Mutations: Somatic and Germ Line

• Genetic information is analyzed to understand how it is expressed in cells.
• Inheritable genetic variations can arise through meiosis, replication errors, or environmental influences.
• Biotechnology's use in forensics, medicine, and agriculture raises ethical questions.
• Mendel's laws explain reproductive variability through meiosis, with mathematical models predicting inheritance.
• A mutation is any change in DNA; it can occur in any cell.

Somatic Mutations

• Somatic mutations occur in body cells, are passed on by mitosis, and can cause cancer.

Germ Line Mutations

• Germ line mutations occur in germ cells, which give rise to gametes, and are passed on by meiosis, potentially leading to mutated offspring.
• Mutations can result from mistakes during DNA replication, mitosis, meiosis, or protein synthesis.
• Mutagens like radiation, UV light, cigarette smoke, and viruses can cause DNA mutations.
• Gene mutations happen during DNA replication and alter the original DNA sequence, such as in Cystic Fibrosis, Dwarfism, and Sickle Cell Anemia.
• Chromosome mutations often occur during meiosis, changing the number or location of genes, examples include Down Syndrome, Klinefelter's Syndrome, and Turner's Syndrome.

Gene Mutations

• • Point mutations are a specific type of genetic mutation that involve the substitution of one nucleotide base for another within the DNA sequence. This can occur due to various reasons, including errors during DNA replication or exposure to environmental factors known as mutagens, which can include radiation or certain chemicals. One well-known example of a point mutation is sickle cell anemia, a hereditary disorder caused by a single nucleotide change in the hemoglobin gene, leading to abnormal red blood cell shape and impaired oxygen transport.
  • Frameshift mutations, on the other hand, occur when nucleotides are inserted into or deleted from the DNA sequence, resulting in a shift in the reading frame of the genetic code. This alteration affects the entire sequence of codons downstream from the mutation, potentially leading to the production of a completely different and usually nonfunctional protein. Common examples of frameshift mutations are deletions or insertions that disrupt the normal triplet grouping of nucleotides.

Chromosome Mutations

• • Duplication is a genetic alteration that significantly impacts the size of chromosomes by resulting in multiple copies of a single gene. This process can lead to gene amplification, which may have various consequences depending on the gene involved, potentially increasing the expression of certain traits or even causing developmental disorders.
  • Translocation is a complex genetic phenomenon where segments of chromosomes are exchanged between non-homologous chromosomes. This event can occur during meiosis, specifically during the crossing-over phase, where homologous chromosomes exchange genetic material. Translocation can disrupt gene function and lead to diseases, including certain types of cancer.
  • Nondisjunction is a critical mistake in cellular division that occurs when chromosomes do not separate properly during anaphase. This leads to cells having an abnormal number of chromosomes—either too many or too few—resulting in an unequal distribution. This can have serious complications for the organism, including various genetic disorders.
  • Down Syndrome, also known as Trisomy 21, is one of the most well-recognized examples of nondisjunction. In this condition, there are three copies of the 21st chromosome instead of just two. This extra genetic material causes a range of developmental and intellectual challenges, along with distinct physical features.
  • A pedigree chart is a powerful tool in genetics that diagrams the inheritance of traits across generations within a family. It is utilized to trace phenotypes (observable characteristics) and genotypes (genetic makeup) to identify whether individuals may be carriers of certain genetic diseases or traits, thus providing valuable information in genetic counseling.

Pedigree Notation

• Squares represent males, while circles represent females.
• Shaded shapes indicates an individual "has it" (affected), while clear shapes indicates an individual "doesn't have it" (unaffected).

Autosomal Recessive Trait/Disease Pedigree

• Most prevalent inheritance for genetic diseases.
• The disease is rare; only a few family members are affected.
• Males and females are equally likely to inherit the disease.
• The Disease often skips generations.
• Examples include Cystic Fibrosis, Sickle Cell Anemia, Phenylketonuria (PKU), and Tay-Sachs Disease.

Autosomal Dominant Trait/Disease Pedigree

• The disease is common afflicting many family members.
• Males and females are equally likely to inherit.
• The Disease never skips a generation.
• Examples include Achondroplasia, Huntington’s Disease, and Neurofibromatosis

Sex-Linked Recessive Trait/Disease Pedigree

• Disease is rare with only a few family members being affected.
• Males are often more affected than females.
• Disease may skip generations.
• Affected fathers don't pass it on their sons.
• Examples include: Hemophilia, Duchene Muscular Dystrophy, and Colorblindness

How to Determine the Pattern of Inheritance in a Pedigree

• If males are more affected, it's sex-linked.
• If not, and parents of the same shade have a child of a different shade, label the child homozygous recessive (rr) with heterozygous parents (Rr).
• If the child is shaded, it's autosomal recessive trait.
• If the parents are shaded, it's autosomal dominant trait.