Cheryl - Genetics
From KstructIB
3.1 Chromosomes, genes and alleles
3.1.1 A eukaryote chromosome is made of DNA and protein.
3.1.2 Chromosomes can be stained to show banding.
3.1.3 This banding and the size and structure of the chromosome can be used to find the homologous pair.
3.1.4 Application: Determining chromosomal genetic disorders (e.g. Down’s Syndrome)
3.1.5 Gene: A self replicating hereditary unit that occupies a specific location on a chromosome and determines a particular characteristic in an organism. Genes exist in a number of different forms and can undergo mutation.
3.1.6 Allele: One of two alternative forms of a gene that can have the same place on homologous chromosomes and are responsible for alternative traits.
3.1.7 Genome: One haploid set of chromosomes with the genes they contain; The full DNA sequence of an organism.
3.2 Gene mutation
3.2.1 Gene Mutation: A rare change in genes that creates genetic diversity.
3.2.2 Insertion/Deletion: Addition or loss of nucleotides in a gene. Severe changes in protein depending on location.
3.2.3 Substitution: Replacement of one nucleotide with another. Some are silent (codon has multiple amino acids), some change protein by one amino acid (different protein). E.g. Sickle Cell: Deformed red blood cells. Normal hemoglobin has ‘T’ and sickle cell has ‘A’ = a change in mRNA = valine instead of glutamic acid.
3.3 Meiosis
3.3.4 Some chromosome abnormalities like Trisomy 21 (Down’s Syndrome), XO, XXY, Trisomy 18, etc. are caused by nondisjuntion. Improper separation of chromosomes in meiosis resulting in gametes that have one too many or one less chromosome.
3.3.5 A) Different alleles of a gene account for variation in inherited characters. B) Each organism receives two alleles for a trait, one from each parent. C) If the two alleles are different; dominant allele is expressed in organism’s appearance.
3.3.6 Two alleles for each trait segregate during gamete production (meiosis). Gametes have only one allele for a trait.
3.4 Theoretical Genetics
3.4.1 Genotype: The genetic makeup of an organism.
3.4.2 Phenotype: The physical and physiological traits of an organism.
3.4.3 Dominant Allele: In a heterozygote, the allele that is fully expressed in the phenotype.
3.4.4 Recessive Allele: In a heterozygote, the allele that is completely masked in the phenotype.
3.4.5 Codominant Allele: Both alleles are expressed in the phenotype.
3.4.6 Locus: A particular place along the chromosome where a given gene is located.
3.4.7 Homozygous: Two identical alleles for a given trait.
3.4.8 Heterozygous: Two different alleles for a given trait.
3.4.9 Carrier: Contains a specific gene (not expressed).
3.4.10 Test Cross: Breeding of an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype.
3.4.13 Some genes have more than two alleles (multiple alleles).
3.4.14 Blood group alleles: IA, i, IB Types Genotypes A IA IA or IAi B IB IB or IBi O ii AB IAIB
3.4.16Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.
3.4.17 Sex Linkage: A gene that is found only on the X chromosome; often associated with diseases.
3.4.18 Examples: Hemophilia and colorblindness.
3.4.19 A human female can be homozygous or heterozygous, with respect to sex-linked genes.
3.4.20 A female can be a carrier if the gene is found only on one X chromosome, a male cannot.
3.5 Applied Genetics
3.5.1 Genetic Screening: Ability to analyze chromosomes and DNA to determine genetic abnormalities and unexpressed genotypes. Done during prenatal testing (amniocentisis/chorionic villi testing [C.V.T]).
3.5.2 Advantages: Prenatal testing can determine abnormalities prior to birth (can provide treatment at birth, gives time to prepare emotionally). Adult testing to determine late onset diseases (Huntington’s, multiple sclerosis, Parkinson’s). Determine animal pedigrees. Disadvantages: May need to make ethical decisions (e.g. abortion). Risk to unborn. Discrimination based on findings. Blood groups are also an example of codominance. If a person has AB blood type they are going to have both A antigens and B antigens on their RBCs.
3.5.3 The Human Genome Project is an international project to sequence the entire human genome (46 chromosomes). It’s two objectives are a) map all genes and bases, and b) sequence all genes and bases. There are three million bases, 47% has been completed (chromosome #22 is complete). They expect to be finished by 2003. Their goals are to store info in a database; develop tools for data analysis; address ethical, legal and social issues.
3.5.4 Advantages: A greater understanding of genetic diseases and more effective treatment. The ability to detect carriers. Production of genetically engineered drugs.
3.5.5 Cloning: Genetically identical cells or organisms all derived from a single ancestor by asexual methods.
3.5.6 Process:
3.5.7 Ethics: Clone exceptional people - Who will decide? Why would we want them? - Genetic diversity decreases, more vulnerability to disease. - Create human monsters or freaks. - Evil dictators may abuse.
10.1 Meiosis
10.1.3 Crossing-Over: Occurs when homologous portions of nonsister chromatids exchange places during Prophase I.
10.1.4 Chiasma(ta): Areas where homologous chromosomes cross over or criss-cross to hold each other together.
10.1.6Recombination: Reassortment of genes or characters into different combinations from those of the parent.
10.1.7 Alleles for different traits segregate independently of each other.
10.3 Autosomal gene linkage and gene mapping
10.3.1 Autosomes are chromosomes that aren’t required for sex determination (22). Sex chromosomes determine sex (X,Y).
10.3.3Linkage Group: A group of genes whose location are on the same chromosome, increasing chances of being passed together when crossing-over occurs.
10.3.4Linked genes: Not linked (different chromosomes):
10.3.5 Recombitants of a dihybrid cross of linked traits:
10.3.6 Crossing over value (COV) = # of Recombitant Offspring/Total # of Offspring
10.5 Polygenic inheritance
10.5.1 Polygenic Inheritance: A characteristic controlled by more than one gene. E.g. Eye color, skin color (3-4 genes), height.
10.5.2 Polygenic inheritance contributes to continuous variation.
10.5.3 Interaction between genes can cause modified Mendelian ratios in dihybrid crosses because multiple genes may interact to produce phenotype, Mendelian ratios will be different.
10.6 Application of genetics to agriculture and horticulture
10.6.1 Inbreeding: Reproduction involving fusion of gametes produced by genetically related individuals. Self breeding in plants together with a small community decrease the number of heterozygotes and increase the number of recessive alleles (phenotype).
10.6.2 Outbreeding: Reproduction involving fusion of gametes produced by genetically unrelated individuals.
10.6.3 Interspecific Hybridization: Sexual reproduction between members of different species. E.g.Donkey + Horse = Mule – Sterile. Very common in plants. E.g. Wheat with wild grass. Broccoli and Cauliflower.
10.6.4 Polyploidy: Having more than two sets of haploid chromosomes. Results in sterility; Very common in plants.
10.6.5 F 1 Hybrid Vigor: Vigor due to high levels of heterozygosity. Crossbreeding of inbred corn of two different varieties results in a more vigorous parent stock. E.g. Corn.
