Unit 14/15: 3.1-3.2 Genes
3.1.U5 New alleles are formed by mutation
New alleles on genes are created by random, permanent changes in the DNA base sequence which are called mutations. There are a variety of different types of mutations that can be either harmful, neutral or beneficial. Base substitution mutations occurs when one base is substituted for another which may or may not result in the change of a single amino acid. There are three types of base substitution mutations: Silent, missense, and nonsense. Silent mutations are changes in the base sequence that have no effect on the amino acid produced. Missense mutations are changes in the base sequence causing one different amino acid to be produced. Nonsense mutations are changes in the base sequence causing a stop codon to be produced which shortens the polypeptide.
3.2.A4 Use of karyograms to deduce sex and diagnose Down syndrome in humans
Normal males have 22 pairs of chromosomes and XY chromosomes. Normal females have 22 pairs of chromosomes with XX chromosmes. Downsyndrome is caused by trisomy 21 in males and females, having an extra chromsome on pair 21.
3.2.U8 The number of chromosomes is a characteristic feature of members of a species
The number of a chromosome does indicate how complex an organism is. Organisms with different numbers of chromosomes are less likely able to successfully interbreed. Chromosomes can fuse of split during evolution (rare events) and the chromosome number will stay the same. The number of chromosomes reflects the complexity of an organism; it is also known as the N number.
3.2.U10 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex
The sex chromosomes that determine the sex of an organism are X and Y. Humans have 23 pairs of chromosomes in diploid somatic cells (2N). 22 homologous pairs of those chromosomes are called autosomes. The X chromosome that are passed from the mother have 2000 genes and the Y pair passed from the father have less than 1000 genes. Individuals with two X's will be of the female gender and individuals with X and Y chromosomes will be males. The Y chromosome is not essential the development of humans but they are essential for males.
3.2.A2 Comparison of genome size in T2 phage, E coli, Drosophilia melanogaster, Homo sapiens and Paris japonica
name: genome length (million base pairs)/number of genes T2 Phage: 0.18 / 300 E Coli: 5 / 4,377 Drosophila melanogaster: 140 / 17,000 Paris japonica: 150,000 / unknown Homo sapiens: 3,000 / 19-23,000
3.1.U1 A gene is a heritable factor that consists of a length of DNA and influence a specific characteristic
A gene can be described as a heritable factor which consist of a length of DNA and influences a specific characteristic. The gene is the basic unit of heredity. The number of genes on a chromosome does not determine the complexity of an organism. There are 22,333 genes in humans.
3.2.U9 A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
A karyotype is the property of a cell which is described by the number and types of chromosomes present in the nucleus of a eukaryote. A karyogram is a diagram or photograph of chromosomes present in the nucleus of eukaryotes, arranged in homologous pairs of decreasing length. The chromosomes are visible in cells undergoing mitosis at the metaphase stage. Stains are then used to make the chromosomes visible by giving them a distinguishable banding pattern. They are arranged by size, beginning with the longest pair to the shortest pair.
3.1.U2 A gene occupies a specific position on a chromosome
All genes occupy a specific location. sometimes called position on a chromosome. This particular position is called a locus or loci for more than one.
3.1.U3 The various specific forms of a gene are alleles
Alleles are different forms of a specific gene. There are alleles differing from other alleles due to one or a few bases only. The alleles with the same genes occupy the same gene locus. Depending on the gene, there can be two or more alleles on that specific gene.
3.2.A1 Cairns' technique for measuring the length of DNA molecules by autoradiography
Autoradiography was used when Cairn tested cells with radioactive isotopes to replace hydrogen in thymidine. The radioactive material will not label RNA, only DNA. Slides are then used to place the intact bacteria on them and cover them with photographic emulsion. The slides are stored in the dark where the films are exposed. The photograph show the regions of labeled DNA, resulting in a semi-conservative mode of replication.
3.2.U3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins
Chromosomes found in eukaryotes are made up of eight histones to help with supercoiling the DNA,which is wrapped around the eight histones twice (nucleosome) because the DNA is too large to fit inside of the nucleus. Eukaryotic chromosomes have up to 85 mm in length and the nucleus has a 10 micrometer diameter.
3.1.S1 Use of a database to determine difference in the base sequence of a gene in two species
Database can be used to analyze the differences in the base sequences of a gene across species. this can be done by aligning the base sequences to visualize the exact differences and understand those differences on a scientific level. Aligning the base sequences can also be used to determine the evolutionary relationships between species.
