DNA and the genetic code

• What is variation?

  Small differences in characteristics between members of a species
• What is continuous variation?

  usually controlled by multiple genes

  can be influenced by the environment

  continuous distribution of values

  quantitative

  range of measurements from 1 extreme to the other
• What is discontinuous variation?

  aka discrete

  distinct categories that individuals can be placed into

  usually qualitative, no overlap

  mostly unaffected by environment

  either have a certain trait or don’t - e.g., blood type, tongue rolling.
• What is the genotype?

  Genetic makeup of organism

  Total DNA in its genes

  All alleles that an organism contains

  Sets limit of how an individual may vary

  Inherited
• What is a gene?

  hereditary material passed from parent made of sequences of DNA, arranged on chromosomes.
• what is an allele?

  different forms of genes found at same place on a chromosome
• what are homologous chromosomes?

  pairs of chromosomes that are similar in shape, size, and type of gene.

  humans have 23 pairs of homologues
• what is a karyotype?

  image of an organisms chromosome
• What is meiosis?

  cell division that halves genetic number, forming 4 genetically unique gametes.

  essential for sexual reproduction

  2 divisions: meiosis 1 and meiosis 2 (both prophase, metaphase, anaphase and telophase)
• what is genetic recombination?

  genetic material being rearranged due to crossing over, recombinant chromosomes contain genes from both mother and father.

  increases genetic diversity, accelerates evolution.
• what are homozygous alleles?

  both loci on separate chromosomes contain the same allele
• what are heterozygous alleles?

  loci of different chromosomes contain different alleles
• what did Mendel’s pea experiment find?

  that there are different alleles for different characteristics (dominant or recessive)
• what do monohybrid crosses test for?

  1 trait, usually 3:1 ratio
• what do dihybrid crosses test for?

  2 traits, usually 9:3:3:1 ratio
• what is Mendel’s test cross?

  tests whether a dominant phenotype is homozygous or heterozygous by crossing it with a recessive phenotype
• What is Mendel’s law of dominance?

  in a pair of alleles, one may be dominant and mask expression of a recessive allele
• What is Mendel’s law of segregation?

  in gamete formation, alleles for each trait separate so each gamete has only one allele
• What is co-dominance?

  When both alleles in a heterozygous individual are fully expressed, resulting in a phenotype that shows a combination of both traits.