Module 5.1

• Genes are units of heredity passed from parent to offspring
• Genes are also distinct set of nucleotides within a chromosome that is , when transcripted, allow or prevent the synthesis of particular amino acid chain or protein.
• Gene dictates the expression of specific traits such as hair/eye color, height, weight, etc.
• Genes are located at a specific loci (sing. locus) .
• Loci (or locus)- specific region/location of a gene in a chromosome. For example, CFTR gene located at 7q31.2
• Locus can be a specific band, sub-band or entire region.
• HLA gene located at 6p21.1-21.3
• PWCR gene located at 15q 11.2 - q13.1
• Alleles are variants of the same gene.
• bey2 gene is one of the gene pairs that dictate eye color. The dominant allele ( BB/ Bb) for brown eyes, while the recessive allele (bb) for blue eyes.
• If both alleles of an organism are the same (BB or bb), that is referred to as homozygous. If alleles are different (Bb), heterozygous.
• Genotype refers to the specific set of genes inherited that Can allow for the development of traits.
• Phenotype refers to the traits that manifest or appear and can be affected outside of genetics.
• Gregor Mendel is the father of genetics whose studies On how traits are inherited built the principles of genetics we refer to us MENDEL'S LAWS.
• law of segregation states that each individual organism has two alleles that can encode a characteristic.
• During meosis or formation of gametes, these alleles contained in a homologous chromosome segregate, resulting into each gamete having only one allele.
• The Law of Independent Assortment states that the alleles of 2 or more different genes get sorted into gametes independently from one another.
• Punnett Square was developed by English geneticist Reginald Punnett in 1917 which is used to predict the outcomes of genetic crosses between the two parents.
• Branch diagrams are a convenient way of organizing all the combinations of characteristics.
• PUNNETT SQUARE testcross can also be used to identify parents.
• punnett square allows for calculation of the probability of a specific genotype in occuring.
• Probability method can be used if we only need to identify the probability of one possible phenotype. We simply need to multiply the probability of each characteristic.
• Gene interaction refers to the relationships between the genes that affect the phenotype of an organism.
• Gene interaction occurs when allelic or non-allelic genes affect the expression of specific phenotypic traits in an organism.
• Allelic gene interaction involves complete, incomplete, and codominance, multiple, and lethal genes.
• Non-allelic Gene Interaction includes complementary genes, epistasis, variable expressivity, penetrance, and anticipation.
• Complete dominance:

  • 2 homozygote phenotypes are expressed: Dominant (DD) or recessive (dd).
  • In heterozygous phenotype (Dd), the dominant trait is expressed.
• Incomplete dominance is when a heterozygous phenotype occurs. That is, the resulting phenotype is intermediate between the two parents. Phenotypic ratio is 1:2:1.
• Codominance express both alleles simultaneously.
• Pleiotropy: One gene affects multiple characteristics.

  Example: Marfan Syndrome Where there is mutation in FBN1 gene that produces protein fibrillin-1 that is found all over the body and its absence will cause multiple disorders throughout the body.
• Lethal allele causes death typically before birth. Alleles associated with this are recessive lethal.

  Example: Achondroplasia

  Normal: Homozygous Dominant (AA)

  Dwarfism: Heterozygous (Aa)

  Fetal Death: Homozygous recessive
• However, some disorders may also be caused by dominant lethal allele.

  Death before birth: Genotype not seen in living population, but rather, as an implantation failure or miscarriage.

  survive Past birth: Genetic disorder

  Example: HUNTINGTON'S DISEASE, a late onset disease that causes degeneration of nerve tissue.
• Complementary genes are type of gene interaction Where two genes work together to create a specific phenotype or visible trait.
• sex Linkage: The absence or presence of the Y chromosome is the major genetic difference because females and males share all 22 autosomes and the X chromosome.