Every living organism inherits a blueprint for life from its parents. GENES Every living organism inherits a blueprint for life from its parents. Topic 3.1 IB Biology Miss Werba

GENETIC MODIFICATION and BIOTECHNOLOGY TOPIC 3 – GENETICS 3.1 GENES 3.2 CHROMOSOMES 3.3 MEIOSIS 3.4 INHERITANCE 3.5 GENETIC MODIFICATION and BIOTECHNOLOGY J WERBA – IB BIOLOGY 2

THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 Statement Guidance A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. U.2 A gene occupies a specific position on a chromosome. U.3 The various specific forms of a gene are alleles. U.4 Alleles differ from each other by one or only a few bases. U.5 New alleles are formed by mutation. Deletions, insertions and frame shift mutations do not need to be included. U.6 The genome is the whole of the genetic information of an organism. U.7 The entire base sequence of human genes was sequenced in the Human Genome Project. J WERBA – IB BIOLOGY 3

THINGS TO COVER A.1 A.2 S.1 Statement Guidance NOS 1.8 The causes of sickle cell anaemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in haemoglobin. Recall one specific base substitution that causes glutamic acid to be substituted by valine as the sixth amino acid in the hemoglobin polypeptide. A.2 Comparison of the number of genes in humans with other species. The number of genes in a species should not be referred to as genome size as this term is used for the total amount of DNA. At least one plant and one bacterium should be included in the comparison and at least one species with more genes and one with fewer genes than a human. S.1 Use of a database to determine differences in the base sequence of a gene in two species. The Genbank® database can be used to search for DNA base sequences. The cytochrome C gene sequence is available for many different organisms and is of particular interest because of its use in reclassifying organisms into three domains. NOS 1.8 Developments in scientific research follow improvements in technology. J WERBA – IB BIOLOGY 4

GENES U.1 U.6 A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. A gene contains the code required to produce a polypeptide. All of the genes carried by an organism are collectively known as the genome. J WERBA – IB BIOLOGY 5

POSITION OF GENES A gene occupies a specific position on a chromosome. This is known as its locus (pl. loci). The same gene will always have the same position on the same chromosome. J WERBA – IB BIOLOGY 6

VERSIONS OF GENES The various forms of a gene are known as alleles. Alleles of a gene always occupy the same locus Each gene is composed of two alleles. These alleles may be the same or different. Chromosome a B c D e f G A b C D E f G Gene Allele J WERBA – IB BIOLOGY 7

VERSIONS OF GENES U.4 Alleles differ from each other by one or only a few bases. eg. AGTCACGGTACG = brown eyes allele (B) eg. AGTACAGGTACG = blue eyes allele (b) Chromosome a B c D e f G A b C D E f G Gene Allele J WERBA – IB BIOLOGY 8

VERSIONS OF GENES U.4 Only identical twins have the exact same allele combinations, and there are still slight differences in their features (eg. mirroring). J WERBA – IB BIOLOGY 9

GENE MUTATIONS Gene mutations form new alleles. Gene mutations are changes in the nucleotide (base) sequence of a gene eg. Sickle cell anaemia is caused by a gene mutation in coding for one of the haemoglobin chains. J WERBA – IB BIOLOGY 10

SICKLE CELL ANAEMIA Haemoglobin is a protein It is composed of 4 polypeptide chains: 2 alpha (α) chains 2 beta (β) chains The instructions for making haemoglobin therefore lie within 2 different genes. J WERBA – IB BIOLOGY 11

SICKLE CELL ANAEMIA A.1 Gene mutation affects the beta (β) chain of the haemoglobin protein Base substitution mutation in 6th amino acid in the beta chain: Changes the DNA nucleotide sequence from CTC to CAC Changes the mRNA codon from GAG to GUG Amino acid changes from glutamic acid to valine J WERBA – IB BIOLOGY 12

SICKLE CELL ANAEMIA A.1 J WERBA – IB BIOLOGY 13

SICKLE CELL ANAEMIA The resulting polypeptide is different. Mutant haemoglobin (HbS) crystallises at low oxygen levels - eg. in the capillaries This causes the HbS blood cells to irreversibly change to a sickle shape. The sickle-cell blood cells can block the capillaries and are less efficient at transporting oxygen. J WERBA – IB BIOLOGY 14

SICKLE CELL ANAEMIA A.1 Can result in acute anaemia, heart damage, kidney damage, or even death. The sickle-cell trait is more common among in West- African and African-American populations. Carrier-testing is advised for people in pre-disopsed families and amniocentesis can be performed to check for disorder in utero. Correlation between malaria and SC anaemia – disease causing plasmodium cannot reproduce in RBCs with HbS, meaning that SC carriers have a reduced chance of contracting malaria. J WERBA – IB BIOLOGY 15

http://youtu.be/9UpwV1tdxcs

HUMAN GENOME PROJECT U.7 The entire base sequence of human genes was sequenced in the Human Genome Project. Comparative genomics is an area of science that is concerned with analysing genomes from different species. This allows researchers to gain a better understanding of evolution and the function of genes and non- coding regions of the genome. They will look at things like DNA base sequence, position of genes, etc. J WERBA – IB BIOLOGY 17

HUMAN GENOME PROJECT U.7 The genomes of ~800 organisms have been sequenced in recent years. Also allows specific proteins to be compared across species. J WERBA – IB BIOLOGY 18

NUMBER OF GENES Organism Estimated number of genes Number of chromosomes Homo sapiens (human) 22,000 – 25,000 46 Mus musculus (mouse) 25,000 40 Arabidopsis thaliana (plant) 23,000 – 25,000 10 Caenorhabditis elegans (roundworm) 19,000 12 Drosophila melanogaster (fruit fly) 13,000 – 14,000 8 Saccharomyces cerevisiae (yeast) 6,000 32 Escherichia coli (bacterium) 1,700 – 3,000 1 J WERBA – IB BIOLOGY 19

NUMBER OF GENES A.2 J WERBA – IB BIOLOGY 20

Developments in scientific research follow improvements in technology GENE SEQUENCING NOS 1.8 S.1 Developments in scientific research follow improvements in technology Gene sequencers are used for the sequencing of genes. J WERBA – IB BIOLOGY 21

GENE SEQUENCING There are now lots of databases that store this info: NOS 1.8 S.1 There are now lots of databases that store this info: eg. the Genbank® database “The Genbank® database can be used to search for DNA base sequences. The cytochrome C gene sequence is available for many different organisms and is of particular interest because of its use in reclassifying organisms into three domains.” http://blast.ncbi.nlm.nih.gov/Blast.cgi J WERBA – IB BIOLOGY 22

GENE SEQUENCING NOS 1.8 S.1 J WERBA – IB BIOLOGY 23

GENES Q1. What is the difference between the alleles of a gene? Their position on the chromosome Their amino acid sequence Their pentose sugars Their base sequence J WERBA – IB BIOLOGY 24

GENES Q2. In a person who is heterozygous for sickle-cell anaemia, where is the mutation found? In every gamete produced Only in gametes carrying an X chromosome In all brain cells In blood plasma J WERBA – IB BIOLOGY 25

GENES Q3. Explain the causes and consequences of sickle-cell anaemia. (5 marks) J WERBA – IB BIOLOGY 26