Notes Chapter 15 – Inheritance in your class10th Biology course. In this chapter, we will delve into the fascinating realm of genetics, where the secrets of heredity and the transmission of traits from one generation to another are unlocked. Prepare to unravel the intricate mechanisms that govern the diversity of life forms and discover how the blueprint of life is passed down through genes.
From Gregor Mendel’s pioneering experiments to the modern understanding of DNA and genetic inheritance, this chapter will provide you with a profound insight into the fundamental principles that shape the characteristics of living organisms. Let’s embark on a journey to uncover the mysteries of inheritance and explore the remarkable ways in which life’s legacy is perpetuated.
Unit 15 Inheritance Long Questions
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Unit 15 Inheritance MCQ’s
Unit 15 Inheritance Short Questions
What is genetics?
Answer: Genetics is the branch of biology that studies inheritance, which involves the transmission of traits from parents to offspring.
What are traits? Give an example.
Answer: Traits are characteristics that can be inherited from parents. Examples of traits include height, eye color, and intelligence.
What are genes made of, and what is their role?
Answer: Genes are made of DNA. They contain specific instructions for protein synthesis, which determine various traits and functions in an organism.
How many chromosomes are present in human body cells, and what are homologous chromosomes?
Answer: Human body cells have 46 chromosomes, arranged in 23 pairs. Each pair consists of homologous chromosomes, which carry similar genetic information but may have different alleles.
What is the composition of chromosomes, and what are nucleosomes?
Answer: Chromosomes are composed of chromatin, a complex material made of DNA and proteins, mainly histone proteins. DNA wraps around histone proteins to form nucleosomes, which are like “beads on a string.”
Explain DNA replication and its purpose.
Answer: DNA replication is the process of copying DNA before cell division. It involves unwinding the DNA double helix and creating two new strands using each existing strand as a template. This process ensures that each daughter cell receives a complete set of genetic information.
How does DNA control the traits and functions of cells?
Answer: DNA contains instructions for protein synthesis, which determines the traits and functions of cells. It does so by directing the sequence of amino acids in specific proteins. These proteins play structural and enzymatic roles in cells.
What is a gene, and how does it relate to alleles?
Answer: A gene is a specific segment of DNA that carries the instructions for a particular trait or function. Alleles are alternate forms of a gene that exist in pairs on homologous chromosomes. Individuals inherit one allele from each parent, contributing to their genetic makeup.
How does the process of transcription and translation contribute to protein synthesis?
Answer: Transcription involves copying the DNA sequence of a gene into messenger RNA (mRNA). mRNA carries this sequence to ribosomes, where translation occurs. During translation, ribosomes read the mRNA sequence and assemble amino acids in the correct order to synthesize a protein.
What is genotype and what are its two types?
Answer: Genotype refers to the specific combination of genes in an individual. It has two types: homozygous genotype (containing two identical alleles) and heterozygous genotype (containing two different alleles).
Explain the terms dominant allele and recessive allele.
Answer: In a heterozygous genotype, the dominant allele is the one that masks or prevents the expression of the recessive allele. The dominant alleles are represented by capital letters, while the recessive alleles are represented by lowercase letters.
How is albinism inherited, and what are the possible genotypes for this trait?
Answer: Albinism is a recessive trait. It is inherited when an individual has two recessive alleles (aa) for the trait. The possible genotypes for albinism are AA (homozygous dominant), Aa (heterozygous), and aa (homozygous recessive).
What is the phenotype, and how does it relate to the genotype?
Answer: The phenotype is the observable trait or characteristic of an individual, such as being albino or having normal pigmentation. It is determined by the expression of the genotype, where certain alleles dominate over others, resulting in specific traits.
Who was Gregor Mendel, and why did he choose pea plants for his experiments?
Answer: Gregor Mendel was a monk who established the fundamental principles of genetics. He chose pea plants for his experiments because they had a variety of different traits, contrasting phenotypes, self-fertilization and cross-fertilization capabilities, and a short life cycle, making them ideal for studying inheritance patterns.
What were Mendel’s contributions to genetics?
