1. Genetics

2. Outline
Structure of DNA
DNA Functions
Transcription
Translation
Mutation
Cytogenetics
Mendelian Genetics
Quantitative Traits
Linkage

3. Structure of DNA
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.

4. Structure of DNA
Four types of DNA nucleotides:
Purines
Adenine (A) and Guanine (G)
Pyrimidines
Cytosine (C) and Thymine (T)

6. Fig. 13.3

7. DNA Functions
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.

8. DNA Functions
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.

9. DNA Replication

10. DNA Functions
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.

11. Transcription
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.

12. Transcription
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.

13. Translation
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.

14. Fig. 13.5

15. Fig. 13.6

16. Fig. 13.6a

17. Fig. 13.6b-1

18. Fig. 13.6b-2

19. Fig. 13.6b-3

20. Fig. 13.6b-4

21. Fig. 13.6c

22. Central Dogma of Molecular Dogma

23. Mutation
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.

24. Cytogenetics
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.

25. Cytogenetics
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.

26. Mendelian Genetics
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)

27. Mendelian Genetics
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).

28. Mendelian Genetics
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.

29. Monohybrid Cross
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.

30. Fig

31. Fig

32. Dihybrid Cross
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.

33. Fig

34. Mendelian Genetics
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.

35. Fig

36. Quantitative Traits
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.

37. Extranuclear DNA
Entranuclear DNA is found in both mitochondria and chloroplasts.
Endosymbiont Hypothesis theorized mitochondria and chloroplasts were free-living, and at some point became incorporated into cells of organisms that evolved into plants and established a symbiotic relationship.

38. Linkage and Mapping
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.

39. Hardy-Weinberg Law
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.

40. Review
Structure of DNA
DNA Functions
Transcription
Translation
Mutation
Cytogenetics
Mendelian Genetics
Quantitative Traits
Linkage

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