Principles of Inheritance and Variation

Introduction

Genetics is the most essential study in the biology that refers to the process of understanding the available attributes of distinguishing factors and similarities in a species. Both variation and inheritance are connected with genetics in biology. Due to inheritance, different traits or characteristics are transferred among species whereas due to the variation, different characteristics can be distinguished and determined in different living beings.

Incomplete Dominance

Figure 1: Incomplete dominance

The situation when neither two alleles are dominant and the phenotype of the heterozygote does not correspond to any of the parents is known as incomplete dominance. The heterozygote represents a medium or a combination of the traits of two parents.

For instance, a flower colour inheritance of snapdragon or dog flower. Due to the procedure of true breeding RR and rr flower which seems red and white colour, the result will be the generation of flowers that are pink coloured in F1. According to the Mendel’s Law of inheritance, self-pollination will give red: pink: white flowers in the ratio of 1:2:1 in the process of F2 generation.

Co-dominance

Co-dominance is the situation when both the alleles represent themselves cooperatively as separate. For instance, the inheritance of the blood group ABO available in the human is managed by the gene I. Moreover, gene I contains three forms of allelic, they are IA, IB and i.

Figure 2: Co-dominance

When a character is controlled by more than two alleles it is referred to as the multiple alleles such as the ABO blood group. Similarly, when a character is controlled by independent genes, it is known as polygenic inheritance. Additionally, when many phenotypic traits are controlled by a single gene it is referred to as pleiotropy.

MCQs on Principles of Inheritance and Variation

Q1. If a hybrid expresses a character, what is it called?

• (a) Epistasis

• (b) Dominant

• (c) Co-dominant

• (d) Recessive

Ans. (b) Dominant

Q2. How many gametes will a plant produce when it has genotype AABbCC?

• (a) 2

• (b) 3

• (c) 4

• (d) 5

Ans. (a) 2

Q3. Which of the following is linked with coloured blindness with the connection of recessive trait?

• (a) X chromosome

• (b) Y chromosome

• (c) Z chromosome

• (d) None

Ans. (a) X chromosome

Q4. In the most common species, what will be the mitochondrial DNA passed from?

• (a) DNA

• (b) Mother

• (c) Father

• (d) Both option (b) and (c)

Ans. (b) Mother

Q5. Where are the genes for cytoplasmic male sterility discovered in plants?

• (a) Chloroplast genome

• (b) Cytosome

• (c) Mitochondrial genome

• (d) None

Ans. (c) Mitochondrial genome

Q6. What is referred to as the type of trait whose phenotype is influenced by more than one gene?

• (a) Oncogenic Trait

• (b) Polygenic trait

• (c) Monogenic trait

• (d) None

Ans. (b) Polygenic trait

Q7. What is an individual’s collection of genes called?

• (a) Genotype

• (b) Phenotype

• (c) Trait

• (d) None

Ans. (a) Genotype

Q8. What is the inheritance known in the case, where both father and mother do not have any inherited disease; however, among their children a few sons suffer from a disease?

• (a) Sex-linked dominant

• (b) Sex-linked recessive

• (c) Autosomal dominant

• (d) None

Ans. (b) Sex-linked recessive

Q9. What is called when a trait that overpowers, hides another trait?

• (a) Overpowering trait

• (b) Complex trait

• (c) Dominant Trait

• (d) Recessive trait

Ans. (c) Dominant Trait

Q10. Why is haemophilia a disease more commonly witnessed in males?

• (a) The disease is Y-linked

• (b) Due to Autosomal dominant

• (c) It’s an X- linked disease

• (d) Both options (a) & (c)

Ans. (c) It’s an X- linked disease

Q11. What determines sex in human children?

• (a) The size of the fertilised eggs

• (b) The size and available number of sperms in semen

• (c) Sex chromosome of the father

• (d) Sex chromosome of the mother

Ans. (c) Sex chromosome of the father

Q12. What is the trait of the male pattern of baldness?

• (a) Influenced by genetics

• (b) Due to chromosomal issues

• (c) Due to the X-link

• (d) None

Ans. (a) Influenced by genetics

Q13. Which of the following is a recessive trait determined by Mendel in the pea garden?

• (a) Violet flower colour

• (b) Yellow pod colour

• (c) Tell stem height

• (d) Axial flower position

Ans. (b) Yellow pod colour

Q14. What is the ultimate source of allelic variation?

• (a) Mutation

• (b) Natural selection

• (c) Recombination

• (d) Drift

Ans. (a) Mutation

Q15. What resembles in the case of the co-dominance, the F1 generation?

• (a) Dominant parent

• (b) Recessive parent

• (c) Both options (a) & (b)

• (d) None

Ans. (c) Both options (a) & (b)

Q16. What is the reason for sickle cell anaemia?

• (a) Non-disjunction of autosome

• (b) A point mutation

• (c) A chromosomal aberration

• (d) Reaction from the blood transfusion

Ans. (b) A point mutation

Q17. How many different genotypes do human ABO blood types contain?

• (a) Six

• (b) Five

• (c) Four

• (d) Three

Ans. (a) Six

Q18. What is the Sex determination chromosome among the male birds from the followings?

• (a) XO

• (b) XX

• (c) ZZ

• (d) None

Ans. (c) ZZ

Conclusion

Variation requires having suitable knowledge of the inheritance and its procedure. Different types of variation is useful in understanding whether the process of inheritance is successful or not. Heredity is also defined as the type of variation to some extent.

FAQs

Q1. What is Turner’s syndrome?

Ans. The situation when one X chromosome is missing from overall 45 chromosomes. In this situation, females are sterile, short height and has under-progressive sexual qualities.

Q2. What is down syndrome?

Ans. Due to the genetic disorder, the creation of the trisomy of chromosome 21 is called down syndrome. Moreover, different symptoms are visible to detect down syndrome such as mental retardation, short height, and opened mouth partially.