Test: Principles of Inheritance and Variation- 1 - NEET MCQ

Because it produces 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.therefore the ratio is 9 : 3 : 3 : 1

Line in NCERT: "In the dihybrid cross (Figure 4.7), the phenotypes round, yellow; wrinkled, yellow; round, green and wrinkled, green appeared in the ratio 9:3:3:1."

As true tall breeding and true dwarf breeding is seen only a single time in F2 generation, and the remaining are hybtid tall...so the ratio becomes 1 : 2 : 2 : 1.

But 1 : 1 is the ratio for only true tall breeding and true dwarf breeding in F2 generation.

Line in NCERT: "From the Punnett square it is easily seen that 1/4th of the random fertilisations lead to TT, 1/2 lead to Tt and 1/4th to tt. This leads to a phenotypic ratio of 3/4th tall: (1/4 TT + 1/2 Tt) and 1/4th tt, i.e., a 3:1 ratio, but a genotypic ratio of 1:2:1."

 When a homozygous dominant tall pea plant (TT) is crossed with a homozygous recessive dwarf pea plant (tt), all the offspring (F1 generation) will be heterozygous (Tt) and exhibit the dominant tall phenotype. This is a classic example of Mendel's law of dominance, where the dominant allele masks the presence of the recessive allele in the heterozygote

Line in NCERT: "it is thus due to this dominance of one character over the other that all the F1 are tall (though the genotype is Tt)"

• Variation is the difference between individuals within a population.
• These arise between the progeny and parents/ancestors and form a backbone for natural selection to act on.

Line in NCERT: "Variation is the degree by which progeny differ from their parents."

A single gene may have two or more phenotypic expressions. The multiple phenotypic effect of a single gene is called pleiotropism. Hence the gene associated with this phenomenon is called Pleiotropic gene.

Line in NCERT: "There are however instances where a single gene can exhibit multiple phenotypic expression. Such a gene is called a pleiotropic gene."

Line in NCERT: "Half of the flowers are violet and half of the flowers are white."

 Test cross is across made to identify hidden recessive alleles in an individual of unknown genotye. This individual is crossed with one that is homozygous for the allele being investigated (i.e., a homozygous recessive). The homozygous recessive individual may be the parent of the individual being investigated.

Line in NCERT: "In a typical test cross an organism (pea plants here) showing a dominant phenotype (and whose genotype is to be determined) is crossed with the recessive parent instead of self-crossing."

All humans have 46 chromosomes, which determine who and what we are genetically. Boys have an X and Y chromosome. Girls have 2 X chromosomes. Turner Syndrome is a chromosomal disorder in girls in which part or all of one of the X-chromosomes is missing.
This loss of genetic material causes 2 primary features: namely, short stature and underdeveloped ovaries causing delayed or absent puberty. It is usually diagnosed when a girl is noted to be very short and a chromosome blood test is obtained. It should also be suspected if a girl has not developed breasts by 13-14 years of age or had her menstrual period by 15-16 years of age.  Effective hormonal treatment is available for both the short stature and to stimulate normal pubertal changes.

The ABO blood group system is determined by three different alleles: A, B, and O. These alleles can combine to form six possible genotypes: AA, AO, BB, BO, AB, and OO. Thus, there are 3 different alleles allowing for 6 different types of genotypes.

Line in NCERT: "Since there are three different alleles, there are six different combinations of these three alleles that are possible, and therefore, a total of six different genotypes of the human ABO blood types."

Multiple alleles refer to a situation where more than two alleles exist for a gene in the population, such as the three alleles (A, B, O) for blood groups in humans (a-ii).
Polygenes involve multiple genes contributing to a trait, such as skin color in humans, which is influenced by multiple genes (b-iii).
Pleiotropy occurs when one gene affects multiple traits, such as phenylketonuria, which affects multiple aspects of health and development (c-i).

Line in NCERT: "Do you realise that the example of ABO blood grouping also provides a good example of multiple alleles? Here you can see that there are more than two, i.e., three alleles, governing the same character." "Human skin colour is another classic example for this. In a polygenic trait the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive." "Occasionally, a single gene product may produce more than one effect."