Biology: CUET Mock Test - 9 - Class 12 MCQ

The skull belongs to Homo erectus erectus, also known as Java man. Chin was absent whereas jaw prognathous. They were omnivorous. Cannibalism was also found.

Homo erectus erectus, also known as Java man used fire for hunting, protection, and cooking. It had complete erect posture and lived in caves. It used tools of bones and stones.

Homo erectus were known as the direct ancestors of humans. It had many similarities to modern man. Their face, skull structure, and posture were the same.

They had a cranial capacity of 650-800 c.c. They were the first human being like and had complete erect posture similar to them. They had the knowledge to create tools of stones to hunt.

Natural selection mainly leads to three selections. They are: Stabilizing selection, directional selection, and disruptive selection. Technical selection does not belong to natural selection. This classification is based on different organism-environmental relationship.

Mortality in babies is an example of stabilizing selection. It is all depended on the baby’s birth weight. The optimum birth weight is 7.3 pounds which favor this selection. Newborn infants with less than 5.5 pounds and more than 10 pounds have the highest mortality rate.

Directional selection is also known as progressive selection. This selection always operates in a changing environment. After this natural selection, mean value always changed.

The graph given belongs to directional selection as the graph shifts to one direction. The resistance of insects to DDT is an example of directional selection. A single mutation which occurred in a specific gene helped them to breakdown the toxin. It shows that it favored one extreme value.

In disruptive selection, most of the individuals get the periphery values at both ends of the curve given in the graph. The population gets divided into two different groups. Hence, they have two peaks which resemble a two-humped camel.

Limpets shell has a continuous pattern with color ranging from pure white to dark tan. They either attached to white gooseneck barnacles or to tan colored rocks. The light-colored limpets camouflaged with white barnacles while tanned limpets camouflaged on tan-colored rocks. But, the limpets with intermediate shell patterns were conspicuous and were preyed by predatory shorebirds.

Marine mollusca is also known as limpets. They are aquatic snails with a conical shaped shell with a muscular foot. They are members of the family Gastropoda. Their shell pattern shows disruptive selection.

In disruptive selection, the members of both extreme are selected. The average gets rejected. Most of the individuals get values other than the mean character value. The naturally selected members are shown by two peaks.

This graph indicates stabilizing selection. As we can see, the peak gets higher and narrower. In this selection, most of the individuals acquire mean character value.

Stabilizing selection operates in a constant environment. It favors the average or complex phenotype and eliminates the extreme values. The mean value never changes. Also, the peak gets higher and narrower.

Cistrons are the segments of the DNA helical structure which code for polypeptide chains. The structural gene in the transcription unit can be either monocistronic or polycistronic. The monocistronic genes are mostly present in eukaryotes.

The sequences of the genes which appear in the mature or processed RNA are called as exons. They are the coding sequences of the gene. These sequences are interrupted by introns. Introns are the intervening sequences which aren’t present in both the mature or the processed RNA.

The polycistronic organisms can code for more than one polypeptide sequence as individuals inside the RNA molecule. Examples of such are the bacteria and prokaryotes.

A cistron is the segment of a DNA. It is responsible for coding polypeptide chains. This is seen during the process of protein synthesis.

The tRNA was known by the name sRNA in its early days. sRNA stands for soluble RNA. This was even before the postulation of the genetic code. But, the role of tRNA as an adapter was assigned much later.

The actual structure of the tRNA is actually a compact molecule which appears to be like an inverted L shaped molecule. But, the secondary structure of the tRNA appears to look like a clover leaf shaped structure.

The stop codons are UAA, UAG and UGA. These codons are absent in the tRNA molecules. tRNA possesses an amino acid acceptor end which is the site for binding the amino acids. Finally, the anticodon loop of the tRNA contains bases that are complementary to the codes.

Amino acids do not have any structural specialties to read a code. Francis Crick came up with an ideology that an adapter molecule will be present. This adapter molecule will be capable of both reading the code and also on binding itself to the specific amino acid.

People who are colour blind fail to distinguish between red and green colours. Colour blindness is a sex-linked recessive trait in which the normal gene and its recessive allele are carried by X-chromosome.

Colour-blindness is a sex-linked trait which shows criss-cross inheritance which means male transmits his trait to his grandson through his daughter, while a female transmits the traits to her granddaughter through her son.

The percentage of children which are colour blind if their father is colour blind and the mother is a carrier for colour blindness is 50% because the father will produce Xc and Y chromosome and the mother will produce Xc and X chromosomes. Their children will have the genotypes- XcY, XY, XcXc and XcX. Therefore, 50% of children are colour blind, 25% have normal vision and 25% are the carriers of the disease.

A female can only be haemophilic if her mother is at least a carrier of this disease and her father is haemophilic. But the possibility of a female becoming haemophilic is extremely rare because being haemophilic for the parents at the later stage of life is unviable.

The percentage of children being a carrier of haemophilia if their mother is a carrier and their father is a normal man is 25% because the gametes formed by mother are X and X^h while the gametes formed by father are X and Y. The genotype of the offspring obtained would be XY, XX, XX^h and X^hY. Thus 50% of children are normal, 25% are carriers of haemophilia and 25% are haemophilic (only son).

Thalassemia is not common in North America. It is common in the Middle East, Indian subcontinent, Mediterranean and South-east Africa. It originated in the Mediterranean region and is caused by the deletion or mutation of the chromosomes.

Alpha-thalassemia is not inherited in a Mendelian dominant fashion. Instead, it is inherited in a Mendelian recessive fashion. It involves the genes HBA1 and HBA2 and it is also connected to the deletion of the 16p chromosome.

 The mutation in the HBB gene on chromosome number 11 leads to the disorder beta-thalassemia. It is inherited as an autosomal recessive trait. The severity of beta-thalassemia depends upon the nature of the mutation.