Overview
This lecture reviews essential genetics terms and concepts relevant to Year 10 Science, focusing on DNA, genes, chromosomes, and inheritance patterns.
DNA and Its Structure
- DNA (deoxyribonucleic acid) is a molecule containing instructions for all cellular functions and heredity.
- DNA is composed of nucleotides, each with a nitrogen base: adenine (A), thymine (T), cytosine (C), guanine (G).
- Adenine pairs with thymine; cytosine pairs with guanine (complementary base pairing).
- RNA (ribonucleic acid) is a complementary copy of DNA that carries genetic instructions from the nucleus to the cytoplasm.
- Thymine in DNA is replaced by uracil in RNA, pairing with adenine.
Genes, Alleles & Chromosomes
- A gene is a segment of DNA containing instructions for a specific trait.
- An allele is a version of a gene; each person inherits one allele from each parent.
- The genotype is the combination of alleles for a trait, while the phenotype is the observable characteristic.
- Homozygous means having two identical alleles; heterozygous means having two different alleles.
- An autosome is a chromosome not involved in sex determination; sex chromosomes determine the sex of an organism.
- A karyotype displays the full set of chromosomes in pairs, ordered by size.
- Diploid cells contain two sets of chromosomes, while haploid cells (gametes) contain one set.
Inheritance Patterns & Genetic Variation
- Dominant traits appear with only one copy of an allele; recessive traits require two identical alleles.
- A carrier has an allele for a recessive trait but does not show it in their phenotype.
- Genetic code refers to the sequence of DNA inherited from parents.
- A Punnett square predicts the possible genetic outcomes of breeding organisms.
Cell Division and Mutations
- Mitosis is cell division for growth or repair, producing genetically identical cells.
- Meiosis produces gametes with half the genetic material of the parent cell.
- Non-disjunction is the improper separation of chromosomes during meiosis, leading to abnormal chromosome numbers.
- A mutagen is an agent causing changes in DNA, resulting in genetic mutations.
- A genetic mutation is a permanent change in DNA sequence.
- A frameshift mutation is caused by the insertion or deletion of nucleotides, disrupting protein formation.
Key Terms & Definitions
- Adenine — nitrogen base; pairs with thymine (DNA) or uracil (RNA).
- Allele — variant form of a gene.
- Autosome — chromosome not involved in determining sex.
- Carrier — individual with a recessive allele not shown in phenotype.
- Complementary base — pairs: A-T, C-G in DNA.
- Cytosine — nitrogen base; pairs with guanine.
- Diploid — cell with two sets of chromosomes.
- Dominant trait — appears with one allele copy.
- Frameshift — mutation altering the reading frame of DNA.
- Genotype — allele combination for a trait.
- Guanine — nitrogen base; pairs with cytosine.
- Haploid — cell with one set of chromosomes.
- Heterozygous — two different alleles for a trait.
- Homozygous — two identical alleles for a trait.
- Karyotype — ordered chromosome display.
- Meiosis — cell division producing gametes.
- Mitosis — cell division for growth/repair.
- Mutagen — agent causing DNA mutation.
- Non-disjunction — failure of chromosome separation in meiosis.
- Nucleotide — DNA subunit.
- Phenotype — observable characteristics from genotype and environment.
- Punnett square — diagram predicting genetic crosses.
- Recessive trait — appears only with two identical alleles.
- RNA — carries genetic message from DNA.
- Sex chromosome — chromosome determining sex.
- Stem cell — undifferentiated cell able to form various specialized cells.
- Thymine — DNA nitrogen base; pairs with adenine.
- Transcription — copying DNA to RNA.
- Translation — forming protein from RNA.
Action Items / Next Steps
- Review all key terms and practice using Punnett squares for genetic crosses.
- Study the differences between mitosis and meiosis.
- Prepare for a quiz on DNA structure and genetic inheritance.