DNA and Genetics basics

• What are the two processes of cell division?

  Mitosis and Meiosis
• Mitosis: what happens during interphase?

  • G1 Phase (Gap 1): The cell grows, prepares to replicate and carries out its normal functions.
  • S Phase (Synthesis): DNA is replicated, ensuring each chromosome now consists of two sister chromatids.
  • G2 Phase (Gap 2): Further growth and preparation for mitosis.
• Mitosis: What happens during prophase?

  • The chromosomes start to condense (making them easier to pull apart later on).
  • The mitotic spindle fibers begin to form on opposite poles of the cell, between the centrosomes.
  • The nuclear membrane breaks down, allowing the spindle fibers to access the chromosomes.
  • The nucleolus (or nucleoli, plural: a part of the nucleus where ribosomes are made), disappears. This is a sign that the nucleus is getting ready to break down.
• Mitosis: What happens during metaphase?

  • The mitotic spindle fibers attach to the centromeres of each chromosome and aligns them at the metaphase plate

  A)

  
• Mitosis: What happens during anaphase?

  • The spindle fibers on opposite poles of the cell contract and separate the chromosomes into sister chromatids
  • The sister chromatids are pulled towards opposite ends of the cell

  
• Mitosis: What happens during telophase?

  • Chromatids reach opposite poles and start to de-condense, transitioning back into chromatin (the stringy form)
  • Two new nuclei form, one for each set of chromosomes. Two Nuclear membranes and nucleoli reappear.
  • The spindle fibers disintegrate

  
• When cytokinesis finishes, we end up with two new identical daughter cells, each with a complete set of chromosomes identical to those of the mother cell.
• Mitosis: cytokinesis

  • The division of the cytoplasm to form two new cells. In animal cells, a cleavage furrow forms, pinching the cell's membrane in two. This process physically divides the cell into two daughter cells. (The cell squeezes in the middle, like pinching and it splits into two new cells)
  • In plant cells, a cell plate forms in the middle, gradually developing into a new cell wall. This division creates two separate plant cells. (instead of pinching, a special wall starts growing in the middle, like building a new fence)

  
• Mutation is a sudden heritable (Heritable" refers to traits or characteristics that can be passed from one generation to the next through genetic information) change occurring in DNA sequences which results in changes in the genotype and phenotype of an organism
• Point Mutations: Changes in a single base pair that alters the sequence of bases within a gene
• Frameshift mutations: Insertions or deletions of more than one base pair. Loss (deletion) or Gain (insertion/duplication) of a DNA segment which causes chromosomal abnormalities (aberrations)
• Pedigree analysis is the study of the genetic relationships between individuals in a family.
• Pedigree analysis helps to understand whether a trait is dominant or recessive.
• A pedigree chart shows how certain traits are inherited by different generations of a family.
• Gregor Mendel is the "father of genetics" who studied pea plants and discovered laws of inheritance
• Genetics is the study of inheritance, heredity and variation of characters or study of genes and chromosomes.
• Variation refers to differences among organisms within a species due to genetic factors.
• Hereditary refers to characteristics that can be passed from parents to offspring through their genes.
• Inheritance refers to the transmission of genetic information from parent to offspring.
• Character is a heritable feature among the parent and the offspring. (ex: eye colour)
• A trait is the variance of a character. Ex: Brown eye colour, blue eye colour.

  The character is the passed down eye colour, the trait is the eye colour itself
• Alleles are alternative forms of a gene, they can be similar or different. (ex: T[tall] and t[dwarf] these are different. together it would be Tt which is a heterozygous combination)
• Genotype is the specific genetic code which determines the offsprings inherited traits and characteristics.
• Phenotype is the observable physical characteristics of an individual.
• Homozygous means having two identical alleles for a particular characteristic. (ex: TT, YY, etc.)
• Heterozygous means having different alleles for a particular characteristic. (ex: Tt, Yy, etc.)
• A dominant character is expressed in heterozygous condition. It indicates with capital letter. (Ex: Tt, the capital T is the dominant character)
• Recessive characters are only expressed when they are homozygous and suppressed in heterozygous. They indicate with lowercase letters. (Ex: Tt, the lower case t is recessive)
• A Hybrid individual is produced by the mating of two genetically unlike parents
• The Punnett Square is used to predict the probability of offspring inheriting certain traits from their parents based on Mendel's Laws
• Genetic variation occurs due to mutations that can be beneficial or detrimental to an organism.
• DNA stands for deoxyribonucleic acid and has a double-helix structure
• DNA resembles a twisted ladder with two long strands of nucleotides coiling around each other
• Nucleotides are the basic building blocks of DNA and consist of a phosphate group, a deoxyribose sugar molecule, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G)
• Adenine always pairs with thymine, and cytosine pairs with guanine, forming stable hydrogen bonds
• Pair between A and T produces 2 hydrogen bonds, and the pair between C and G produces 3 hydrogen bonds
• DNA strands run in opposite directions—one from the 5' end to the 3' end and the other from the 3' end to the 5' end
• Double-stranded DNA with complementary base pairing ensures the accuracy of DNA replication during cell division
• DNA has major and minor grooves along its helical structure, providing access points for cellular machinery involved in processes like replication and transcription
• Genes are specific sequences of nucleotides that encode instructions for an organism's development and function