misterdogman
06-21-2005, 02:59 PM
. http://www.apbtconformation.com/genetic1b.jpg
GO OVER OUR RED NOSE BLACK NOSE EXPERIMENT USING THE DIAGRAM
In the figure above the top blue blob represents our original pure blacknose homozygous B/B http://www.apbtconformation.com/blackblob.jpg(Parental strain of black noses) the yellow blob represents our original pure (parental) strain of red noses homozygous b/bhttp://www.apbtconformation.com/redblob.jpg. Notice that there are two letters in the blobs. Yep, these represent the gene pairs. B = Black nose gene and b = red nose gene. Each of these original bloodlines has been line bred and the characteristics of the specific nose colors has been aligned.
TERM: The word we use to describe when we have two exact or functionally exact copies of the same gene on both the maternal and paternal supplied pairs is homozygous. Thus both of the P generation are homozygous for their respective nose colors.
Out of each of the P parents we see a separate smaller yet similarly colored blob for representing the egg and sperm. Notice that the egg and sperm do not have paired letters. This is because they do not contain both pairs of chromosomes. They actually are haploid. (again the dogs themselves are dipliod but the sex cells are haploid) In essence all the paired genes from the parents are separated somewhat randomly and the spermatazoon and egg are formed from only half of the chromosomes of the original parent. (this is segregation and we will come back to this in the next segment of the primer) In this case the only possible genes for nose color from the red nose homozygote P generation is b http://www.apbtconformation.com/egg.jpgand the only possible gene from the black nose homozygous P generation is Bhttp://www.apbtconformation.com/sperm.jpg. (note this has nothing to do with whether the rednose is a male and the black nose is a female. The red nose homozygous P generation can only produce egg or sperm that is b. The black nose homozygous P generation can only produce egg or sperm that is B.
The dogs themselves are diploid but both the egg and sperm are haploid meaning that they (unlike the actual dogs) only contain one of the two alleles encoded by the dog. This is what is known as segregation. Segregation is the next concept of importance. Segregation as a concept, is vital to understanding what goes on when you are doing outcrosses, family and line-breeding. We will delve more into segregation and random selection later. However, what we mean by segregation is that when the bitch produces eggs, her chromosome pairs are segregated equally into haploid states in the eggs. Meaning The members of the gene pairs segregate (separate) equally into the gametes. The same is true for the male. His diploid genome is segregated equally into individual sperm which are haploid. A good example to use and one we will return to eventually is sex determinant. Thus the Gametic content states that each gamete (sperm or egg) carries only one member of each pair.
http://www.apbtconformation.com/j0281142(p).gif
Thus, when the sperm and egg combine to create the new dog these two gene pairs (one from the male sperm and one from the female egg) are combined to form a new genotype B/b which is completely different from either parent. The F1 generation is not homozygous (B/B or b/b) for nose color instead they are heterozygous (B/b). However, as we saw the phenotype (what we see) produced in the F1 generation is exactly the same as the black nose parent because the black nose gene is dominant The genotype is different from either parent http://www.apbtconformation.com/heterozygote.jpg. This is seen by the large green blob representing the F1 generation. This F1 generation can produce sperm and egg which are of course haploid but when the separation of the chromosomes occurs when the eggs or sperm is produced equal portions of B and b haplotypes are formed.
PUNNET SQUARE
http://www.apbtconformation.com/punnet1.jpg
Next we notice that the F1 generation (green blob) has arrows that point to the top and side of a four squared box. This box is a Punnet-square and is used to visualize the possible recombination of genetic pairs in a diploid organism. Here the two possible sperm haplotypes are on the verticle axis and the two possible egg haplotypes are on the horizontal top axis. To create the data in the punnet square we simply drop the letters from the top of the box down into each cell in the column below it. Similarly the letters on the side are placed across in each box in their own row. Below is an example of how this is done.
If we continued to experiment with our dog inbreeding and produced a few more litters of F1 dogs. Then if at random we began breeding all the black nose dogs with only other black nose dogs, in the resulting F2 litters we would begin to see as second trend. We would find a population of F1 black noses that would not produce red nose dogs no matter how often they are bred. We would also see a population about twice this size which (like the F1 generation) produced a few red nose dogs (about 1:3 ratio just like the F1). But if we inbred the red noses from the F2 generation, only with the red nose dogs, we would only obtain red nose dogs no matter how many times we bred them. If you understood the dominant recessive concept you begin to understand what is occurring within this F2 generation.
