This much was well known that the purpose of a gene is to store the re

This much was well known that the purpose of a gene is to store the recipe for making proteins and that we inherit from our parents a gigantic list of recipes for making proteins and protein-making machines. What was not clear as late as the early 20th century until Gregor Mendel’s experiments were published and understood was that when crossed, the expression of these genes skipped a generation.

Mendel discovered that when white flower and purple flower plants are crossed, the result is not a blend. Rather than being a mix of the two, the offspring was purple flowered. He then conceived the idea of heredity units, which he called "factors", one of which is a recessive characteristic and the other dominant. Mendel said that factors, later called genes, normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. The dominant gene, such as the purple flower in Mendel's plants, will hide the recessive gene, the white flower. Mendel crossed over 29,000 plants including inflated seed pods with wrinkled seed pods, green unripe pods with yellow unripe pods, and axial flowers with terminal flowers. In every case the resulting hybrids were just like one parent with the essence of other parent missing. However, as these hybrids were allowed to self-fertilize, the essence of the recessed parent re-appeared in exactly one third of the cases. This re-appearance is called the law of thirds. This law is not just obeyed in plants but also in every living species as demonstrated by Nageli’s experiment on crossing angora cats with another breed. Nageli observed that the angora coat disappeared in the next generation but re-appeared in the kittens in the third.

Mendel’s law has been put to a variety of uses such as selecting the right plants to hybridize to get the desired mix of dominant factors. A surprising use of the law has been to explain Alkaptonuria in which the patients suffered from arthritis and their urine and the ear wax turned reddish black upon exposure to air. Rare in the general population but frequent in children of first-cousin marriages, the incidence of Alkaptonuria is attributed to expression of recessive factors.

Q1. E is the correct answer. The passage references are marked in color blue to arrive at the correct answer.

Q2. Straight B, passage reference is marked in red color.

Q3. A: Correct answer, Para 1 gives us a background, para 2 describes the law and para 3 mentions its applications.
B: Wrong, time and formalization has not been discussed in the passage.
C: Wrong, the law of thirds is only a part of the passage and not its main point.
D: Incorrect, the examples given in the passage states that the offsprings do contain either dominant or recessive factors belonging to one of the parents, and not to neither of the parents. Also, this choice only points to an application of the law observed so it doesn't cover the central idea of the passage.
E: Wrong, again it is not the central idea, only described in para 3, option A is a better choice.

Q4: Straight D, passage references are marked in pink color.

Here are my 2 cents!

1. According to the passage, all of the following about Mendel’s dominant factors are true except

A. They were later called genes-True they were indeed called genes.
B. They exist in all living organisms including human beings.-True mentioned in last para.
C. They belong to only one of the crossed parents-True mentioned in second para.
D. They define some of the key characteristics of the first offspring.-True mentioned in second and third para.
E. They are responsible for the incidence of Alkaptonuria-Our answer! False, recessive genes are responsible for "Alkaptonuria".

2. The author mentions Nageli’s experiment to illustrate

A. How unique property of the Angora cat – its fur can be transferred to another cat species-No this is the description of experiment not the motive.
B. An example of the validity of law of thirds in other living organisms.-Correct! Mentioned in para that it is also applicable to every single living species and that is proven by nageli's experiment.
C. That it is possible to cross-fertilize extremely distinct species-No not mentioned thru this experiment.
D. An instance in which the recessive factor dominates the first offspring.-Recessive factors dominate but not the first offspring..False
E. Demonstrate how selective species when cross-hybridized could lead to an offspring with extremely desirable characteristics.-NO,"extremely desirable characteristics" is wrong!


3. The primary purpose of the passage is to

A. Explain Mendel's law and its utilities-Bingo! that is what it shows! First para depicts how Mendel's law was conceptualized. Second says how it was conducted and what is its other implications. Third says the utility of Mendel's law.
B. Describe why a phenomena that was readily observed took so long to be formalized-Nowhere mentioned
C. Illustrate how Mendel discovered the law of thirds.-Partial scope
D. Show with appropriate examples, that crossbreeding can lead to offsprings that may show characteristics that are present in neither of the parents.-Partial scope
E. To evaluate some of the benefits of Mendal’s law of thirds-Third para only


4. According to the passage, which of the following is not true about genes?

A. Genes store a recipe for making proteins-True mentioned in first para.
B. We inherit a number of genes from our parents.-True mentioned
C. They occur in pairs in every cell but those that govern our sex.-True mentioned.
D. The dominant genes in crossed offspring may never allow the recessive gene to express even in a future generations-Our answer! False, mentioned in para and is opposite to "Law of thirds"
E. The recessive gene in a crossed offspring is not expressed in the first generation-True mentioned.

As per the passage, 'heredity units' were called 'factors' which were later called 'genes'. Factors were of two types: dominant and recessive. So how can we say dominant factors were later called genes. What's wrong with option A? Please correct me if I'm going wrong.

Cheers!

1. According to the passage, all of the following about Mendel’s dominant factors are true except.
A. They were later called genes. True given in passage
B. They exist in all living organisms including human beings. True
C. They belong to only one of the crossed parents. True
D. They define some of the key characteristics of the first offspring. True
E. They are responsible for the incidence of Alkaptonuria. false regressive genes are responsible (Alkaptonuria is attributed to expression of recessive factors.)

2. The author mentions Nageli’s experiment to illustrate
A. How unique property of the Angora cat – its fur can be transferred to another cat species. not mentioned in passage
B. An example of the validity of law of thirds in other living organisms. True (This law is not just obeyed in plants but also in every living species as demonstrated by Nageli’s experiment on crossing angora cats with another breed)
C. That it is possible to cross-fertilize extremely distinct species. False
D. An instance in which the recessive factor dominates the first offspring. Not part of Nagelis experiment
E. Demonstrate how selective species when cross-hybridized could lead to an offspring with extremely desirable characteristics. False

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