Answer: Mendel proposed the existence of “special factors” that control the expression and transmission of traits across generations. These factors were later termed genes. He established the principles of dominant and recessive alleles, and he conducted extensive experiments with pea plants, analyzing the results using statistical ratios to formulate Mendel’s Laws of Inheritance.
What did Mendel study in relation to inheritance initially?
Mendel studied the inheritance of seed shape.
What is a monohybrid cross, and how did Mendel use it?
A monohybrid cross is a cross in which only one trait is studied at a time. Mendel used a monohybrid cross to study the inheritance of seed shape in pea plants.
How did Mendel describe the traits “round seeds” and “wrinkled seeds” based on his experiments?
Mendel described “round seeds” as dominant and “wrinkled seeds” as recessive.
What were the parental generation, F1 generation, and F2 generation in Mendel’s experiments?
The parental generation (P1) consisted of true-breeding round-seeded and true-breeding wrinkled-seeded plants. The offspring of P1 generation were the F1 generation (first filial). The cross in the F1 generation produced the F2 generation (second filial).
What did Mendel’s experiments with tall and short plants reveal about inheritance?
Mendel’s experiments showed that tallness was a dominant trait, and shortness was a recessive trait. When “true-breeding” tall plants were crossed with “true-breeding” short plants, all offspring of the F1 generation were tall.
Explain Mendel’s Law of Segregation.
Mendel’s Law of Segregation states that genes exist in pairs in organisms, and during gamete formation, these gene pairs segregate from each other. Each gamete receives one gene from the pair. When gametes from male and female parents unite during fertilization, the resulting offspring again have genes in pairs.
What did Mendel study in dihybrid crosses, and how did he perform these experiments?
Mendel studied two contrasting traits at a time in dihybrid crosses. He performed experiments on seed traits like shape and color.
What is the ratio of phenotypes observed in Mendel’s dihybrid cross involving seed shape and seed color?
The ratio of phenotypes observed in Mendel’s dihybrid cross involving seed shape and seed color was 9:3:3:1.
What did Mendel conclude from his second experiment involving dihybrid crosses?
Mendel concluded that different traits, such as seed shape and seed color, are inherited independently of one another. This principle is known as the law of independent assortment. It states that the alleles of a gene pair segregate independently from the alleles of other gene pairs.
What are co-dominance and incomplete dominance?
Co-dominance and incomplete dominance are deviations from Mendel’s laws of inheritance where traits are controlled by more than one pair of genes or where more than two alleles are present in a gene pair.
Explain co-dominance with an example.
Co-dominance occurs when both alleles of a gene pair are fully expressed in the heterozygous organism. An example is the human ABO blood group system, where alleles IA and IB produce antigens A and B, respectively. In the heterozygous genotype IAIB, both antigens A and B are expressed.
What is the outcome of co-dominance in the ABO blood group system?
In the ABO blood group system, when an individual has a heterozygous genotype IAIB, both antigens A and B are expressed, resulting in the blood group AB.
Describe incomplete dominance using the example of Four ‘O’ Clock plants.
Incomplete dominance is when alleles in a heterozygous genotype express as a blend, leading to an intermediate phenotype. In Four ‘O’ Clock plants, the alleles for red flowers (R) and white flowers (r) blend to produce pink flowers (a blend of red and white). Neither allele is dominant over the other.
What is the main difference between discontinuous and continuous variations?
Discontinuous variations show distinct phenotypes that cannot be measured, such as blood groups. Continuous variations involve a complete range of measurements from one extreme to another, like height, weight, and intelligence.
Explain how variations lead to evolution.
Variations are inheritable differences in traits among individuals of a population. Over time, these variations can accumulate, leading to changes in the characteristics of a population or species. These changes, when inherited, contribute to the process of organic evolution.
Who proposed the theory of natural selection and what did it propose?
Charles Darwin proposed the theory of natural selection. This theory suggests that organisms with advantageous traits are more likely to survive and reproduce, passing on their traits to the next generation. Over time, these traits become more common in the population, leading to evolutionary changes.
What is natural selection?
Natural selection is the process by which better genetic variations become more common in successive generations of a population.
What does fitness mean in the context of natural selection?
