Chapter 7C

• Key biological concepts


  • Chromosomes
  • Genes
  • Alleles
  • DNA
  • Karyotypes
• 2022 Unit 2 Biology AOS 1
• Genes, alleles and genome


  • The distinction between them
  • The nature of a homologous pair of chromosomes (one maternal and one paternal) as carrying the same gene loci
  • Variability of chromosomes in terms of size and the number in different organisms
  • The distinction between an autosome and a sex chromosome
• Presentation of an organism's set of chromosomes

  As a karyotype that can be used to identify chromosome number abnormalities including Down's, Klinefelter's and Turner's syndromes in humans
• Chromosomes


  Structures that package DNA<|>Found within the nucleus of most living cells<|>Consist of DNA that is tightly wound into thread-like structures<|>DNA is coiled around histone proteins to form nucleosomes then wrapped into chromosomes<|>The extent of packaging affects how accessible it is to enzymes that read and translate the DNA's code into proteins
• Chromosome


  A single chromosome contains one sister chromatid<|>A duplicated chromosome has two sister chromatids
• Homologous chromosome


  Chromosome with the same length, centromere and gene loci
• Homozygous chromosome


  Chromosome with the same alleles
• Types of chromosomes based on centromere position

  • Metacentric
  • Submetacentric
  • Acrocentric
  • Telocentric
• Chromosome arms


  The shorter section is called p (always on top in a picture)<|>The longer section is called q<|>The centromere or dividing point is not necessarily in the middle point of the chromosome
• Genes


  Each chromosome contains a number of genes<|>The location of the gene on the gene is called a Loci/locus<|>Genes are separated by Spacer DNA that does not code for a particular protein<|>The largest human chromosome (Chromosome 1) contains about 2000 genes<|>The Human Genome (total of all Genes) contains between 20,000 -25,000 genes
• Karyotype


  Complete set of chromosomes of an organism<|>Chromosomes are arranged into pairs in size order<|>Each pair are 'homologous chromosomes' because they are the same size and shape and code for the same genes, but may have different alleles<|>An individuals complete set of chromosomes can be prepared and displayed in a karyogram<|>Each chromosome has specific distinguishing features which the banding pattern represents regions containing up to many hundreds of genes
• Ploidy


  The number of chromosome sets the cell carries<|>Gamete cells that contain only one set of chromosomes are called haploid (n)<|>Somatic cells that contain two sets of chromosomes are called diploid (2n)<|>Humans have 46 chromosomes (22 autosomal pairs and a pair of sex chromosomes for a total of 23 pairs) and a ploidy level of 2n
• Karyotyping


  1. Used to identify anomalies in a person's chromosomal make-up, notably the addition or subtraction of chromosomes

  2. Can be used to determine the person's gender, the size of a chromosome, and the position of the centromere
• Different species have different chromosome numbers
• Vocabulary to know


  • Chromosome
  • Allosome
  • Homologous Chromosomes
  • Autosomes
  • Chromatid
  • Haploid
  • Nucleosome
  • Diploid
  • Centromere
  • Loci/Locus
  • Ploidy/Aneuploidy
  • DNA
  • Down Syndrome, Turners Syndrome, Klinefelters Syndrome
  • Types of chromosomes (metacentric, submetacentric, acrocentric, telocentric)
• A gene is the basic biological unit within each of our cells that is responsible for the process of inheritance. Each gene is composed of specific sequences of deoxyribonucleic acid (DNA) and carries the genetic instructions required for the development of particular proteins.
• Deoxyribonucleic acid (DNA) sits inside the nucleus of your cells and is formed by the continuous pairing of base pairs into a longer, double-stranded nucleic acid chain (Figure 1). These base pairs are part of individual nucleic acid molecules known as nucleotide monomers, each of which consists of the same basic structure (Figure 1a): • a phosphate group • a deoxyribose sugar • a nitrogen-containing base, which can be one of four varieties: − adenine (A) − thymine (T) − guanine (G) − cytosine (C)