| How does Asexual Reproduction work (& Examples) | - Only one parent is needed
- 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:
- bacteria
- production of spores by fungi
- some plants, such as strawberries, use runners
- formation of tubers in potatoes and bulbs in daffodils |
| Sexual Reproduction, Meiosis & Fertilisation | SEXUAL REPRODUCTION:
- Gametes in: animals - sperm and eggs; flowering plants - pollen & eggs
- Offspring in sexual reproduction are genetically different to each other and the parents, resulting in variation as genetic info mixes
MEIOSIS:
Sexual reproduction uses the process of meiosis, which creates gametes, it 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
FERTILISATION:
- The fusion of the nucleus of a male gamete with the nucleus of a female gamete
- 23 chromosomes in a gamete - a haploid. When 2 gametes combine, they merge the 2 sets of chromosomes to have 46 - a diploid
- This produces a new cell called a zygote, which matures into an embryo, the no. of cells increase by mitosis & the cells begin to differentiate as the embryo develops |
| Dis/advantages of Sexual Reproduction | ADVANTAGES:
- 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
DISADVANTAGES:
- time and energy are needed to find a mate
- it is not possible for an isolated individual |
| Dis/advantages of Asexual Reproduction | ADVANTAGES:
- 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
DISADVANTAGES:
- 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 |
| Organisms Which use Asexual & Sexual Reproduction | SEXUAL REPRODUCTION:
- Fungi reproduce sexually to generate variation
- Plants use sexual reproduction to produce seeds
- Malarial parasites reproduce sexually in the host mosquito
ASEXUAL REPRODUCTION:
- Fungi release spores by asexual reproduction
- Plants such as strawberries reproduce asexually by sending out runners, or daffodils when their bulbs divide
- Malarial parasites reproduce asexually in the human host |
| What are DNA, Chromosomes & Genes | 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: Contained in cell nucleus, long threads of DNA which are made up of genes
GENES: 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 |
| The Human Genome & Disease ascociated genes | HUMAN GENOME:
The genome of an organism is the entire genetic material of that organism. The human genome has great importance in medicine. It enables us to:
- search for genes linked to different types of disease
- understand inherited disorders and their treatment
- trace human migration patterns from the past
DISEASE ASCOCIATED GENES:
- Scientists are searching for disease associated genes. One example was those that can contribute to breast cancer, which are known as BRCA1 and BRCA2.
- Mutations in these genes account for approximately 10% of all inherited breast cancer cases detected. Scientists studied families where it was known to be inherited and were able to create a pedigree analysis, which is similar to a family tree diagram that showed the close relationship of those affected and unaffected within the family, differences in DNA can be analysed.
- It is now possible to detect the presence of the genes by having a simple blood test |
| DNA Strucure | - James Watson and Francis Crick worked out the structure of DNA in 1953. By using data from other scientists they were able to build a model of DNA. The X-ray crystallography data they used showed that DNA consists of two strands coiled into a double helix
- DNA is a polymer made from four different nucleotides. These repeat. Each nucleotide consists of alternating sugar and phosphate sections with one of the four different bases attached to the sugar
BASE PAIRS(Each strand of DNA is made of chemicals called bases):
- thymine, T
- adenine, A
- guanine, G
- cytosine, C
There are chemical cross-links between the two strands in DNA, formed by pairs of bases.
A sequence of three bases is the code for a particular amino acid - known as a triplet or the triplet code. The order of the bases controls the order in which amino acids are assembled to produce a particular protein |
| 7 Facts in relation to Protein Synthesis | 1- The DNA code for the protein remains in the nucleus, but a copy, called mRNA, moves from the nucleus to the ribosomes where proteins are synthesised in the cytoplasm.
2- Amino acids are connected together in a specific order at the ribosome (see diagram) to create a specific protein molecule
3- The protein produced depends on the template used, and if this sequence changes a different protein will be made
4- Carrier molecules bring specific amino acids to add to the growing protein in the correct order (there's about 20 different naturally-occurring amino acids)
5- DNA structure determines the protein synthesised. If this changes a different protein will be made
6- Each protein molecule has hundreds, or even thousands, of amino acids joined together in a unique sequence. It is then folded into the correct unique shape. This allows the protein to do their jobs, such as enzymes or hormones and it can form structures within the body, such as collagen
7- Not all parts of the DNA code for proteins, there is a coding and non-coding part of DNA, which can switch genes on and off, so variations in these areas may affect gene expression, and if the correct protein is synthesised or not |
| What are Mutations, How do they work? | Mutation - a change in a gene or chromosome. It is a rare, random change in the genetic material and it can be inherited. It's continuous and can be spontaneous, also happens due to:
- ionising radiation
- chemical mutagens - such as tar from cigarette smoke
1) Ionising radiation includes gamma rays, X-rays and ultraviolet rays. The greater the dose of radiation a cell gets, the greater the chance of a mutation
2) Mutations could cause different genes to be switched on or off, and this could create a different or faulty protein to be synthesised. For example, if the protein is an important enzyme, the specific substrate might not fit into the substrate binding site. If it is a structural protein such as collagen, it might lose its strength
3) However, most DNA mutations do not alter a protein, they only alter it slightly so its appearance or function is not changed
4) These mutations may change the activity of a protein, in a coding part of the DNA, or it might change how the genes are expressed if the change is in a non-coding section of DNA/. May result in a serious consequence, such as genetic disease such as cystic fibrosis
5) Different types of gene mutation(self-explanatory): Substitution, insertion, deletion, inversion |
| 4 Steps of Mitosis | MITOSIS:
1) Chromosomes in nucleus - copied
2) Chromosomes & their copies pulled apart & move towards poles
3) Chromosomes separate
4) Cells divide into2 genetically identical daughter cells |
| How does Sexual Reproduction | SEXUAL REPRODUCTION:
- Gametes in: animals - sperm and eggs; flowering plants - pollen & eggs
- Offspring in sexual reproduction are genetically different to each other and the parents, resulting in variation as genetic info mixes |
