Biology - Genetics and DNA notes

Genetics and DNA:

  • Genetics is the study of genes and hereditary (genetic heritage)
  • Genetic material is encoded and passed down through DNA
  • DNA stands for Deoxyribonucleic acid and is found in the nucleus
  • DNA stores the genetic information needed to build and control the cell
  • DNA has a double helix structure where two separate strands of
  • DNA are connected together
  • Code in DNA gives instructions for building proteins and other molecules
  • RNA - (partial copy of DNA) ribonucleic acid, contains bases A-U C-G, made according to DNA
  • DNA is made up of chemical building blocks called nucleotides which are made of three parts: phosphate group, sugar group and 1 of 4 types of nitrogen bases The 4 types of nitrogen bases found in DNA are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases determine the biological instruction contained in the strand of DNA. They are often referred to as base pairs as they always pair up in the same way and can only bond in this way, due to their shape. For this reason we call this complementary base pairing.
  • Pairs are: Adenine bonds with Thymine (or vise versa) Cytosine bonds with Guanine (or vise versa)
  • Sugar and phosphate groups bond together alternating one to the other to form the side structure of the DNA that holds the nitrogen bases
  • Sugar and phosphate groups are stronger than nitrogen bases
  • The complete DNA instruction book or genome for a human contains about 3 billion bases and 20,000 genes on 23 pairs of chromosomes
  • The first 22 pairs of chromosomes are called autosomes, they are contain genes for non-sex linked traits e.g. hair and eye colour
  • Vertical gene transfer: when a cell, formed through the mitosis process, duplicates a copy of it’s mother cell’s DNA. This process is completed by the cell’s daughter cell and so on
  • Chromosomes are made of DNA (genes) 64 possible combinations of codons that code for 20 amino acids
  • Amino acids create proteins by telling them they shape they must form
  • Human proteins are made of 20 amino acids 1 amino acid can be coded for by more than one codon
  • Codons are sets of 3 bases in DNA code for different amino acids in a protein
  • Formula for the number of possible permutations (an ordered group of objects) = L to the power of S, where L is the number of letters and S is the number of positions
  • Amino acids are the building blocks of proteins, a chain of amino acids = a protein UGA, UAG, UTAA code for the end of protein creation AUG (codes for methionine) is the amino acid found at the start of every gene

  Mutations:

  • Mutations are changes that can be passed down to new generations
  • There are many forms of mutations: Point mutations = the alteration of one base (deleting, substituting or inserting a new one) Substitution = change a single base to any base Deletion = remove a base; causes frameshift (codons to move position to fill missing base) Insertion = adds a base; causes frameshift (codons to move position to make space for added base)
  • If a point mutation causes a frameshift, the resulting protein will probably not function properly as all codons after the changed base are different, causing different amino acids.

  Genes:

  • Genes are a specific sequences of DNA bases that build a specific protein
  • You receive 1 copy of genes from your each of your parents
  • Alleles are the different versions of a gene, for example, the genes for hair colour could be blond and brown, each of these is an allele for the hair colour gene
  • Dominant and recessive genes: Dominant genes dominate over the other gene they matched with, if it is recessive
  • You can get 4 possibilities occurring with 2 different alleles

  Allele matching:

  • The allele for blue eyes is recessive and represented by ‘b’ The allele for brown eyes is dominant and represented by ‘B’ Dominant allele will take over so if 1 parent has ‘bb’ and other parent has ‘BB’ the child will have brown eyes as ‘BB’ will take over ‘bb’ but if the 1 parent has ‘bb’ and the other has ‘Bb’ or ‘bB’ the child has a 50 percent chance of having blue eyes To find out which colour eyes they will have, make a table.
  • Genotype = genetic composition
  • Phenotype = physical charastics, what you can actually see
  • Homozygous = both alleles in the gene are the same
  • Heterozygous = alleles in the genes are different

  Sex-linked inheritance:

  • Sex-linked inheritance are specific sex-linked patterns inherited from either the X or Y chromosome
  • Discovered by biologist Thomas Morgan in 1910
  • The last pair of the 23 chromosomes are the sex chromosomes, X chromosomes and Y chromosomes
  • Y chromosome usually determines male sex
  • Females have 2 large X chromosomes and their genotype is written as (XX)
  • Males have an X chromosome and 1 smaller Y chromosome and their genotype is written as (XY)
  • Other combinations of sex chromosomes can also occur
  • Someone with a genotype (XY) has equal chance of passing either chromosome and have a child of either gender
  • Sex-lined trait is a trait linked to a sex chromosomes
  • Case Study: Males are more likely to be colour blind. Males are more likely to become bald. Genotypes for color deficiency: XB is the dominant allele for "normal" colour vision Xb is the recessive allele for colour vision deficiency Y is the male sex chromosome, which doesn't contain this gene and has no impact on colour vision A female with XBXb = not colour blind but is a carrier A male with XbY = colour blind Codominant inheritance: Codominance is when two alleles, dominant, are expressed together in the phenotype