Inheritance Flashcards
Genome
The entire DNA of an organism
Gene
A section of DNA which codes for a particular protein
What does the nucleus of a cell contain?
Chromosomes on which genes are located
DNA molecule
Two strands coiled to form a double helix, the strands being linked by a series of bases: Adenine with Thymine, and Cytosine with Guanine
RNA molecule
Single stranded and contains Uracil instead of Thymine
Transcription
When two strands of DNA double helix are separated. One strand is used as a template and the RNA bases are lined up in correct order using complementary base pairing.
Translation
Involves assembling amino acids in correct order following the sequence of bases on mRNA. It takes place at one of many small structures in the cell cytoplasm called ribosomes. The mRNA travels out of the nucleus and attaches to a ribosome.
Protein synthesis
The code for making the protein is read such that every three bases on the mRNA codes for one amino acid. This triplet of bases is know as a codon. Amino acids are carried to the ribosome by another molecule called tRNA which also has a triplet of bases called an anticodon and this can match up with the complementary bases on the mRNA. The ribosome then forms peptide bonds between the amino acids and a polypeptide chain is formed. This can then fold and join up with other polypeptides to form a protein.
Alleles
Alternate forms of a gene which give rise to differences in inherited characteristics
Dominant
Allele of a gene that is expressed in the heterozygote
Recessive
Allele that is not expressed in the phenotype when a dominant allele is present (i.e. the heterozygote)
Homozygous
Genotype with the same allele of a gene e.g. AA or aa
Heterozygous
Genotype with different alleles of a gene e.g. Aa
Phenotype
How a gene is expressed. The “appearance” of an organism resulting from its genotype
Genotype
Alleles an organism has for a certain characteristic
Codominance
Pattern of inheritance where neither allele of a gene is dominant over the other so that both alleles are expressed in the phenotype
What are most phenotypic features a result of?
Polygenetic inheritance rather than single genes
What is our sex determined by?
The presence of the Y chromosome, XX in a female and XY in a male
Prophase
Before mitosis the DNA replicates and chromosomes formed 2 exact copies called chromatids. In prophase the chromatids become visible, joined at a centromere. The nuclear membrane breaks down.
Metaphase
A structure called the spindle forms. The chromosomes line up at the “equator” of the spindle, attached to it by centromeres.
Anaphase
The spindle fibres shorten and pull the chromatids to opposite ends (“poles”) of the cell. The chromatids separate to become the chromosomes of the two daughter cells.
Telephase
Two new nuclei form at the poles of the cell. The cytoplasm starts to divide to produce two daughter cells. Both daughter cells have identical sets of chromosomes.
When does mitosis occur?
During growth, repair, cloning and asexual reproduction
What does the division of a cell by meiosis produce?
Four cells, each with half the number of chromosomes, this results in the formation of genetically different haploid gametes
What does random fertilisation produce?
Genetic variation of offspring
What is the diploid number in human cells?
46
What is the haploid number in human cells?
23
What causes variation within a species?
Genes, environment or both
Mutation
A rare, random change in genetic material that can be inherited
How can a change in DNA affect the phenotype?
By altering the sequence of amino acids in a protein
ATT TCC GTT ATC
ATT TTC CGT TAT C
Duplication
ATT TCC GTT ATC
ATT CCG TTA TC
Deletion
ATT TCC GTT ATC
ATG TCC GTT ATC
Substitution
ATT TCC GTT ATC
ATT CCT GTT ATC
Inversion
Why do most genetic mutations have no change?
The same amino acids is coded for because multiple codons code for the same amino acid (Substitution, Inversion)
Why do some genetic mutations have a small effect?
One amino acid changes (Substitution, Inversion)
Why do genetic mutations rarely have a significant effect?
The protein changes (Duplication, Deletion)
What can increase the incidence of mutations?
Exposure to ionising radiation (e.g. gamma rays, X-ray and UV) and some chemical mutagens (e.g. tobacco)
What is the process of natural selection?
- Individuals in a species show variation that is caused by differences in genes
- Individuals with a characteristic that is advantageous in the environment have a higher chance of survival
- Surviving individuals are more likely to reproduce and so are more likely to pass on their advantageous alleles
- Over many generations the advantageous characteristics become more common in the population
How can antibiotic resistance increase in bacterial populations?
- A random mutation can give rise to a new bacterial allele that code for antibiotic resistance
- When the bacterial population is exposed to an antibiotic any individuals without the resistant allele die, while those with the resistant allele survive
- The surviving bacteria are more likely to reproduce, passing on their resistant alleles their offspring
- Over several generations the frequency of the resistant allele increases, eventually resulting in an antibiotic resistant strain of bacteria
Why is antibiotic resistance a problem?
Bacteria can only be treated with the application of a different antibiotic; in some cases several antibiotics need to be used to treat a resistant infection. Antibiotic resistance therefore makes bacterial infections more difficult to control
