Genetics Flashcards
what is the basic unit of hereditary?
a gene
what is a gene?
o Composed of DNA and located on chromosomes
o Alternatives forms of genes are called alleles
o Genotype=genetic makeup
o Phenotype=physical manifestation of genetic makeup
♣ Some phenotypes correspond to a single genotypes
♣ Some phenotypes correspond to several different genotypes
what is mendel’s first law?
law of segregation
what is the law of segregation?
• 1. Genes exist in alternative forms (alleles)
o genes control specific traits in organisms
• 2. An organism has two alleles for each inherited trait, one from each parent
• 3. The two alleles segregate during meiosis
o results in gametes carrying only one allele
• 4. If two alleles in an organism are different, only one will be fully expressed
o the expressed allele is dominant
♣ usually denoted by capital letters
o the silent allele is recessive
♣ usually denoted by lower case letters
o organisms that carry two copies of the same allele are said to be homozygous for that trait
♣ organisms that carry two copies that are different are heterozygous
o the dominant allele is expressed as phenotype
this is known as Mendel’s Law of Dominance
what is a monohybrid cross?
♣ Only one trait is being studied
♣ The individuals being crossed are the parental or P generation
♣ The progeny is filial or the F generation
• Each generation is numbered sequentially (F1, F2, etc)
what is a test-cross?
♣ Used to determine the genotype of an organism
♣ Only with a recessive phenotype can a genotype be predicted with 100% accuracy
what is mendel’s second law?
♣ The inheritance of one trait is completely independent of any other
• As in, a plant with purple flowers is not more likely to be a dwarf plant than a plant with white flowers is.
♣ According to modern, non-Mendelian genetics, genes on the same chromosome do not follow this rule
what is the Hardy-Weinburg principle?
♣ Evolution can be viewed as a change in gene frequencies in a population
♣ Gene frequency is the relative frequency of a particular allele
♣ When gene frequencies are not changing, the genetic pool is stable and the population is not evolving
• This is only true in ideal situations where the following criteria are met:
o The population is very large
o No mutations affect the gene pool
o Mating between individuals in the population is random
o There is no net migration of individuals in or out of the population
o The genes in the population are all equally successful at reproducing
• Under these idealized conditions, a certain equilibrium will exist among all of the genes in a gene pool
Described by the Hardy-Weinberg equation
what is microevolution?
o Agents of microevolution
♣ Natural selection
• Genotypes with favourable mutations are selected
• Frequency of favourable genes increases within the gene pool
♣ Mutation
• Gene mutations change allele frequencies in a population
• Shift the gene equilibria by introducing additional alleles
• Can either be advantageous, disadvantageous, or neutral?
♣ Assortive mating
• If mates are chosen for a certain phenotype (sexual selection) the relative genotypes ratios will be affected and will stray from the H-W equilibrium prediction
♣ Genetic drift
• Changes in the composition of the gene pool due to chance
• Tends to be more pronounced in small populations or new populations
o Sometimes is called the founder effect
♣ Gene flow
• Migration of individuals between populations results in the loss or gain of genes
Changes the composition of the gene pool of the population
evidence of evolution
fossil records; comparative anatomy, comparitive embryology; comparative embryology