Fitness refers to an organism’s ability to survive and reproduce. Organisms with higher fitness are better adapted to their environment.
How does natural selection lead to the transmission of genetic variations?
Organisms with favorable variations have a better chance of reproducing and passing those variations to their offspring, while organisms with unfavorable variations have a lower chance of reproducing.
What does “selected for” and “selected against” mean in natural selection?
“Selected for” means that favorable variations are more likely to be passed on to the next generations, while “selected against” means that unfavorable variations are less likely to be passed on.
Provide an example of natural selection involving a mouse population and a predator.
In a mouse population, light and medium-colored mice were preyed upon by a cat. As the environment changed and only dark-colored mice survived, natural selection led to the dominance of the dark-colored variation.
Explain the concept of artificial selection.
Artificial selection, also known as selective breeding, involves intentional breeding between individuals with desired traits. It is used to develop new generations with specific characteristics in animals and plants.
How does artificial selection differ from natural selection?
In artificial selection, humans deliberately choose and breed individuals with desired traits, while in natural selection, the environment determines which traits are advantageous for survival and reproduction.
Give an example of artificial selection in livestock and crops.
In livestock, various breeds of animals like sheep, cows, and hens have been produced through artificial selection for specific traits such as increased wool, meat, milk, or egg production. Similarly, plant varieties (cultivars) with improved quantity and quality of cereals, fruits, and vegetables have been developed through artificial selection.
Question: Describe the structure of chromatin.
Answer: Chromatin is the material found inside the nucleus of cells and is composed of DNA, proteins, and RNA. The DNA wraps around histone proteins to form nucleosomes, which are the basic structural units of chromatin. Nucleosomes appear like “beads on a string,” where the DNA between nucleosomes also plays a role in chromatin structure. Chromatin can be further condensed into chromosomes during cell division.
Question: Describe Mendel’s law of segregation.
Answer: Mendel’s Law of Segregation
Mendel’s Law of Segregation states that each individual carries two alleles for each trait, and these alleles segregate (separate) during the formation of gametes. As a result, each gamete carries only one allele, and when fertilization occurs, the alleles from each parent recombine in the offspring.
Question: Explain how Mendel proved the law of independent assortment.
Answer: Mendel’s experiments with pea plants allowed him to prove the Law of Independent Assortment. He conducted dihybrid crosses, where he studied the inheritance of two different traits at the same time. One of his experiments involved studying seed shape and seed color. He crossed true-breeding round-seeded plants (RRYY) with true-breeding wrinkled-seeded green plants (rryy).
Mendel’s observations from this cross provided evidence for the Law of Independent Assortment. He found that the traits of seed shape and seed color segregated independently during gamete formation. In the F1 generation, all the offspring had round yellow seeds (RrYy). When he allowed the F1 generation to self-fertilize, he observed that the traits segregated into various combinations in the F2 generation:
- Round yellow (RRYY or RrYy): 9/16
- Round green (RRyy or Rryy): 3/16
- Wrinkled yellow (rrYY or rrYy): 3/16
- Wrinkled green (rryy): 1/16
The observed phenotypic ratio of 9:3:3:1 supported the idea that the alleles for seed shape and seed color segregated independently during gamete formation, following the Law of Independent Assortment. This law states that alleles of different gene pairs segregate independently of each other during gamete formation, which contributes to genetic diversity in offspring.
Question: How would you prove that variations lead to evolution?
Answer: Variations are the raw material for evolution. They arise from genetic mutations, recombination during sexual reproduction, and other genetic processes. Over time, variations can accumulate within a population, leading to changes in the gene pool. These changes can result in new traits and characteristics that provide advantages or disadvantages in specific environments. Here’s how you could demonstrate that variations lead to evolution:
Collect Data: Gather data on a specific trait within a population. For example, you could study the beak size of finches on an island.
Measure Variations: Measure the range of beak sizes within the finch population. Note the different sizes and variations.
Environmental Change: Introduce a change in the environment that affects the availability of food. For instance, you could simulate a drought that reduces the availability of large seeds.
Natural Selection: Monitor how the change in the environment affects the finch population. In this case, finches with larger beaks may have an advantage in cracking the remaining harder seeds, while smaller-beaked finches struggle to feed.
