3.13 Understand that the nucleus of a cell contains chromosomes on which genes are located.
In the nucleus of a cell chromosomes can be found.
Chromosomes are long sections of tangled DNA, sections of which are different genes.
Chromosomes are long sections of tangled DNA, sections of which are different genes.
3.14 Understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein.
A gene is a section of a molecule of DNA.
Different genes code different proteins.
Different genes code different proteins.
3.15 Describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G).
3.16 Understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics.
Genes come in a variety of forms:
For example the gene that codes for hair can come in many different colours.
These different forms are different alleles, having these differences is where you vary in inherited characteristics (If there was only one allele for hair we would all have exactly the same hair.)
For example the gene that codes for hair can come in many different colours.
These different forms are different alleles, having these differences is where you vary in inherited characteristics (If there was only one allele for hair we would all have exactly the same hair.)
3.17 Understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance.
Dominant: A dominant allele is the one that will be made.
Recessive: A recessive allele will be masked by a dominant one and not visible.
Homozygous: If you have two of the same alleles for a gene in one persons DNA.
Heterozygous: If you have two different alleles for a gene in in someones DNA.
Phenotype: What allele is expressed as a protein.
Genotype: What alleles you have in your DNA for a gene.
Codominance: When two alleles have equal dominance (they will both be expressed).
Recessive: A recessive allele will be masked by a dominant one and not visible.
Homozygous: If you have two of the same alleles for a gene in one persons DNA.
Heterozygous: If you have two different alleles for a gene in in someones DNA.
Phenotype: What allele is expressed as a protein.
Genotype: What alleles you have in your DNA for a gene.
Codominance: When two alleles have equal dominance (they will both be expressed).
3.18 Describe patterns of mono-hybrid inheritance using a genetic diagram.
3.19 Understand how to interpret family pedigrees.
3.20 Predict probabilities of outcomes from monohybrid crosses.
From mono-hybrid cross diagrams there are four outcomes, some times some of the out comes are the same.
How to work out the probability of a child inheriting a genotype:
First see how many times it comes up and divide it by 4 then multiply by 100 for a percentage.
How to work out phenotype probability:
You work out how many times they will express a characteristic and divide it by four then times by 100 for a percent.
How to work out the probability of a child inheriting a genotype:
First see how many times it comes up and divide it by 4 then multiply by 100 for a percentage.
How to work out phenotype probability:
You work out how many times they will express a characteristic and divide it by four then times by 100 for a percent.
3.21 Understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male.
One pair of chromosomes (out of 23 pairs) controls the gender of a person. XX is female; XY is male.
3.22 Describe the determination of the sex of offspring at fertilisation, using a genetic diagram.
3.23 Understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.
3.24 Understand that mitosis occurs during growth, repair, cloning and asexual reproduction.
Mitosis cell division is the type that occurs in growth, repair cloning and asexual reproduction.
3.25 Understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes.
3.26 Understand that random fertilisation produces genetic variation of offspring.
Because gametes contain a random selection of genetic information from each parent, the fertilised egg will be a mix of different genotypes which is why offspring are genetically different to their parents.
3.27 Know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23.
The diploid number is how many chromosomes each cell is meant to have: 46 in humans (23 pairs).
The haploid number is half of the diploid number: so 23.
The haploid number is half of the diploid number: so 23.
3.28 Understand that variation within a species can be genetic, environmental, or a combination of both.
Variation in a species is the differences between the members of a species.
- Genetic is caused by what genes are inherited.
- Environmental is caused by some action after birth (e.g the sun giving you a tan.)
- Some variations can be a combination of both.
3.29 Understand that mutation is a rare, random change in genetic material that can be inherited.
A mutation is when a gene is copied incorrectly, this gene can be passed down.
It doesn't happen very often or on purpose.
It can have positive impacts (rarely) and/or negative impacts (common).
It doesn't happen very often or on purpose.
It can have positive impacts (rarely) and/or negative impacts (common).
3.30 Describe the process of evolution by means of natural selection.
Evolution is a change in species over a very long time (sometimes into different species.)
Natural selection is survival of the fittest.
What happens is:
Natural selection is survival of the fittest.
What happens is:
- A mutation occurs
- If the mutation is beneficial, the animal will survive longer and reproduce more
- Some of its offspring will inherit the mutation
- These offspring will also have better chance of survival, meaning they live longer and reproduce more
- Over a long period of time this process is repeated and gradually the mutation becomes a common gene in a species and those with the mutation become the only ones, as those without cannot compete with those expressing the mutated gene
3.31 Understand that many mutations are harmful but some are neutral and a few are beneficial.
A lot of mutations are harmful like genetic diseases:
- E.g. cystic fibrosis.
- E.g. having a different colour hair.
- E.g. an insect pollinated plant becoming brighter.
3.32 Understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control.
- Bacteria experience mutations (the reproduce very frequently so it is not rare.)
- These mutations can mean that they are no longer affected by a certain antibiotic, this makes it easier for them to survive.
- If bacteria evolve to be resistant to drugs we are treating them with then they are difficult to control;
- Sometimes they can be stopped using a different antibiotic, but some are becoming resistant to all drugs.