Biology Notes – Grade 10
National Curriculum Pakistan - NCP
Chapter 7: Inheritance
Aligned with: National Curriculum Pakistan, Federal Board, NBF, PTB
This page covers important concepts related to genetics and inheritance in biology, ideal for exam preparation and revision.
Introduction to Inheritance in Biology
Inheritance is a key topic in biology that explores how traits and genetic information are passed from one generation to the next. Below are frequently asked questions and answers on the topic, including Mendelian genetics, DNA, genes, and chromosomes.
1. What is inheritance in biology?
Inheritance is the process by which traits are passed from parents to their offspring, leading to similarities and variations across generations.
2. What are inherited traits?
Inherited traits are characteristics that are genetically determined and passed down from parents to offspring through genes.
3. Who is considered the "father of genetics" and what organism did he primarily study?
Gregor Mendel is considered the "father of genetics." He primarily studied pea plants to understand the principles of inheritance.
4. What did Mendel's work reveal about inherited traits?
Mendel's work showed that inherited traits are governed by predictable rules, with some traits being dominant and others recessive.
5. What is the focus of the chapter on inheritance?
This chapter explores the basic principles of inheritance, including how traits are passed on and how variations arise, providing insight into the genetic mechanisms driving biological diversity.
6. What are chromosomes composed of?
Chromosomes are thread-like structures found in the nucleus of eukaryotic cells, composed of DNA tightly coiled around proteins.
7. Where is DNA located within a chromosome?
DNA, the genetic material, is present as long, thin fibers that are highly coiled and condensed during cell division to form visible chromosomes.
8. What is the role of DNA in inheritance?
DNA carries the genetic information that determines the traits of an organism and is passed from parents to offspring, thus playing a central role in inheritance.
9. What are genes and where are they located?
Genes are specific segments of DNA that contain the instructions for building and maintaining an organism. They are located at specific positions on chromosomes.
10. What are the main parts of a chromosome?
The main parts of a chromosome include chromatids (duplicated copies), the centromere (where chromatids are joined), and telomeres (protective ends).
11. What is a duplicated chromosome composed of?
A duplicated chromosome, formed after DNA replication during cell division, consists of two identical sister chromatids joined at the centromere.
12. What is the centromere and its function?
The centromere is the constricted region of a chromosome where the sister chromatids are attached. It is also the site where the kinetochore forms.
13. What is the kinetochore and its role during cell division?
The kinetochore is a protein complex that assembles on the centromere and serves as the attachment point for spindle fibers during cell division, ensuring proper chromosome segregation.
14. What are telomeres and their function?
Telomeres are the protective caps at the ends of chromosomes. They help maintain the integrity and stability of chromosomes, protecting them from degradation and loss of genetic information during cell division.
15. What is the focus of Mendelian genetics?
Mendelian genetics focuses on understanding basic genetic terms such as gene, allele, genotype, phenotype, dominant, and recessive to explain how traits are inherited.
16. What is a monohybrid cross?
A monohybrid cross is a genetic cross between parents that differ in only one specific trait or gene.
17. What is a phenotype?
A phenotype is the observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype and the environment.
18. What is a genotype?
A genotype is the genetic makeup of an organism, referring to the specific combination of alleles it possesses for a particular trait or set of traits.
19. What is a gene?
A gene is a specific segment of DNA on a chromosome that contains the instructions for a particular trait, usually by coding for a specific protein.
20. How are genes passed on to offspring?
Genes are passed on to offspring through the gametes (sperm and egg) during sexual reproduction, with offspring inheriting one allele for each gene from each parent.
21. What is an allele?
An allele is one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
22. What is a locus (plural loci)?
A locus is the specific physical location of a gene on a chromosome. Alleles of a gene are found at the same locus on homologous chromosomes.
22. What are homologous chromosomes?
Homologous chromosomes are pairs of chromosomes in a diploid organism that have the same genes in the same order but may have different alleles of those genes.
23. What is a homozygous condition?
A homozygous condition occurs when an individual has two identical alleles for a particular gene at a specific locus on homologous chromosomes.
