Calico-colored cats are almost exclusively female, with male calico cats being extremely rare. In 3-5 sentences, explain why this color trait is inherited in this way, with calico color being inherited by female cats. Be sure to use complete sentences.(4 points)
The inheritance of calico color in cats is due to a gene located on the X chromosome. This gene, known as the orange gene, controls the production of orange pigment in the fur. Female cats have two X chromosomes, while males have one X and one Y chromosome. As a result, female cats can inherit two copies of the orange gene, allowing them to display the calico color pattern. On the other hand, male cats only inherit one copy of the orange gene, making it extremely rare for them to exhibit the calico coloration.
Some genes are expressed or repressed based on environmental factors. For example, the lactose (lac) operon in the bacterium E. coli is an example of a gene that is repressed when lactose is not available in a cell. In 3-5 sentences, explain what this means, focusing on the transcription of the gene itself.(4 points)
The lactose operon in E. coli is a group of genes that are responsible for the metabolism of lactose. The key gene in this operon is the lacZ gene, which encodes an enzyme called β-galactosidase. The expression of the lacZ gene is tightly regulated by a regulatory gene called lacI. When lactose is not available in the cell, the lacI regulatory protein binds to the lacZ gene, preventing its transcription. This binding mechanism blocks RNA polymerase from initiating the transcription of the lacZ gene, resulting in the repression of gene expression. However, in the presence of lactose, it interacts with the regulatory protein, altering its conformation and preventing it from binding to the lacZ gene. As a result, RNA polymerase can now access the lacZ gene and initiate its transcription, leading to the production of β-galactosidase.
Homozygous tall pea plants look the same as heterozygous tall pea plants. Imagine you are going to conduct a pollination experiment to identify whether a tall pea plant is homozygous or heterozygous.
1. What would your experiment look like? How would you set it up?
2. What results would you expect to see in the offspring if the unknown parent pea plant were heterozygous? What would you expect to see if the unknown parent pea plant were homozygous?
1. To conduct the pollination experiment, I would first identify the unknown parent tall pea plant as either homozygous or heterozygous for the trait of height. Let's assume we suspect it is heterozygous. I would then select a true-breeding short pea plant as the other parent for the cross. Next, I would manually transfer pollen from the anthers of the unknown tall pea plant to the stigma of the short pea plant. Alternatively, I could use a paintbrush or other tool to transfer the pollen. This step ensures cross-pollination between the two plants. Finally, I would allow the pollinated short pea plant to grow and produce offspring.
2. If the unknown parent pea plant is indeed heterozygous, the offspring generation would exhibit a phenotypic ratio of 3:1 for tall to short plants. This is because when a heterozygous parent is crossed with a short parent, the genetic ratio expected in the offspring is 1:1 for the dominant and recessive alleles. This ratio is then doubled when it comes to the phenotypic expression of the trait. On the other hand, if the unknown parent pea plant is homozygous, all the offspring from the cross would be tall plants. This is because a homozygous plant carries two copies of the dominant allele responsible for tall height, resulting in the expression of the dominant trait in all offspring.
Can you summ that down?
1. To determine if a tall pea plant is homozygous or heterozygous, I would cross it with a short pea plant.
2. If the tall plant is heterozygous, the offspring would have a 3:1 ratio of tall to short plants.
3. If the tall plant is homozygous, all of the offspring would be tall.