Bio Study Guide Essay

Vivian So

1) Mendelian Genetics
a) Difference between monohybrid and dihybrid crosses, and using a punnett square or mathematically.
Monohybrid - A genetic cross made to examine the distribution of one specific set of alleles in the resulting offspring
Example: tall peas x short peas or TT x tt
Dihybrid - Hybridization using two traits with two alleles each.
Example: tall peas with round seeds x short peas with wrinkled seeds or TTRR x ttrr
Math-
Monohybrid- just do punnett square normally
Dihydrid – do the punnett square for the similar ones(ex. SSxss) first between the 2 people. Then multiply the 2 non similar ones (ex. SSxNN) together in a 4by4.
b) understand pedigree chart
-square = male, circle = female
-shaded in = affected, not shaded in = not affected
-half shaded in = carrying the trait
-diagonal line crossing = decease
c) Heterozygous: Presence of two alleles of dissimilar characters on a homologous chromosome. (ex: Aa or Bb)
Homozygous: Presence of two alleles of similar characters on a homologous chromosome. (ex: AA or aa)
Carrier: if someone has a disease/gene characteristic in their genes but it is unexpressed, they are a carrier.
Dominant: An allele or a gene that is expressed in an organism’s phenotype, masking the effect of the recessive allele or gene when present.
Recessive: Of, or pertaining to, a gene (or allele) whose phenotypic expression is masked by a dominant gene.
Co-dominance: a condition in which both alleles of a gene pair are fully expressed, with neither being dominant or recessive to the other.
Incomplete dominance: Incomplete dominance is a biology term referring to the results of a pairing. When a allele is dominant, it is expected for a larger ratio of the offspring to have that trait. In incomplete dominance, the offspring will have a mix of the dominant and non-dominant trait(ex: white and red flower makes a pink flower).
X-linked: the trait is found only on the x chromosome.
Phenotype: what you see when you look at someone.
Genotype: is actual chemical DNA.
2) DNA replication
a) enzymes required for replication
Helicase – unwinds the DNA
Polymerase- adds nucleotides to the 3 prime end.
DNA Ligase – goes along to connect the strands and RNA that are separated.

b) Semiconservative replication would produce two copies that each contained one of the original strands and one new strand
c) The Leading Strand - continuous, no complications
Since DNA replication moves along the parent strand in the 5' to 3' direction, replication can occur very easily on the leading strand. RNA primase adds the first nucleotide to the newly forming chain, the DNA polymerase simply sits near the replication fork, moving as the fork does, adding nucleotides one after the other in continuous replication fashion..
The Lagging Strand - discontinuous
The lagging strand replicates in small segments, called Okazaki fragments. These fragments are then stitched together by DNA ligase, creating a continuous strand. This type of replication is called discontinuous
d)5’ to 3’ end
3) Gene Expression
a) What Gene Expression Means
Conversion of the information encoded in a gene first into messenger RNA and then to a protein.
b)Central Dogma describes the flow of genetic information within a biological system.(dna->rna->protein).
c) The same genes are in every cell of the body but what differentiates one cell from another is which genes are “turned on” and which are “turned off”.
d) Transcription is a process which occurs during DNA synthesis, it is when the DNA helix is unwound and one of the strands read and copied by RNA, transcription is when the amino acid bases are copied onto this RNA strand. Occurs in the nucleus.
-initiation is when the rna polymerase goes on the dna.
-In elongation it melts and unwinds it, travelling down the dna then it the rna polymerase goes off and u have rna in eukaryotic cells, the transcription of DNA occurs within the nucleus of the cell.

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