AP Biology - BCSD



AP Biology

Genetics Review

I. DNA Structure

a. History

i. Griffith

ii. Avery

iii. Hershey & Chase

iv. Chargaff, Franklin, Watson & Crick

II. DNA Structure

a. Nucleotides

b. Folding/packing

III. Replication

IV. Mendelian inheritance

a. Punnett squares

b. multiple alleles

i. incomplete dominance

ii. codominance

iii. epistasis

c. gene maps & linkage

V. Protein Synthesis

a. Transcription

b. splicing

c. Translation

VI. Gene Regulation

a. Operons

b. transcription factors

c. cytoplasmic determinants

d. Hox genes

e. non-chromosomal regulation

AP Biology - Genetics Review ANSWERS

I. DNA Structure

a. History

i. Griffith – 2 strains of pneumonia (pathogenic and non-pathogenic) found that heat killed bacteria can move it’s genetic material into the non-pathogenic (transformation)

ii. Avery – looked at DNA, RNA, and protein and found that DNA was transfered

iii. Hershey & Chase – radiolabeled DNA w/ P and protein w/ S found that DNA transferred in viruses

iv. Chargaff – found A&T, C&G in equal concentrations

v. Franklin – found DNA nucleotides to be equally distant from each other

vi. Watson & Crick – connected information to determine double helix structure

II. DNA Structure

a. Nucleotides

[pic]

Note the 3’ and 5’ orientation of the nucleotide

b. Folding/packing

[pic]

III. Replication

[pic]

IV. Mendelian inheritance

a. Punnett squares

[pic]

b. multiple alleles

i. incomplete dominance – the alleles blend the trait – F1 generation is pink

[pic]

ii. codominance - both alleles are expressed as in the roan horse or blood typing

[pic][pic]

iii. epistasis – one allele is dominant over another – normal dihybrid cross different phenotypic ratio

[pic]

c. gene maps & linkage

Gene linkage is when the two different genes are located on the same arm of the chromosome. We can use this to determine the relative proximity of those genes to each other and map where the genes are based on the number of times crossing over occurs.

Map distances: One linkage map unit (LMU) is 1% recombination. Thus, the linkage map distance between two genes is the percentage recombination between those genes.

In this case, we have a total of 60 recombinant offspring, out of 1000 total offspring. Map distance is calculated as (# Recombinants)/(Total offspring) X 100. So our map distance is (60/1000)x100, or 6 LMU.

V. Protein Synthesis

a. Transcription

[pic]

b. spicing

During splicing the introns (green) are deleted and the exons are kept. Eukaryotes can rearrange these exons to create new proteins.

c. Translation

Diagram moves from right to left creating the primary protein structure or amino acid chain

VI. Gene Regulation

a. Operons

The lac operon is inducible by using lactose as the allosteric repressor to inactivate the repressor allowing polymerase to go through transcription

The tryp operon is a repressible operon. It is normally on and activation of the repressor will prevent transcription.

b. transcription factors

[pic]

c. cytoplasmic determinants

Cytoplasmic determinants in the egg. Maternal cytoplasmic determinants play a vital role in early development. These substances regulate expression of genes that affect the cell’s developmental fate.

d. Hox genes

Hox genes are master regulatory genes that control spatial organization by turning on/off other genes for the fate map or body plan

e. Epigenetic effects (individually called epigenetic markers) are reversible, heritable changes to the way the body interprets and expresses its genetic code (DNA). Epigenetic effects occur without changing the DNA sequence (i.e., without changing genotype).

Methylation-DNA methylation occurs when a methyl group becomes fixed to a particular segment of DNA. The presence of the methyl group changes the way the body reads the particular DNA sequence. Usually, methylation in a particular section of DNA effectively “turns off” that gene, leading to lower gene expression.

Acetylation - Acetylation of the lysine residues at the N terminus of histone proteins removes positive charges, thereby reducing the affinity between histones and DNA.  This makes RNA polymerase and transcription factors easier to access the promoter region.  Therefore, in most cases, histone acetylation enhances transcription while histone deacetylation represses transcription.

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