Genetics and Heredity

Genetics

• Genetics studies heredity, which involves the process of parents passing genes to offspring.
• Children inherit genes that express specific traits, such as physical characteristics, talents, and genetic disorders from their biological parents.

Genetic Concepts

• Heredity describes the passing of traits from parents to children.
• Genes, small sections of DNA, express traits coded for specific characteristics.
• Genes are found on chromosomes.
• Humans have two sets of 23 chromosomes, one set from each parent, totaling 46.

Mendelian Inheritance

• Alleles are variations of genes that express different traits that a person inherits two copies of for every gene, one from mom and one from dad.
• A trait may not be observable, but its gene can be passed to the next generation.
• Gregor Mendel was born in 1822 and began his work at age 21.
• Mendel, a monk and school teacher with a passion for plant breeding, studied pea plants.
• Mendel discovered the basic principles of heredity.
• Mendel used pea plants due to their flower structure, pollination/fertilization process, and offspring.
• Mendel looked at seven traits or characteristics of pea plants.
• These traits include round vs wrinkled peas, yellow vs green peas and green or yellow unripe pods
• He also looked a purple or white petals, inflated or pinched ripe pods, axial or terminal flowers, long or short stems.

Mendel's Laws of Inheritance

• Law of Dominance states that some alleles, variants of a gene at a chromosomal locus, are dominant over others for a given gene.
• Law of Segregation indicates that the two alleles for each gene separate during gametogenesis so that the parent may only pass off one allele, meaning offspring can only inherit one allele from each parent.
• Law of Independent Assortment states that alleles of different genes segregate independently during gametogenesis and are distributed independently in the next generation.
• Only one characteristic can be found in a gamete.
• For two characteristics, genes are inherited independently of one another in the Law of Independent Assortment, also known as the "Inheritance Law."
• The dominant allele is expressed when an organism has two different alleles for a trait.
• If the genotype is AaBb, the gametes will contain the combinations of either AB, Ab, aB, or ab.
• As an eye color example, blue eyes are recessive to brown eyes, (Bb- brown is expressed therefore it is dominant).

Monohybrid Crosses

• A Punnett Square is a grid used for organizing genetic information and making predictions.
• A monohybrid cross studies the inheritance of only one trait.
• Complete dominance occurs when one allele completely dominates over the other.
• Use a capital letter for dominant and a lowercase letter for recessive.
• Segregate and place each parent's alleles on the top and side of the four-squared grid (mom's on one side and dad's on the other).
• Combine parent alleles inside boxes; letters inside boxes show POSSIBLE offspring genotypes (not ACTUAL).
• Determine the phenotypic ratio and possible genotypes with Fraction, probability statement, phenotype (genotype).
• The format should be "1/4 cbetb (Could Be Expected To Be) purple (PP, Pp) 1/2 cbetb white (pp)".

Dihybrid Crosses

• Dihybrid crosses are like tossing two coins (outcome of one doesn't affect the outcome of the other)
• Dihybrid crosses involve two separate traits and use two different letters.
• Determine all possible allele combinations.
• Place combinations for both male and female on top and side of 16 square Punnett.
• Combine parent alleles inside boxes.
• Determine phenotypic ratios without having to go through genotypes.
• For AaBb one will have AB, Ab, aB, ab as allele combinations.
• For AABB one will have AB, AB, AB, AB or just AB as allele combinations.
• For aabb one will have ab, ab, ab, ab or just ab allele concentrations.
• For AAbb one will have Ab, Ab, Ab, Ab or just Ab allele combinations.

Other Patterns of Inheritance

• Not all traits are completely dominant or as simple as basic Mendelian inheritance.
• Incomplete dominance appears when heterozygous offspring show a phenotype somewhere between the phenotypes of the parents
• As an example, neither allele is expressed fully - a red flower and white flower yielding pink flowers.
• With codominance, both alleles in the heterozygous offspring are fully expressed.
• Human blood type presents an example Type is Phenotype, Letters are genotype, e.g., Type A: AA, AO; Type B: BB, BO, Type AB: AB (Only heterozygous); Type O: OO (Only homozygous)
• Sex-linked inheritance affects phenotypic expression of an allele and is dependent on the individual's gender on either sex chromosome (X or Y)
• Men = XY, women = XX.
• Many more genes are carried on the X chromosome; more X-linked vs. Y-linked traits
• Examples include hemophilia and color-blindness.
• If there is one healthy X, it dominates over the infected X (in females)
• If there is only one infected X, Y can't dominate over it.
• Pleiotropy means a single gene affects more than one trait. Sickle cell disease and Marfan's syndrome are examples.
• Polygenic traits are when one trait is controlled by two or more genes. Human skin color is an example of this.
• Epistasis is when one gene masks or modifies the effect of another gene and interaction involves interactions between genes at different loci.
• Albinism is an example of epistasis
• Allele are when there is more than two alleles for the same human blood type; phenotypes are produced by 3 different alleles.

