CBSE Questions for Class 12 Medical Biology Principles Of Inheritance And Variation Quiz 9 - MCQExams.com

• Gaucher's disease happens because of a recessive mutation in a gene called GBA. GBA is located on chromosome 1. Humans normally have two copies of the genes that tell the body to produce the enzyme glucocerebrosidase, and both copies work correctly.
• Lesch-Nyhan syndrome is inherited as an X-linked recessive genetic disorder that, with rare female exceptions, most often affects males. The symptoms of Lesch-Nyhan syndrome include impaired kidney function, acute gouty arthritis, and self-mutilating behaviors such as lip and finger biting and/or head banging.
• Hunter syndrome is caused by a defective chromosome, and a child must inherit the defective chromosome to develop the disease. Hunter syndrome is what's known as an X-linked recessive disease, which means that women carry the defective disease-causing X chromosome and can pass it on.
• Fabry disease is an inherited disorder that results from the buildup of a particular type of fat, called globotriaosylceramide, in the body's cells.

In the hybridization experiments, crossing of parents, yields F₁ generation.

A.Probability of homozygous dwarf progeny in a cross TT x Tt is zero – True because in this cross all progeny formed are tall,either homozygous  or heterozygous.

B.Probability of homozygous tall progeny in a cross TT x TT is one – True, because all progeny formed in the cross are tall.

C.Probability of heterozygous tall progeny in a cross TT x tt is 0.5 – False, because, all the progeny are formed are heterozygous and the probability is 1.

D.Probability of homozygous dwarf progeny in a cross TT x TT is zero – True, because in this cross not dwarf progeny is involved.

A pea plant with heterozygous round shaped seeds(Rr) is selfed, in the next generation, 1600 seeds are formed. When these seeds germinated, 1200 plants with round seeds and 400 plants with wrinkled seeds are formed.

In garden pea, the traits for the given characters are as follows-

• Wrinkled seeds – a recessive trait 
• Tall stem – a dominant trait 
• Round seeds – a dominant trait 
• Coloured seed coat – a dominant trait  

Phenylketonuria is a recessive autosomal disorder related to phenylalanine metabolism. This disorder is due to the absence of a liver enzyme phenylalanine hydroxylase. Due to the lack of this enzyme, phenylalanine follows another pathway and gets converted into phenyl pyruvic acid. This phenyl pyruvic acid upon accumulation in joints causes arthritis. If it hits the brain, it causes mental  retardation known as phenyl pyruvic idiocy.

A cross is made between two tall Garden pea plants, produces all tall plants. The genotypes of the parent plants are TT x TT or TT x Tt.

i)F₁ progeny is first hybrid generation and progeny resembles either of parent – True.

ii)F₂ progeny is a resultant hybrid generation of cross pollination among F₁ progeny and the progeny shows both dwarf and tall plants – False, because F₂ progeny is a resultant hybrid generation of cross pollination among F₁ progeny and the progeny shows either  dwarf or tall plants.

iii)F₂ progeny is second hybrid generation produced by selfing F₁ hybrids and progeny contains both dwarf and tall plants – True.

• A trisomy is a chromosomal disorder characterised by an additional chromosome, so the person has 47 instead of 46. Down syndrome, Edward syndrome and Patau syndrome are the most common forms of trisomy.
• Monosomy is a form of aneuploidy with the presence of only one chromosome from a pair.
  
• Polyploidy is the state of a cell or organism having more than two paired (homologous) sets of chromosomes.
• Nullisomic is a genetic condition involving the lack of both the normal chromosomal pairs for a species (2n-2).

• Erythroblastosis fetalis is hemolytic anemia in the fetus (or neonate, as erythroblastosis neonatorum) caused by transplacental transmission of maternal antibodies to fetal RBCs.
  
• Down syndrome also known as trisomy 21, is a genetic disorder caused by the presence of all or part of the third copy of chromosome 21.
• Males have an X and a Y (XY). But in rare cases, a male is born with an extra X chromosome (XXY). This is Klinefelter syndrome. It's also called Klinefelter's or XXY.
• The faulty 'gene' for color blindness is found only on the X chromosome.

• Mutations are random changes taking place at the level nucleotide sequence in DNA. Mutation is directionless means that nobody knows if it might result in something beneficial for the organism or harmful.
• Darwinian variations are small and directional.
  
• Fitness means reproductive fitness in the context of evolution. Population of all organisms have variations in characteristics, which make them adapt better to the environment. Some of these characteristics enable individuals to survive better in natural conditions and reproduce. This is called survival of the fittest.
• The organisms which adapt well in the environment will be selected by nature and will survive more in nature. This is called natural selection. Adaptability is inherited and fitness is the end result of the ability to adapt and get selected by nature.
• So, the correct options are 'Mutations are random and directionless.' and 'Fitness is the end result of the ability to adapt and get selected by nature.'

• Euploidy is the gain of one or more complete sets of chromosomes. Monosomy is the absence of one chromosome and falls under the category of aneuploidy whereas nullisomy is the absence of two chromosomes and also falls under the category of aneuploidy.
• Polyploidy is common in plants than in animals because in animals sex determination mechanism involves number and type sex chromosomes. Polyploidy will interfere with this mechanism and hence it is seen rarely in animals. Plants, on the other hand, do not have any such sex determination (based on number or type of chromosomes) and a majority of them can also reproduce vegetatively. This vegetative propagation enables multiplication of polyploid plants
• Polyploidy arises as the result of total nondisjunction of chromosomes during mitosis or meiosis.
•  Autopolyploidy is the containment of multiple sets of chromosomes that are derived from the same species.