24. What is a heterozygous condition?
A heterozygous condition occurs when an individual has two different alleles for a particular gene at a specific locus on homologous chromosomes.
25. Where are alleles of a gene located on homologous chromosomes?
Alleles of a gene are found at the same specific locus (position) on homologous chromosomes, representing different versions of that gene.
26. How many alleles for a particular gene does a diploid organism typically inherit?
A diploid organism typically inherits two alleles for each gene, one from each parent, located at the same locus on homologous chromosomes.
27. What are different forms of a gene called?
Different forms of a gene, which may result in different expressions of a trait, are called alleles.
28. In Mendel's pea plants, what are the alleles for flower color?
In Mendel's pea plants, the alleles for flower color are typically represented as 'P' for purple (dominant) and 'p' for white (recessive).
29. What determines the phenotype of a heterozygous individual if one allele is dominant and the other is recessive?
In a heterozygous individual with a dominant and a recessive allele, the phenotype will be determined by the dominant allele, masking the effect of the recessive allele.
30. What does the genotype of an organism represent?
The genotype of an organism represents its specific genetic makeup, particularly the combination of alleles it possesses for a given trait or set of traits.
31. What does a homozygous genotype indicate?
A homozygous genotype indicates that an individual has two identical alleles for a particular gene (e.g., PP or pp).
32. What does a heterozygous genotype indicate?
A heterozygous genotype indicates that an individual has two different alleles for a particular gene (e.g., Pp).
33. In the example of pea plant height, what genotypes correspond to a tall phenotype if 'T' is dominant for tallness and 't' is recessive for dwarfness?
The genotypes 'TT' (homozygous dominant) and 'Tt' (heterozygous) both result in a tall phenotype because the dominant 'T' allele masks the recessive 't' allele.
34. What genotype corresponds to a dwarf phenotype in pea plants with 'T' and 't' alleles?
Only the homozygous recessive genotype 'tt' results in a dwarf phenotype because there is no dominant allele to mask the expression of the recessive trait.
35. What determines the phenotype of an organism?
The phenotype of an organism is determined by its genotype (the specific alleles it possesses) and can also be influenced by environmental factors.
36. In the example of earlobe attachment, what genotypes might correspond to free earlobes if 'E' is dominant for free and 'e' is recessive for attached?
The genotypes 'EE' (homozygous dominant) and 'Ee' (heterozygous) would likely result in the phenotype of free earlobes.
37. What genotype corresponds to attached earlobes in the 'E' and 'e' allele system?
Only the homozygous recessive genotype 'ee' would result in the phenotype of attached earlobes.
38. Who is credited with establishing the fundamental principles of inheritance?
Gregor Mendel is credited with establishing the fundamental principles of inheritance through his meticulous experiments with pea plants.
39. What was the key publication that documented Mendel's work?
Mendel's pioneering work on inheritance was published in 1866.
40. What organism did Mendel use for his genetic experiments?
Mendel conducted his groundbreaking genetic experiments using garden pea plants (Pisum sativum).
41. Why was the pea plant a good choice for Mendel's studies?
Pea plants were a good choice because they have clearly defined contrasting traits, are easy to cultivate, have a short generation time, and can be easily cross-pollinated or allowed to self-pollinate.
42. How did Mendel control pollination in his pea plants?
Mendel controlled pollination by carefully cross-pollinating plants with desired traits and preventing self-pollination to study the inheritance of specific characteristics.
43. How many contrasting traits in pea plants did Mendel consistently study?
Mendel consistently studied the inheritance of seven different contrasting traits in pea plants, such as seed color, seed shape, and flower color.
44. What type of plants did Mendel use as the parental generation in his crosses?
Mendel used true-breeding plants as the parental generation, meaning they consistently produced offspring with the same trait when self-pollinated.
45. What is a monohybrid cross, and what does it study?
A monohybrid cross is a cross between parents that differ in only one specific trait. It studies the inheritance of a single characteristic.
46. What type of cross did Mendel perform to study the inheritance of a single trait?
To study the inheritance of a single trait, Mendel performed a monohybrid cross, involving parents that differed in only one characteristic.