Reproduction: Observe which finches are more successful at reproducing and passing on their traits. Finches with larger beaks are better adapted to the new food source and are more likely to survive and reproduce.
Generation Success: As generations pass, the proportion of finches with larger beaks increases because those with smaller beaks are at a disadvantage. This gradual change in the trait distribution within the population demonstrates the role of variations and natural selection in driving evolution.
Long-Term Impact: Over many generations, the population could evolve to have predominantly larger beaks as the advantageous trait becomes more common.
This example illustrates how variations, combined with changes in the environment and natural selection, can lead to the evolution of traits that increase an organism’s fitness in its specific surroundings.
Question: Explain the phenomenon of incomplete dominance with the help of example.
Answer: Incomplete dominance is a genetic phenomenon where the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes. In this case, neither allele is completely dominant over the other. Let’s use the example of flower color in snapdragons to explain incomplete dominance:
Snapdragons have two alleles that determine flower color: “R” for red flowers and “W” for white flowers.
RR (homozygous dominant): Red flowers
WW (homozygous recessive): White flowers
RW (heterozygous): Pink flowers (intermediate between red and white)
When a homozygous red-flowered plant (RR) is crossed with a homozygous white-flowered plant (WW), all the F1 generation plants (RW) have pink flowers. This is because neither the red allele nor the white allele is dominant, resulting in an intermediate phenotype.
The F1 generation plants with pink flowers can then be crossed with each other. In the F2 generation, you would observe a 1:2:1 ratio of red:pink:white flowers, further demonstrating the concept of incomplete dominance.
Question: What do you mean by co-dominance? Give an example
Answer: Co-dominance is a genetic phenomenon where both alleles of a gene pair are fully expressed in the heterozygous condition. Unlike incomplete dominance, where an intermediate phenotype is produced, co-dominant alleles are both visibly expressed side by side. Each allele contributes its distinct trait to the phenotype. Here’s an example of co-dominance:
Example: Blood Type System (ABO Blood Groups)
In the ABO blood group system, three alleles control blood type: IA, IB, and i.
- IA produces antigen A.
- IB produces antigen B.
- i does not produce any antigens.
- When two alleles IA and IB are present together in an individual (heterozygous condition), both antigens A and B are expressed on the surface of red blood cells. Neither allele is dominant over the other. This results in the AB blood type, which is characterized by the co-expression of both antigens.
- IAIA or IAi: Blood type A (only antigen A expressed)
- IBIB or IBi: Blood type B (only antigen B expressed)
- IAIB: Blood type AB (both antigens A and B expressed)
- ii: Blood type O (no antigens expressed)
- In the case of blood type AB, the alleles IA and IB are co-dominant because both are expressed equally on the surface of red blood cells, leading to the presence of both antigens A and B.
Question: Define genotype and phenotype.
Answer: Genotype: The genetic makeup of an organism, representing the specific combination of alleles present for a particular trait or traits.
Phenotype: The observable physical and functional traits of an organism, resulting from the interaction between its genetic makeup (genotype) and the environment.
Question: What do you mean by dominant and recessive alleles?
Answer: Dominant and Recessive Alleles: Dominant alleles are versions of a gene that, when present in an individual’s genotype, will express their associated trait in the phenotype, masking the expression of any recessive allele. Recessive alleles are versions of a gene that will only be expressed in the phenotype if an individual carries two copies of the recessive allele (homozygous recessive).
Question: What are the homozygous and heterozygous genotypes?
Answer: Homozygous and Heterozygous Genotypes: Homozygous genotypes have two identical alleles for a specific trait (e.g., AA or aa), while heterozygous genotypes have two different alleles for the same trait (e.g., Aa).
Question: Differentiate between natural and artificial selection.
Answer: Natural Selection vs. Artificial Selection
Natural Selection: The process by which organisms that possess advantageous traits for their environment are more likely to survive, reproduce, and pass those traits to the next generation. The environment plays a key role in selecting which traits are advantageous.
Artificial Selection: The deliberate breeding of organisms with specific desirable traits by humans. Humans act as the selective agent, choosing which individuals will reproduce to propagate certain traits.