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Questions and Answers
Which of the following statements accurately describes the relationship between genes, chromosomes, and DNA?
Which of the following statements accurately describes the relationship between genes, chromosomes, and DNA?
- Chromosomes are segments of DNA that contain multiple genes.
- DNA is organized into genes, which are then organized into chromosomes. (correct)
- Chromosomes are composed of proteins that encode for DNA, which contains genes.
- Genes are composed of chromosomes, which are made of DNA.
A researcher is studying a newly discovered species of plant. They observe that the plant has 30 chromosomes in its somatic cells. What is the haploid number of chromosomes for this plant?
A researcher is studying a newly discovered species of plant. They observe that the plant has 30 chromosomes in its somatic cells. What is the haploid number of chromosomes for this plant?
- 45
- 15 (correct)
- 30
- 60
Which of the following is an example of homozygous alleles?
Which of the following is an example of homozygous alleles?
- Tt - where 'T' represents tallness and 't' represents shortness
- bb - where 'b' represents brown hair (correct)
- Gg - where 'G' for green and 'g' for yellow
- Rr - where 'R' represents round and 'r' represents wrinkled
In a certain species, the number of chromosomes does NOT directly determine which of the following?
In a certain species, the number of chromosomes does NOT directly determine which of the following?
If a plant inherits a gene that instructs it to produce more of a certain growth hormone, what would be the most likely outcome?
If a plant inherits a gene that instructs it to produce more of a certain growth hormone, what would be the most likely outcome?
If a scientist discovers a new organism with 150 chromosomes in its diploid cells, how many chromosomes would be present in its haploid cells?
If a scientist discovers a new organism with 150 chromosomes in its diploid cells, how many chromosomes would be present in its haploid cells?
During DNA replication, adenine on the template strand binds with which nitrogenous base on the new strand?
During DNA replication, adenine on the template strand binds with which nitrogenous base on the new strand?
Which statement is true regarding homologous chromosomes?
Which statement is true regarding homologous chromosomes?
In a monohybrid cross, if the F1 generation shows only the dominant trait, what can be inferred about the parents?
In a monohybrid cross, if the F1 generation shows only the dominant trait, what can be inferred about the parents?
What is the significance of the 3:1 ratio observed in the F2 generation of a monohybrid cross?
What is the significance of the 3:1 ratio observed in the F2 generation of a monohybrid cross?
Why are recessive traits only expressed in individuals with a homozygous genotype?
Why are recessive traits only expressed in individuals with a homozygous genotype?
According to the law of segregation, what happens to the alleles of a gene during gamete formation?
According to the law of segregation, what happens to the alleles of a gene during gamete formation?
In a dihybrid cross, what phenotypic ratio in the F2 generation typically indicates independent assortment?
In a dihybrid cross, what phenotypic ratio in the F2 generation typically indicates independent assortment?
What is the relationship between the law of independent assortment and genes located on the same chromosome?
What is the relationship between the law of independent assortment and genes located on the same chromosome?
A plant with round, yellow seeds (RRYY) is crossed with a plant with wrinkled, green seeds (rryy). What will be the genotype of the F1 generation?
A plant with round, yellow seeds (RRYY) is crossed with a plant with wrinkled, green seeds (rryy). What will be the genotype of the F1 generation?
In Mendel's experiments, why was it important to use true-breeding plants for the P generation?
In Mendel's experiments, why was it important to use true-breeding plants for the P generation?
A scientist is studying a new species of plant. They observe that some plants have red flowers, while others have white flowers. They cross-breed a red-flowered plant with a white-flowered plant and observe that all of the offspring have pink flowers. Which concept is best illustrated by this experiment?
A scientist is studying a new species of plant. They observe that some plants have red flowers, while others have white flowers. They cross-breed a red-flowered plant with a white-flowered plant and observe that all of the offspring have pink flowers. Which concept is best illustrated by this experiment?
A dog breeder selectively breeds dogs with a specific coat color over several generations. This is an example of artificially selecting for:
A dog breeder selectively breeds dogs with a specific coat color over several generations. This is an example of artificially selecting for:
If a scientist discovers a new species of beetle where some individuals have longer antennae due to a mutation in their reproductive cells, this is an example of:
If a scientist discovers a new species of beetle where some individuals have longer antennae due to a mutation in their reproductive cells, this is an example of:
Which of the following scenarios best illustrates the concept of heredity?
Which of the following scenarios best illustrates the concept of heredity?
In a population of birds, some develop stronger beaks due to consistently feeding on hard seeds. If this trait is NOT passed on to their offspring, it would be considered:
In a population of birds, some develop stronger beaks due to consistently feeding on hard seeds. If this trait is NOT passed on to their offspring, it would be considered:
Why is variation important for the survival and evolution of species?
Why is variation important for the survival and evolution of species?