47. What did Mendel observe in the F1 generation when he crossed true-breeding plants with contrasting traits?
In the F1 generation of a monohybrid cross, Mendel observed that all the offspring exhibited only one of the parental traits, the dominant trait. The other parental trait (recessive) seemed to disappear.
48. What did Mendel do to obtain the F2 generation in his monohybrid crosses?
To obtain the F2 generation, Mendel allowed the F1 generation plants to self-pollinate.
49. What phenotypic ratio did Mendel observe in the F2 generation of a monohybrid cross when one allele showed complete dominance?
Mendel observed a consistent phenotypic ratio of approximately 3:1 in the F2 generation, with three individuals showing the dominant trait for every one individual showing the recessive trait.
50. What genotypic ratio did Mendel find in the F2 generation of a monohybrid cross?
The underlying genotypic ratio in the F2 generation was 1:2:1, representing homozygous dominant, heterozygous, and homozygous recessive individuals, respectively.
51. What conclusions did Mendel draw from his monohybrid crosses?
Mendel concluded that traits are controlled by factors (genes) that exist in pairs (alleles), and that during gamete formation, these pairs separate, with each gamete receiving only one allele.
52. What is Mendel's Law of Segregation?
Mendel's Law of Segregation states that the two alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes.
53. What is a dihybrid cross?
A dihybrid cross is a cross between parents that differ in two distinct traits or genes.
54. What traits did Mendel often study in his dihybrid crosses with pea plants?
Mendel often studied traits like seed shape (round or wrinkled) and seed color (yellow or green) simultaneously in his dihybrid crosses.
55. What were the genotypes of the true-breeding parental plants in Mendel's dihybrid cross for seed shape and color?
The true-breeding parents had genotypes RRYY (round, yellow) and rryy (wrinkled, green), producing gametes RY and ry, respectively.
56. What was the genotype and phenotype of the F1 generation in Mendel's dihybrid cross?
The F1 generation had a genotype of RrYy and exhibited the dominant phenotypes for both traits, being round and yellow.
57. What phenotypic ratio did Mendel observe in the F2 generation of a dihybrid cross when the genes assorted independently?
Mendel observed a phenotypic ratio of 9:3:3:1 in the F2 generation, representing round yellow, round green, wrinkled yellow, and wrinkled green phenotypes.
58. What is Mendel's Law of Independent Assortment?
Mendel's Law of Independent Assortment states that alleles of different genes assort independently of one another during gamete formation if the genes are located on different chromosomes.
59. What is the basis for the independent assortment of genes?
The independent assortment of genes occurs because the orientation of homologous chromosome pairs during meiosis I is random, leading to different combinations of alleles in the gametes.
60. What type of cross can be used to determine the genotype of an individual showing the dominant phenotype?
A test cross, where an individual with an unknown genotype (showing the dominant phenotype) is crossed with a homozygous recessive individual, can determine the unknown genotype based on the offspring's phenotypes.
61. In the context of genetics, what does the term "true-breeding" refer to?
True-breeding organisms are homozygous for a particular trait and consistently produce offspring with the same phenotype when self-pollinated.
62. What is the purpose of performing a test cross in genetic studies?
A test cross helps determine if an individual expressing a dominant phenotype is homozygous dominant or heterozygous by crossing it with a homozygous recessive individual.
63. How does the behavior of chromosomes during meiosis explain Mendel's Laws of Segregation and Independent Assortment?
The separation of homologous chromosomes during meiosis I explains the Law of Segregation, while the random alignment of these pairs explains the Law of Independent Assortment for genes on different chromosomes.
64. If a plant with a genotype of AaBb is self-crossed, what are the possible genotypes of the gametes it can produce according to the Law of Independent Assortment?
A plant with the genotype AaBb can produce four possible gamete genotypes: AB, Ab, aB, and ab, with equal probability.
65. Why is understanding the principles of Mendelian inheritance important in the field of biology?
Understanding Mendelian inheritance provides the foundation for comprehending how traits are passed down, predicting genetic outcomes, and exploring the mechanisms of evolution and genetic disorders.