The answer is that in the F1 generation we have a Phenotype (seen) ratio of 1:3 but we also have an actual genetic distribution (genotype) of 1:2:1 (1 B/B: 2 B/b: 1 b/b). Which is to say that 1 out of 4 of the F2 generation are homozygous (has two identical copies of the black nose gene BOTH FROM THE P SIRE) for the black nose. Two out of 4 dogs from the F2 are heterozygous for the black and red nose genes (ONE FROM P DAM ONE FROM P SIRE). This means that they carry the dominant black nose gene which is expressed phenotypically (they have black noses) and they also carry a copy of the recessive red nose gene, which is not expressed phenotypically because it is recessive. Finally we also have produced 1 out of 4 red nose puppies that is homozygous for the recessive genotype (BOTH GENES DERIVED FROM THE P DAM).
Continuing to drive home the point
For this reason when we breed the homozygous GENOTYPE dominant we obtain only black nose dogs. When we breed the heterozygous dogs we get the same phenotypic mixture (1:3) seen in the original F2 generation (1 out of 4 will be red nose). This is because this heterozygous F2 population has the same genotype (B/b) as the F1 generation. If we breed the homozygous recessives we get only red nose dogs.
The final concept we have to grasp is that ofRandom fertilization. The union of one gamete from each parent to form the first cell (zygote) of a new puppy occurs randomly, This means there is nothing guiding the good red nose genes to align with other red nose genes. Segregation and joining of alleles occurs without regard to which member of a gene pair is carried.
REVIEW
In our previous work we discovered that phenotypic traits are the product of genes. These genes are individual packets of information. Together all these paired-packets of information combine to create type. We also came to recognize that heredity is not a fluid blending of characteristics it is particulate in nature.
Mendel’s original experiments with peas and our experiments with inbreeding have taught us very important concepts. There are two copies of each of these genes within an individual dog (pea) otherwise how did we get red noses from black noses? When breeding what we will get is one copy of a gene from the dam and one copy of a gene from the sire, both of which are transferred to the puppy.
Alternative phenotypes of a particular trait (red nose or black nose) are determined by different forms of a single type of gene called an allele. In example the heterozygous dogs contain alleles for both nose colors (a red allele and a black allele). One of these alleles may be dominant which means that if both are present only the dominant is seen phenotypically.
Genetic 102 to be continued again
GO OVER OUR RED NOSE BLACK NOSE EXPERIMENT USING THE DIAGRAM
In the figure above the top blue blob represents our original pure blacknose homozygous B/B http://www.apbtconformation.com/blackblob.jpg(Parental strain of black noses) the yellow blob represents our original pure (parental) strain of red noses homozygous b/bhttp://www.apbtconformation.com/redblob.jpg. Notice that there are two letters in the blobs. Yep, these represent the gene pairs. B = Black nose gene and b = red nose gene. Each of these original bloodlines has been line bred and the characteristics of the specific nose colors has been aligned.
TERM: The word we use to describe when we have two exact or functionally exact copies of the same gene on both the maternal and paternal supplied pairs is homozygous. Thus both of the P generation are homozygous for their respective nose colors.
Out of each of the P parents we see a separate smaller yet similarly colored blob for representing the egg and sperm. Notice that the egg and sperm do not have paired letters. This is because they do not contain both pairs of chromosomes. They actually are haploid. (again the dogs themselves are dipliod but the sex cells are haploid) In essence all the paired genes from the parents are separated somewhat randomly and the spermatazoon and egg are formed from only half of the chromosomes of the original parent. (this is segregation and we will come back to this in the next segment of the primer) In this case the only possible genes for nose color from the red nose homozygote P generation is b http://www.apbtconformation.com/egg.jpgand the only possible gene from the black nose homozygous P generation is Bhttp://www.apbtconformation.com/sperm.jpg. (note this has nothing to do with whether the rednose is a male and the black nose is a female. The red nose homozygous P generation can only produce egg or sperm that is b. The black nose homozygous P generation can only produce egg or sperm that is B.
