DONE: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
1. What did Mendel observe in pea plants that enabled him to discover homologous pairs, reduction division, and dominance? DONE, NOTICE HOW I MOVED YOUR SECOND PARAGRAPH INTO QUESTION 2. I MOVED SOME WORDS AROUND, BUT KEPT MOST OF WHAT YOU WROTE.
Gregor Mendel grew 10,000 plants and observed 300,000 peas in 8 years of research that led him to make discoveries 40 years ahead of the rest of the world by simply breeding pure lines of pea plants. At first he took the P generation of pure lines of white and purple pea plants and observed that 100% of the f1 generation was purple but that 1/4 of the f2 generation was white. The white reappearing in the F2 generation proving that it was not destroyed, but "hidden" in the f1 generation. Mendel reasoned that a white allele in the f1 generation must be "recessive" to the dominant purple allele. His discovery that a purple and a white allele was present in the f1 generation anticipated the eventual discovery of homologous pairs of chromosomes. When the homologous pairs align with one set of duplicated chromosomes from each parent, the offspring will receive just one allele from its mother and one from its father. Possessing two alleles, but passing on one is what occurs in meiosis during reduction division.
2. What did Mendel observe in pea plants that led him to write his Law of Segregation? What part of meiosis does the Law of Segregation relate to? DONE, WITH SOME HELP FROM PEOPLE THAT ANSWERED #1 (PARAGRAPH 2). NOTICE HOW THIS SECOND PARAGRAPH HELPS EXPLAIN WHAT'S STATED IN THE FIRST PARAGRAPH.
The 3:1 ratio of purple to white flowers in the F2 generation led Mendel to write his Law of Segregation, which states that the factors that determine inheritance are particles that separate from each other during gamete formation and are allotted to a particular gamete by chance. Basically, each individual has two copies, or alleles, of every gene. The two particles, or alleles, separate during Anaphase 1.
You can explain a 3 to 1 ratio in the F2 generation by foiling Pp X Pp. This shows that the particles that determine traits must separate (or segregate) and pass only a haploid number of chromosomes to the next generation. The two heterozygotes in the F1 generation will produce a ratio of offspring with the genotype of 1 PP 2 Pp and 1 pp as the P and p from each F1 parent match up in all possible combinations. If the P and p alleles of the heterozygotes in the F1 generation did not separate and recombine like this, you could not produce a 3 to 1 ratio.
3. What did Mendel observe to explain his Law of Independent Assortment? DONE (I reworded this some. What you had written was correct and very good)
If two genes did not assort independently, Mendel would have gotten the ratio 3:1 in his F2 generation, when studying the inheritance of two traits simultaneously. This would be the expected ratio if the dominant purple and the dominant green were always inherited together and if the recessive white and recessive yellow were always inherited together. This is the case because, for example, if you had RrYy parents in the F1 generation then the only gametes they could make would be RY and ry, and the only offspring they could make would b RRYY, RrYy, RrYy, and rryy. However, if RrYy separated independently, then there would be four gamete genotypes possible - RY, rY, Ry, and ry. This would then yield the phenotypic ratio of 9:3:3:1 in the offspring, which Mendel observed.
4. How do the events of meiosis and sexual reproduction relate to the steps involved in filling out a dihybrid Punnett Square? DONE
The events of meiosis and sexual reproduction relate to the steps of filling out the Punnett Square because when you use the FOIL method to make all possible gene combinations for each parent, it's like independent assortment. Each gene combination is a possible sperm/egg. This gives you the column and row headings for the square. When you fill out the squares its like the sperm and egg making a zygote. Any sperm can combine with any egg so you get all possible trait combinations of the hypothetical couples children.
5. What is test crossing used for? Explain how it works. DONE
Test crossing is used to figure out the unknown genotype of a plant, animal, etc. that expresses a dominant trait. For example, a purple flower may either be purple heterozygous Pp or homozygous PP. In order to figure out the genotype for the purple flower, it is bred with a white homozygous recessive, pp. Thus, if the offspring produced are all purple in appearance then it means that the genotype of the original purple flower in question had a genotype of PP. However, if the offspring of the homozygous white flower and the purple flower result in a white flower half of the time, then that means that the genotype of the purple must have been Pp.
