Cells and Tissues Test - 2

In case of human diploid genome, 44 autosomes (22 pairs) are present along with 2 allosomes (a normal female will have a pair of X chromosome whereas a normal male will have a pair of X and Y chromosome)

The nuclear division that forms haploid cells, which is called meiosis, is related to mitosis. As you have learned, mitosis is the part of a cell reproduction cycle that results in identical daughter nuclei that are also genetically identical to the original parent nucleus.

As Mendel found the phenotype of the F heterozygote Tt to be exactly like the TT parent in appearance, he proposed that in a pair of dissimilar factors, one dominates the other (as in the F1 ) and hence is called the dominant factor while the other factor is recessive . In this case T (for tallness) is dominant over t (for dwarfness), that is recessive. He observed identical behaviour for all the other characters/trait-pairs that he studied.

Normal chromosomes are reported as: 44 autosomes plus two X chromosomes for a woman (karyotype 46, XX) 44 autosomes plus one X and one Y chromosome for a man (karyotype 46, XY)

The genotypes of both the parents Tt and Tt.

The letters T and t are used to represent the alleles of the gene that determine plant height by conventions. The upper case letter (T) represents the dominant allele and the recessive allele (t) is represented by the same letter in lower case. Thus, the tall parents plants having heterozygous alleles, results in off springs which comprises of both tall and dwarf plants. For the parental cross, both the parents are true-breeding plants, the tall plant is homozygous for the tall allele T, while the dwarf plant is homozygous for the dwarf allele 't'. Mendel tracked each trait through two generations. When true-breeding plants were crossed to each other, this is called a parental cross and offspring comprise the first filial or F1 - generation. When the members of theF1 - generation were crossed, this produced the F2 generation or second filial generation. A cross between true-breeding tall and dwarf plants of the parent generation yield phenotypically tall plants. The cross between TT and Tt is called the back cross, which results in two homozygous and two heterozygous dominant gametes. The cross between Tt and tt is called testcross which results in a 1:1 ratio of gametes.

Hence, the correct option is (B).

The parents contain two alleles . During gamete formation, the factors or alleles of a pair seperate from each other such that a gamete receives only one of the two factors. This process is called segregation.

Gene Mutation. The term mutation was originally coined by Dutch botanist Hugo De Vries (1848–1935) to describe a new approach to explain evolution, although it is quite different than the current definition. De Vries discovered new forms of the Evening Primrose (Oenothera lamarcklana) that were growing in a meadow.

Mendel chose Pisum sativum (pea plant) for his experiments. It excludes plant colour. He chose characters like flower colour, flower position, stem length, seed shape, seed colour, pod shape and pod colour.

Haemophilia C is an X-linked disorder showing this type of inheritance. There is passage of the trait from the father to daughter or mother to son. If the father is the affected, the trait is passed to the daughter and she is a carrier.

The cell progresses through defined phases of the cell cycle during its division. first, the G1 in which some organelles starts their duplication then comes S phase where DNA has doubled then G2 phase and finally the M phase. So the correct sequence is 'G1,S,G2,M'.

The Principle of Independent Assortment describes how different genes independently separate from one another when reproductive cells develop. Independent assortment of genes and their corresponding traits was first observed by Gregor Mendel in 1865 during his studies of genetics in pea plants.

A monohybrid cross between two pure breeding varieties obtains all dominant F1 generation which in turn produces F2 generation upon selfing and gives the monohybrid phenotypic ratio of 3 (dominant):1 (recessive). The monohybrid genotypic ratio is 1 homozygous tall: 2 heterozygous tall: 1 homozygous dwarf.

A monohybrid cross is a cross between two organisms with different variations at one genetic chromosome of interest. The character(s) being studied in a monohybrid cross are governed by two or multiple variations for a single locus. A cross between two parents possessing a pair of contrasting characters is known as monohybrid cross. To carry out such a cross, each parent is chosen to be homozygous or true breeding for a given trait (locus). When a cross satisfies the conditions for a monohybrid cross, it is usually detected by a characteristic distribution of second-generation (F₂) offspring that is sometimes called the monohybrid ratio.

Genes which code for a pair of contrasting traits are known as allelomorph. It is nowadays commonly known as alleles (allele). It is called the variant form of a given gene. Many a times, different alleles may result in different observable phenotypic characteristics.

AaBbCC will produce 4 types of gametes which are as follows- ABC, AbC, aBC, abC. The number of gametes formed is decided by the number of heterozygous alleles present in the given genotype. 2^n is the formula used to find it out, where n=number of heterozygous alleles present in the genotype. Say for example, in the above genotype Aa & Bb are the 2 heterozygous alleles, so here n=2. Putting the values in the formula , we get 2^2=4. Hence 4 types of gametes are formed.

So the correct option is 'four'.

Eukaryotic chromosomes consist of a DNA-protein complex that is organized in a compact manner which permits the large amount of DNA to be stored in the nucleus of the cell. The nucleosome consists of about 200 bp wrapped around a histone octamer that contains two copies of histone proteins H2A, H2B, H3 and H4.

a) Dihybrid cross refers to inheritance of two pairs of contrasting characters by two parents at the same time. 

b) Monohybrid cross refers to inheritance of singe contrasting trait by two parents at a time. 

c) A test cross is a cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual.

d) A trihybrid cross is between two individuals that are heterozygous for three different traits.

So, the correct answer is option C.

Mendel studied inheritance in peas (Pisum sativum). He chose peas because they had been used for similar studies, are easy to grow and can be sown each year. Pea flowers contain both male and female parts, called stamen and stigma, and usually self-pollinate.

The S Phase of Interphase

The S phase of a cell cycle occurs during interphase, before mitosis or meiosis, and is responsible for the synthesis or replication of DNA.

A dihybrid cross describes a mating experiment between two organisms that are identically hybrid for two traits. A hybrid organism is one that is heterozygous, which means that is carries two different alleles at a particular genetic position, or locus. Therefore, a dihybrid organism is one that is heterozygous at two different genetic loci. In 1865, Gregor Mendel performed dihybrid crosses on pea plants and discovered a fundamental law of genetics called the Law of Independent Assortment. Mendel began his experiments by first crossing two homozygous parental organisms that differed with respect to two traits. An organism that is homozygous for a specific trait carries two identical alleles at a particular genetic locus.

Mendel chose to cross a pea plant that was homozygous and dominant for round (RR), yellow (YY) seeds with a pea plant that was homozygous and recessive for wrinkled (rr), green (yy) seeds, represented by the following notation:

RRYY x rryy

Organisms in this initial cross are called the parental, or P generation. The offspring of the RRYY x rryy cross, which is called the F1 generation, were all heterozygous plants with round, yellow seeds and the genotype RrYy.

Next, Mendel crossed two plants from the F1 generation. This step is the dihybrid cross, and it is represented as:

RrYy x RrYy

Mendel observed that the F2 progeny of his dihybrid cross had a 9:3:3:1 ratio and produced nine plants with round, yellow seeds, three plants with round, green seeds, three plants with wrinkled, yellow seeds and one plant with wrinkled, green seeds. From his experiment, Mendel observed that the pairs of traits in the parental generation sorted independently from one another, from one generation to the next.