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Basic Understanding of Genetics

About the Authors

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Mark L. Weiss, Ph.D.

Professor

Department of Anatomy and Physiology at Kansas State University

Professor Weiss is part of the KSU Stem Cell Biotechnology Research team where his current work has been to focus on characterizing non-embryonic stem cells that have been discovered in the umbilical cord matrix and rat embryonic stem cell.  The point of this research is to characterize the role of human and animal umbilical cord matrix stem cells to reverse the behavioral deficits in a rat model of Parkinson’s disease.  Dr. Weiss received his Ph.D in biology from the University of Pennsylvania (1986) and in his postdoctoral from Michigan State University (1986-1989).

Justin Tackney

Ph.D. Graduate Research Assistant

Department of Anthropology at the University of Utah

Justin Tackney is a Ph.D. graduate student studying social and behavioral sciences at the University of Utah

Basic Genetics

  • Basic concepts formed by Gregor Mendel (1822-1884)
  • Mendel conducted series of experiments on the passage of traits from generation to generation of pea plants.
  • Key Terms created by Mendel:
    • Gene- The basic unit of inheritance; each parent contributes on copy
    • Diploid State- cells that contain two genes for each trait
    • Mendel’s Principle of Segregation- States that each sexually reproducing organism has two genes per trait, but only one pair of each gene is passed on to the offspring of the parents.
    • Meiosis- The reproduction of haploid gametes (sex cells)
    • Mitosis- Process of cell division producing cells with same number of chromosomes as parental cell
    • Recombination- Process of forming associations of genes at different loci after chromosomal crossing over
    • Allele- Various forms of a gene
    • Homozygous- Possessing two identical alleles for a trait
    • Heterozygous- Possessing two different alleles for a trait
    • Genotype- Combination of alleles that one posses for a specific trait
    • Phenotype- Visible appearance of trait
    • Dominate Trait- When an allele masks the presence of another allele
    • Recessive Trait- The allele that is masked by the dominate trait.
    • Codominate Trait- When an allele is neither dominate or recessive. Both are expressed in the phenotype.
    • Genes are composed of nucleic acids
      • Two kinds
        • DNA (deoxyribonucleic acid)- the genetic material for most species
        • RNA (ribonucleic acid)- nucleic acid where the sugar is the backbone and substitution of uracil for thymine
          • These nucleic acids transmit information
          • In humans, DNA is the genetic material and the RNA helps the DNA carry out tasks

DNA’s Two Roles

  1. It must be able to transmit information from one generation to the next
  2. Directing the production of proteins

DNA Replication

  • DNA Replication is semiconservative. This means that one double strand of DNA serves as the basis for making two double strands; each of the new double strands contains one old and one new strand of DNA.
  • DNA is able to reproduce with few errors due to the constructing pairing
  • Mutation- Alteration in the DNA sequence

DNA Makes Protein

  • Most genes direct the production of polypeptide chains. These are then assembled into protein s
  • Proteins- molecules constructed out of amino acids
    • Twenty amino acids are arranged into protein molecules
    • Thymine pairs with adenine (T-A)
    • Cytosine pairs with guanine (C-G)
    • DNA is located in the nucleus of the cell
    • Proteins and ribosomes are assembled in the cytoplasm
    • Transcription- process by which mRNA is constructed
    • DNA is constructed in a double helix
    • Transcription- Process of converting DNA into RNA
    • Translation- Process of converting mRNA into amino acid.

Studying the DNA

  • Major developments in the study of DNA
    • Restriction enzymes- Due to their discovery the cutting of DNA is now more predictable. This allows one to produce recombinant DNA.
    • Polymerase chain reaction (PCR)- Technique that allows researchers to reproduce almost limitless copies of DNA by using only one piece of it.
      • This has been helpful to anthropologists who deal with ancient bone and tissue

Gene Structure

  • Eukaryotes- Organisms with a nucleus
    • Split into alternating DNA segments
    • Exon- DNA sequence that is expressed
    • Interons or IVSs- unexpressed sequences
  • Prokaryotes- Organisms without a nucleus

Gene Families

  • Some genes are similar to other in their functions and evolutionary history
  • Gene families help to connect one species to another throughout evolution
  • Gene families can be analyzed for gene duplication and divergence

Other sorts of DNA

  • DNA is contained inside chromatin because all of our DNA cannot fit into a nucleus
  • Purifying selection- method for identifying functional genome sequences

Pseudogenes

  • Non-functional DNA sequence that has a resemblance of a functional gene
  • May represent the relics of once- functional genes that experienced a mutation that prevented their expression

Repetitive DNA Sequences

  • Sometimes referred to as satellite DNA
  • Three types
    • a-satellite DNA
    • minisatellite DNA
    • microsatellites or short tandem repeats (STRs)

Mitochondrial DNA

  • Referred to as mtDNA
  • Maternally inherited DNA found in the mitochondria
  • Resent study of mtDNA in the mid-1980’s indicated an earlier divergence of human groups
  • Allowed for a common ancestor in Africa to be discovered
  • Used to help reconstruct the human population history
  • Used to decipher interplay between social rules and genetic phenomena

The Y Chromosome

  • Y contains few genes and is small in size compared to the X chromosome
  • The Y chromosome in chimps and gorillas does not have the same sequences as humans
    • This implies they have gone under alterations since humans diverged

Comparing the Human and Chimpanzee Genomes

  • Differences
    • Human chromosome 2 evolved from two ancestral chromosomes still present in apes
    • There are none pericentric chromosomal inversions in humans but not chimps
    • Human chromosomes have human-specific heterochromatin additions and apes do not have this

Pattering in the Genes

  • Genetic variants in human can be used to trace back lines of evolutionary relatedness between populations and other parts of human population history
  • Evidence that a small number of critical genetic changes cause significant change in a phenotype.

Rise of Genomics

  • Genomics helps give a better understanding of what defines us as Homosapiens. This can help us trace back our lineage.

Genetics and the Evolution of the Modern Human Brain

  • Researchers are hoping to eventually discover what lead to humans having distinctively large brains
    • This trait cannot be limited to protein- coding loci and must extend to proteins that regulate the expressions of proteins

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