Science Midterm Study Guide

Enviro also affects traits: twins raised in seperate enviros not identicle, plant blocked from sun wont produce chlorophyl, etc.

During the formation of gametes (sex cells), the alleles responsible for a trait separate from each other, alleles recombined at fertilization

Offspring heterozygous but will express only the dominant trait

Alleles of different traits are distributed to sex cells-> illustrated using dihybrid crosses (ex: both red hair and freckles)

Studies 7 traits in peas, results successful because each trait carried on a diff chromosometests are quantitative and carefully designed

To determine if an organism has a pure trait or is heterozygous, it is bred with a pure recessiveif results all dominant: organism pure dominantif results are 3:1 dominant to recessive, organism heterozygous

• Genes are located on the X chromosome
• -Drosophila eye color was one of the first examples of X-linkage
• -Hemophilia: blood can't clot properly
• females: either normal, carrier but nonhemophilic, or hemophilic
• males: either normal or hemophilic
• males are thus more likely to have sex linked disorders

• Linked genes on same chromosome
• ex: if i inherit red hair, I will also get freckles

• Interphase: chromosomes are duplicated
• MEIOSIS I: the overall result of meiosis I are two cells that have different sets of chromosomes and alleles. they are not identicle to the diploid cell that entered meiosis I
• Prophase I: Each chromosome pairs with its corresponding homologous chromosome to form a tetrad (and crossing over)
• Metaphase I: Spindle fibers attach
• Anaphase I: Homologous chromosomes to opp ends
• Telophase I and cytokinesis: two haploid cells

• MEIOSIS II: Four haploid
• metaphase II: chromosomes line up
• anaphase II: sister chromatids seperate
• telophase II: 4 new cells

At the end of meiosis, 4 genetically different haploid cells are produced. at the end of mitosis, two genetically identical diploid cells are produced

during prophase I, chromosomes pair with homologous chromosome (4 chromatids)

prophase I: pairing of homologous chromosomes, forms tetrad

• during synapsis in the first meiotic division, the chromatids in a homologous pair of chromosomes often twist around each other, break, exchangesegments and rejoin
• **
• Crossing over results in the rearrangement of linked genes and increases the variability of offspring.

• Types of Chromosomal Alterations
• 1. Nondisjunction: homologous chromosomes fail to separate during meiosis, producing offspring with one chromosome more or less than is normal disjunction -- the separation of homologous chromosomes during meiosis **
• If disjunction fails to occur (nondisjunction), gametes with an addition or a missing chromosome will be produced.

turner syndrome: female only has one chromosometrisomy: down syndrome is trisomy 21, three copies of a chromosome

• 1. Translocation: transfer of one section of a chromosome to a nonhomologous chromosome
• 2. Addition: a portion of one chromosome is attached to another chromosome
• 3. Deletion: a portion of a chromosome is taken away from a chromosome
• 4. Inversion: a portion of a chromosome breaks off and then becomes reattached to the same chromosome in an inverted (upside down) fashion

• one gene one enzyme hypothesis
• bread mold

came up with DNA double helix model, displays base pairing

• Wilkins’s idea to study DNA by X-ray crystallographic techniques
• worked with franklin

• made DNA diffraction x-ray (Photo 51)
• essential for final DNA model

determined the structure of a class of proteins is a helix (alpha)

• forms rules of base paring (A=T, G=C)
• foundation for watson crick DNA model

• bacteriophage experiment
• proves DNA can transfer genetic info but protein cant (thru radioactivity tests)

• double stranded double helix
• sugar is deoxyribose
• 4 nitrogenous bases

• Phosphate-sugar backbone (covalent-phosphodiester bond)
• hydrogen bonds

• mRNA: single uncoiled strand
• tRNA: clover shaped
• rRNA: irregular/ squigly

genetic info

• mRNA: carries the genetic info out from the nucleus to the cytoplasm (where the ribosomes are)
• tRNA: brings the amino acids to the mRNA (at the ribosomes) to form polypeptide chains
• rRNA: Mostly just structural for the ribosomes/ composes ribosomes (as do proteins)

only one strand underwinds, RNA polymerase

Info in sequence of nucelotides--> amino acids

semi-conservative, DNA polymerase base pairing

• the flow of genetic info can be moved from DNA to RNA to protein
• DNA--> transcription mRNA---> translation peptide

segment of DNA that contains all the info needed for protein or RNA synthesis

• The genetic code is the set of rules by which information encoded in sequence
• codon: group of 3
• anticodon: tRNA

• 1. Artificial Selection-individuals with desirable traits are mated to produce offspring with those traits
• 2. Inbreeding- offspring produced by artificial selection are mated with one another to reinforce those desirable traits
• 3. Hybridization--crossing two individuals with different desirable traits to produce offspring with a combination of both desirable traits
• 4. Mutations may be preserved by vegetative propagation. (ex. seedless oranges)
• 5. Recombinant DNA (genetic engineering) --- new varieties of plants and animals can be created by manipulating the genetic instructions of these organisms to produce new characteristics

• Making genetic copies of an existing plant or animal
• Cloning
• A “clone” is a copy of something.
• Computers that mimic IBMs are called “clones.”
• In genetics, a clone is a genetic copy of another organism.
• Clones occur naturally:
• Asexual breeding in plants & lower animalsIdentical twins (triplets) in higher animals
• We now realize that each specialized cell has all the genetic information, but much of it is turned off.Problem – how to reset the “program” so this information is usable?Cloning of frogs successful in 1950sCloning of livestock from fetal cells in 1970sDolly - 1996Clone from an adult sheep cell by Scots researchers under Ian WilmutHad only one success in 300 tries.Dolly grew to maturity, and successfully had a lamb by natural means in 1998.But Dolly seems to be prematurely old.Cloning DollyCloning since DollyCloning of this sort has now been done on cattle, pigs, cats, dogs and mice.The success rate has improved considerably.Cloning humans begins to show up in science fiction in 1970s.This is now a realistic possibility.Advantages of CloningWith an adult plant or animal, the breeder knows what its traits are; this is not the case with fetal cell cloning.Cloning allows making a genetically identical copy of the desired plant or animal.Concerns re/ CloningThe success rate from adult animal cells is still rather low.This would be unacceptable for cloning humans in most societies.The evidence suggests that the clones which survive are still not right.The genetic program has probably not been completely reset.We still don’t understand what we are doing in cloning from adult cells.

Genetic tests are tests on blood and other tissue to find genetic disorders.

Mutation: a random change in thechemical nature of the genetic material (DNA) **Mutagenic Agents-- increase the random incidence of mutations 1. Radiation -- X-rays, ultraviolet, radioactive substances, and cosmic rays 2. Chemicals -- formaldehyde, benzene, asbestos fibers, THC, nicotine

Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells (sperm and egg) have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number (n) is the number of chromosomes in a gamete. A somatic cell has twice that many chromosomes (2n).Humans are diploid. A human somatic cell contains 46 chromosomes: 2 complete haploid sets, which make up 23 homologous chromosome pairs. However, many organisms have more than two sets of homologous chromosomes and are called polyploid.

autosomal recessive