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

• Mendel discovered the laws of inheritance.
• He attributed these traits being encoded by factors.
• Later studies showed that these factors are genes.

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.

 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

• 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.

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.

 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.

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.

Group O is often referred to as the universal red cell donor.