Genetics

• Sex linked inheritance


  Inheritance of traits determined by genes located on the sex chromosomes, especially the X chromosome
• Why are sex-linked disorders more common in males than in females?

  Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive. For a recessive allele to be expressed in females, there must be two copies of an allele, one on each of the two X chromosomes.
• X Linked Diseases


  • Color blindness
  • Hemophilia
  • Duchenne muscular dystrophy
• Color blindness


  Three human genes associated with color vision are located on the X chromosome. In males, a defective version of any one of these genes produces color blindness.
• Hemophilia


  The X chromosome also carries genes that help control blood clotting. A recessive allele in either of these two genes may produce hemophilia. In hemophilia, a protein necessary for normal blood clotting is missing. Hemophiliacs can bleed to death from cuts and may suffer internal bleeding if bruised.
• Duchenne Muscular Dystrophy


  Duchenne muscular dystrophy is a sex-linked disorder that results in the weakening and loss of skeletal muscle. It is caused by a defective version of the gene that codes for a muscle protein.
• Autosome


  A chromosome that is not a sex chromosome
• Karyotype


  A picture of an individual's chromosomes grouped in an orderly way
• Pedigree


  A chart that shows the relationships within a family
• Sex determination in humans

  Determined by the sex chromosome in the sperm cell
• Mendelian inheritance in humans


  • Typically studied by making inferences from family pedigrees
• Blood type O


  Can receive blood from individuals with blood type O
• Individuals who are heterozygous for the sickle cell allele are generally healthy and resistant to malaria
• Genetic variation refers to differences between individuals or populations in their inherited characteristics, such as height, eye color, or susceptibility to certain diseases.
• Many human traits are controlled by multiple genes.  This type of pattern is called polygenetic inheritance.
• Skin color is controlled by three genes that interact additively to influence the melanin cells produce. The more melanin produced, the darker the pigmentation of the skin.

  It is also called quantitative inheritance because each gene “adds” to the amount of melanin. 
• The likelihood that a particular event will occur is

  called probability. The principles of probability can be used to

  predict the outcomes of genetic crosses.
• The gene combinations that might result

  from a genetic cross can be determined by

  drawing a diagram known as a Punnett

  square.

  Punnett squares can be used to predict

  and compare the genetic variations that

  will result from a cross.
• A lowercase letter

  represents the

  recessive allele for

  short.
• A capital letter

  represents the

  dominant allele for tall.
• Organisms that have two identical alleles for a

  particular traits are said to be homozygous. Homozygous organisms are true-breeding for a

  particular trait.
• Organisms that have two different alleles for the same

  trait are heterozygous. Heterozygous organisms are hybrid for a particular

  trait.
• Probabilities predict the average outcome of a large number of events.

  Probability cannot predict the precise outcome of an individual event.

  In genetics, the larger the number of offspring, the closer the resulting numbers

  will get to expected values.
• Genetics is the scientific study of heredity.
• During sexual reproduction, sperm and egg cells join

  in a process called fertilization.

  Fertilization produces a new cell.
• The seeds that are produced by self-pollination inherit

  all of their characteristics from the single plant that

  bore them.
• The principle of dominance states that

  some alleles are dominant and others are

  recessive.
• The law of segregation states that each individual that is a diploid has a pair of alleles (copy) for a particular trait. Each parent passes an allele at random to their offspring resulting in a diploid organism.
• Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.
• Genetics


  Study of heredity/inheritance
• Genetics


  Transmission of characteristics from parent to offspring
• Heredity


  A genetically determined characteristic
• Trait


  Instructions on DNA that code for specific proteins or traits
• Alleles

  Two forms of a gene
• Dominant allele


  Stronger of two alleles that masks the expression of the recessive allele
• Capital/upper case letter


  Type of letter used to represent a dominant allele
• Recessive allele


  The weaker of two alleles in a pair that is often masked by the dominant allele
• Lower case letter


  Type of letter used to represent a recessive allele
• Homozygous


  Having identical alleles (ex-AA or aa)
• Heterozygous


  A genotype having one dominant and one recessive allele Ex - Aa