Chapter 14 Flashcards
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What is the significance of Gregor Mendel’s experiments with pea plants?
Mendel’s experiments with pea plants laid the foundation for modern genetics. He discovered the basic principles of heredity, including the laws of segregation and independent assortment, by studying the inheritance of traits such as flower color and seed shape.
What is the Law of Segregation?
The Law of Segregation states that each individual has two alleles for each gene, which segregate during gamete formation, resulting in offspring receiving one allele from each parent.
What is the Law of Independent Assortment?
The Law of Independent Assortment states that genes for different traits assort independently of one another during gamete formation, leading to genetic variation.
How did Mendel’s background influence his scientific approach?
Mendel’s background in physics and chemistry, along with his training in agriculture, influenced his systematic and quantitative approach to studying inheritance. His education under physicist Christian Doppler and botanist Franz Unger helped shape his experimental methods.
Why did Mendel choose pea plants for his experiments?
Mendel chose pea plants because they have distinct, easily observable traits, short generation times, and the ability to self-pollinate or be cross-pollinated. This allowed him to control the breeding and study the inheritance of specific traits.
What is a true-breeding plant?
A true-breeding plant is one that, when self-pollinated, produces offspring with the same traits as the parent. Mendel used true-breeding plants to ensure consistent and predictable results in his experiments.
Describe Mendel’s experimental procedure with pea plants.
Mendel cross-pollinated true-breeding plants with contrasting traits (e.g., purple vs. white flowers) and observed the traits in the F1 and F2 generations. He removed immature stamens to prevent self-pollination and transferred pollen from one plant to another.
What were the results of Mendel’s monohybrid crosses?
In Mendel’s monohybrid crosses, the F1 generation exhibited only the dominant trait (e.g., purple flowers). When the F1 hybrids were self-pollinated, the F2 generation showed a 3:1 ratio of dominant to recessive traits (e.g., purple to white flowers).
What is the concept of alleles?
Alleles are different versions of a gene that determine specific traits. For example, the gene for flower color in pea plants has two alleles: one for purple flowers (dominant) and one for white flowers (recessive).
What is the difference between homozygous and heterozygous?
Homozygous individuals have two identical alleles for a gene (e.g., PP or pp), while heterozygous individuals have two different alleles for a gene (e.g., Pp).
What is a phenotype?
A phenotype is the observable physical or physiological traits of an organism, determined by its genotype. For example, purple flowers or white flowers are phenotypes.
What is a genotype?
A genotype is the genetic makeup of an organism, consisting of the alleles it possesses for a particular gene. For example, PP, Pp, and pp are different genotypes for the flower color gene.
What is a testcross and its purpose?
A testcross involves crossing an individual with a dominant phenotype (but unknown genotype) with a homozygous recessive individual. The purpose is to determine the genotype of the dominant individual by analyzing the phenotypes of the offspring.
Describe the results of Mendel’s dihybrid crosses.
In Mendel’s dihybrid crosses, the F1 generation exhibited both dominant traits (e.g., yellow round seeds). When the F1 hybrids were self-pollinated, the F2 generation showed a 9:3:3:1 phenotypic ratio, demonstrating independent assortment of genes.
What is complete dominance? .
Complete dominance occurs when the phenotype of the heterozygote is identical to the phenotype of the homozygous dominant individual. The dominant allele completely masks the effect of the recessive allele.
What is incomplete dominance?
Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the homozygous dominant and homozygous recessive individuals. Neither allele is completely dominant.
What is codominance?
Codominance occurs when both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits simultaneously. An example is the MN blood group in humans
What is pleiotropy?
Pleiotropy occurs when a single gene influences multiple, seemingly unrelated phenotypic traits. An example is cystic fibrosis, where a mutation in one gene affects multiple systems in the body.
What is epistasis?
Epistasis occurs when the expression of one gene is affected by another gene. For example, in Labrador retrievers, one gene determines coat color, while another gene determines whether the pigment is deposited in the fur.
