Inheritance, Variation and Evolution

Inheritance, Variation and Evolution

1. Asexual Reproduction

   • Only one parent is needed in asexual reproduction. There is no fusion of gametes so genetic material does not mix, which means that the offspring produced through this process are genetically identical clones to the parent. Examples of organisms that use asexual reproduction include: bacteria /production of spores by fungi /some plants, such as strawberries, use runners /formation of tubers in potatoes and bulbs in daffodils
   • Asexual reproduction uses the process of mitosis to create the identical copies (clones) of the parent cell.
   • The advantages of asexual reproduction include:
     • the population can increase rapidly when the conditions are favourable /only one parent is needed/it is more time and energy efficient as you don't need a mate/ it is faster than sexual reproduction
   • The disadvantages of asexual reproduction include:
     • it does not lead to variation in a population/ the species may only be suited to one habitat /disease may affect all the individuals in a population

2. Mitosis

   • Mitosis is part of the cell cycle, which involves: cell growth, and the increase of the number of structures in the cell (mitochondria, ribosomes)/ genetic material is copied /mitosis occurs leading to chromosomes separation and cell division Mitosis is also used for: growth /repair to damaged tissue /replacement of worn-out cells

3. Sexual Reproduction

   • The advantages of sexual reproduction:
     • Produces variation in the offspring /The species can adapt to new environments due to variation, which gives them a survival advantage /A disease is less likely to affect all the individuals in a population /Humans can speed up natural selection through selective breeding, which can increase food production
   • Meiosis
     • Reduction division in a cell in which the chromosome number is halved from diploid to haploid.
     • The process of meiosis happens in the male and female reproductive organs. As a cell divides to form gametes: copies of the genetic information is made/the cell divides twice to form four gametes, each with a single set of chromosomes (haploid)/all gametes are genetically different from each other
   • The disadvantages of sexual reproduction:
     • time and energy are needed to find a mate /it is not possible for an isolated individual

4. DNA

   • The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA is a polymer, a large and complex molecule. It is made up of two strands forming a twisted ladder structure called a double helix. It carries the genetic code, which determines the characteristics of a living organism.
   • Chromosomes
     • The cell's nucleus contains chromosomes. These are long threads of DNA, which are made up of many genes.
   • Genes
     • A gene is a small section of DNA in a chromosome. Each gene codes for a particular sequence of amino acids in order to make a specific protein. It is the unit of heredity, and may be copied and passed on to the next generation.

5. Variation

   • Individuals in a population are usually similar to each other, but not identical. Some of the variation within a species is genetic, some is environmental - the conditions in which they have developed and some is a combination of both.
   • Natural selection
     • Natural selection is a process where organisms that are better adapted to an environment will survive and have more offspring.

6. Evoloution

   • Darwin
     • He is associated with the term 'survival of the fittest' which describes how natural selection works, by selecting the best examples of an organism to survive. For example, individuals that are best adapted to their environments are more likely to survive and therefore reproduce.
   • Lamarck
     • a characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used eventually disappears /any feature of an organism that is improved through use is passed to its offspring
     • WRONG

7. Fossils

   • A fossil is the preserved remains of a dead organism from millions of years ago. Fossils are found in rocks and can be formed from:
     • hard body parts, such as bones and shells, which do not decay easily or are replaced by minerals as they decay
     • parts of organisms that have not decayed because one or more of the conditions needed for decay are absent. For example, dead animals and plants can be preserved in amber, peat bogs, tar pits, or in ice
     • preserved traces of organisms, such as footprints, burrows and rootlet traces - these become covered by layers of sediment, which eventually become rock

8. Classification of living organisms

   • Kingdom
   • phylum
   • class
   • order
   • family
   • genus
   • species