Which of the following statements accurately distinguishes between somatic and gametic variations?
Which of the following statements accurately distinguishes between somatic and gametic variations?
If a new species of mammal is discovered, and scientists observe a wide range of differences in fur thickness among individuals, what can they infer about this variation?
If a new species of mammal is discovered, and scientists observe a wide range of differences in fur thickness among individuals, what can they infer about this variation?
Which of the following best describes the 'phenotype' of an organism?
Which of the following best describes the 'phenotype' of an organism?
What is the primary purpose of a Punnett square in genetic studies?
What is the primary purpose of a Punnett square in genetic studies?
Why was Pisum sativum (garden pea) an ideal choice for Mendel's experiments?
Why was Pisum sativum (garden pea) an ideal choice for Mendel's experiments?
In Mendel’s experiments crossing true-breeding tall plants with true-breeding dwarf plants. What was consistently observed in the first filial (F1) generation?
In Mendel’s experiments crossing true-breeding tall plants with true-breeding dwarf plants. What was consistently observed in the first filial (F1) generation?
Which of the following is the best definition of a 'true breeding plant'?
Which of the following is the best definition of a 'true breeding plant'?
A bacterial colony is exposed to a sudden and drastic change in temperature. Which statement best describes the role of variation in its survival?
A bacterial colony is exposed to a sudden and drastic change in temperature. Which statement best describes the role of variation in its survival?
What does the term 'genome' refer to in genetics?
What does the term 'genome' refer to in genetics?
Which of the following mechanisms is primarily responsible for introducing significant variation in sexually reproducing organisms?
Which of the following mechanisms is primarily responsible for introducing significant variation in sexually reproducing organisms?
If Mendel crossed two F1 generation pea plants (both heterozygous for tallness, Tt), what would be the expected ratio of tall to dwarf plants in the F2 generation?
If Mendel crossed two F1 generation pea plants (both heterozygous for tallness, Tt), what would be the expected ratio of tall to dwarf plants in the F2 generation?
Considering the structure of chromosomes, what is the functional significance of the DNA component?
Considering the structure of chromosomes, what is the functional significance of the DNA component?
How does the accumulation of variations over successive generations contribute to the process of evolution?
How does the accumulation of variations over successive generations contribute to the process of evolution?
What critical step did Mendel take to ensure accurate results when cross-pollinating pea plants?
What critical step did Mendel take to ensure accurate results when cross-pollinating pea plants?
In asexual reproduction, what is the primary source of variation?
In asexual reproduction, what is the primary source of variation?
What role do gametes play in heredity?
What role do gametes play in heredity?
Considering the structure of DNA, which statement accurately describes its configuration?
Considering the structure of DNA, which statement accurately describes its configuration?
Suppose a population of insects exhibits variation in their camouflage patterns, with some blending better into their environment than others. How does this variation relate to natural selection?
Suppose a population of insects exhibits variation in their camouflage patterns, with some blending better into their environment than others. How does this variation relate to natural selection?
In a dihybrid cross, if the F1 generation is selfed, what is the probability of obtaining a plant with the homozygous recessive genotype for both traits?
In a dihybrid cross, if the F1 generation is selfed, what is the probability of obtaining a plant with the homozygous recessive genotype for both traits?
Two parents, one with blood type A (genotype $I^AI^O$) and the other with blood type B (genotype $I^BI^O$), have a child. What are all the possible blood types the child could have?
Two parents, one with blood type A (genotype $I^AI^O$) and the other with blood type B (genotype $I^BI^O$), have a child. What are all the possible blood types the child could have?
A woman with blood type O, Rh-negative has a child with a man who is blood type AB, Rh-positive (heterozygous for the Rh factor). What is the probability their child will be blood type A, Rh-negative?
A woman with blood type O, Rh-negative has a child with a man who is blood type AB, Rh-positive (heterozygous for the Rh factor). What is the probability their child will be blood type A, Rh-negative?
In humans, which parent determines the sex of the offspring and why?
In humans, which parent determines the sex of the offspring and why?
In a species of reptile, eggs incubated at high temperatures produce males, while eggs incubated at low temperatures produce females. If a population experiences a period of rising average temperatures, what is the most likely outcome?
In a species of reptile, eggs incubated at high temperatures produce males, while eggs incubated at low temperatures produce females. If a population experiences a period of rising average temperatures, what is the most likely outcome?
A scientist is studying a population of turtles where the sex of the offspring is determined by incubation temperature. They observe that the majority of nests are located in sunny areas with high incubation temperatures. What prediction can they make about the sex ratio of the turtle population?
A scientist is studying a population of turtles where the sex of the offspring is determined by incubation temperature. They observe that the majority of nests are located in sunny areas with high incubation temperatures. What prediction can they make about the sex ratio of the turtle population?
