Genetic variation Flashcards
Revision
Chromosome
A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
Crossing over
the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.
Gene
sequence of DNA that codes for a protein and thus determines a trait
Trait
A characteristic that an organism can pass on to its offspring through its genes.
Locus
Location of a gene on a chromosome
Mutation
change in a DNA sequence that affects genetic information
Mutagen
A chemical or physical agent that interacts with DNA and causes a mutation.
Meiosis
a type of cell division that results in four daughter cells each with half the number of chromosomes (haploid) of the parent cell, as in the production of gametes.
Crossing over
Process in which homologous chromosomes exchange portions of their chromatids during meiosis.
Chiasma
site of crossing over
Independent assortment
the random distribution of the pairs of genes on different chromosomes to the gametes
Segregation
Separation of alleles during gamete formation
Gamete
Sex cell, e.g. egg (ovum) or sperm in humans
Somatic cell
any cell of a living organism other than the reproductive cells.
Diploid
An organism or cell having two sets of chromosomes or twice the haploid number
Haploid
An organism or cell having only one complete set of chromosomes
Gene pool
All the genes, including all the different alleles for each gene, that are present in a population at any one time
Dihybrid cross
A cross between two individuals, concentrating on two definable traits
Homozygous dominant
Both alleles (factors) for a trait are the same and dominant (AA)
Heterozygous
An organism that has two different alleles for a trait
Pure breeding
Individuals that are homozygous that will always produce the same offspring when crossed together
Pedigree chart
A chart which shows several generations of related families and how traits are passed down through the offspring.
Incomplete dominance
Situation in which one allele is not completely dominant over another allele, so heterozygotes will be a blend of the two phenotypes.
Co-dominance
situation in which both alleles of a gene contribute to the phenotype of the organism, so heterozygotes will have BOTH shown in their phenotype
Multiple alleles
three or more forms of a gene that code for a single trait
Lethal alleles
Alleles that cause an organism to die when present in homozygous condition.
Allele frequency
Number of times that an allele occurs in a gene pool compared with the number of alleles in that pool for the same gene
Evolution
The gradual change in a species over time
Genetic drift
A change in the allele frequency of a population as a result of chance events rather than natural selection.
Natural Selection
A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits (and how suitable they make the organism to the environment).
Founder effect
Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.
Bottleneck effect
Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.
Allele
An alternative form of a gene.
Test cross
the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype
Linked genes
Genes located on the same chromosome that tend to be inherited together in genetic crosses.
