Chapter 13 - Mendelian Genetics and Probability 

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• The transmission of genetic information is an important function in living organisms.

  • During protein synthesis, information is transported inside an organism from the nucleus to the ribosome.
  • Information is passed down from generation to generation by inherited units of chemical information known as genes.

• Through the processes of conjugation, transformation, or transduction, information can be passed across individuals of the same generation.

  • DNA and RNA are the bearers of this genetic information in all circumstances.
  • All forms of life have DNA, RNA, and ribosomes.
  • DNA and RNA employ a genetic code that all living species share.
  • This provides compelling evidence for the shared ancestry of all living species on Earth.

• Mendel's rules of segregation and independent assortment describe how genetic inheritance works.

  • Mendel's rules of segregation and independent assortment describe how genetic information is passed down from generation to generation.
  • It is crucial to emphasize that Mendel's rules of segregation and independent assortment only apply to features that are coded for by genes on distinct chromosomes.
  • Genes that are near together on the same chromosome are related and are more likely to be inherited together.
  • The principles of segregation and independent assortment established by Mendel do not apply to connected genes.
  • ^^According to Mendel's rule of segregation, each organism has two variants of each trait (called alleles), one from each parent, and these alleles segregate, or separate, independently into gametes.^^
  • This segregation takes place during the anaphase of meiosis.
  • The alleles on those chromosomes will separate during anaphase I.

• The alleles on those chromosomes will partition into different gametes during anaphase I.

  • Each gamete receives one variant (or allele) for a characteristic.
  • When two gametes fuse during fertilization, the child has two alleles for the characteristic.
  • @@According to Mendel's law of independent assortment, genes for distinct characteristics segregate independently of one another.@@

• During metaphase I of meiosis, this independent sorting occurs.

  • In pea plants, for example, acquiring the gene for purple blossom color is a separate event from inheriting the allele for wrinkled peas.
  • This is due to the fact that the gene for pea blossom color is on a different chromosome than the one for pea form.
  • In metaphase I of meiosis, these chromosomes assort separately.
  • In metaphase I of meiosis, these chromosomes assort separately.

• A pedigree is a chart that shows how a trait is passed down across generations.

  • Horizontal lines between two people in a pedigree indicate that they have had children together.
  • Vertical lines represent the offspring of these people.
  • Circles are often used to symbolize ladies, whereas squares are used to represent males.

• Examining the inheritance pattern of a characteristic presented in a pedigree can provide information about the trait's likely mode of inheritance.

  • Because only one allele for the characteristic is necessary for it to be produced, dominant traits tend to be exhibited in at least one parent and their children.
  • Because the parents are heterozygous carriers of the trait, recessive characteristics are frequently displayed in kids but not in either parent.
  • Males are more likely than females to have sex-linked recessive characteristics.
  • Having two copies of the same allele for a characteristic is referred to as being homozygous (i.e., AA or aa).

• ^^Heterozygous—having two distinct alleles for a characteristic (for example, Aa); Mendel called this a "hybrid."^^

  • ^^Dominant—only one copy of the allele is required for the characteristic to be present.^^
  • Dominant characteristics require just one copy of the allele for the trait to be expressed in the phenotype; dominant traits are those that are expressed in heterozygous organisms.
  • Recessive—requires two copies of the allele for the trait to be expressed in the phenotype; heterozygous organisms do not exhibit recessive characteristics.

• A dihybrid cross examines the outcome of crossing two organisms (both heterozygous for the same two characteristics).

  • Math is your friend when it comes to solving dihybrid crosses!
  • Treat each attribute independently, calculate the odds of each result for each trait, then solve the issue using probability rules.

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