Explain each of these inheritance patterns. Include an example.
6. Multiple Alleles: DONE. NOTE THE CHANGES I MADE. IT'S VARIATION IN A POPULATION THAT'S SPECIAL HERE, NOT VARIATION IN THE OFFSPRING FROM THE MATING OF JUST TWO INDIVIDUALS.
In each person there are two alleles for a gene which will determine a particular trait. However, for some genes there are several alleles in a population that the person could have, thus creating a wider variety of a particular trait. This allows for a wider range of traits that are determined by a particular gene. For example, in Colias butterflies, there are 11 possible alleles for the color pattern on the wings, creating 66 possible genotypes and many phenotypes. Although the offspring of two parents might be limited to just a few phenotypes they could show, in a large population, many phenotypes could be seen.
7. Incomplete dominance: DONE. NOTE THE FEW CHANGES I MADE.
For some characters, when the phenotype (outside appearance) of the F1 hybrids falls between the phenotypes of the two "parental varieties" (the two organisms creating offspring), incomplete dominance is created. The F1 generation can be considered an offspring from two parental varieties. An example of incomplete dominance can be seen when red and white snapdragon flowers are bred together. When the red flower (RR) and the white flower (rr) come together, they create an Rr offspring. In cases of complete dominance, this Rr offspring would have a phenotype of being red because R is the dominant allele. In the case of these snapdragon flowers, the R allele in the Rr offspring is incompletly dominant. Therefore, the heterozygous offspring has a phenotype of a light red, or pink. The red and white do not mix though to create this seemingly mixed offspring. This can be proved because when bred with each other, these Rr pink F1 snapdragons produce both R and r gametes allowing for both solid red (RR), solid white (rr), or pink (Rr) offspring to be produced in the F2 generation.
8. Pleiotropy: DONE
Pleiotropy is when one gene with two alleles has multiple different phenotypic effects. This type of inheritance pattern occurs most often with genes that play important roles in many aspects of building or running a body. An example of pleiotropy would be the disease Sickle-Cell Anemia. Here, a defect in the one gene coding for hemoglobin can lead to effects such as weakness, impaired mental function, heart failure, paralysis, and many other different problems.
9. Polygenic inheritance: DONE
Polygenic inheritance is associated with traits which are determined by a number of different genes. Skin color and height are prime examples. Usually expressed in the form of a bell curve, polygenic inheritance usually results with an outcome appearing as a mixture of the parents. The number of genes involved increases the possible genotypes. The equation 3^g explains that everytime you add one more gene to the number that determine a trait, the possible number of genotypes triples. This explains why there is so much variety in these traits and why a bell curve can occur when two individuals mate and have many offspring.
10. Linkage: DONE, only change was your reference to 7:1:1:7 - it's not always this ratio, the ratio will change, depending on how far the genes are apart on the chromosome.
This appears as an unusual phenotypic ratio observed when studying the inheritance of two genes. The ratio that Punnett and Bateson observed in bush beans that led them to discover linkate was 7:1:1:7. It is caused by two genes being linked on the same chromosome. For example a parent with the genotype AaBb, the Ab are linked and the aB are linked. This limits the possible outcomes, except when there is crossing over, which accounts for the 1:1 ratio in the middle.
11. Sex-linkage: DONE
This refers to genes that are located on the X chromosome. Usually the male is more likely to show sex-linked traits because they can never be heterozygous with the sex-linked traits. The gene is only located on the X chromosome and can affect traits other than gender. Because males only have one X chromosome, if that particular chromosome had the particular gene then it couldn't be hidden by another X chromosome because instead of another X chromsome, males have a Y chromosome.
12. Epistasis: DONE
Epistasis is when one gene counters or blocks the effect of another gene in an organism. An example of this is if a cat were to have the gene for a black coat, yet it has albino/white fur. This would be caused by a gene being blocked by another gene during epistasis causing there to be no creation of melanocytes, which create pigment in fur, so the cat would be albino and no black would be expressed.