What is polygenic inheritance?
Polygenic inheritance occurs when multiple genes contribute to a single phenotypic trait, resulting in continuous variation. Examples include human skin color and height.
How do environmental factors influence phenotype?
Environmental factors can affect the expression of genes and influence an organism’s phenotype. For example, soil pH can affect the color of hydrangea flowers, and nutrition can influence human height.
What is the significance of the “one gene-one enzyme” hypothesis?
The “one gene-one enzyme” hypothesis, proposed by Beadle and Tatum, states that each gene encodes a specific enzyme that affects a single step in a metabolic pathway. This hypothesis was later refined to “one gene-one polypeptide.”
Describe the experiments of Beadle and Tatum with Neurospora crassa.
Beadle and Tatum used X-rays to induce mutations in the bread mold Neurospora crassa. They isolated mutants with specific nutritional requirements and showed that each mutation affected a single enzyme in a metabolic pathway, supporting the “one gene-one enzyme” hypothesis.
What is the role of RNA in gene expression?
RNA acts as an intermediary between DNA and protein synthesis. Messenger RNA (mRNA) carries the genetic information from DNA to ribosomes, where it is translated into proteins.
What is the process of transcription?
Transcription is the process of synthesizing RNA from a DNA template. RNA polymerase binds to the promoter region of a gene, unwinds the DNA, and synthesizes a complementary RNA strand.
What is the process of translation?
Translation is the process of synthesizing a polypeptide (protein) from an mRNA template. Ribosomes read the mRNA sequence and use transfer RNA (tRNA) to bring the appropriate amino acids, forming a polypeptide chain.
What are the three main stages of transcription?
The three main stages of transcription are initiation, elongation, and termination.
What are the three main stages of translation?
The three main stages of translation are initiation, elongation, and termination.
What is the role of ribosomes in translation?
Ribosomes facilitate the binding of tRNA and mRNA, catalyze peptide bond formation, and ensure the correct assembly of the polypeptide chain during translation.
What is the significance of the start codon in translation?
The start codon (AUG) signals the beginning of translation and specifies the amino acid methionine, which is the first amino acid in the newly synthesized polypeptide.
How does termination of translation occur?
Termination occurs when a stop codon (UAA, UAG, or UGA) is reached on the mRNA. A release factor binds to the stop codon, causing the ribosome to release the completed polypeptide and disassemble.
What are polyribosomes and their role in protein synthesis?
Polyribosomes (or polysomes) are clusters of ribosomes simultaneously translating a single mRNA molecule. They increase the efficiency of protein synthesis by producing multiple copies of a polypeptide from one mRNA.
What are point mutations and their potential effects on protein synthesis?
Point mutations are changes in a single nucleotide pair in a gene. They can result in:
Silent mutations: These do not change the amino acid sequence of the protein due to the redundancy of the genetic code.
Missense mutations: These result in the substitution of one amino acid for another in the protein, which can affect the protein’s function depending on the role of the altered amino acid.
Nonsense mutations: These create a premature stop codon, leading to a truncated and usually nonfunctional protein.
What are frameshift mutations and their impact on protein synthesis?
Frameshift mutations occur due to insertions or deletions of nucleotides that are not in multiples of three. They alter the reading frame of the mRNA, leading to extensive missense or nonsense mutations and often resulting in nonfunctional proteins.
What is the role of the signal recognition particle (SRP) in targeting proteins to the ER?
The SRP recognizes the signal peptide on a newly synthesized polypeptide and directs the ribosome to the ER membrane, where translation continues and the polypeptide is translocated into the ER.
How do mutations contribute to genetic diversity and evolution?
Mutations introduce genetic variation by altering DNA sequences. While most mutations are neutral or harmful, some can provide beneficial traits that enhance survival and reproduction, driving evolution through natural selection.