Pedigree Charts

• Pedigree is a chart of a family's history regarding a genetic trait.
• Males are squares, and females are circles.
• Shading represents individuals expressing a disorder, while half shading represents a carrier.
• A horizontal line represents the union of parents.
• Vertical line represents a child of the parental union.
• A counselor may already know inheritance pattern, and then predict the chance a child born to a couple would have an abnormal phenotype.
• Recessive alleles mean two people, neither having the disease, produce one or more children who do have it. They must be heterozygous.
• Every sufferer of a dominant allele would have one parent whom also suffers from the disease.
• The presence of two sufferers producing some children who do not have the disease is indicative of a disease caused by a dominant allele.

DNA Recombination

• Recombinant DNA (rDNA) is the artificial/natural DNA created by combining sequences that would not normally occur together through gene splicing, like a DNA insert and a Plasmid vector.
• Homologous recombination occurs between nearly identical sequences, typically during meiosis.
• Site-specific recombination occurs between sequences with a limited stretch of similarity and involves specific sites. Transposition involves movement of DNA element moves from one site to another, usually involving little sequence similarity.
• Generating new gene/allele combinations, generating new genes, integration of a specific DNA element, and DNA repair are biological roles for recombination.
• Recombinant DNA technology allows artificial DNA production and has been used to change DNA in living organisms, with practical results possible in the future.
• Restriction Enzymes and plasmids made gene cloning a reality.
• Stanley N. Cohen and Herbert Boyer developed Recombinant DNA technology in 1973.
• Isolating (vector and target gene), cutting, joining, transforming, cloning, and selecting (screening) are the main steps.
• Restriction Enzymes are used to cut DNA.
• A plasmid will contain DNA and go through the process of DNA ligase to bond covalently.
• Cloning vectors allow insert DNA to be replicated (or expressed) in a host cell.

Genetic Engineering

• Genetic engineering modifies an organism's genome, which is the DNA list specific traits (genes).
• Changing genomes enables engineers to give different organisms properties.
• GMOs result from genetic engineering.
• The first GMOs were developed with genetically modified bacteria in 1973
• The creation of genetically modified mice happen in 1974
• The first commercial development of GMOs (insulin-producing bacteria) happened in 1982
• Begin to sell genetically modified food in 1994.
• Begin to sell GMOs as pets (Glofish) in 2003.

The GMO Process

• All genetic changes affect organism protein synthesis
• Genetic engineers influence overall traits by changing proteins.
• There are different methods to modify genetics including: Inserting new randomly or in targeted locations, direct replacement, removal, or mutation of existing genes.

GMO Products

• Cyanobacteria have been modified to produce plastic (polyethylene) and fuel (butanol) as byproducts of photosynthesis.
• E. Coli bacteria have been modified to produce diesel fuel
• In 2010 in the US, 93% of soybeans, 93% of cotton, 86% of corn, 95% of sugar beets were produced using GMOs.
• Bt-corn is one common example, where a gene form Bt bacteria are added so that the corn produces a protein that is poisonous to insects, but not humans. Another example can be found where where scorpion genes are added to cabbage to prevent insects from eating.
• Modified virus injected in sapling tree causes bananas to contain virus proteins, creating banana vaccines.
• Insect/herbicide/drought/freeze/disease resistance, higher yield, improved nutrition, faster growth and a longer shelf life can all be obtained through GMOs.
• Disease detection, novelty pets, and protein tracking are uses for bioluminescent animals.
• Faster-growing salmon contain genes from two fish that cause the salmon to produced continuous growth hormone.
• 25% less flatulence has been obtained by modifying bacteria responsible for methane production in cattle.
• Spider genes in goats enable the production of spider silk in goat milk.

GMO Concerns

• Some concerns are risk to human health/environment/wildlife, increased pesticide/herbicide use, farmers' health, creation herbicide-resistant weeds, seed/pollen drift and genetic engineering in humans.
• GMO foods have enacted bans or restrictions in almost 50 countries.
• GMO labeling requirements have been enacted in 64 countries