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Genetics

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Chris Maltby

on 9 January 2012

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Transcript of Genetics

Heredity
(cc) photo by Metro Centric on Flickr
(cc) photo by Franco Folini on Flickr
(cc) photo by jimmyharris on Flickr
(cc) photo by Metro Centric on Flickr
Genetics
-- the field of biology dedicated to understanding how characteristics are transmitted from parents to offspring.
Gregor Mendel
The Godfather of Genetics
Austrian Monk (1842)
Studied Math, Science, and Statistics
Crossed Pea Plants
Mendel's Discoveries
Seven

Characteristics
of pea plants existing in contrasting
Traits
Plant height
--
long or short stem
Flower position
--
axial or terminal
Pod Color
--
green or yellow
Pod Appearance
--
inflated or constricted
Seed Texture
--
smooth or wrinkled
Seed Color
--
yellow or green
Flower Color
--
purple or white
Mendel's Experiment
Used
Pure
plants -- plants that always produced the same trait when self-pollinated.
P1 generation
-- the first cross (Pure x Pure)
P1 (Green) x P1 (Yellow) --
F1 generation
F2 genertion

-- Self pollinated F1 generation
Mendel's Contributions to Genetics
Dominant
-- some traits are dominant over others.
Recessive
-- some traits are masked by dominant traits.
Law of Segregation
-- A pair of factors (traits) are segregated (separated into single factors) to offspring with the same probability.
Law of Independent Assortment
-- Factors (traits) are distributed to gametes independently.
Allele
-- Traits or factors. Opposite forms of a gene.
More Cowbell (Heredity)
Probability -
The likelihood a specific event will occur. 3/4 3:4 0.75 75%
Genotypic Ratio -
The ratio of genotypes that statistically CAN appear in offspring.
Phenotypic Ratio -
The ratio of phenotypes that statistically CAN appear in offspring.
Test Cross -
A cross used to determine genotype. a KNOWN HETEROZYGOUS is crossed with an unknown.
B=Black
b= Brown
B
b
?
?
Bb
bb
bb
Bb
B
b
Bb
Bb
Bb
BB
BB
?
?
BB
?
?
B
b
Bb
bb
Phenotype - The physical expression of genes (Brown).
Genotype - The genetic make up of an organism (Bb).
Heredity: the saga continues
Monohybrid cross -- crossing on characteristic (e.g. Flower Position).
Dihybrid cross -- crossing two characteristics
***Both are types of punnett squares****
Gametes -- Reproductive cells
Expressed as single letters in a punnett square.
The Dihybrid Cross
Nucleic Acids & Protein Synthesis
DNA
Deoxyribonucleic acid
Nucleotide
- repeating subunits of DNA.
Sugar
+
phosphate-group
+
nitrogen-containing-base
= ONE NUCLEOTIDE.
Four Nitrogen containing bases
- Adenine, Guanine, Cytosine, Thymine.
More on DNA . . .
Purines -
Adenine & Guanine (two rings of carbon)
Pyrimidines -
Cytosine & Thymine (one ring of carbon)
The Double Helix -
Model proposed by Watson and Crick (1953).
Franklin and Wilkins provided X-ray
proof.
1962 -- Franklin, Wilkins, Watson, & Crick won the Noble Prize in Medicine for their DNA work.
The Double Helix
Nucleotides
are

connected by
covalent bonds
at the outside of the model.
Alternating Deoxyribose (sugar) and Phosphate form the "backbone" of the helix (via covalent bonds).
Nitrogen-containing bases are connected with
hydrogen bonds.
Complimentary Base Pairing
(Nucleotides only pair a certain way)
Base Pairing Rules:
Cystosine - Guanine (3 bonds)
Adenine - Thymine (2 bonds)
Replication of DNA
The process of copying DNA in a cell
Replication Fork
The point at which the two nucleotide chains separate.
Helicases
The enzymes that unzip the base hydrogen bonds.
DNA Polymerase
Enzymes that bind to the separated chains.
Construct more DNA using sugars, phosphates and complimentary base pairs.
Mutations
Errors in DNA assembly.
Proof reading enzymes & repair enzymes exists.
Error rate: 1 in every 10,000 paired nucleotides.
RNA
RNA -- provides the information to make proteins.
RNA Structure
Just like DNA but Ribose is the sugar.
Single stranded not double.
Has nucleotides (phosphate, sugar, NCB).
There is no Thymine - Uracil instead.
Three Types of RNA (m+t+r=proteins)
Messenger RNA (mRNA) -
Single uncoiled chain. Carries info from the Nucleus to cytosol.
Transfer RNA (tRNA) -
Single chain of 80 nucleotides. Folded hair pin shape. Binds to specific amino acids (parts for proteins).
Ribosomal RNA (rRNA) -
RNA in globular form (ribosomes). The site of protein synthesis.
mRNA
tRNA
rRNA
Transcription:
RNA creation
RNA Polymerase
The primary transcription enzyme (synthesizes RNA)
Promoters
Marks the start point on the DNA template for transcription (RNA synthesis) to begin.
Termination Signal
The nucleotide that stops transcription.
Products of Transcription
mRNA, rRNA, tRNA
Copies of messages in genes
Protein Synthesis
- occurs when an mRNA trascript is translated into a sequence of amino acids.
Translation - The process of the three RNA types assembling proteins (polypeptides).
Start Codon (AUG) - The codon that signals a ribosome (rRNA) to begin translation.
Codon - Three mRNA nucleotides.
Stop Codon - The three mRNA sequence that signals a ribosome to stop translation (UAA, UAG, UGA).
Anticodon - found on tRNA and is complementary to the mRNA codon. It assures tRNA brings the correct amino acid.

Homozygous - BB, bb - same alleles
Heterozygous - Bb - different alleles.
Incomplete Dominance - When a heterozygous offspring leads to an intermediate.

Co-Dominance - when a heterozygous offspring leads to the expression of both traits in the phenotype.
Full transcript