Biology: Chapter 12 Flashcards
Genes
DNA sequences that code for heritable traits that can be passed from one generation to the next
Genotype
the genetic combination possessed by an individual
Phenotype
the manifestation of a given genotype as an observable trait
Dominant
if only one copy of an allele is needed to express a given phenotype
Recessive
if two copies are needed to express a given phenotype
Complete dominance
-when only one dominant and one recessive allele exist for a given gene
-dominant allele will mask the recessive allele
Codominance
more than one dominant allele exists for a given gene
Incomplete dominance
heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes
Penetrance
-population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype
-Full penetrance: 100% of the individuals who have the allele show symptoms or the trait
Expressivity
-varying phenotypes despite identical genotypes
-Constant expressivity: all individuals with a given genotype express the same phenotype
-Variable expressivity: individuals with the same genotype may have different phenotypes
Mendel’s First Law: Law of Segregation
-Genes exist in alternative forms (alleles)
-An organism has two alleles for each gene- one inherited from each parent
-The two alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait
-If two alleles of an organism are different, only one will be fully expressed and the other will be silent. The expressed allele is said to be dominant, while the silent allele is recessive (codominance and incomplete dominance are exceptions to this rule)
Mendel’s Second Law: Law of Independent Assortment
-The inheritance of one gene does not affect the inheritance of another gene
-Segregation and independent assortment allow for greater genetic diversity in the offspring
Mutations
-a change in DNA sequence, and it results in a mutant allele
-Mutagens: substances that can cause mutations
-Transposons: can insert and remove themselves from the genome; if a transpon inserts in the middle of a coding sequence, the mutation will disrupt the gene
Point mutations
occur when one nucleotide in DNA (A, C, T, or G) is swapped with another
Silent mutation
-point mutation
-change in nucleotide has no effect on the final protein synthesized from the gene
Missense mutation
-point mutation
-the change in nucleotide results in substituting one amino acid for another in the final protein
Nonsense mutation
-point mutation
-the change in nucleotide results in substitution a stop codon for an amino acid in the final protein
Frameshift mutations
-occur when nucleotides are inserted into or deleted from the genome
-Insertion of deletion of nucleotides can shift the reading frame, resulting in changes in the amino acid sequence or premature truncation of the protein
-Insertion or deletion mutations
Deletion mutations
-a large segment of DNA is lost from a chromosome
-small deletion mutations are considered frameshift mutations
Duplication mutations
a segment of DNA is copied multiple times in the genome
Inversion mutations
a segment of DNA is reversed within the chromosome
Insertion mutations
-a segment of DNA is moved from one chromosome to another
-Small insertion mutations are considered frameshift mutations
Translocation mutations
a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome
Genetic leakage
-a flow of genes between species
-Individuals from different (but closely related) species can mate to produce hybrid offspring (ex: mule which is a hybrid of a male horse and female donkey)