Consider a population of snails that can change sex. If the population density increases significantly, potentially leading to resource scarcity, what would be an adaptive strategy for some of the snails to enhance reproductive success of the population?
Consider a population of snails that can change sex. If the population density increases significantly, potentially leading to resource scarcity, what would be an adaptive strategy for some of the snails to enhance reproductive success of the population?
If a plant breeder wants to develop a true-breeding variety of tomato that is both resistant to a particular disease (R) dominant and has large fruit size (L) dominant, what initial cross would be most efficient, assuming they have access to plants with all combinations of these traits?
If a plant breeder wants to develop a true-breeding variety of tomato that is both resistant to a particular disease (R) dominant and has large fruit size (L) dominant, what initial cross would be most efficient, assuming they have access to plants with all combinations of these traits?
Study Notes
- Reproduction is the process of creating new organisms.
- Heredity causes individuals in a species to resemble one another, and organisms maintain continuity.
- Variations are the differences between organisms.
- Heredity is the transfer of genetically based characteristics from parents to offspring and ensures relations continue between successive generations.
- A trait is any inherited characteristic, ensuring feature continuity from prior to the next generation via the zygote.
- Genetics is the study of heredity and variation, dealing with the transmission of body features and related laws.
- Bateson coined the term 'Genetics' in 1905.
- Gregor Johann Mendel is known as the 'Father of Genetics'.
- Variation refers to the differences in characters/traits between parents and offspring; no two individuals in a species are identical.
Types of Variations
- Somatic Variation: takes place in the body cell, develops during an individual's lifetime, is neither inherited nor transmitted, and is known as acquired traits.
- Gametic Variation: takes place in the gametes/reproductive cells, is inherited and transmitted, can undergo direct evolution, and is known as inherited traits.
- Variation occurs whether organisms multiply sexually or asexually and accumulates in successive generations if inherited.
- Variations are fewer in asexual reproduction because they occur due to small inaccuracies in DNA copying.
- Variations are large in sexual reproduction because they occur due to independent assortment, crossing over during meiosis, random union of gametes during fertilization, and mutation.
- Variations provide different kinds of advantages and can enable species to survive in changing environments.
- Variation can lead to organic evolution, an orderly change of various forms through slow but continuous processes.
- Gametes are heredity carriers, transmitting traits from parent to offspring and forming the link between generations.
- Chromosomes in a cell's nucleus carry hereditary traits and are rod-like structures seen in dividing cells.
- Chromosomes contain 40% DNA and 60% histone proteins; chromatin fibers are seen in the nucleus of non dividing cells
- Chromosomes consist of DNA (deoxyribonucleic acid) and histone proteins.
- DNA carries the genetic code and has a double helix structure formed of 2 polynucleotide chains.
- James D. Watson and Francis H.C. Crick discovered the double helix structure of DNA.
- DNA is made of nucleotides containing nitrogenous bases (adenine, guanine, cytosine, and thymine), a pentose sugar, and a phosphate group.
- Adenine bonds with thymine, and cytosine bonds with guanine.
- The number of chromosomes is constant in the cells of each species.
- Haploid cells contain all types of chromosomes in a single set.
- Diploid cells contain two sets of all types of chromosomes.
Chromosome Examples
- Dog and Fowl have 78 chromosomes.
- Humans have 46 chromosomes.
- Mice have 40 chromosomes.
- Gorillas have 48 chromosomes.
- Crayfish have 200 chromosomes.
- Ascaris have 2 chromosomes.
Homologous Chromosomes
- Two chromosomes of one pair that are similar in shape, size, and structure, bearing genes controlling the same characteristics.
- Each parent shares one homologous chromosome to their offspring.
- Genes are specific DNA parts of chromosomes, the units of heredity responsible for inheritance.
- The expression of characteristics is contained in genes, and different genes form different traits.
- A gene carries the genetic code for a particular characteristic.
- Genes contain the genetic code for protein synthesis, where proteins control specific traits in organisms.
- Alleles are pairs of genes coding for a particular trait and are slightly different forms of the same gene.
- Alleles are alternate forms of the same gene occupying the same position on a homologous chromosome, affecting the same character in two different ways.
- Homozygous allele pairs for height are identical (e.g., TT or tt).
- Heterozygous alleles express contrasting characters (Tt).
- Genetic information is carried within chromosomes, made of long, coiled DNA molecules found in the cell's nucleus.
- Genes, contained in DNA code for units of heredity and are responsible for inheritance, and controls the height and facial features.
- Inheritance of characteristics is contributed equally by the mother and father, providing equal amounts of genetic material.
- Each trait has two factors, one from each parent.
- DNA has the information source for making proteins, and a section providing information for one protein is a gene for that protein.
- Plant height depends on the amount of a particular plant hormone secreted.
- The amount of hormone made depends on the efficiency of its production process.
