediate” (red and white = pink)
iii. Doesn’t support blended theory because alleles maintain their segregation abilities
b. Codominance
i. Both alleles are fully expressed
ii. Resulting offspring exhibit both alleles
iii. Represented by different capital letters (Ex. Black = B, White = W, Gray = BW)
c. Multiple alleles
i. Some genes may have multiple alleles with more than just to alternative forms of a gene
ii. Ex. A, B, and O blood groups
d. Polygenetic Inheritance
i. Many characteristics are quantitative that vary in a continuum in the population
ii. Not an either- or trait (ex. Height, hair color)
iii. Two or more genes determine a particular trait
Book Notes 10/22
Character- heritable feature
Trait- each variant for a character
True-breeding- when self- pollinate, all offspring are of the same variety
Hybridization- crossing of two varieties
Monohybrid cross- tracks single character
P generation- parents
F generation- filial generation, or offspring
F2 generation- second filial generation
Alleles- alternative versions of a gene
1. Alternative variations of genes account for variations in inherited characters
2. For each character, an organism inherits one gene from each parent
3. If two alleles differ, the dominant allele is fully expressed. The recessive allele has no affect on the organism’s appearance
4. The two genes for each character segregate during gamete production. Law of Segregation
Homozygous- has identical alleles for a character
Heterozygous- has two different alleles for a character
Phenotype- an organism’s appearance—can refer to one feature or complete appearance
Genotype- an organism’s genetic makeup—can refer to all or part
Testcross- breeding a recessive homozygote with an organism with dominant phenotype but unknown genotype. Devised by Mendel
Dihybrid cross- mating varieties with two differing characteristics
Law of Independent Assortment- behavior of alleles during gamete formation—phenotype ratio for dihybrids 9:3:3:1
Incomplete dominance- F1 hybrids have an appearance in between the phenotypes of two parental varieties (ex. Red x white = pink)
Complete dominance- phenotypes of heterozygotes and dominant homozygotes are indistinguishable
Codominance- both alleles are separately manifest in phenotype
Most genes exist in more than two allelic forms
Pleiotropy- genes have multiple phenotypic affects
Epistasis- a gene at one locus alters the phenotypic expression of a second gene
Quantitative characters- classified on either- or basis
Polygenic inheritance- an additive effect of two or more genes on a single phenotypic character
Nature vs. Nurture: Outside affects also have affects on organism’s phenotypes
Norm of Reaction- phenotypic range
Multifactoral- many factors (genetic and environmental) influence the phenotype
Pedigree- family tree describing interrelationships of parents and children across generations. Squares: Males Circles: Females
- Used to track harmful genetic traits
Consanguinity- “same blood” mating
Amniocentesis- test on amniotic fluid to determine disease—takes several weeks
Chorionic villi sampling- test fetal tissue (from placenta)—takes 24 hours
Genes 11/4/03
Punnett Squares- combinations resulting forma genetic cross may be predicted by using one of these
Test Cross- used to determine an organisms genotype that expresses a dominant phenotype by crossing it with an organism that expresses the recessive trait (homozygous)
Probability- can be determined by looking at the Punnett square to determine the chances of an organism expressing a particular trait or having a particular phenotype.
Homozygous- having two identical alleles for a given trait
- All gametes carry that allele
- Are true- breeding
Heterozygous- having two different alleles for a trait
- ½ gametes have dominant, ½ recessive
Phenotype- expressed (visible) traits
Genotype- genetic makeup (Bb, BB, bb)
Pedigree- a family tree; diagrams the relationships among parents and offspring across generations and shows the inheritance pattern of a particular trait.
- square- male
- circle- female
- shaded- has trait
- Used by genetic counselors
Consanguinity- a genetic relationship that results from shared ancestry- increases the chances of inheriting some rare genetic disorder
Just because a trait is dominant doesn’t mean it shows up with higher frequency in the human population
- ex. Dwarfism, 6 fingers
11/7/03
Morgan- fruit flies
Wild type- phenotype most common in natural population
Mutant phenotypes- alternatives of wild type traits
Sex- linked genes- genes located on a sex chromosome
- only x carries
Linked genes- genes on the same chromosome (a chromosome has hundreds or thousands of genes, and they travel together) are inherited together
Genetic recombination- Ummmm…
Parental types- Offspring that have same phenotype as one of parents
Recombinates- Offspring have different combinations of phenotypic ratios that either parent
Biotechnology 11/18/03
Biotechnology- using living things to improve life, solve problems, etc.
Old- selective breeding
New- cellular/molecular level Electron Scanning Microscope
Biotechnological tools
- Biosensor technology- can measure small concentrations (concentrations = [ ])
- Tissue engineering- making tissues
- Cell and tissue culture technology- cells/tissue- making—stem cells
- Genetic engineering- recombinant DNA
- DNA chip technology- analyze DNA information
- Monoclonal antibody technology- making antibodies
- Protein engineering- making proteins (as enzymes/catalysts)
- Antisense technology- block the production of proteins
- Bioprocessing technology- use cells for various functions (produce energy, break down substances, etc.)
Genetic Engineering 11/19/03
Genetic Engineering- adding, deleting or altering organism’s DNA. Also known as gene splicing, recombinant DNA technology
- Done “in vitro” (in glass/outside body) and transferred to desired area
How it’s done:
1. Isolate DNA (from desired organism and a host (usually bacteria))
2. Use a restriction enzyme to cut DNA (both organism’s and host’s)
3. DNA Ligese (protein ) will connect DNA (goal getting host’s and organism’s to combine. This is called recombinant DNA, or rDNA)
4. Insert into host
5. Host will replicate (clone) DNA
Uses:
- Human Genome Project (sequencing DNA)
- Diagnosis of disease
- Gene therapy (take out bad genes, insert good)
- Vaccines
- Drugs (insulin)
- DNA fingerprinting
- Agriculture (resistant plants, etc)
DNA Fingerprinting 11/21/03
DNA fingerprinting- process that separates DNA fragments to create a “unique” image, or fingerprint
- 99.9% of the 3 billion base pairs are the same. This calculates out to one difference every 10,000 base pairs.
How it’s done:
1. Cut DNA with a restriction enzyme
2. Place fragments in gel (agarose)
3. Electric current is put through the gel to separate the fragments (DNA is naturally negative)
4. Creates banding appearance (smallest fragments move furthest)