Inheritance, Variation and Evolution (T6)

• DNA is made up of two strands coiled together in the shape of a double helix
• The DNA molecule has four bases - adenine, thymine, cytosine and guanine
• Adenine always pairs with thymine and cytosine always pairs with guanine
• Mutations can change the DNA base sequence in different ways
• Insertions are mutations where a new base is inserted into the DNA base sequence where it shouldn't be
• Every three bases in a DNA base sequence codes for a particular amino acid
• An insertion changes the way groups of three bases are 'read', which can change the amino acids they code for
• Insertions can change more than one amino acid as they have a knock-on effect on the bases further on in the sequence
• Mutations are changes to the Genetic Code
• What are the three types of mutations?

  Insertion

  Deletions

  Substitutions
• substitution is when a base is replaced by another base in a DNA sequence, resulting in a different amino acid
• A gene is a small section of DNA found on a chromosome.
• A genome is the entire set of genetic material.
• DNA molecules contain a genetic code that determines which proteins are built
• DNA strands are polymers made up of repeating units called nucleotides
• Each nucleotide consists of a sugar, a phosphate group, and one 'base'
• The sugar and phosphate groups in the nucleotides form a 'backbone' to the DNA strands, alternating with one of four different bases: A, T, C, or G
• In DNA, A always pairs up with T, and C always pairs up with G, known as complementary base pairing
• The order of bases in a gene determines the order of amino acids in a protein
• Each amino acid is coded for by a sequence of three bases in the gene
• The amino acids are joined together to make various proteins, depending on the order of the gene's bases
• Parts of DNA that don't code for proteins can switch genes on and off, controlling whether or not a gene is expressed to make a protein
• mRNA is a copy of a code from the DNA. It acts as a messenger between the DNA and ribosome.
• The three functions of proteins are proteins, hormones and structural proteins.
• Sexual reproduction involves the fusion of male and female gametes. Because there are two parents, the offspring contain a mixture of their parents genes.
• In asexual reproduction there’s only one parent. There’s no genetic variation between parent and offspring.
• • Advantages of sexual reproduction
  • Only needs to be one parent
  • Uses less energy
  • Faster
  • Many can be produced in favourable conditions
• Meiosis is a process that involves two cell divisions and produces cells with half the normal number of chromosomes
• Before cell division in meiosis, genetic information is duplicated, forming two-armed chromosomes where one arm is an exact copy of the other
• During the first division in meiosis, chromosome pairs line up in the center of the cell and are then pulled apart so each new cell only has one copy of each chromosome
• In the second division of meiosis, the chromosomes line up again in the center of the cell and the arms of the chromosomes are pulled apart, resulting in four gametes, each with only a single set of chromosomes
• Offspring from sexual reproduction have a mixture of two sets of chromosomes, inheriting genes from both parents, which produces variation in the offspring
• Variation from sexual reproduction increases the chance of a species surviving a change in the environment, as some offspring may be better adapted to the new conditions
• Individuals with characteristics better adapted to the environment have a higher chance of survival, leading to successful breeding and passing on of genes - known as natural selection
• Selective breeding can speed up natural selection by producing animals with desirable characteristics, where individuals with a desirable trait are bred to produce offspring with the same trait, increasing food production
• Protein Synthesis:

  • Code is copied by mRNA (transcription), taken to ribosomes which assembles amino acids into polypeptides then proteins (translation) that are then folded into shape.
• What are the four stages Selective Breeding?

  1. Choose desired characteristic
  2. Choose parents with these characteristics and breed them together
  3. Choose the best offspring with the best desired characteristics and breed
  4. Repeat the process over many generations
• Alleles are different versions of the same gene.
• Homozygous is two of the same alleles whilst heterozygous is

  two different alleles.
• Polydactyl is caused by a dominant gene.