1. Genetics – a name for a phenomenon recognized for millenia
Humans have been aware of genetics, via selective breeding, for over 10,000 years (plants and domestic animals)
Exploration and understanding of the principles of heredity is a more recent development 1

2. Mendelian (Transmission) Genetics
An amateur botanist named Gregor Mendel published an explanation of hereditary transmission in plants in 1866
No longer content to “observe” transmission of traits from one generation to the next, Mendel devised experiments to determine what the unit of inheritance might be 2

3. Early Genetic Concepts (Mendel)
Phenotype: the observable traits of an organism (e.g. flower color; petal shape, etc)
Genotype: the genetic constitution of an organism
Alleles: alternative (variant) forms of a gene (e.g. flower petal color can come in various forms: white vs purple vs…) 3

4. Genes and Chromosomes
Genes are the physical units of heredity, as originally posited by Mendel; now known to be defined DNA sequences
Chromosomes are long molecules of double-stranded DNA and protein, which contain genes 4

5. Modern Genetics Has Three Major Branches
Transmission genetics (Mendelian genetics) is the study of the transmission of traits in successive generations
Molecular genetics goes to the molecular level to understand the structure and function of genes (nucleic acids: DNA and RNA; proteins)
Evolutionary genetics studies the origins of and genetic relationships between organisms, and evolution of genes and genomes.
Three branches are interdependent and overlapping: Evolutionary relationships between genes, for example, can provide insight into the functional importance of particular regions of the protein they encode. 5

6. DNA Is the Hereditary Material
Avery, MacLeod, and McCarty identified deoxyribonucleic acid (DNA) as the hereditary material (The Rockefeller University – NYC, 1944)
This inaugurated the “molecular era” of the field of genetics, in the second half of the 20th century 6

7. Frederick Griffith, 1928 7

8. Avery,
McCarty,
McCleod
1944 8

9. DNA is the genetic material for all living organisms.
Genes and Chromosomes
DNA is the genetic material for all living organisms.
All living organisms have genes and chromosomes, but the chromosomes are slightly different in structure (although all are composed of DNA!), are found in different numbers and in different places, depending on the type of organism 9

10. Genetics – Central to Modern Biology
All life on Earth shares a common origin, or progenote (DNA is the common denominator)
The three domains of life:
Eukarya (true nucleus, multiple chromosomes)
Bacteria (no true nucleus, single chromosomes)
Archaea (no true nucleus, single chromosomes) 10

11. Three
Domains
Of Life
Last universal
Common ancestor
LUCA 11

12. Mitochondria and Chloroplasts (evidence of bacterial invasion of eukarya)
Plant and animal cells contain mitochondria
Plant cells contain chloroplasts
These organelles contain their own DNA on single circular chromosomes and are derived from bacterial invasion of these eukarya in the evolutionary past 12

13. The DNA Double Helix
Watson and Crick published the structure of DNA in 1953
The structure was described as a double helix with sugar phosphate backbones on the outsides and nucleotide bases arrayed in complementary pairs toward the center
Other researchers made significant contributions to understanding DNA structure 13

14. DNA Nucleotides DNA nucleotides are composed of 3 parts: Adenine (A)
a) a deoxyribose (5-carbon) sugar
b) a phosphate group, and
c) one of four nitrogenous bases designated:
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C) 14 14

15. Why is the phosphate group called the “5’ phosphate”?
Why are these called “deoxyribo” nucleotides?
Why is the hydroxyl (OH) group called the “3’ OH”? 15

16. Nucleotides are linked together by a phosphodiester bond between the 3’ hydroxyl group of one nucleotide and the 5 phosphate of another.

17. Sugar-phosphate “backbone”17

18. What suggested a “double helix”?18

19. X-ray crystallography; Rosalind Franklin in lab of Maurice Wilkins
(helix = spiral staircase vs straight ladder) 19

20. What suggested the helices were aligned through “base-pairing”?
A with T; G with C 20

21. Chargaff’s “rule” was…?: what was notable, G+C or G/C? Why?
What do you expect is the value of A/T? Why? What about A/G? 21

22. Complementary Base Pairing
Complementary base pairing occurs between an A on one strand and a T on the other, or a G on one strand and a C on the other
Hydrogen bonds form between the complementary base pairs. Question: is this the same kind of bond that joins phosphate and hydroxyl in the “sugar backbone” of the DNA molecule?
The 5 and 3 designations of the phosphate and hydroxyl at the ends of the DNA strands establish polarity; the two strands are antiparallel. What is meant by antiparallel and why must the strands BE antiparallel? 22 22

23. Focus on hydrogen bonding of bases…
And orientation of sugars in two strands… 23

24. 24

25. If you have one of the strands (e.g. strand 1) you can predict
the sequence of nucleotides in the other (e.g. strand 2) 25

26. Three common models of DNA replication after DNA structure was solved
Notice that if you were able to distinguish “hybrids” of new/old vs “parental” – you can only distinguish “conservative” from the other two models in First Cycle. Now look at Second cycle – how distinguish Semi-conserv from dispersive replication?
Three common models of DNA replication after DNA structure was solved 26

27. DNA isolated from E. coli in each flask
Each DNA sample mixed with CsCl solution
Put into centrifuge tube
Spun at high speed to allow CsCl solution to form a gradient
double-stranded DNA molecules separate, based on how much
14N and 15N in them
Meselson-Stahl expt. 1958 27

28. E. coli grown in 15N E. coli grown in 14N mix DNA (15N) DNA (14N) spin28

30. t0 first cycle second cycle third cycle
Blue = heavy = 15N
Red = light = 14N
Blue is heavy, red is light
t first cycle second cycle third cycle 30

31. Three Attributes of DNA Replication Shared by All Organisms
Each strand of the parental DNA molecule remains intact during replication
Each parental strand serves as a template for formation of an antiparallel, complementary daughter strand
Completion of replication results in the formation of two identical daughter duplexes composed of one parental and one daughter strand 31