The dogs themselves are diploid but both the egg and sperm are haploid meaning that they (unlike the actual dogs) only contain one of the two alleles encoded by the dog. This is what is known as segregation. Segregation is the next concept of importance. Segregation as a concept, is vital to understanding what goes on when you are doing outcrosses, family and line-breeding. We will delve more into segregation and random selection later. However, what we mean by segregation is that when the bitch produces eggs, her chromosome pairs are segregated equally into haploid states in the eggs. Meaning The members of the gene pairs segregate (separate) equally into the gametes. The same is true for the male. His diploid genome is segregated equally into individual sperm which are haploid. A good example to use and one we will return to eventually is sex determinant. Thus the Gametic content states that each gamete (sperm or egg) carries only one member of each pair.
http://www.apbtconformation.com/j0281142(p).gif
Thus, when the sperm and egg combine to create the new dog these two gene pairs (one from the male sperm and one from the female egg) are combined to form a new genotype B/b which is completely different from either parent. The F1 generation is not homozygous (B/B or b/b) for nose color instead they are heterozygous (B/b). However, as we saw the phenotype (what we see) produced in the F1 generation is exactly the same as the black nose parent because the black nose gene is dominant The genotype is different from either parent http://www.apbtconformation.com/heterozygote.jpg. This is seen by the large green blob representing the F1 generation. This F1 generation can produce sperm and egg which are of course haploid but when the separation of the chromosomes occurs when the eggs or sperm is produced equal portions of B and b haplotypes are formed.
PUNNET SQUARE
http://www.apbtconformation.com/punnet1.jpg
Next we notice that the F1 generation (green blob) has arrows that point to the top and side of a four squared box. This box is a Punnet-square and is used to visualize the possible recombination of genetic pairs in a diploid organism. Here the two possible sperm haplotypes are on the verticle axis and the two possible egg haplotypes are on the horizontal top axis. To create the data in the punnet square we simply drop the letters from the top of the box down into each cell in the column below it. Similarly the letters on the side are placed across in each box in their own row. Below is an example of how this is done.
If we continued to experiment with our dog inbreeding and produced a few more litters of F1 dogs. Then if at random we began breeding all the black nose dogs with only other black nose dogs, in the resulting F2 litters we would begin to see as second trend. We would find a population of F1 black noses that would not produce red nose dogs no matter how often they are bred. We would also see a population about twice this size which (like the F1 generation) produced a few red nose dogs (about 1:3 ratio just like the F1). But if we inbred the red noses from the F2 generation, only with the red nose dogs, we would only obtain red nose dogs no matter how many times we bred them. If you understood the dominant recessive concept you begin to understand what is occurring within this F2 generation.
The answer is that in the F1 generation we have a Phenotype (seen) ratio of 1:3 but we also have an actual genetic distribution (genotype) of 1:2:1 (1 B/B: 2 B/b: 1 b/b). Which is to say that 1 out of 4 of the F2 generation are homozygous (has two identical copies of the black nose gene BOTH FROM THE P SIRE) for the black nose. Two out of 4 dogs from the F2 are heterozygous for the black and red nose genes (ONE FROM P DAM ONE FROM P SIRE). This means that they carry the dominant black nose gene which is expressed phenotypically (they have black noses) and they also carry a copy of the recessive red nose gene, which is not expressed phenotypically because it is recessive. Finally we also have produced 1 out of 4 red nose puppies that is homozygous for the recessive genotype (BOTH GENES DERIVED FROM THE P DAM).
Continuing to drive home the point
For this reason when we breed the homozygous GENOTYPE dominant we obtain only black nose dogs. When we breed the heterozygous dogs we get the same phenotypic mixture (1:3) seen in the original F2 generation (1 out of 4 will be red nose). This is because this heterozygous F2 population has the same genotype (B/b) as the F1 generation. If we breed the homozygous recessives we get only red nose dogs.
The final concept we have to grasp is that ofRandom fertilization. The union of one gamete from each parent to form the first cell (zygote) of a new puppy occurs randomly, This means there is nothing guiding the good red nose genes to align with other red nose genes. Segregation and joining of alleles occurs without regard to which member of a gene pair is carried.
REVIEW
In our previous work we discovered that phenotypic traits are the product of genes. These genes are individual packets of information. Together all these paired-packets of information combine to create type. We also came to recognize that heredity is not a fluid blending of characteristics it is particulate in nature.
Mendel’s original experiments with peas and our experiments with inbreeding have taught us very important concepts. There are two copies of each of these genes within an individual dog (pea) otherwise how did we get red noses from black noses? When breeding what we will get is one copy of a gene from the dam and one copy of a gene from the sire, both of which are transferred to the puppy.
Alternative phenotypes of a particular trait (red nose or black nose) are determined by different forms of a single type of gene called an allele. In example the heterozygous dogs contain alleles for both nose colors (a red allele and a black allele). One of these alleles may be dominant which means that if both are present only the dominant is seen phenotypically.
Genetic 102 to be continued again