- The process is as follows: Cellular DNA -> Synthesis of Proteins (Enzyme) -> Works efficiently - More Hormone -> produced Tallness of plant.
Key Terminologies
- Locus: the position on the chromosome where the allele of a given trait occurs.
- Dominant Gene: expresses itself even with a contrasting trait in the pair (Heterozygous - Tt) and is denoted using capital letters.
- Recessive Gene: unexpressed unless present on both chromosomes (homozygous - tt) and denoted using small letters.
- Genotype: Description of the genes present in an organism represented by a pair of letters, with each letter inherited from each parent.
- Phenotype: The visible expression of characteristics in an organism, like eye and hair color.
- First Filial Generation (F1): Progeny produced when true breeding plants are crossed.
- Second Filial Generation (F2): Offspring produced when the first filial generation is crossed among themselves.
- Punnett Square: A graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross.
- Genome: The complete set of genes or genetic material present in a cell or organism.
Mendel's Work
- Gregor Johann Mendel (1822-1884) began plant breeding and hybridization experiments and proposed inheritance laws.
- He is known as the Father of Genetics.
- Mendel selected the Pisum Sativum plant (garden pea) and used 14 true breeding pea plant varieties differing in one contrasting trait.
- True breeding plants undergo continuous self-pollination, showing stable traits, inheritance, and expressions for generations.
- Mendel chose the garden pea (Pisum sativum) for its contrasting traits, availability of true breeding varieties, short reproductive span, bisexual flowers, and ease of controlled pollination and seed production.
Mendel's experiments
- Crossed pollinated plants to study one character at a time.
- In a hybridization experiment, Mendel crossed one pure breeding tall plant with one pure breeding dwarf plant.
- All plants in the first hybrid generation (F1) were tall.
- Mendel repeated the experiment with other traits and each time the F1 progeny resembled either one of the parent and the other parent trait was not seen.
Law of Dominance
- In the presence of a contrasting allele, the factor/allele that expresses itself phenotypically is called dominant, while the one that doesn't express itself is called recessive.
- On selfing (self-fertilization) the F1 plants, the F2 generation showed the parent trait that was not expressed in F1 generation, both tall and dwarf plants were produced in the ratio 3:1.
- The 3:1 ratio of tall to dwarf plants emerged in F2.
- Traits expressed in F2 were identical to the parent trait, with no mixing/blending.
- None of the offspring showed intermediate traits.
- The dwarf plants were possible from the F1 tall plants only because the gene of dwarfness had segregated or separated from the gene of tallness and a result of the tallness gene masking or blening with dwarfness.
- Phenotypically dominant individuals can be homozygous (TT) or heterozygous (Tt), but recessive plants are always homozygous (tt).
Law of Segregation
- Two factors or genes controlling one character separate/segregate without blending/influencing each other during gamete formation, so each gamete receives one factor/gene for each character.
- Genes for different characteristics assort independently without influencing each other during gamete formation.
- Mendel explained the law of independent assortment using a dihybrid cross.
- In the F1 generation, all plants produced round and yellow seeds.
- By selfing the F1 plants, the F2 generation showed the parent trait that was not expressed in F1 generation.
- The F2 generation showed four combinations in the following ratios: (Round Yellow) 9: (Round Green) 3: (Wrinkled Yellow) 3: (Wrinkled green) 1.
Human Blood Group
- ABO blood groups are controlled by a gene denoted by symbols IA , IB and IO (sometimes denoted as i).
- Genes IA and IB show no dominance over each other, or are codominant.
- Both genes are dominant over the gene IO.
- Blood type depends on which genes are present.
Blood Type Gene Types
- Blood group A: IA IA or IA IO
- Blood group B: IB IB or IB IO
- Blood group AB: IA IB
- Blood group O: IO IO
- Rh factor is a particular protein type found on the outside of blood cells.
- People are either Rh-positive (have the protein) or Rh-negative (do not have the protein).
- This distinction matters when you are Rh-negative and your child is Rh-positive.
- The sex of a newborn individual is determined genetically.
- Humans have 23 pairs of chromosomes, with 22 pairs (autosomes) being similar in both males and females.
- One pair is a sex chromosome; XY for males and XX for females.
- Males produce sperm with either X or Y chromosomes, while females produce eggs with only X chromosomes.
- If an X sperm fertilizes the egg, the baby will be female (XX).
- If a Y sperm fertilizes the egg, the baby will be male (XY).
- The ovum has an equal chance of being fertilized by a sperm bearing an x/y chromosome.
- Sex is determined at the time of fertilization.
- In some animals sex is determined by environmental factors.
Environmental Factors
- In reptiles, the temperature at which a fertilized egg is incubated determines the offspring's sex.
- High incubation temperatures of turtle eggs lead to development of female offspring.
- High incubation temperatures of lizard eggs leads to development of male progeny.
- An individual snails change sex.
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