What is the f2 generation? | Socratic
evidence for discrete units of heredity, as "green" unit obviously present in F1, appears in F2 ( ratio of Yellow: Green in F2). *Parental Generations (P1 and P2). P - parent generation F1-first filial generation Fnd filial generation. These letters are used in genetics to denote different generations for better systematism . Gregor Mendel developed the model of heredity that now bears his name by model explains the ratio of tall to short plants in the F2 generation. In the F1 generation each plant had one T and one t allele of the gene controlling height.
The Greek philosophers had a variety of ideas: Theophrastus proposed that male flowers caused female flowers to ripen; Hippocrates speculated that "seeds" were produced by various body parts and transmitted to offspring at the time of conception, and Aristotle thought that male and female semen mixed at conception.
Aeschylus, in BC, proposed the male as the parent, with the female as a "nurse for the young life sown within her". During the s, Dutch microscopist Anton van Leeuwenhoek discovered "animalcules" in the sperm of humans and other animals. Some scientists speculated they saw a "little man" homunculus inside each sperm.
These scientists formed a school of thought known as the "spermists". They contended the only contributions of the female to the next generation were the womb in which the homunculus grew, and prenatal influences of the womb.
An opposing school of thought, the ovists, believed that the future human was in the egg, and that sperm merely stimulated the growth of the egg. Ovists thought women carried eggs containing boy and girl children, and that the gender of the offspring was determined well before conception. Pangenesis was an idea that males and females formed "pangenes" in every organ. These pangenes subsequently moved through their blood to the genitals and then to the children. The concept originated with the ancient Greeks and influenced biology until little over years ago.
- Describes Mendel's first set of experiments involving monohybrid crosses and his conclusions.
The terms "blood relative", "full-blooded", and "royal blood" are relicts of pangenesis. Francis Galton, Charles Darwin's cousin, experimentally tested and disproved pangenesis during the s. Blending theories of inheritance supplanted the spermists and ovists during the 19th century. The mixture of sperm and egg resulted in progeny that were a "blend" of two parents' characteristics.
Sex cells are known collectively as gametes gamos, Greek, meaning marriage. According to the blenders, when a black furred animal mates with white furred animal, you would expect all resulting progeny would be gray a color intermediate between black and white. This is often not the case. Blending theories ignore characteristics skipping a generation. Charles Darwin had to deal with the implications of blending in his theory of evolution. He was forced to recognize blending as not important or at least not the major principleand suggest that science of the mids had not yet got the correct answer.
That answer came from a contemporary, Gregor Mendel, although Darwin apparently never knew of Mendel's work. The Monk and his peas Back to Top An Austrian monk, Gregor Mendel, developed the fundamental principles that would become the modern science of genetics. Mendel demonstrated that heritable properties are parceled out in discrete units, independently inherited.
These eventually were termed genes. Gregor Mendel, the Austrian monk who figured out the rules of hereity.
What is the f2 generation?
The above photo is from http: Mendel reasoned an organism for genetic experiments should have: Mendel's experimental organism was a common garden pea Pisum sativumwhich has a flower that lends itself to self-pollination. The male parts of the flower are termed the anthers.
They produce pollenwhich contains the male gametes sperm. The female parts of the flower are the stigmastyleand ovary.
The egg female gamete is produced in the ovary. The process of pollination the transfer of pollen from anther to stigma occurs prior to the opening of the pea flower.
The pollen grain grows a pollen tube which allows the sperm to travel through the stigma and style, eventually reaching the ovary.
The ripened ovary wall becomes the fruit in this case the pea pod. Most flowers allow cross-pollination, which can be difficult to deal with in genetic studies if the male parent plant is not known.
Since pea plants are self-pollinators, the genetics of the parent can be more easily understood. Peas are also self-compatible, allowing self-fertilized embryos to develop as readily as out-fertilized embryos. Mendel tested all 34 varieties of peas available to him through seed dealers. The garden peas were planted and studied for eight years. Each character studied had two distinct forms, such as tall or short plant height, or smooth or wrinkled seeds.
