Genetics Flashcards
Mendelian Genetics
Gregor Mendel
Laws that describe family patterns of inheritance of single genes.
Cytogenetics
Uses techniques of cytology and microscopy to study chromosomes and their relationships to hereditary traits.
Molecular Genetics
Studying structure and function of DNA at the molecular level.
How genes control cellular functions, development, and disease.
Genomic Medicine
Application of knowledge of the human genome for prediction, diagnosis, and treatment of genetic diseases.
DNA
Each cell:
46 human chromosomes
2m of DNA
3 billion DNA subunits (the bases: A, T, C, G)
20,000-25,000 genes code for proteins that perform all life functions.
DNA Molecular Structure
A kind threadlike molecule with a uniform diameter but varied.
2 meters in length.
A polymer that encodes hereditary information; 4 different repeating monomers(nucleotides) make up DNA polymer.
Each nucleotide consists of one sugar(deoxyribose), one phosphate group, one nitrogenous base:either pyrimidine (single carbon-nitrogen ring) or purine (double ring); A, T, C, G
Nitrogen bases
Purines:double ring(adenine,guanine)
Pyrimidines:single ring(cytosine,thymine)
DNA Structure
Molecular shape is a double helix(staircase)
Each side piece is a backbone composed of phosphate groups alternating with the sugar deoxyribose.
Steplike connections between backbones are pairs of nitrogen bases.
Complimentary Base Pairing
Nitrogenous bases united by hydrogen Bonds. Purine on one backbone always base pairs with a pyrimidine on the other.
A-T two hydrogen bonds
C-G three hydrogen bonds
Law of Complimentary Base Pairing
One strand determines base sequence of other.
DNA Function
Genes-genetic instructions for synthesis of proteins.
Gene-segment of DNA that tells how to make a certain protein(codes for protein)
Genome-all the genes of one person
-humans have estimated 25,000 to 35,000 genes.
-2% of total DNA
-Other 98% in noncoding DNA; plays role in chromosomes structure, very important regulation of gene activity, same has no function at all-junk DNA.
Chromatin
In the nucleus, DNA is complexed with protein to form threadlike Chromatin:
- nondividing state and the DNA molecules are highly compacted.
- coiled around core histone proteins to form nucleosides.
- zig-zagged, looped and coiled into itself.
- functions to package DNA into small volumes to fit the cell.
- chromatin condense to chromosomes during mitosis(higher order DNA Organization)
Flow of Genetic Information
Replication(DNA-DNA)
Transcription(DNA-RNA)
-in nucleus DNA is transcribed or copied into a messenger RNA(mRNA) molecule
Translation(RNA-Proteins)
-in the cytoplasm, the mRNA code is translated into amino acids.
Production of Amino Acids
- DNA double helix
- seven base triplets from DNA; 3 base pairs in gene code for one amino acid.
- the corresponding codons of mRNA transcribed from the DNA triplets
- the anticodons of tRNA that bind to the mRNA codons
- the amino acids are carried by those 6 tRNA molecules
- the amino acids linked into a peptide
Human Genome
Humans have 46 chromosomes
-23 from mom and 23 from from dad
Genome-all the DNA in one 23-chromosomes set
An organisms complete set of genetic instructions
-3.1 billion nucleotide pairs in human genome
Every cell in our body has the same DNA
Gene Regulation
What makes one cell type different from another.
Genes are turned on and off from day to day
Their products are needed or not
Many genes are permanently turned off in any given cell
Gene
Body had 20,000 genes.
Not a separate gene for every protein.
A gene is a segment of DNA that tells the cell how to make a certain protein (codes for protein)
Amino acid sequence is determined by the nucleotide sequence in DNA.
A Information containing segment of DNA that codes for the production of a molecule of RNA that plays a role in synthesizing one or more products.
The Human Genome Project(1990-2003)
International effort to decipher the blueprint of a human being.
Hundreds of scientists at 20 sequencing centers in China , France, Germany, Great Britain, Japan, and United States collaborated to discover the complete set of human genes.
Findings of Human Genome Project
Homosapiens have only about 20,000 genes;not the 100,000 formerly believed
Genes generate millions of different proteins; single gene can code for many different proteins
Genes average about 3,000 bases long; range up to 2.4 million bases
All humans are at least 99.9% genetically identical; 0.01% variation that we can differ from one another in more than 3 million base pairs called single nucleotide polymorphisms(SNP);various combinations of these single nucleotide polymorphisms account for all human variation
Some chromosomes are gene rich and some are gene poor
We now know the location of many disease producing mutations; opens the door for a new branch of medical diagnosis and treatment called Genomic Medicine; we previously only knew fewer than 100 locations
Errors and Mutations
Error rates of DNA polymerase
- likely about 60 errors occur with each new generation; you have 60 different DNA bases you did not inherit from either parents
- Mutations are changes in DNA structure due to replication error of environmental factors
- some cause no effect; some kill cell; turn it cancerous; or cause genetic defects in future generations
Heredity
Transmission of genetic characteristics from parent to offspring.
