Sebia Guinyang

• Gregor Mendel


  Father of Genetics
• Principle of Independent Assortment


  Inheritance of one trait has no effect on the inheritance of another trait
• Traits


  Determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.
• Homologous pairs


  Matching genes - one from female parent and one from male parent
• Humans have 46 chromosomes or 23 pairs
• One set from dad - 23 in sperm, one set from mom - 23 in egg
• Alleles


  Different genes (possibilities) for the same trait - e.g. blue eyes or brown eyes
• Dominant gene


  Gene that prevents the other gene from "showing"
• Recessive gene


  Gene that does NOT "show" even though it is present
• Dominant and Recessive Genes


  • Straight thumb (T) is dominant to hitchhiker thumb (t)
• Homozygous


  Both genes of a pair are the same
• Heterozygous


  One dominant and one recessive gene
• Genotype


  Combination of genes an organism has (actual gene makeup)
• Phenotype


  Physical appearance resulting from gene make-up
• Punnett Square


  Used to predict the possible gene makeup of offspring
• Black fur (B) is dominant to white fur (b) in mice
• Cross a heterozygous male with a homozygous recessive female
• Genotypic ratio = 2 Bb : 2 bb, Phenotypic ratio = 2 black : 2 white
• Genotypic ratio = 1 BB : 2 Bb : 1 bb, Phenotypic ratio = 3 black : 1 white
• Cross 2 hybrid mice

  Give the genotypic ratio and phenotypic ratio
• A man and woman, both with brown eyes (B) marry and have a blue eyed (b) child
• Genotypes of the man, woman and child: Bb, Bb, bb
• Dihybrid crosses


  Crossing involving 2 traits
• In rabbits black coat (B) is dominant over brown (b) and straight hair (H) is dominant to curly (h)
• Cross 2 hybrid rabbits and give the phenotypic ratio for the first generation of offspring: 9:3:3:1
• Cross a rabbit that is homozygous dominant for both traits with a rabbit that is homozygous dominant for black coat and heterozygous for straight hair
• Phenotypes: 100% black and straight
• Autosomes


  22 homologous pairs of chromosomes that determine body traits
• Sex chromosomes


  1 pair that determines sex (male or female)
• Females have XX sex chromosomes, males have XY sex chromosomes
• Probability of having a boy or girl is 50/50
• Father determines the sex of the child
• Incomplete dominance


  One allele is not completely dominant over another, they blend
• Incomplete dominance


  • In carnations, red (R) is incompletely dominant over white (W), resulting in pink
• Genotypic ratio = 1 RR : 2 RW : 1 WW, Phenotypic ratio = 1 red : 2 pink : 1 white
• Codominance


  Both alleles are expressed
• Codominance


  • In certain chickens, black feathers are codominant with white feathers, resulting in black and white speckled feathers
• Sex-linked traits


  Genes for these traits are located only on the X chromosome (not on the Y chromosome)
• Recessive sex-linked disorders


  • Colorblindness, hemophilia
• A female carrier for colorblindness marries a male with normal vision, expected phenotypes of their children