3.2.S1 Use of databases to identify the locus of a human gene and its polypeptide product
Databases can be used to find the locus of human genes and what polypeptide it forms by analyzing the sequences of the genes.
3.2.U6 Diploid nuclei have pairs of homologous chromosomes
Diploid nuclei have two copies of each type of chromosome (known by 2N). They also have two copies of one of each gene aside from the genes found on the chromosome. An example of diploid nuclei is humans having 46.
3.1.U4 Alleles differ from each other by one or only a few bases
Each human cell consists of two copies of each chromosome meaning that there are two copies of each gene. A person can have two of the same allele (homozygous) or two different alleles (heterozygous). Organisms of the same species have the same genes and gene locus but, they have different alleles which produce variations within a species.
3.2.U4 In a eukaryote species there are different chromosomes that carry different genes
Eukaryotes have multiple chromosomes and all individuals of a species possess the same chromosomes with the same gene loci. Chromosomes are linear, various lengths with the position of the centromere that keeps the sister chromatids attached. There is still variation within species because the chromosmes carrying the same genes can have genes with different alleles, producing the features of an organism.
3.2.U7 Haploid nuclei have one chromosome of each pair
Haploid nuclei have either one copy of each chromosome or one full set of the chromosomes in that species. An example of haploid nuclei are gametes (sex cells). These gametes, sperm and eggs, are fused during sexual reproduction to produce a zygote with a diploid nucleus. The cell is then divided through mitosis, producing various cells.
3.2.U5 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
Homologous chromosomes are chromosomes found within cells that have the same genes. One pair of the chromosome are paternal, coming from the father and the other pair is maternal, coming from the mother. These types of chromosomes have the same size, structure, genes and gene loci. Even with these chromosomes carrying the same genes, they have different alleles. 22 pairs of chromosomes are homologous.
3.1.A2 Comparison of the number of genes in humans with other species
Oragnism # of genes Virus: Influenza 11 Bacterium: E. coli 4,149 Insect: Fruit Fly 12,889 Bird: Chicken 16,736 Mammal: Human 22,333 Plant: Grape 30,434
3.2.U2 Some prokaryotes also have plasmids but eukaryotes do not
Plasmids are small, circular molecules of DNA only found in some prokaryotes. These plasmids are considered to have naked DNA meaning that they are not associated with histone proteins. Although some prokaryotes have these structures, they are not responsible for normal life processes which are controlled by the nucleiod DNA. The genes found in plasmids often contain survival characteristics such as antibiotic resistance. They can be passed to another bacterial cell through conjugation. Plasmids can also be incorporated into the nucleiod chromosome.
3.2.U1 Prokaryotes have one chromosome consisting of a circular DNA molecule
Prokaryotes have two types of DNA: Single chromosome (bacterial DNA) and Plasmids. The single prokaryotic chromosome is coiled up and concentrated in the nucleoid region because there is only a single chromosome there is only one copy of each gene. A copy of the chromosomes is made just before cell division. Prokaryote bacteria may have plasmids, but they are controlled by nucleoid DNA.
3.1.A1 The causes of sickle cell anemia, 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 hemoglobin
Sickle Cell Anemia is caused by a single base substitution mutation on chromosome 11. The sequence is altered due to the change in the bases from GGA CTC CTC to GGA CAC CTC. This change produces the amino acids proline, valine and glutamic acid; Instead of proline, glutamic acid and glutamic acid. People with one copy of the faulty gene produce some abnormal hemoglobins but those with two faulty genes produce all abnormal hemoglobins. Individuals who are diagnosed with Sickle Cell Anemia are resistant to Malaria.
3.2.A3 Comparison of diploid chromosome numbers of Homo sapiens, Pan trogloglodytes, Canis familiaris, Oryza sativa, Parascaris equorum
Species: # of chromosomes Homo sapien: 46 Oryza sativa: 24 Parascaris equorum: 2 Canis familiaris: 78 Pan troglodytes: 48
3.1.U7 The entire base sequence of human genes was sequenced in the Human Genome Project
The Human Genome Project was an international 13 year effort beginning in 1990 and ending in 2003. There were several goals of the Human Genome Project such as discovering the complete set of human genes, making the discovered genes accessible to further biological development and study, and determining the complete sequence of DNA bases in the human genome. The completion of the project meant being able to identify and treat diseases and more.
3.1.U6 The genome is the all of the genetic information of an organism
The genome is all of the genetic information of an organism. There are 46 chromosomes in the human genomes along with the mitochondrial DNA. The plant genome also consists of chloroplast DNA on their chromosomes and mitochondrial DNA. The genome of prokaryotes and eukaryotes differ.