6.1 Flashcards
Describe what mitosis and meiosis lead to.
- Mitosis leads to identical cells being formed.
- Meiosis leads to non-identical cells being formed.
What are the differences between asexual and sexual reproduction?
Sexual reproduction:
- Fusion of gametes in animals (sperm and egg) and plants (pollen and egg).
- Mixing of genetic information leads to variety in offspring.
- Involves meiosis (formation of gamete) and mitosis (formation of embryo).
Asexual reproduction:
- One parent so no fusion of gametes.
- No mixing of genetic information leads to identical offspring (clones).
- Only involves meiosis.
Where does meiosis occur?
Reproductive organs of organisms (e.g. testes and ovaries for humans).
Explain how meiosis halves the chromosomes in gametes.
- Copies of genetic information are made.
- Cell divides twice to form four gametes, each with 23 single chromosomes.
- All gametes are genetically different from each other.
Explain how fertilisation restores the full number of chromosomes.
- Gametes fuse to form zygote with 23 pairs of chromosomes.
- Zygote divides by mitosis, so that number of cells increase, to form embryo.
- As embryo develops, cells differentiate.
What are the advantages and disadvantages of sexual reproduction?
Advantages
- Produces variation in offspring.
- If environment changes, variation gives survival advantage by natural selection.
- Selective breeding can be used to increase food production, by speeding up natural selection.
What are the advantages and disadvantages of asexual reproduction?
- Only one parent needed.
- More time and energy efficient as mate doesn’t need to be found.
- Faster than sexual reproduction.
- Many identical offspring can be produced when conditions are favoured.
What are examples of organisms that can reproduce asexually and sexually?
- Malarial parasites reproduce asexually in mosquitoes and sexually in humans.
- Some fungi reproduce asexually by spores and sexually to produce variation.
- Many plants reproduce asexually by runners (e.g. strawberry plants) or bulbs (e.g. daffodils) and sexually by producing seeds.
Describe the physical structure of DNA.
Two polymers strands forming a double helix.
What is a genome?
The complete genetic material of an organism.
Why has the understanding of the human genome been important?
- Help identify genes linked to different diseases.
- Helps to understand and make treatments for inherited diseases.
- Helps trace human migration patterns in the past to track ancestry.
Describe the molecular structure of DNA.
- DNA is a polymer made from four different nucleotides.
- Each nucleotide contains a common phosphate group and a sugar molecule which is connected to one of four bases (A,C,G,T).
- A sequence of three bases (codon) is the code for a particular amino acid.
Describe the stages of protein synthesis.
- Base sequence of gene copied into mRNA.
- mRNA passes out of nucleus and into cytoplasm.
- mRNA molecule attaches to ribosome and tRNA bring amino acids to it.
- Ribosomes reads base triplets on mRNA and joins correct amino acids to it in correct order.
- Once chain is complete, it folds into unique shape which enables the proteins to do their jobs as enzymes, hormones or forming structures such as collagen.
Explain simply how the structure of DNA affects the protein made
- Different proteins have different orders of amino acids.
- The specific order of amino acids determine the shape of the protein which determines its function.
- The different orders of amino acids are determined by the sequence of bases in the gene for that protein.
Describe how genetic variants (mutations) may influence phenotype in coding DNA (codes for protein) by altering the activity of a protein.
- Most mutations do not alter the protein (as some base triplets code for the same amino acid), or only alter it slightly so that it’s appearance or function is not changed.
- Few mutations cause by a change in the amino acid which codes for the protein, alter the protein’s shape or function (e.g. enzyme’s active site may no longer fits substrate, or structural protein loses its strength)
Describe how genetic variants may influence phenotype in non-coding DNA by altering how genes are expressed.
- These parts of DNA can switch genes on and off, so mutations may affect how the genes are express (e.g. a gene that is meant to be turned off is now on which may lead to cancer)
What is a dominant allele?
A characteristic that is expressed anytime the allele is present.
What is a recessive allele.
A characteristic that is only expressed when there are two of the same allele.
What is meant by homozygous and heterozygous?
- Homozygous: When a person has two copies of the same alleles of a gene.
- Heterozygous: When a person has two different alleles of a gene.
What is meant by phenotype and genotype?
- Genotype: The alleles present in an organism
- Phenotype: The characteristic expressed in an organism.
What is a gamete?
A reproductive cell with half the usual number of chromosomes.
What is a chromosome?
A long, coiled molecule of DNA that carries genes.
What is a gene?
A section of DNA that codes for a specific amino acid sequence.
What is an allele?
A version of a gene.
What is complementary base pairing?
When complementary bases pair together from separate DNA strands (e.g. A to T; C to G)
What commonly is the cause for most phenotype features?
Multiple genes are responsible rather than one single gene (e.g. height)
What is polydactyl?
Genetic disorder which causes extra fingers or toes
- Caused by dominant allele.
What is cystic fibrosis?
Genetic disorder of cell membranes which causes thick mucus in airways and pancreas.
- Caused by recessive allele.
- Either both parents are carriers or one is a carrier whilst the other has cystic fibrosis.
What are the arguments for and against embryonic screening?
For
- Ethical: reduces number of people suffering
- Economic: treating disorders is very expensive.
- Social: multiple regulations to avoid it getting out of hand.
Against
- Ethical: encourage people to pick certain characteristics - make designer babies.
- Economical: expensive to carry out.
- Social: promote prejudice as implies those with genetic disorder are unwanted or won’t live a full life; decisions about abortion have to be made; procedure can lead to miscarriage.
What is gene therapy?
Where faulty genes can be corrected to treat inherited disorders - experimental.
How many chromosomes out of the 23 pairs carry the gene to determine sex and what are the alleles?
One pair of the 22 pairs.
- Female: XX
- Male: XY
