Transcript Understanding Our Environment

Genetics
Chapter 13
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Required for Reproduction or Display
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Outline
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Structure of DNA
DNA Functions
Transcription
Translation
Mutation
Cytogenetics
Mendelian Genetics
Quantitative Traits
Linkage
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Structure of DNA
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DNA molecule organized into chain of
nucleotides composed of three parts:
 Nitrogenous Base
 5-Carbon Sugar (Deoxyribose)
 Phosphate Group
Nucleotides bonded to each other forming a
helix.
 Hydrogen bonds hold each base on one
side of the helix to another base on the
other side.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Structure of DNA
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Four types of DNA nucleotides:
 Purines
- Adenine (A) and Guanine (G)
 Pyrimidines
- Cytosine (C) and Thymine (T)
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
DNA Functions
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Storage of Genetic Information
 Gene - Segment of DNA that directs
protein synthesis.
- Protein may act as an enzyme
influencing cell activities.
 Genome - Sum total of DNA in an
organism’s chromosomes.
- Codon - Groups of three nucleotides.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
DNA Functions
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Replication of Information
 Occurs during S phase of cell cycle.
- Strands of double helix unzip allowing
DNA polymerase to pair individual
nucleotides with the template strands.
 Semi-Conservative Replication
 Occurs simultaneously in both
directions, and begins at several
points simultaneously.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
DNA Replication
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DNA Functions
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Expression of Information
 Different subset of the genetic information
is read in each cell type.
 Expression requires two processes.
- Transcription - Copy of gene message
using RNA.
- Translation
 Messenger RNA (mRNA) translated to
produce proteins.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Transcription
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Three different types of RNA produced:
 Messenger RNA (mRNA)
 Transfer RNA (tRNA)
 Ribosomal RNA (rRNA)
RNA Synthesis
 Nucleotides added to single stranded DNA
molecule by RNA polymerase.
- Only portions of the genome replicated.
 Remainder is noncoding DNA.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Transcription
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Promoter Region signals transcription
enzymes to attach to the DNA.
 Single-stranded RNA transcript produced.
Chromosomes contain genes for building
tRNA.
 Each form of tRNA has a specific
anticodon loop.
- Base pairs with codon.
Genes for rRNA also transcribed in the
nucleus - Used to construct ribosomes.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Translation
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mRNA transcripts are decoded into proteins.
 Genetic code based on codons.
- 64 possible combinations
 Code for 20 amino acids.
tRNA acts as a translator.
 Anticodon binds to mRNA codon.
Start of translation signaled by a ribosome in
the cytoplasm binding to the mRNA.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Central Dogma of Molecular Dogma
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Mutation
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Mutations - Changes in DNA sequence.
 Mutagens - Agents that alter DNA.
- Ultraviolet light
- Ionizing radiation
 Somatic Mutation - Occurs in body cell.
 Germ-Line Mutation - Occurs in tissues that
will produce sex cells.
- Passed on to future generations.
All genetic variability due to mutations.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Cytogenetics
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Cytogenetics is the study of chromosome
behavior and structure, from a genetic point
of view.
Changes in Chromosome Structure
 Inversion - Chromosomal piece is broken
and reinserted in the opposite orientation.
 Translocation - Chromosomal piece breaks
off and attaches to another chromosome.
- Important in speciation.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Cytogenetics
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Changes in Chromosome Number
 Mistakes during chromosome pairing and
separation can result in gametes carrying
extra or missing chromosomes.
- Aneuploid - Carries, or is missing, an
extra chromosome(s).
- Polyploid - Has at least one complete
extra set of chromosomes.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Mendelian Genetics
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Mendel crossed self-pollinated pea plants
and recorded his observations.
 Crossed a tall plant with a short plant.
 Parental Generation (P)
- All offspring were tall.
- First Filial Generation (F1)
 Cross offspring yielded a ratio of three
tall individuals to one short individual.
 Second Filial Generation (F2)
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Mendelian Genetics
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Law of Unit Characters
 Factors (Alleles), which always occur in
pairs, control the inheritance of various
characteristics.
- Genes are always at the same position
(locus) on homologous chromosomes.
Law of Dominance
 For any given pair of alleles, one
(dominant) may mask the expression of
the other (recessive).
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Mendelian Genetics
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Phenotype refers to an organism’s physical
appearance.
Genotype refers to the genetic information
responsible for contributing to the phenotype.
 Homozygous - Both alleles identical.
 Heterozygous - Alleles are contrasting.
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Monohybrid Cross
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A cross is made between two true-breeding
parents differing for a single trait, producing
an F1 generation.
 These plants are intercrossed to produce
an F2 generation.
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Dihybrid Cross
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Cross made for parents differing in two traits.
 Mendel’s Law of Independent Assortment
- Factors (genes) controlling two or more
traits segregate independently of each
other.
 Linked genes do not segregate
independently.
- Punnett Square used to determine
genotypes of the zygotes.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Mendelian Genetics
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Backcross
 A cross between a hybrid and one of its
parents.
- Can be used to test inheritance theory.
Incomplete Dominance
 Some genes exhibit traits in which a
heterozygote is intermediate in phenotype
to the two homozygotes.
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Quantitative Traits
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Quantitative traits exhibit a range of
phenotypes rather than discrete phenotypes
studied by Mendel.
 Molecular geneticists are able to identify
chromosomal fragments, quantitative trait
loci, associated with quantitative traits.
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Extranuclear DNA
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Entranuclear DNA is found in both
mitochondria and chloroplasts.
 Endosymbiont Hypothesis theorized
mitochondria and chloroplasts were freeliving, and at some point became
incorporated into cells of organisms that
evolved into plants and established a
symbiotic relationship.
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Linkage and Mapping
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Genes that are together on a chromosome
are said to be linked.
 Each gene has a specific location (locus)
on a chromosome.
- Crossing-over should be more likely
between two genes located far apart on
a chromosome that between two genes
located closer together.
 Crossing over frequency can be used
to construct a genetic map.
 1 map unit = 1% crossing over.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Hardy-Weinberg Law
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Hardy-Weinberg states the proportions of
dominant alleles to recessive alleles in a
normally interbreeding population will remain
the same from generation to generation in
the absence of external forces.
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Review
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Structure of DNA
DNA Functions
Transcription
Translation
Mutation
Cytogenetics
Mendelian Genetics
Quantitative Traits
Linkage
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display
Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies