17 Inheritances
(Core / Extended)


17.1 Chromosomes, genes and proteins
What you need to know:
  1. State that chromosomes are made of DNA, which contains genetic information in the form of genes
  2. Define a gene as a length of DNA that codes for a protein
  3. Define an allele as an alternative form of a gene
  4. Describe the inheritance of sex in humans with reference to X and Y chromosomes
  5. State that the sequence of bases in a gene determines the sequence of amino acids used to make a specific protein (knowledge of the details of nucleotide structure is not required)
  6. Explain that different sequences of amino acids give different shapes to protein molecules
  7. Explain that DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters
  8. Explain how a protein is made, limited to: (a) the gene coding for the protein remains in the nucleus (b) messenger RNA (mRNA) is a copy of a gene (c) mRNA molecules are made in the nucleus and move to the cytoplasm (d) the mRNA passes through ribosomes (e) the ribosome assembles amino acids into protein molecules (f) the specific sequence of amino acids is determined by the sequence of bases in the mRNA (knowledge of the details of transcription or translation is not required)
  9. Explain that most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs
  10. Describe a haploid nucleus as a nucleus containing a single set of chromosomes
  11. Describe a diploid nucleus as a nucleus containing two sets of chromosomes
  12. State that in a diploid cell, there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs
Videos: DNA Strucure, Bases, MRNA
Videos: Chromosome-Gene-Allele-Protein
  • Inheritance and Chromosome
  • GDifference between Gene and allele
  • How protein is made
  • Function of DNA
  • Haploid Nucleus and Diploid Nucleus
17.2 Mitosis
What you need to know:
  1. Describe mitosis as nuclear division giving rise to genetically identical cells (details of the stages of mitosis are not required)
  2. State the role of mitosis in growth, repair of damaged tissues, replacement of cells and asexual reproduction
  3. State that the exact replication of chromosomes occurs before mitosis
  4. State that during mitosis, the copies of chromosomes separate, maintaining the chromosome number in each daughter cell
  5. Describe stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions 
17.3 Meosis
What you need to know:
  1. State that meiosis is involved in the production of gametes
  2. Describe meiosis as a reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells (details of the stages of meiosis are not required)
Videos: Mitosis and Meosis
Videos: Stem Cells
17.4 Monohybrid Inheritance
What you need to know:
  1. Describe inheritance as the transmission of genetic information from generation to generation 2
  2. Describe genotype as the genetic make-up of an organism and in terms of the alleles present
  3. Describe phenotype as the observable features of an organism
  4. Describe homozygous as having two identical alleles of a particular gene
  5. State that two identical homozygous individuals that breed together will be pure-breeding
  6. Describe heterozygous as having two different alleles of a particular gene
  7. State that a heterozygous individual will not be pure-breeding
  8. Describe a dominant allele as an allele that is expressed if it is present in the genotype
  9. Describe a recessive allele as an allele that is only expressed when there is no dominant allele of the gene present in the genotype
  10. Interpret pedigree diagrams for the inheritance of a given characteristic
  11. Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios, limited to 1 : 1 and 3: 1 ratios
  12. Explain how to use a test cross to identify an unknown genotype
  13. Use Punnett squares in crosses which result in more than one genotype to work out and show the possible different genotypes
  14. Describe codominance as a situation in which both alleles in heterozygous organisms contribute to the phenotype
  15. Explain the inheritance of ABO blood groups: phenotypes are A, B, AB and O blood groups and alleles are IA , IB and Io
  16. Describe a sex-linked characteristic as a feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in the other
  17. Describe red-green colour blindness as an example of sex linkage
  18. Use genetic diagrams to predict the results of monohybrid crosses involving codominance or sex linkage and calculate phenotypic ratios
Videos: Genotype, Phenotype, Pedigree and Codominance
Videos: Monohybrid Inheritance
Videos: Monohybrid Cross Examples
Videos: Blood Types Inheritance
Videos: Colour Blindness Inheritance plus questions
EXAMPLE QUESTIONS
Videos: Inheritance and Genetic Crosses Exam Questions
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