Molecules Of Genetic Inheritance

MOLECULES OF GENETIC INHERITANCE

GENETIC MATERIAL: The material in living beings that is responsible for the inheritance of characteristics is called genetic material. The molecule of genetic inheritance must possess four major characteristics: •Replication •Storage of information •Expression of information •Variation by mutation

•Pre-Mendelian ideas on heredity 1859 Charles Darwin Published The Origin of Species.

•1865 Mendelian Inheritance •Classical genetics 1900 Hugo de Vries, Carl Correns and Erich von Tschermak 1903 Chromosomes are discovered to be hereditary units 1905 British biologist William Bateson coins the term "genetics" 1908 Hardy-Weinberg law derived. 1910 Thomas Hunt Morgan shows that genes reside on chromosomes 1913 Alfred Sturtevant makes the first genetic map of a chromosome 1913 Gene maps show chromosomes containing linear arranged genes 1927 Physical changes in genes are called mutations 1928 Frederick Griffith transformation experiment 1931 Crossing over is the cause of recombination 1941 Edward Lawrie Tatum and George Wells Beadle show that genes code for proteins.

Mutation and adaptation: Jean-Baptiste Lamarck (1744-1829) •

Proposed “inheritance of acquired traits” ~1801; induction by the environment; also known as transformism or transmutation.

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Ideas largely ignored or attacked during his lifetime.

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Never won the acceptance and esteem of his colleagues and died in poverty and obscurity.

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Today Lamarck is associated with a discredited theory of heredity (but Lamarckism persisted until 1930s/1940s).

Charles Darwin (1809-1882) •

Heritable adaptive variation results from random mutation and natural selection (1859, The Origin of Species).

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Contrary to Larmarck, inheritance of adaptive traits does not result from induction by environmental influences.

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But differential survival (selection) and heritable variation (originally arising from mutation).

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Years following Darwin and rediscovery of Mendel resulted in controversy (until 1930s/1940s) about the relative importance of mutation and selection.

Experimental test of Lamarck’s “inheritance of acquired traits” Salvador Luria and Max Delbrück (1943) •

An E. coli population started from one cell should show different patterns of T1 resistance depending on which theory is correct.

1. Adaptive theory states that cells are induced to become resistant when T1 is added; proportion of resistant cells should be the same for all cultures with the same genetic background. 2. Mutation theory states that random events confer resistance to T1; duplicate cultures with the same genetic background should show different numbers of T1 resistant cells.

Fig. Fluctuating populations of E. coli infected with T1 phage. Luria and Delbrück (1943) Adaptive theory prediction: proportions or resistant cells are the same

Mutation theory prediction: proportions are function of genotypes

Gregor Mendel

• Formulated basic laws of heredity during mid 1800’s • Austrian Botanist and monk • Experimented with peas

Mendel • Studied inheritance of seven pairs of traits • Bred and crossbred thousands of plants • Determined that some traits were dominant and other recessive

Mendel • Findings were published in 1866 • Largely ignored for 34 years

Johan Friedrich Miescher • Swiss Biologist • Isolated nuclei of white blood cells in 1869 • Led to identification of nucleic acid by Walter Flemming

Walter Sutton • Determined in 1903 that chromosomes carried units of heredity identified by Mendel • Named “genes” in 1909 by Wilhelm Johannsen, Danish Botanist

Thomas Hunt Morgan • Studied genetics of fruit flies • Early 1900’s • Experimented with eye color • His work contributed to the knowledge of X and Y chromosomes

Thomas Hunt Morgan • Nobel Peace Prize in 1933 for research in gene theory

Griffith's Transformation Experimen(1928)

Avery, MacLeod and McCarty Experiment (1944)

Fraenkel-Conrat and Singer (1956)

