17. Inheritance
17.1 Inheritance
Core
Define inheritance as the transmission of genetic information from generation to generation
17.2 Chromosomes, genes and proteins
Core
Define chromosome as a thread-like structure of DNA, carrying genetic information in the form of genes
Define gene as a length of DNA that codes for a protein
Define allele as a version of a gene
Describe the inheritance of sex in humans with reference to XX and XY chromosomes
Supplement
Explain that the sequence of bases in a gene is the genetic code for putting together amino acids in the correct order to make a specific protein (knowledge of the details of nucleotide structure is not required)
Explain that DNA controls cell function by controlling the production of proteins (some of which are enzymes), antibodies and receptors for neurotransmitters
Explain how a protein is made, limited to: – the gene coding for the protein remains in the nucleus
– mRNA molecules carry a copy of the gene to the cytoplasm
– the mRNA passes through ribosomes
– the ribosome assembles amino acids into protein molecules
– the specific order of amino acids is determined by the sequence of bases in the mRNA (knowledge of the details of transcription or translation is not required)
Explain that all 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
Define a haploid nucleus as a nucleus containing a single set of unpaired chromosomes, e.g. in gametes
Define a diploid nucleus as a nucleus containing two sets of chromosomes, e.g. in body cells
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
Chromosomes, genes and DNA
Genes and DNA
Alleles
Protein synthesis
17.3 Mitosis
Core
Define mitosis as nuclear division giving rise to genetically identical cells (details of stages are not required)
State the role of mitosis in growth, repair of damaged tissues, replacement of cells and asexual reproduction
Supplement
State that the exact duplication of chromosomes occurs before mitosis
State that during mitosis, the copies of chromosomes separate, maintaining the chromosome number (details of stages of mitosis are not required)
Describe stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions
Mitosis
Mitosis
17.4 Meiosis
Core
Define meiosis as nuclear division giving rise to cells that are genetically different (details of stages are not required)
State that meiosis is involved in the production of gametes
Supplement
Define meiosis as reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells (details of stages are not required)
Explain how meiosis produces variation by forming new combinations of maternal and paternal chromosomes (specific details are not required)
17.5 Monohybrid inheritance
Core
Define genotype as the genetic make-up of an organism in terms of the alleles present
Define phenotype as the observable features of an organism
Define homozygous as having two identical alleles of a particular gene
State that two identical homozygous individuals that breed together will be pure-breeding
Define heterozygous as having two different alleles of a particular gene
State that a heterozygous individual will not be pure-breeding
Define dominant as an allele that is expressed if it is present
Define recessive as an allele that is only expressed when there is no dominant allele of the gene present
Interpret pedigree diagrams for the inheritance of a given characteristic
Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios, limited to 1:1 and 3:1 ratios
Use Punnett squares in crosses which result in more than one genotype to work out and show the possible different genotypes
Supplement
Explain how to use a test cross to identify an unknown genotype
Explain codominance by reference to the inheritance of ABO blood groups
– phenotypes being A, B, AB and O blood groups and alleles being IA , IB and IO
Define a sex-linked characteristic as a characteristic in which the gene responsible is located on a sex chromosome and that this makes it more common in one sex than in the other
Describe colour blindness as an example of sex linkage
Use genetic diagrams to predict the results of monohybrid crosses involving codominance or sex linkage and calculate phenotypic ratios
17.5 Monohybrid inheritance
Interpret pedigree diagrams
What is a test cross
Co-dominance
Blood types
Punnet squares and Sex linked traits
Colour blindness - sex linkage