Mendelian Genetics Definitions• Allele - one alternative form of a • Heterozygote - an individual given allelic pair; tall and dwarf which contains one of each are the alleles for the height of a member of the gene pair; for pea plant; more than two alleles example the Dd heterozygote can exist for any specific gene, • Phenotype - literally means "the but only two of them will be form that is shown"; it is the found within any individual outward, physical appearance of• Homozygote - an individual which a particular trait contains only one allele at the • Genotype - the specific allelic allelic pair; for example DD is combination for a certain gene or homozygous dominant and dd is set of genes homozygous recessive; pure lines • Monohybrid cross - a cross are homozygous for the gene of between parents that differ at a interest single gene pair (usually AA x aa)• Allelic pair - the combination of two alleles which comprise the gene pair
Mendelian Genetics Definitions• Dominant - the allele that • Dihybrid cross - a cross expresses itself at the expense between two parents that of an alternate allele; the differ by two pairs of alleles phenotype that is expressed in (AABB x aabb) the F1 generation from the • Dihybrid- an individual cross of two pure lines heterozygous for two pairs of• Recessive - an allele whose alleles (AaBb) expression is suppressed in the presence of a dominant allele; the phenotype that disappears in the F1 generation from the cross of two pure lines and reappears in the F2 generation
Mendelian Genetics Definitions• Backcross - the cross of an • Monohybrid - the offspring of F1 hybrid to one of the two parents that are homozygous parents; for pea homozygous for alternate plant height the cross would alleles of a gene pair be Dd x DD or Dd x dd; most • Dominance - the ability of one often, though a backcross is a allele to express its phenotype cross to a fully recessive at the expense of an alternate parent allele; the major form of• Testcross - the cross of any interaction between alleles; individual to a homozygous generally the dominant allele recessive parent; used to will make a gene product that determine if the individual is the recessive can not; homozygous dominant or therefore the dominant allele heterozygous will express itself whenever it is present
Mendel’s Genetics• By the 1890s, the invention of better microscopes allowed biologists to discover the basic facts of cell division and sexual reproduction.• The focus of genetics research then shifted to understanding what really happens in the transmission of hereditary traits from parents to children.• A number of hypotheses were suggested to explain heredity, but Gregor Mendel , a little known Central European monk, was the only one who got it more or less right.
Mendel’s Genetics• His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death.• His early adult life was spent in relative obscurity doing basic genetics research and teaching high school mathematics, physics, and Greek in Brno (now in the Czech Republic).• In his later years, he became the abbot of his monastery and put aside his scientific work.
Mendel’s Genetics• Mendel picked common garden pea plants (Pisum sativum) for the focus of his research because they can be grown easily in large numbers and their reproduction can be manipulated• Mendel discovered that certain traits show up in offspring without any blending of parent characteristics.
Mendel’s Genetics• The seven traits that are easily recognized and only occur in one of two forms:1) flower color is purple or white2) flower position is axil or terminal3) stem length is long or short4) seed shape is round or wrinkled5) seed color is yellow or green6) pod shape is inflated or constricted7) pod color is yellow or green
Mendel’s Genetics• Pea plants have both male and female reproductive organs. As a result, they can either self-pollinate themselves or cross-pollinate with another plant.• In his experiments, Mendel was able to selectively cross- pollinate purebred plants with particular traits and observe the outcome over many generations.• This was the basis for his conclusions about the nature of genetic inheritance.
Mendel’s Genetics• In cross-pollinating plants that either produce yellow or green pea seeds, Mendel found that the first offspring generation (f1) always has yellow seeds.• However, the following generation (f2) consistently has a 3:1 ratio of yellow to green. (all heterozygous)
Mendel’s Genetics• This 3:1 ratio occurs in later generations as well. Mendel realized that this was the key to understanding the basic mechanisms of inheritance.
Mendel’s Genetics• He came to three important conclusions from these experimental results:1) that the inheritance of each trait is determined by "units" or "factors" that are passed on to descendents unchanged2) that an individual inherits one such unit from each parent for each trait3) that a trait may not show up in an individual but can still be passed on to the next generation.
Mendel’s Genetics• With all of the seven pea plant traits that Mendel examined, one form appeared dominant over the other, which is to say it masked the presence of the other allele.• For example, when the genotype for pea seed color is YG (heterozygous), the phenotype is yellow. However, the dominant yellow allele does not alter the recessive green one in any way.• Both alleles can be passed on to the next generation unchanged.
Mendel’s Genetics• Mendels observations from these experiments can be summarized in two principles:1) the principle of segregation2) the principle of independent assortment
Segregation• for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parents pair of alleles is inherited is a matter of chance.• this segregation of alleles (Segregation of alleles in the production occurs during the process of sex cells) of sex cell formation
Independent Assortment• Independent assortment answers the question of what happens when two parent cells differ in two or more genes• Mendel discovered independent assortment when he performed experiments called dihybrid crosses
Independent Assortment• alleles of different genes assort independently from one another during gamete formation• happens when genes are on different chromosomes• does not hold true for genes that are on that same chromosome because if two genes are close enough together on the same chromosome then they may be linked in which case they stay together while crossing over. This phenomenon is called linkage