12th Class Biology Chapter 8 Variation and Genetics Short Questions Answer

Phenotype is the form of appearance of a trait.Genotype is the genetic complement i.e.the genes in an individual for a particular trait.

Any group sexually interbreeding organisms of the same species that exist together in both time and space is called a population.

When two independent events are occurring simultaneously like in Dihybird cross the ratio of each joint phenotypic combination can be obtained by multiplying the probabilities of individual phenotypes.It is called product rule.

There are four types fo dominance relations among alleles each indicating a different style of their functional effects upon each other. i) Complete dominance ii) Incomplete dominance iii) Coddominance iv) Over dominance

Karl Landsteiner discovered ABO blood group system in 1901.

When an effect caused by a gene or gene pair at one locus interferes with or hides the effect caused by another gene or gene pair at another locus such a phenomenon of gene interaction is called epistasis.

A continuously varying trait is encoded by alleles of two or more different gene pairs found at different loci,all influencing the same trait in an additive way.These quantitative traits are called polygenetic traits and their genes are polygenes.

Many species of eukaryotic microorganisms kike yeast do not have sex chromosome.

Monochromacy is true color blindness.

Mendelian factors behave like chromosomes because these factors are located on the chromosomes or in other words they are part of chromosomes.

Male and female Drosophila shows sexual dimorphism i.e.these aremorphologically distinct from each other.Male is smaller in size with black rounded abdomen.Female is large with pointed abdomen.Male has sex combs on front legs.

Dene is the basic unit of biological information.Hereditary characteristics pass from parents to offspeing through genes in their gemetes. The genetic material of an organism is the genome.

Gene is the basic unit of biological information.Genes are actually parts of DNA comprising its base sequences.An allele is a member of the gene pair.

A hybrid for a single trait under consideration insaid to be monohybrid while a hybrid for two traits under consideration is called dihybrid.

When both the alleles of a gene pair in an organism are same the organism is homozygous for that gene pair e.g RR or rr’. When the two alleles of a gene pair in an organism are different the organism is heterozygous for that gene pair e.g.Rr’

Dominance is a physiological effect of an allele over its partner allele on the seme gene locus.When an effect caused by a ene or gene pair at one locus interferes with or hides the effect caused by another gene or gene pair at another locus,such a phenomenon of gene interaction is called epistasis.

All chromosome other than sex-chromosomes are called autosomes.X and Y chromosomes are called sex-chromosomes because these have genes for determination of sex.

Partners of a gene pair are called alleles.Each allele of a gene pair occupies the same gene locus on its respective homologue e.g. Rror Rr etc.All the altered alternate forms of a gene whose number is more than two are called multiple alleles e.g.

A sex-limited trait is limited to only one sex dur to anatomical differences.e.g. beard growth in humans is humans is limited to men.Sex influenced trait occurs in both males and females but it is more common on one sex.Pattern baldness is a sex influenced trait that is more common in men.

When the dphenotype of the geterozygote is intermediate between phenotypes of the two homzygotes it is called incomplete or partial dominance e.g.4 O-clock pink flower.Different alleles of a gene that are both expressed in a heterozygous condition are called codminant and the phenomenon is called codominance e.g.MN blood type.

A trait that appears in a hybrid between two true breeding varieties is called dominant trait while a trait that is suppressed or masked in a hybrid between two true breeding varieties it is said to be recessive.

Some traits show more than two qualitatively different phenotypes this is called continuous variations e.g.weat grain color human height skin color and intelligence.There are many traits which have only two sharply defined phenotype this is called discontinuous variation e.g. height color shape in pea plant as studied by Mendel.

An organism with normally existing traits is called wild type while an orgenism with a trait developed due to mutation is said to be mutant.

All the genes/alleles found in a breeding population at a given time are collectively called the gene pool.It is the total genetic information encoded in the total genes in a breeding population existing at a given time.

Yes pea was a lucky choice for Mendel as he studied seven traits and pea plant has seven pairs of chromosomes.The genes of these traits were luckily located on separate chromosomes so he found independent assortment.If he had studied the eighth found independent assortment.If he had studied the eighth character he might be encountered with deviation from independent assortment.

Test cross is a mating in which an individual showing a dominant phenotype is crossed with an individual showing its recessive phenotype.This cross finds out the homozygous or heterozygous nature of the genotype.Mendel devised a cross to test the genotype of an individual showing a dominant phenotype.

If alleles of a pair do not segreagate at meiosis some gametes have an extra chromosome while others would lack one chromosome.This process is called non-disjunction.This phenomenon disturbs the purity of gametes according to which each gamete should receive only one of the two alleles.

The recombinants would be missing in the progeny.

It is because of meiosis and segregation.

The dominant allele does not modify the determunative nature of its recessive partner.Dominace is a physiological effect of an allele over its partner allele on the same locus.When one allele is completely dominant over the other presence of recessive allele is functionally hidden.So the heterozygote has the same phenotype as homozygote.

The traits located on different chromosomes can assort independently.

