CH. 3 - Genetics

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1. Keywords

1. Allele - alternative forms of gene

2. Colchicine - inhibits spindle formation

3. Down Syndrom - classic trisomy of chromosome 21

4. Episome - plasmids capable of integration into bacterial genome

5. Filial - F generation in genetic crossing

6. Gene - basic unit of heredity, composed of DNA and located on chromosome

7. Genotype - genetic makeup of the individual

8. Monosomy - somatic cells having 2N-1 chromosomes

9. Operon - consists of structural gene, operator gene, and promoter gene

10. Phenotype - the physical manifestation of the genotype

11. Plasmids - contain one or more genes, cytoplasmic DNA

12. Provirus - viral DNA phages into bacteria and become integrated to host bacteria

13. Purine - Guanine and Adenine

14. Pyramidine - Cytosine and thymine

15. Testcross - Only recessive phenotype can genotype be predicted 100%, test cross determines the genotype of a dominant phenotype

16. Trisomy - somatic cells having 2N+1 chromosomes

17. True-breeding - self-crossed would produce progeny with the parental phenotype

  Mendelian Genetics

1. Mendel's First Law - Law of Segregation

1. Genes exists in alternative forms and each organism has two alleles for each trait

2. During meiosis, the two alleles segregate, resulting in gamete with only one allele

3. If two alleles are different, the expressed is dominant, the other is recessive

4. Mendel's Law of Dominance - dominant allele appears in the phenotype

2. Mendel's Second Law - Law of Independent Assortment

1. As long as two genes are on separate chromosomes, they will assort independently during meiosis.

3. Non-Mendelian Inheritance Patterns

1. Incomplete Dominance

1. Blends of phenotype, red + white = pink

2. Codominance

1. Both expressed at the same time

2. Blood type is a very classic example

4. Sex Determination

1. Sex determined by a pair of sex chromosomes while the rest are autosomes

2. Human gender is determined by the genetic contribution of male only

3. Sex-linked traits are genes located on the X or Y chromosomes

5. Sex-linkage

1. If X-recessive, it'd always be expressed in males

1. Hemophilia and color blindness are two examples

2. Sex-linked trait skip a generation because father cannot pass to son, only daughter.  So the daughter would be carrier and then the grandson would be afflicted.

6. Drosophila Melanogaster

1. Short life cycle

2. Large sample size

3. Chromosomes are large and easily recognizable

4. Few chromosomes (2n = 8)

5. Mutations occur frequently

7. Environmental factors

1. Environment can affect the expression of a gene

2. Examples

1. Dropsophila with crooked wings at low temperature and straight wings at high

2. Himalayan hare has white hair in warmer part, and black in colder part

Genetic Problems

1. Nondisjuction

1. Failure of chromosomes to separate

2. Trisomy - having 2N+1 somatic chromosomes

3. Monosomy - somatic cells having 2N-1 chromosomes

2. Chromosomal Breakage

1. Exposure to mutagenic agents or X-rays where chromosomes would lose a fragment

3. Mutations

1. Changes in the genetic information of a cell

2. Mutations in the somatic cells can lead to tumors

3. Mutations in the sex cells would be passed to offspring

4. Mutagenic Agents

1. Induces mutations

2. Cosmic rays, X-rays, UV rays, radioactivity

3. Chemical compounds like colchicine (inhibits spindle formation

4. Mustard gas

5. Usually carcinogenic

5. Mutation Types

1. Added - a base is added

2. Deleted - base is deleted

3. Substituted - base is changed

4. Frameshit

6. Examples of Diseases

1. Phenylketonuria (PKU) - molecular disease caused by inability to produce the proper enzyme for metabolism of phenylalanine.

2. Sickle cell anemia - blood cells sickles and cannot carry oxygen

Molecular Genetics

1. General

1. Genes are composed of DNA

2. Has ability to self-replicate

3. DNA is basis for heredity

4. DNA s mutable and can be changed

2. Structure of DNA

1. Basic unit of DNA is made of nucleotide

2. Nucleotide consists of deoxyribose, bonded to a phosphate and a base

3. The bases are of two types

1. Purines

1. Adenine and Guanine

2. Pyramidines

1. Cytosine, thymine (uracil)

4. Double-stranded helix with sugar-phosphate chains on the outside and bases on the inside

5. Thymine forms 2 hydrogen bonds with Adenine

6. Guanine forms 3 hydrogen bonds with Cytosine

DNA & RNA

1. DNA Replication

1. The double helix is split open and each act as a template for complementary base pairing

2. DNA replication is semiconservative

2. Genetic Code

1. G, C, A, T make up the letters of the DNA and together, they can write 20 different words or amino acids

2. DNA must be translated into mRNA and this is universal for almost all organism

3. Amino acids are degenerate - each amino acids have more than one codon

4. Condons are unambiguous - each triplet codes for one amino acid only

3. Structure of RNA

1. Same as DNA except it uses a ribose sugar and contains uracil instead of thymine

2. Usually single stranded instead of double

3. Many types - mRNA, tRNA, rRNA

1. Messenger mRNA

1. Carries the complement of DNA and transport it to the ribosomes for translation

2. Transfer RNA

1. Brings the amino acids to the ribosomes for protein synthesis

3. Ribosomal RNA

1. Synthesized in the nucleolus, it makes up the ribosomes

4. Protein synthesis

1. Transcription

1. DNA is transcribed into strand of mRNA and goes out into cytoplasm through nuclear pores

2. Translation

1. Initiation

1. Ribosome binds to the mRNA near its 5' end and gets up to the start codon, AUG

2. Brings in the initiatior aminoacyl-tRNA complexx, or methionine-tRNA would base pair with the start codon

2. Elongation

1. Hydrogen bonds form between mRNA codon in the A site and the complementary anti-codon from the aminoacyl-tRNA complex

2. Peptide bond is formed that'd join the new amino acid in the A site and the P site.

3. Translocation

1. The ribosome would advance three nucleotides along the mRNA in 5' to 3' direction

2. Uncharged tRNA is expelled through the E site, and the chain moves from the A site to P site.

4. Termination

1. Terminates when we reaches three special mRNA termination codons, UAA, UAG, UGA

3. Polyribosome

1. Multiple ribosomes synthesizing polypeptides with one mRNA

4. Primary sequence is made, and through interactions, goes into secondary to tertiary

5. Other type of DNA and inheritance

1. DNA is found in chloroplast and mitochondria, they can interact with nuclear genes and can be changed

2. Plasmids - contain one or more genes