ICSE-X-Biology
02 Genetic: Some Basic Fundamentals
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- Qstn #5In a certain species of animals, black fur (B) is dominant over brown fur
(b) Show the possible ratio of genotypes and phenotypes of the offspring of the pure breeding different coloured parents.Ans : Phenotypic Ratio - 3 (Black Fur) :1 (Brown Fur)
Genotypic Ratio - 1(Homozygous Black Fur):2 (Heterozygous Black Fur): 1 (Homozygous Brown Fur)
- #Section : DD. Long
- #1-aheterozygousAns : Heterozygous: The condition in which a pair of homologous chromosomes carries dissimilar alleles for a particular character.
For example -
(i) A daughter (XX°) from a normal homozygous mother for colour vision (XX) and a colour blind father has one normal and one defective allele (X˚Y).
(ii) Certain tongue rollers are heterozygous with Rr genotype.
- #1-bHomozygousAns : Homozygous: The condition in which a pair of homologous chromosomes carries similar alleles for a particular character.
For example -
(i) A colorblind daughter (XoXo will have both the X chromosomes with defective alleles.
(ii) A non-roller will have rr (homozygous) genotype.
- #1-cpedigree chart.Ans : Pedigree Chart: A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next. In the pedigree chart, males are shown by squares and females by circles.
- Qstn #2State the three mendel's laws of inheritance.Ans : Mendel's laws of inheritance are:
(i) Law of Dominance: Out of a pair of contrasting characters present together, only one is able to express itself while the other remains suppressed. The one that expresses is the dominant character and the one that is unexpressed is the recessive one.
(ii) Law of Segregation: The two members of a pair of factors separate during the formation of gametes. The gametes combine together by random fusion at the time of zygote formation. This law is also known as 'law of purity of gametes'.
(iii) Law of Independent Assortment: When there are two pairs of contrasting characters, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.
- Qstn #3Does the sex of the child depend on the father or it is just a matter of chance? DiscussAns : The sex of the child depends on the father. The egg contains only one X chromosome, but half of the sperms contain X-chromosome whereas the other half contains Y-chromosome. It is simply a matter of chance as to which category of sperm fuses with the ovum and this determines whether the child will be male or female.
If the egg fuses with X-bearing sperm, the resulting combination is XX and the resulting child is female.
If the egg fuses with Y-bearing sperm, the resulting combination is XY and the resulting child is male.
E. Structured Application and Skill Type
- #Section : E
- Qstn #1In a certain species of animals, black fur (B) is dominant over brown fur
(b) Predict the genotype and phenotype of the offspring when both parents are ‘Bb' or have heterozygous black fur.Ans :
Genotype - 1(Homozygous Black Fur) :2 (Heterozygous Black Fur):1 (Homozygous Brown Fur)
Phenotype - 3 (Black Fur) : 1(Brown Fur)
- #2-aCan you tell which coat colour (black or white) is dominant?Ans : Black
- #2-bIs the coat colour sex-linked? .......Ans : No
- Qstn #3Make a Punnett square for finding out the proportion of different genotypes in the progeny of a genetic cross between.
- #3-aA pure tall (TT) pea plant with a pure dwarf (tt) pea plant.Ans :
Genotype - 1(Homozygous tall) :2 (Heterozygous tall):1 (Homozygous dwarf)
Phenotype - 3 (Tall) :1(Dwarf)