Biology Chapter on DNA and Genetics

DNA Structure and Characteristics

• DNA (deoxyribonucleic acid) is a double helix structure composed of nucleotide units.
• Nucleotides consist of a sugar, phosphate group, and nitrogenous base.
• The four nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G), which form complementary base pairs: A-T and C-G.
• DNA is organized into structures called chromosomes.

Chromosomes and Human Count

• Humans have 46 chromosomes arranged in 23 pairs.
• Each pair consists of one chromosome from each parent, providing genetic diversity and redundancy.
• 22 pairs are autosomes, and the 23rd pair consists of sex chromosomes (XX in females, XY in males).

Karyotypes and Chromosomal Composition

• A karyotype is a visual representation of an individual's chromosomes used to identify chromosomal abnormalities.
• Diploid (2n) refers to cells with two sets of chromosomes (46 in humans), while haploid (n) cells have one set (23).

Genetic Inheritance

• Alleles are different versions of a gene that can exist at the same locus.
• Dominant alleles mask the expression of recessive alleles; a dominant trait appears in the phenotype if at least one dominant allele is present.
• Punnett squares can be used to predict the probability of inheriting certain traits based on parental genotypes.

Genotypes, Phenotypes, and Sex-linked Traits

• Genotype refers to the genetic constitution of an individual (e.g., BB, Bb, bb), while phenotype is the observable physical or biochemical characteristics.
• Sex-linked characteristics are traits associated with genes located on sex chromosomes, often affecting males more due to the presence of a single X chromosome.

Mutations and Their Types

• Mutations are changes in the DNA sequence that can affect gene function and traits.
• Types of mutations include:
  • Substitutions: Replacement of one nucleotide with another.
  • Deletions: Removal of one or more nucleotides.
  • Insertions: Addition of one or more nucleotides.
  • Inversions: Reversal of a sequence of nucleotides.
• Mutations can arise from errors during DNA replication, environmental factors, or chemical exposure.

Genetic Processes

• Transcription: The process where DNA is copied into messenger RNA (mRNA).
• Translation: The conversion of mRNA into a protein at the ribosome.

Mitosis Overview

• Mitosis is the process of cell division that results in two identical daughter cells, crucial for growth, development, and maintenance.
• Interphase: The preparatory phase before mitosis, where the cell grows and DNA replicates.
• Mitosis consists of four main phases:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• The purpose of mitosis is to ensure the equal distribution of genetic material to daughter cells, maintaining the original cell’s genetic identity.

Test your knowledge on the structure of DNA, chromosomes, and inheritance. This quiz covers essential topics such as complementary base pairs, genotypes, and mutations. Challenge yourself with questions on mitosis and transcription to master the fundamentals of genetics.