Karyotype-chart of 46 chromosomes laid out in order by size and other physical features
23 pairs of chromosomes,the 2 members of each pair are called homologous chromosomes
-22 pairs called autosomes(look alike and carry the same genes)
-1pair of sex chromosomes (x and y; female have xx and male have xy)
Diploid-any cell with 23 pairs of chromosomes
Haploid-contain half as many chromosomes as somatic cells; only sperm and egg cells are haploid (germ cells)
Locus
The location of a particular gene on a chromosome
Alleles
Different forms of same gene on 2 homologous chromosomes
Dominant Allele
Represented by capitol letter. Corresponding trait is usually detectable in the individual. Masks the effect of any recessive allele that may be present. Produces protein responsible for visible trait.
Recessive Allele
Expressed only when present on both of the homologous chromosomes (inherited from Mom and Dad) or no dominant alleles at that locus
Genotype
The alleles that an individual possesses for a particular trait; homozygous alleles are 2 identical alleles for a trait, heterozygous alleles are different alleles for that gene.
Phenotype
An observable trait of a genotype. An allele is expressed if it shows in the phenotype of an individual.
Genetic Counselors
Perform genetic testing or refer clients for tests, advise couples on the probability of transmitting genetic diseases, and assist people on coping with genetic disease.
Punnett Square
Graphical method showing all possible combinations of offspring genotypes. Ex:shows how heterozygous carriers of hereditary diseases such as cystic fibrosis can have an affected offspring
Monohybrid crosses
Cross that involved one pair of contrasting traits. Solve using Punnett Square. Sample problems:
- Rr x rr
- RR x rr
- Rr x Rr
- Rr x RR
Gene Pool
Collective genetic makeup of population.
Multiple Alleles
More than 2 alleles for a trait.
Codominant
Both alleles expressed such as AB blood type.
Incomplete Dominance
Phenotype intermediate between traits for each allele
Polygenic Inheritance
2 or more loci to a single phenotypic trait(skin and eye color, height, cholesterol levels, and heart disease)
Pleitropy
One gene produces multiple phenotypic effects. Ex:darkened sclera of eye
Sex Linkage
Sex-linked traits- carried on the x and Y chromosomes and therefore tend to be inherited by one sex more than the other.
Recessive color blindness allele on x, no gene locus for trait on y, so red green color blindness more common on men( mother is carrier)
Penetrance
The percentage of a population with a given genotype that actually exhibits the predicted phenotype.
Role of Environment
Environmental factors play an important role in the expression of all genes; all gene expression depends on nutrition; brown eye color requires phenylalanine from diet to produce melanin pigment; need both the genetic recipe(genotype) and the ingredients (phenotype).
Dominant and Recessive Alleles at the Population Level
- common misconception that dominant alleles must be more common in the gene pool than recessive alleles
- some recessive alleles, blood type O, are the most common
- some dominant alleles, polydactyl and blood type AB, are rare in the population
Cancer
Uncontrolled division of cells in a part of the body.
Genetic disease.
Carcinogens environmental cancer-causing agents.
Can trigger new gene
-mutations; carcinogens, radiation, ultraviolet rays, x-rays;
-chemical; cigarette tar, food preservatives, industrial chemicals
-viruses; human papilloma virus, hepatitis C, and type 2 herpes simplex
5-10% of cancers are hereditary
Benign Tumors
Slow growth, contained in fibrous capsule
Will not metastasize, usually easy to treat
Malignant Tumor
Fast growing
Metastasize-give off cells that sees the growth of multiple tumors elsewhere
Oncology
Medical specialty that deals with both benign and malignant tumors.
Cancer Names
Named for the tissue of origin
- carcinomas:epithelial tissue
- lymphomas:lymph nodes
- melanomas:pigment cells of epidermis (melanocytes)
- leukemias:blood forming tissues
- sarcomas:in bone, other connective tissue or muscle
Chromosome
Threadlike structure found in the nucleic acid of a cell that carries all the genetic information. 46 in humans.
Central Dogma
DNA to messenger RNA (mRNA) to proteins. Flow of genetic information.
