Genetic Notes

• Genetics: Scientific study of heredity.
• Heredity: The passing of traits from one generation to the next.
• Trait: Any observable characteristics an organism may have.
• Who was the first person to study genetics?

  Gregor Mendel
• Why did Mendel study peas?

  1.They reproduced quickly.

  
  

  2.Their traits were easily observable.

  
  

  3.They were readily available.

  
  

  4. They could self pollinate meaning he could control which plants pollinated.
• Principal of Dominance: When an organism is crossed for a pair of contrasting traits only the dominant trait can be seen in the hybrid. The recessive factor was hidden.
• Allele: This is the form a gene can be. It can be dominant or recessive, but not both.
• F1 Generation is the first set of offspring that are produced by parents.
• F2 Generation is the second set of offspring created from the offspring of the parents. These offspring are the same thing as grandchildren.
• Pure Breed/Strain is a term that refers to an organism having either two dominant factors or two recessive factors as a trait.
• Homozygous is a term meaning that an organism has the same alleles for a gene. (Same as pure breed)
• Heterozygous is a term meaning that an organism has different alleles for a gene.
• Genotype is the genetic makeup of an organism. It is the combination of alleles for an organism.
• Phenotype is the physical characteristics displayed by an organism. It is the appearance of a trait in an organism.
• A punnet square is a square that is used to help determine the possible/probable outcomes of a cross between two individuals.
• Cross is another way of saying that a female has been mated with a male.
• 1. Principle of Dominance: A principle proposed by Mendel that stated that the Dominant form of a gene (trait) will always be expressed.
• 2. Law of segregation: A law proposed by Mendel that stated that pair of factors (alleles) for a trait separated during the formation of gametes and then recombined during fertilization.
• 3. Law of Independence Assortment: A law stating that during meiosis, genes for different traits are separated and distributed to gametes independently of one another.
• Single factor cross: A cross that is done for one trait.
• A monohybrid cross is a single factor cross where the parents are heterozygous or hybrid for the trait in question.
• A test cross is a cross in which an individual of unknown genotype is crossed with a homozygous recessive individual.
• A two factor cross is performed where two traits are involved at the same time.
• A dihybrid cross is a two factor cross where both parents are heterozygous for both traits.
• Incomplete dominance is a situation where neither of the two alleles for a trait is dominant.
• Co-Dominance is a situation where both alleles for a trait may be dominant. Both alleles are expressed in the heterozygous individual.
• Some genetic traits are expressed by multiple (many) alleles. Such a trait is blood type in Humans. The blood type of humans is controlled by many alleles and not just one or two as is the norm.
• Walter Sutton and Thoeodor Boveri studied chromosomes during various phases of meiosis. They found out that chromosomes occur in pairs, that chromosomes separate during anaphase 1 and align themselves independently.
• Thomas Morgan studied fruit flies and found that chromosomes in them are the same except for one pair. (Sex chromosomes -> sex-linked genes or traits)
• Sex-linked traits are recessive.

  Sex-linked traits are carried on the X chromosome, normally.

  If a person has a big allele and a small allele, they are a carrier of the trait.
• Polygenic Inheritance is the idea that traits are affected by more than one gene.
• Polygenic Inheritance: Two genes work at the same time for the same trait. This leads to variations in the expression of the trait.