The Evolving Helix

Part 2 of 2Year 10 Science

Mr Isgro

Charles Darwin

• Darwin's theory of evolution explains how species of living things have changed over geological time.

• The theory is supported by evidence from fossils, and by the rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria.

Charles Darwin

• Charles Darwin was an English naturalist. He studied variation in plants and animals during a five-year voyage around the world in the 19th century. He explained his ideas about evolution in a book called On the Origin of Species, which was published in 1859.

• Darwin's ideas caused a lot of controversy, and this continues to this day, because the ideas can be seen as conflicting with religious views about the creation of the world and creatures in it.

Charles Darwin – Natural Selection• The theory of evolution states that evolution happens by natural

selection. Here are the key points:• Individuals in a species show a wide range of variation.• This variation is because of differences in genes.• Individuals with characteristics most suited to the

environment are more likely to survive and reproduce.• The genes that allowed the individuals to be successful are passed

to the offspring in the next generation.• Individuals that are poorly adapted to their environment are less

likely to survive and reproduce. This means that their genes are less likely to be passed to the next generation. Given enough time, a species will gradually evolve.

• The basic idea behind the theory of evolution is that all the different species have evolved from simple life forms.

• These simple life forms first developed more than three billion years ago - the Earth is about 4.5 billion years old.

6. Explain how fossil evidence supports Darwin’s Theory and therefore relate natural

selection to the evolution of organisms.

• Most of the evidence for evolution comes from the fossil record. Fossils show how much, or how little, organisms have changed over time.

• One of the problems with the fossil record is that it contains gaps. Not all organisms fossilise well, and there will be many fossils that have been destroyed by the movements of the Earth, or simply not yet been discovered.

• One of the few animals for which we have a fairly complete evolutionary record is the horse. All the main stages of the evolution of the horse have been preserved in fossil form.

Evolution of the horse over 60 million years

Peppered moths – evidence for natural selection

• Rapid changes in species have been observed. These support the theory of evolution.

• Peppered moths• Before the industrial revolution in Britain, most peppered moths were of the

pale variety. This meant that they were camouflaged against the pale birch trees that they rest on.

• Moths with a mutant black colouring were easily spotted and eaten by birds. This gave the white variety an advantage, and they were more likely to survive to reproduce.

• Airborne pollution in industrial areas blackened the birch tree bark with soot. This meant that the mutant black moths were now camouflaged, while the white variety became more vulnerable to predators.

• This gave the black variety an advantage, and they were more likely to survive and reproduce.

• Over time, the black peppered moths became far more numerous in urban areas than the pale variety.

Peppered moths – evidence for natural selection

Antibiotic Resistant Bacteria

• Microorganisms such as bacteria and viruses reproduce very rapidly and can evolve in a relatively short time. One example is the bacterium E. coli.

• Its DNA can be damaged or changed (mutate) during replication, and most of the time this causes the death of the cell.

• But occasionally, the mutation is beneficial - for the bacteria. For example, it may allow resistance to an antibiotic.

• When that antibiotic is present, the resistant bacteria have an advantage over the bacteria that are not resistant.

9. Describe the relationship between DNA, genes and chromosomes.

• DNA (deoxyribose nucleic acid) molecules are large and complex. They carry the genetic code that determines the characteristics of a living thing.

• Except for identical twins, each person’s DNA is unique. This is why people can be identified using DNA fingerprinting. DNA can be cut up and separated, forming a sort of 'bar code' that is different from one person to the next.

8/9. Describe the relationship between DNA, genes and chromosomes.

Genes• A gene is a short section of DNA. Each gene codes for

a specific protein by specifying the order in which amino acids must be joined together.

Chromosomes• The cell’s nucleus contains chromosomes made from

long DNA molecules.

7/8/9. Describe the relationship between DNA, genes and chromosomes.

• Chromosomes are found in the nucleus of eukaryotic cells and are made from DNA. Genes are short sections of DNA.

10. James Watson ad Francis Crick

• Scientists who received the 1962 Nobel Prize for discovering the structure of DNA.

10. James Watson ad Francis Crick

• In 1953 American biochemist James D. Watson and British biophysicist Francis Crick published the first description of the structure of DNA.

• Their model proved to be so important for the understanding of protein synthesis, DNA replication, and mutation

• They were awarded the 1962 Nobel Prize for physiology or medicine for their work.

11. Cell replication

• Cells must replicate for an organism to grow, repair itself and reproduce.

Cell replication

• For a cell to replicate the following must occur:

1) chromosomes are pulled apart (Mitosis); 2) the cell divides (Cytokinesis); and 3) the strands of DNA are then replicated.

The Cell Cycle: How cells replicate• For a cell to divide, the DNA must be replicated.

Advantages of DNA replicating exactly

• Specialised cells form tissue which make organs that are part of out body systems.

- Since DNA controls cell function, healthy DNA will result in specialized cells that are capable of performing a specific function that will keep an organism alive.