Mendel's experiments used some 28, pea plants. Some of Mendel's traits as expressed in garden peas. Images from Purves et al. Mendel's contribution was unique because of his methodical approach to a definite problem, use of clear-cut variables and application of mathematics statistics to the problem.
Gregor Using pea plants and statistical methods, Mendel was able to demonstrate that traits were passed from each parent to their offspring through the inheritance of genes. Each parent contributes one factor of each trait shown in offspring. The two members of each pair of factors segregate from each other during gamete formation. The blending theory of inheritance was discounted. Males and females contribute equally to the traits in their offspring.
Acquired traits are not inherited. Principle of Segregation Back to Top Mendel studied the inheritance of seed shape first. A cross involving only one trait is referred to as a monohybrid cross. Mendel crossed pure-breeding also referred to as true-breeding smooth-seeded plants with a variety that had always produced wrinkled seeds 60 fertilizations on 15 plants.
All resulting seeds were smooth. The following year, Mendel planted these seeds and allowed them to self-fertilize. He recovered seeds: To help with record keeping, generations were labeled and numbered. The parental generation is denoted as the P1 generation.
The offspring of the P1 generation are the F1 generation first filial.Dihybrid Cross
The self-fertilizing F1 generation produced the F2 generation second filial. Inheritance of two alleles, S and s, in peas. Image from Purves et al. Punnett square explaining the behavior of the S and s alleles. The inheritance of the S and s alleles explained in light of meiosis. Mendel studied seven traits which appeared in two discrete forms, rather than continuous characters which are often difficult to distinguish.
When "true-breeding" tall plants were crossed with "true-breeding" short plants, all of the offspring were tall plants. The parents in the cross were the P1 generation, and the offspring represented the F1 generation. The trait referred to as tall was considered dominan t, while short was recessive. Dominant traits were defined by Mendel as those which appeared in the F1 generation in crosses between true-breeding strains.
Recessives were those which "skipped" a generation, being expressed only when the dominant trait is absent. Mendel's plants exhibited complete dominancein which the phenotypic expression of alleles was either dominant or recessive, not "in between". When members of the F1 generation were crossed, Mendel recovered mostly tall offspring, with some short ones also occurring. Upon statistically analyzing the F2 generation, Mendel determined the ratio of tall to short plants was approximately 3: Short ; seed color yellow vs.
Green ; seat coat smooth vs. The other traits Mendel studied can be substituted for tall and short. Mendel started out with plants that "bred true". That is, when tall plants were self-pollinated or cross-pollinated with others like themplants in following generations were all tall; when the short plants were self-pollinated or cross- pollinated with others like them the plants in following generations were all short.
Mendel found that if true breeding Tall [T] plants are crossed bred with true breeding short [t] plants, all the next generation of plants, called F1, are all tall. This is the same proportion of tall to short that F1 plants produce. Q1, When Mendel put pollen from tall plants into the flowers of short plants, the seeds produced an F1 generation with all tall plants. But the short trait was not lost.
How did Mendel demonstrate this? The following summarizes the model's first basic feature. Mendel's model for the F1 generation is summarized in the table at the right.
The model states that each trait is controlled by a pair of hereditary packets we now call genes. One packet comes from each parent. Cross breeding T T with t t plants produces T t plants in the first or F1 generation. The F1 plants receive a T allele from the tall parent and a t allele from the short parent. The F1 plants are tall because the T allele is expressed and "cover up" the t allele.
So the T tall allele is called dominant and t short allele is called recessive.
The diagram at the right shows how Mendel's model explains the 3: In the F1 generation each plant had one T and one t allele of the gene controlling height. Plants in the F2 generation had a The diagram shows that this results in 1 out of 4 plants getting only t genes and 3 plants getting at least one T gene which makes the plant tall, because T is dominant over t The diagram also shows that the F2 generation actually has three kinds of plants.
When self pollinated, they produce a pattern exactly like the F1 generation: These plants are exactly like the F1 generation. From these and similar breeding experiments, Mendel deduced figured out, proved logically how traits are transmitted from generation to generation.