Biology Answer Note #3

Question 1 If there are 20 chromatids in a cell, how many centromeres are there? Exam Code: 421 Use Instruction B to answer questions number 21 to 22. (A) 10 (B) 20 (C) 30 (D) 40 (E) 80 Answer Based on my research and understanding of cell division, there would be a total of 10 centromeres in a cell with 20 chromatids. This can be calculated by dividing the number of chromatids by two since each chromatid pair has one centromere. Therefore, 20 chromatids divided by 2 would equal 10 centromeres. Question 2 complete the two punnet square problems . write down the pheontypic percentages for each promplem. Brown eyes are dominant ( B) over blue eyes ( b) . Cross two heterozygous brown eyed parents. What are the phenotypic ratios? Answer In order to answer this question accurately, let's first revise the concept of Punnett squares and how they are used to predict the probabilities of different genotypes and phenotypes in offspring. A Punnett square is a graphical representation of the potential combinations of alleles from both parents. It helps in determining the genotypes and phenotypes of the offspring by combining the alleles from two parents and predicting the possible genotypes and phenotypes. Now, let's apply this concept to the given problem. We are given that brown eyes are dominant (B) over blue eyes (b). This means that if an individual carries at least one B allele, they will have brown eyes. However, if an individual has two b alleles, they will have blue eyes. Therefore, the parents in this problem are heterozygous for brown eyes, meaning they both carry one B allele and one b allele. To solve this problem, we will use a 2x2 Punnett square. We will place the possible parental alleles (B and b) along the top and left-hand side of the square. Then, we will fill in the squares with the possible combinations of alleles that the offspring may inherit from the parents. ||B|b| |-------|-------|-------| | **B** | BB | Bb | |-------|-------|-------| | **b** | Bb | bb | According to this Punnett square, there are four possible genotypes that the offspring may have - BB, Bb, Bb, and bb. However, since brown eyes are dominant, both BB and Bb genotypes will result in brown eyes, while bb genotype will result in blue eyes. Therefore, the phenotypic ratios for this problem will be 3:1, with 75% of the offspring having brown eyes and 25% having blue eyes. Question 3 complete the two punnet square problems . write down the pheontypic percentages for each promplem. in a species of flowers purple ( p ) is dominant over white. Cross a heterozygous purple flower flower with a white flower. Answer To solve this question, we need to understand the basic principles of genetics and Punnett squares. Punnett squares are diagrams used to predict the possible outcomes of a genetic cross. In this case, we are crossing a heterozygous purple flower (Pp) with a white flower (pp). According to the law of dominance, the dominant allele (P) will mask the recessive allele (p), resulting in a purple flower. Therefore, the genotypes of the offspring will be Pp and pp, with a phenotypic ratio of 1:1. To create a Punnett square, we need to write the allele combinations of each parent on the outside of the box, with P representing the dominant allele and p representing the recessive allele. Pp P | PP | Pp p | Pp | pp. From the Punnett square, we can see that there is a 50% chance of producing a heterozygous purple flower (Pp) and a 50% chance of producing a recessive white flower (pp). Therefore, the phenotypic percentage for heterozygous purple flowers is 50%, while the percentage for white flowers is also 50%. To double-check our results, we can also use the formula for calculating phenotype ratio: Number of individuals showing the dominant phenotype / Total number of individuals. In this case, the number of individuals showing the dominant phenotype (purple) is equal to the number of heterozygous purple flowers, which is 1. The total number of individuals is 2. So, using the formula, we get a 50% phenotypic percentage for both heterozygous purple and white flowers. Question 4 What did Jean-Baptiste Lamarck believe about traits such as large muscles that are acquired during one's lifetime? They are acted on by natural selection. They can be passed on to offspring. They are shared equally by all offspring. They are the result of a change of alleles. Answer Jean-Baptiste Lamarck was a prominent French biologist who proposed a theory of evolution prior to Charles Darwin's theory of natural selection. Lamarck's theory, known as the "Inheritance of Acquired Characteristics," suggested that traits acquired by an organism during its lifetime could be passed on to its offspring. In this theory, Lamarck also believed that acquired traits were influenced by the environment and were the result of a change in the organism's alleles. In conclusion, Jean-Baptiste Lamarck believed that traits acquired during an organism's lifetime could be passed on to its offspring. He also believed that these acquired traits were the result of a change in an organism's alleles. While his theory has been largely discredited, it played a significant role in shaping our understanding of evolution and the mechanisms behind it. Question 5 As a baby, Gina was exposed to a pathogen. Because of passive immunity, Gina's body was able to fight off the pathogen before she got sick. Which statement describes what enabled Gina to fight the pathogen? a high fever caused by the pathogen antibodies she received from her mother antibodies she received from a vaccination inflammation caused by antibodies Answer Passive immunity, also referred to as acquired immunity, is a type of immunity that is acquired from an external source, rather than from the individual's own immune system. This type of immunity can be either natural or artificial. In the case of Gina, she was protected by passive immunity from the pathogen she was exposed to as a baby. There are several mechanisms that contribute to passive immunity, but in this case, the most likely mechanism is the transfer of antibodies from her mother to the fetus during pregnancy. When a mother is exposed to a pathogen, her immune system produces specific antibodies to fight off the infection. These antibodies can then cross the placenta and enter the bloodstream of the developing fetus, providing protection against the same pathogen. This transfer of antibodies is called passive transfer and it is essential for the protection of newborn babies who have not yet developed their own immune system. Another possible mechanism for passive immunity in Gina's case is through the transfer of antibodies in breast milk. Breast milk contains high levels of antibodies, specifically Immunoglobulin A (IgA), which can provide passive immunity to the baby against pathogens that the mother has been exposed to. This type of immunity is important in the first few months of life when the baby's immune system is still developing.