- Harmful mutations that can result in deformities or cancer cells.

Mitosis – Cell divisonMaking body (somatic) cells

• Mitosis is the process of cell division that produces new body cells with 46 chromosomes necessary for human cells.

Phases of Mitosis

In a typical animal cell, mitosis can be divided into four principals stages:• Prophase: The chromatin, diffuse in interphase,

condenses into chromosomes. Each chromosome has duplicated and now consists of two sister chromatids. At the end of prophase, the nuclear envelope breaks down into vesicles.

• Metaphase: The chromosomes align at the equitorial plate and are held in place by microtubules attached to the mitotic spindle and to part of the centromere.

Phases of Mitosis:• Anaphase: The centromeres divide. Sister chromatids

separate and move toward the corresponding poles. • Telophase: Daughter chromosomes arrive at the

poles and the microtubules disappear. The condensed chromatin expands and the nuclear envelope reappears.

Cytokinesis is NOT a phase of mitosis. It is when the cytoplasm divides, the cell membrane pinches inward ultimately producing two daughter cells. It proceeds mitosis.

Asexual and Sexual Reproduction

• Some plants and animals can reproduce asexually to form an identical clone. This is mitosis.

• Some plants and animals must reproduce sexually. For this to happen, sex cells (gametes) must be made. This process is called meiosis.

- The gametes fuse (fertilisation) to form a unique individual (offspring in the form of

a zygote – fertilised egg).

Meiosis – Reduction division(making sex cells - gametes)

• Meiosis is a process carried out in the gonads (male – testicles / female – ovaries) that produces sex cells with 23 necessary chromosomes necessary for reproduction.

• Meiosis differs from Mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes (gametes [sex cells] such as sperm and ova).

- The number of chromosomes are halved (ready for reproduction – formation of a zygote).

Phases of Meiosis:

Four stages can be described for each nuclear division.• Interphase: Before meiosis begins, genetic material is

duplicated.• First division of meiosis• Prophase 1: Duplicated chromatin condenses. Each

chromosome consists of two, closely associated sister chromatids. Crossing-over can occur during the latter part of this stage.

• Metaphase 1: Homologous chromosomes align at the equatorial plate.

• Anaphase 1: Homologous pairs separate with sister chromatids remaining together.

• Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

• Second division of meiosis: Gamete formation• Prophase 2: DNA does not replicate.• Metaphase 2: Chromosomes align at the equatorial

plate..

• Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.

• Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.

Mitosis (above) compared to Meiosis (bottom)

Mutations

• DNA can change (mutate) due to environmental factors called mutagens.

- chemicals- UV radiation- atomic radiation

Mutations

Advantages (beneficial mutations)

Disadvantages (harmful mutations)

Adaptations that result in better chance of survival

Physical deformities

Cancer cells

Disease

16/18/19. Alleles are alternative forms of a gene

Alleles are alternative forms of a gene (e.g. Height, Hair colour, Eye colour, Blood type, Skin colour, etc…).Alleles can be dominant (black coat - BB) or recessive (white coat - bb).The letters used to describe the alleles are called genotype (BB and bb). [Note: Use the letter of the dominant allele. Dominant is capital and recessive is the same letter but lower-case].

19. Alleles

• When the genotype is expressed (seen in the offspring) we call it phenotype.

• Some alleles can be equally strong (we call this co-dominance). Example: A red (RR) Shorthorn bull and white (WW) Shorthorn cow will produce roan (RW) coloured offspring.

17. Genes are inherited in pairs

• Homozygous (pure) – Example: Pure black cattle (BB) have a black phenotype.

• Heterozygous (hybrid) – Example: hybrid black cattle (Bb) have a black phenotype, but carry a white gene (which is masked).

Punnett Squares

Punnett Squares

Roles of genes and environmental factors on the phenotype of an organism

• Genes are segments of DNA that code for specific traits (characteristics) that help organisms survive (adaptations).

• As the environment changes, so must our genes. This is the driving force behind evolution.

- As an organism’s environment changes, so must the organism if it is to survive long enough to pass on its genes!

Biotechnology

• Biotechnology is the practice of using plants, animals and micro-organisms such as bacteria, as well as biological processes to some benefit.

• http://www.biotechnologyonline.gov.au

Biotechnology

Example of biotechnology used in industry: • Medicial industry - medicines, test for diseases • Agricultural industry - produce

foods/materials • Remediation of contaminated land (remove

waste).• Forensic Science - DNA profiling is useful for

identification.

Genetically Modified Organisms (GMO) used in Australian Agriculture:

- Bt Cotton (cotton plant that contains a bacterial gene that prevents Heliothis caterpillar from damaging the crop).

Genetically Modified Organisms (GMO) used in Australian Agriculture:

- Roundup® ready Canola (canola plant that contains DNA from bacteria and virus to prevent it from being affected by Roundup® herbicide).