Pertemuan 2. history of genetics Bu Rani Wulandari

台大農藝系遺傳學 601 20000 Chapter 1 slide 1

CHAPTER 1

History of Genetics

• Biji bulat warna kuning x Biji kerut warna hijau

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F1 AaBb

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aaB- : kerut kuning = 3

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History of Genetics

• People have known about inheritance for a long time.

• --children resemble their parents

• --domestication of animals and plants,

• --selective breeding for good characteristics

• --Sumerian horse breeding records

• --Egyptian data palm breeding

• --Hemophilia

Old Ideas

• Despite knowing about inheritance in general, a number of incorrect ideas had to be generated and overcome before modern genetics could arise.

• 1. All life comes from other life. Living organisms are not spontaneously generated from non-living material. Big exception: origin of life.

• 2. Species concept: offspring arise only when two members of the same species mate. Monstrous hybrids don’t exist.

More Old Ideas

• 3. Organisms develop by expressing information

carried in their hereditary material. As opposed to

“preformation”, the idea that in each sperm (or

egg) is a tiny, fully-formed human that merely

grows in size.

• 4. The environment can’t alter the hereditary

material in a directed fashion. There is no

“inheritance of acquired characteristics”.

Mutations are random events.

More Old Ideas

5. Male and female parents contribute equally to the

offspring.

• --ancient Greek idea: male plants a “seed” in the

female “garden”.

• --alleged New Guinea belief: sex is not related to

reproduction.

Mid 1800’s Discoveries Three major events in the mid-1800’s led directly to

the development of modern genetics.

1859 Charles Darwin publishes The Origin of

Species, which describes the theory of evolution

by natural selection. This theory requires

heredity to work.

1866 Gregor Mendel publishes Experiments in Plant

Hybridization, which lays out the basic theory of

genetics. It is widely ignored until 1900.

1871 Friedrich Miescher isolates “nucleic acid” from

pus cells.

Major Events in the 20th Century

1900 rediscovery of Mendel’s work by Robert Correns, Hugo de Vries,

and Erich von Tschermak .

1902 Archibald Garrod discovers that alkaptonuria, a human disease,

has a genetic basis.

1904 Gregory Bateson discovers linkage between genes. Also coins

the word “genetics”.

1910 Thomas Hunt Morgan proves that genes are located on the

chromosomes (using Drosophila).

1918 R. A. Fisher begins the study of quantitative genetics by

partitioning phenotypic variance into a genetic and an

environmental component.

More 20th Century Events

1926 Hermann J. Muller shows that X-rays induce mutations.

1944 Oswald Avery, Colin MacLeod and Maclyn McCarty show that

DNA can transform bacteria, demonstrating that DNA is the

hereditary material.

1953 James Watson and Francis Crick determine the structure of the

DNA molecule, which leads directly to knowledge of how it

replicates

1966 Marshall Nirenberg solves the genetic code, showing that 3 DNA

bases code for one amino acid.

1972 Stanley Cohen and Herbert Boyer combine DNA from two different

species in vitro, then transform it into bacterial cells: first DNA

cloning.

2001 Sequence of the entire human genome is announced.

Classical and Modern Genetics

1. Humans have long understood that offspring tend to

resemble parents,

2. and have selectively bred animals and plants for many

centuries.

3. The principles of heredity were first explained by

Mendel in the mid nineteenth century, using defined

crosses of pea plants.


2. In the last century, genetics has become an important biological tool, using mutants to gain an understanding of specific processes. This work has included: a. Analyzing heredity in populations.

b. Analyzing evolutionary processes.

c. Identifying genes that control steps in processes.

d. Mapping genes.

e. Determining products of genes.

f. Analyzing molecular features of genes and regulation of gene expression.


3. Recent important milestones in genetics include:

a. Berg’s construction (1972) of the first recombinant DNA

molecule in vitro.

b. Boyer and Cohen’s first cloning (1973) of a recombinant

DNA molecule.

c. Invention by Mullis (1986) of the polymerase chain reaction

(PCR) to amplify specific DNA sequences


4. Completion of genomic sequencing for an increasing

number of organisms has spawned the new field of

genomics. Knowledge of individual genes and their

regulation will be important to basic biological

research, as well as to specific applications such as

medical genetics.

5. Powerful new techniques in genetics raise important

ethical, legal and social issues that will need

thoughtful solutions.

DNA, Genes and Chromosomes

1. Genetic material of both eukaryotes and prokaryotes

is DNA (deoxyribonucleic acid). Many viruses also

have DNA

2. DNA has two chains, each made of nucleotides

composed of a deoxyribose sugar, a phosphate

group and a base. The chains form a double helix

Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.


3. There are four bases in DNA: A (adenine), G

(guanine), C (cytosine) and T (thymine).

a. In RNA, U (uracil) replaces T.

b. The sequence of bases determines the genetic information.

c. Genes are specific sequences of nucleotides that pass traits from

parents to offspring.


4. Genetic material in cells is organized into chromosomes (literally “colored body” because it stains with biological dyes). a. Prokaryotes generally have one circular chromosome.

b. Eukaryotes generally have:

i. Linear chromosomes in their nuclei, with different species having different numbers of chromosomes.

ii. DNA in organelles (e.g., mitochondria and chloroplasts) that is usually a circular molecule.

Eukaryotic and Prokaryotic Chromosome

Eucaryote

Eucaryote

Eucaryote

Cell Cycle (1) The cycle of cell growth, replication of the genetic material, nuclear and

cytoplasmic division.

1. Mitosis (nuclear division)

: corresponding to the separation of

daughter chromosomes and usually

ending with cell division. The events

in this stage of the cell cycle leading

to cell division are prophase,

metaphase, anaphase and telophase.

2. Interphase

: is the time during which both cell

growth and DNA replication occur

in an orderly manner in preparation

for cell division.

Eukaryotic Cell Cycles

The eukaryotic cell cycle is divided into 4 major periods:

1. M phase (mitotic phase or mitosis) is the period when cells prepare for and

then undergo cytokinesis. During mitosis the chromosomes are paired and

then divided prior to cell division.

2. G1phase corresponds to the gap in the cell cycle that occurs following

cytokinesis. During G1 cells begin synthesizing all the cellular components

needed in order to generate two identically complimented daughter cells. As a

result the size of cells begins to increase during G1.

3. S phase is the phase of the cell cycle during which the DNA is replicated. This

is the DNA synthesis phase.

4. G2 phase is reached following completion of DNA replication.

The high variability of cell cycle times is due to the variability of the G1

phase of the cycle.

Cell Cycle (2) The ultimate conclusion of one cell cycle is cytokinesis

resulting in two identical daughter cells.

Mitosis

Replikasi DNA

DNA Replication

(M.S. Meselson and F.W. Stahl, 1957)