The blood group phenotype is controlled by genes which will never change or mutate during the life time of a person so blood group phenotype remains constant throughout the life.

O blood group individuals are called universal donors.Phenotype O can also be used as donor for small transfusions to A,B and AB recipients because donor’s antibodies are quickly absorbed by other tissues or greatly diluted in the recipient’s blood stream.

If O^– mother  conceives A⁺ or B⁺ baby any foetal  A or B type RBC entering the mother’s blood are quickly destroyed by ger anti-A or anti-B antibodies before she can form anti-Rh antibodies.

The genes located on the same chromosome do not obey law of independent.

The linked genes can be separated from each other by crossing over.

The ingeritance of a trait which is controlled by several genes and is affected by environmental factors as well is called multifactorial inheritance.

About 2% – 5% of type II diabetics get the disease early in life before 25 years of age.It is called maturity onset diabetes of the young.MODY can ingerited as an autosomal dominant trait.About 50% of cases of MODY are caused by mutions in glucokinase gene.

Yes,a child may have more interlligence than his parents.

The position of a gene on the chromosome is called its locus.

Partners of a gene pair are called alleles.Each allele of a gene pair occupies the same gene locus on its respective homologue.Both alleles on one locus may be identical or different from each other.

Gregor johann Mendel laid the foundation of classical genetics by formulating two laws of heredity.Law of segregation and law of independent assortment.

According to law of segragation the two coexisting alleles for each trait in an individual segregate from each other so that each gamete receives only one of the two alleles.

Punnett square is a checker box in which male gametes are put on one side and female gemetes on the other side and their combined results are placed in corresponding boxes to get the genotypic and phenotypic ratios of the next generation.

Mendel formulated law of independent Assortment When two contrasting pairs of traits are followed in the same cross their alleles assort independently into gametes.

All the genes present on a homologous pair of chromosome are linked to each other in the form of a linkage group.These cannot assort independently.

In this case the over dominant heterozygote exceeds in quantity the phenotpic expression of both the homozygotes.

ABO blood group system was discovered by karl landsteiner in 1901.

Bernstein explained the genetic basis of ABO system in 1925.

The branch of biology which deals with the study of inheritance (heredity) is called genetics.

These have now been named as genes by Johannsen.

A gene is the unit of inheritance.

The position occupied by a gene on a chromosome is called its locus. Alleles of a gene occupy the same locus on homologous chromosomes.

The alternative forms of a gene, occupying the same locus on homologous chromosomes, are called alleles or allelomorphs.

An allele that masks the expression of the other allele at the same locus is called dominant while the other which is masked is termed as the recessive.

The sum total and variety of all the genes and their alleles present in a breeding population (or species) at one time is called gene pool.

Gregor Mendel formulated the laws of inheritance viz. the law of segregation and the law of independent assortment.

An organism which produces offspring identical to the parent with respect to a character is known as true-breading.

P₁ means parental generation in which both the parents are homozygous (true-breeding) for a pair of traits whereas F₁ means the first filial generation comprising the offspring of the P₁ generation.

The phenotypic ration is 3:1 and the genotypic ratio is 1:2:1.

The phenotype means the appearance of a trait and the genotype means its genetic makeup.

The true-breeding organisms for a particular trait are called homozygous while the hybrid ones are known as heterozygous.

According to this law, the two alleles of a trait exist together in an individual but tend to separate in its gametes.

The homzoygosity or heterozygosity of an individual with regard to a particular dominant character can be known by the test cross.

The expression of both the alleles of a character in heterozygous individuals giving intermediate phenotype is called incomplete or partial dominance.

Yes. Pea was a lucky choice for Mendel. If Mendel had studied an eighth character, his results would have not obeyed laws of segregation and independent assortment, due to linkage of genes.

Monohybrid is the individual that is heterozygous in respect of a single gene (a pair of alleles) while dihybrid is the individual that is heterozygous for two genes (two pairs of alleles).

Codominance is the phenomenon in which both the alleles of a gene in a heterozygote are expressed in the phenotype.

The gametes produced under such a condition would never be pure.

If the alleles do not assort independently, the genetic recombinations (new phenotypic combinations) may be missing in the progeny.

Of the two alleles of a gene, each is situated on one of a pair of homologous chromosomes. During meiosis at the time of gamete formation, each gamete gets only one (anyone) chromosome of the pair along with its allele. Each gamete, therefore, has equal chance of getting one or the other allele of a pair.

The traits whose alleles are situated on different (non-homologous) chromosomes can assort independently.

The law of independent assortment states that if two (or more) contrasting pairs of traits are followed together in the same cross, alleles of each pair are inherited independently of the other pair.

If for a trait there are more than two different alleles of the gene that affects the trait; these are called as multiple alleles.

Karl Landsteiner discovered ABO-blood groups in 1901.

Bernstein explained the genetic basis of ABO-blood groups in 1925.

Three alleles are responsible for these four types of blood groups.

Pleiotropy is the phenomenon in which a single gene affects two or more traits.

It is controlled by three to six gene pairs.