•The DNA era 1944 Oswald Theodore Avery, Colin McLeod and Maclyn McCarty prove DNA as the genetic material 1950 Erwin Chargaff 1950 Barbara McClintock discovers transposons in maize 1952 Hershey-Chase prove the genetic material of phages to be DNA 1953 James D. Watson and Francis Crick DNA structure is a double helix 1958 Meselson-Stahl demonstrate that DNA is semiconservatively replicated 1961The genetic code is arranged in triplets 1970 Howard Temin showed using RNA viruses that Watson's central dogma is not always true 1970 Restriction enzymes discovered

•The genomics era 1977 Fred Sanger, Walter Gilbert, and Allan Maxam sequenced DNA 1985 Kary Banks Mullis discovers the polymerase chain reaction 1989 Francis Collins and Lap-Chee Tsui, sequence the first human gene encoding the CFTR protein, defects in this gene cause cystic fibrosis 1995 The genome of of a free living organism Haemophilus influenzae sequenced 1996 Saccharomyces cerevisiae is the first eukaryote genome sequence to be released 1998 The first genome sequnce for a multicellular eukaryote, C. elegans is released 2001 First draft sequences of the human genome are released simultaneously by the Human Genome Project and Celera Genomics. 2003 (14 April) Successful completion of Human Genome Project with 99% of the genome sequenced to a 99.99% accuracy

Erwin Chargaff (1950) Erwin Chargaff was a biochemist who first figured out the equation for the different bases. He concluded that: •

The amount of adenine (A) will always equal the amount of thymine (T).

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The amount of guanine (G) will always equal the amount of cytosine (C).

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The sum of the purines (A+G) equals the sum of pyrimidines (C+T).

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The ratio [C+G] / [A+T] was typically less than unity (that is, [C+G] is less abundant).

Franklin's X-Ray Crystallography Experiments (1950s)

The X-Ray photograph shows the diffraction pattern of a crystallized DNA molecule. The cross pattern in the middle is characteristic of a helical molecule with regular repeats; the broad bands at top and bottom give some indication of the periodicity.

James Watson and Francis Crick (1953)

There are three main kinds of ribonucleic acid, each of which has a specific job to do. •Ribosomal •Messenger •Transfer •RNA is used as the genetic material in some viruses e.g.Human • Immunodeficiency Virus (HIV) •dsRNA is also involved in some cellular processes, such as RNA • interference •Some RNAs are known with catalytic activity and are called ribozymes •Certain RNAs are associated with specific proteins to form ribonucleoproteins that participate in post-transcriptional processing of other RNAs.

Baltimore(1971) classification of Viruses Class Nucleic acid

Replication

Example

Semiconservative

T4,adeno and herpes viruses

I

Duplex DNA

II

Single-stranded Via duplex replicative ΦX, minute virus of DNA(+) form mouse(MVM)

III

Duplex RNA

Via (+) strand RNA intermediate

Reovirus

IV

+ strand RNA

Via(-)strand RNA intermediate

MS2,polio,foot and mouse disease virus

V

(-) strand RNA Via(+)strand RNA intermediate

Measeles, flu and rabies viruses

VI

+ strand RNA

Leukemia virus, HIV

Via DNA duplex

The 1970 version of the Central Dogma.

What Drives Evolution? There are 5 forces of change.

Only natural selection makes a population better adapted (more fit) to its environment.

Microevolution

Microevolution considers mechanisms that cause generation-to-generation changes in allele frequency within populations. Changes in allele frequency within populations drive evolution.

Gene Flow or Migration

Populations Are the Units of Evolution

The Genetic Basis of Evolution

For evolution to occur, genetic differences must at least partially account for phenotypic differences.

Mutations “Just Happen”

Mutations occur at random without regard to whether they have a beneficial, neutral or harmful effect. For this reason, mutations are a randomly acting evolutionary force.

Endangered Species Are in the Narrow Portion of a Genetic Bottleneck and Have Reduced Genetic Variation

A Galapagos Finch, the Subject of a Classic Study of Evolution in Action

Peter and Mary Grant and their colleagues observed how beak depth, a significant trait for feeding success, varied in populations experiencing climactic variations.