Protein Synthesis and Genetics

• When do mutations happen?

  Mutations happen when the sequence of DNA changes.
• Mutations can be ...

  fatal, negative, benign (have no effect) or beneficial
• Somatic mutation= in the body cell- not passed to the next generation
• Gametic mutation = occurs in the gametes, can be passed on to the next generation
• • Point mutation = a substitution (one base pair is changed)- the other codons are unaffected
• • Frameshift mutation = a single base pair is lost or added- all codons “downstream” are affected
• • Deletion - part of the chromosome is left out
• • Translocation - a broken piece attaches to a non-homologous chromosome
• • Duplication - a piece of a chromosome is repeated
• • Non-disjunction - a pair of chromosomes fails to separate during cell division (can result in a zygote with an extra chromosome)
• • Inversion - a piece of the chromosome breaks off and reattaches in reverse order
• A mutagen is an outside agent that causes mutations. For example: UV rays, cigarette smoke, radiation, some chemicals and viruses
• A gene is a piece of DNA that has the instructions to make a protein.
• Genes on homologous chromosomes are located in the same position. * This locus (or specific position) helps scientists study genes.
• The same gene can have many versions.
• An allele is any version of a gene that occurs at the same locus (position on a chromosome).
• Dominant allele: the allele that gets expressed when an individual has two different alleles.
• Recessive allele: the allele that gets hidden when an individual has two different alleles. 
• Heterozygous: 2 different alleles
• Homozygous: 2 of the same allele
• Genotype is an organism’s genetic makeup (genes/alleles). 
• Phenotype is an expression of an organism’s DNA; often it’s appearance.
• Punnett squares are tables that show all the possible combinations of gametes. 
• Punnett squares are used to determine the probability of an offspring having a particular genotype.
• With incomplete dominance, a cross between organisms with two different phenotypes (like red and white flowers) produces an offspring with a third phenotype (pink flowers) that is a blending of parental traits. 

  Both alleles show dominance, both are assigned capital letters.  
• With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental phenotypes appear together, side by side. 
• Genes can have multiple (more than 2) alleles
• Blood Type is an example of multiple alleles. 
• Possible blood types : A, B, AB, O
• I^A allele is dominant to i
• I^B allele is dominant to i
• I^A and I^B alleles are codominant
• Type A: I^A I^A , I^A i
• Type B: I^B I^B , I^B i
• Type AB: I^A I^B
• Type O: i i
• Polygenic traits are traits that are controlled by more than one gene.
• Genes on sex chromosomes are called sex-linked genes. 
• Males have an XY genotype
• Females have an XX genotype