Biology Flashcards
Reproductive organs in mammals
Testes and ovaries
Process of fertilisation
- Sperm and egg united in fallopian tubes
- They form a zygote
- Zygote reaches the uterus and becomes a blastocyst
- The blastocyst burrows into the lining of the uterus and is implanted
- Inner cells of blastocyst become the embryo
Define chromosomes
Thread-like structures found in the nuclei of cells that carries genetic information in the form of genes
Importance of chromosomes to inheritance
Each person has 23 chromosomes from both their father and mother, making 46. This means that your features are a mix of both father and mother. People who don’t have 46 usually have syndromes which can affect their height and intellect
Significance of karyotypes
A karyotype is a person’s complete set of chromosomes. Presence of the Y chromosome indicates sex. Abnormal karyotypes can reveal disorders
Compare mitosis and meiosis
Mitosis is done everywhere outside the reproductive organs. The nucleus is split in two and the parent cell splits into two daughter cells. Full genetic information is passed onto them.
Meiosis is done only in the reproductive organs. The cell is split into four daughter cells and half the information is carried on.
Explain how genes are passed from parents to offspring in the gametes
A gamete (reproductive cell) contains one set of 23 chromosomes. When male and female gametes fertilise, the embryo has 2 sets of 23 chromosomes, fusing the parents’ characteristics.
Referring to gene inheritance, explain the similarities between parents and offspring
Parents and offspring are similar due to how inheritance works. The embryo contains one set of 23 chromosomes from both parents so they will share traits
Define a gene
A length of DNA that codes for a specific characteristic
Outline the key components of DNA
Double helix strand, sugar phosphate backbone, hydrogen bonding between bases of adenine, thymine, guanine and cytosine. Information is passed from DNA to RNA to proteins.
Outline the Strawberry DNA experiment
- Crush a strawberry in a plastic bag
- Create a dish soap water solution
- Add in crushed strawberries
- Add in salt
- Mix well
- Pour through gauze to remove solids
- Add the same amount of isopropyl alcohol as there is strawberry solution
- Observe white strands of DNA become isolated on top
Distinguish between DNA, genes and chromosomes
A chromosome is the DNA packaged into an X or Y shaped structure located in the nucleus of a cell. A gene is a segment of DNA. DNA is a double-helix strand containing a sugar-phosphate backbone and has bases of adenine, thymine, guanine and cytosine.
Explain how DNA is replicated.
- The double helix is opened by an initiator protein
- Helicase breaks the hydrogen bonds between the ATGC bases
- Primase briefly attaches to each base and assembles a foundation for replication
- DNA polymerase wraps itself around the bases
- Attaches new nucleotides in two ways: leading strand is continually attached, and the lagging strand is attached in discontinuous bursts
Outline the nature of the genetic code and base triplet hypothesis
Genetic code refers to the sequence of codons (or bases) in DNA or RNA. 3 bases form a codon. Each codon stands for 1 amino acid. There is a start codon (TAC) and stop codon (ATT, ATC or ACT). Most codons represent a specific amino acid
Steps involved in protein synthesis
- A gene’s DNA sequence is transcribed to make an RNA molecule.
- Transcription begins when RNA polymerase binds to a promoter sequence then uses DNA strands to make a new, complementary RNA molecule
- Transcription ends in a process called termination.
- Process is initiated when a ribosome combines with mRNA
- Amino acids are brought to the ribosomes to elongate the chain
- Polypeptide is released
Define mutation and mutagen
Mutation: Any change in the nucleotide sequence (ATGC)
Mutagen: Something which causes the DNA to permanently change (e.g. UV exposire)
Describe how mutations change phenotypes
Mutations can generate new alleles which can change a person’s appearance and hence phenotype
Are mutations harmful?
Most are harmful, some are neutral and a few are beneficial
How is mutation important to natural selection and variance?
Mutation can create new alleles, which introduces new alleles to a population. New adaptive features can be created and this means some animals may have an advantage, allowing them to survive
Outline Mendel’s work
Mendel ran an experiment selectively breeding peas. His work established traits are passed from parents to offpsring.
Define the following: allele, homozygous, heterozygous, recessive, dominant, homologous, phenotype, genotype
Allele: The letters denoting a genotype
Homozygous: Identical alleles (BB)
Heterozygous: Different alleles (Bb)
Recessive: Allele that can be masked by a dominant
Dominant: Allele that masks a recessive
Homologous: Similar features internally or in a chromosome (e.g. same bone in different animals)
Phenotype: Physical appearance resulting from a gene combination
Genotype: 2 alleles resulting in genetic makeup
Compare dominant-recessive inheritance patterns with those traits showing co-dominance, partial dominance and sex linkage
Dominant-recessive inheritance: Usually looks like Bb, where one allele is masked by another
Co-dominance: Both traits are expressed equally
Partial dominance: Trait is expressed to an extent
Sex linkage: Some diseases (e.g. hemophilia) can only be carried in the sex chromosomes
Dominant and recessive genetic diseases
Dominant: Huntington’s disease (Breakdown of brain function), Marfan syndrome (affects connective tissues and alters the normal body length ratio - short torso, long digits and long limbs)
Recessive: Sickle-cell anemia, cystic fibrosis (damages lungs and digestive tract)
How fossils are used to suggest age of earth
Fossils and rocks can be carbon dated, the oldest rock found being 4.3b years old suggesting the Earth is at least 4.6b years old
