BIO 222 Chapter 3: Basic Principles of Heredity
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Questions and Answers

Which principle states that alleles separate independently of other loci during meiosis?

  • Principle of recombination
  • Principle of segregation
  • Principle of independent assortment (correct)
  • Principle of dominance

What does the term 'dihybrid cross' refer to?

  • Crossing two individuals with two traits (correct)
  • Crossing individuals with different genotypes for one trait
  • Crossing individuals of the same genotype
  • Crossing two homozygous individuals

In a chi-square goodness-of-fit test, a probability of 0.72 indicates what?

  • The results obtained are incorrect
  • There is a significant difference between observed and expected numbers
  • The test is inconclusive
  • The difference between observed and expected numbers could be due to chance (correct)

Which phase of meiosis is primarily concerned with the principles of segregation?

<p>Anaphase I (C)</p> Signup and view all the answers

What is likely true about the expected ratios of progeny in a genetic cross?

<p>They may deviate from the observed ratios by chance (A)</p> Signup and view all the answers

What is the outcome of applying a branch diagram in genetics?

<p>It visually represents the distribution of allele combinations in dihybrid crosses (C)</p> Signup and view all the answers

Which of the following statements is true about alleles during meiosis?

<p>Alleles separate and are distributed randomly into gametes (A)</p> Signup and view all the answers

What does a high chi-square value indicate in a goodness-of-fit test?

<p>Observed numbers significantly differ from expected numbers (C)</p> Signup and view all the answers

Which factor was not a key contributor to Mendel's success in his study of heredity?

<p>His study of plant chromosomes (B)</p> Signup and view all the answers

What term describes an individual organism with two different alleles at a locus?

<p>Heterozygote (A)</p> Signup and view all the answers

Which term refers to the specific location on a chromosome where an allele resides?

<p>Locus (C)</p> Signup and view all the answers

Which statement accurately distinguishes genotype from phenotype?

<p>Genotype is the set of alleles, while phenotype is the observable characteristics. (D)</p> Signup and view all the answers

What is an allele?

<p>An alternative form of a gene (A)</p> Signup and view all the answers

Which of these terms is synonymous with an observable characteristic of an organism?

<p>Phenotype (B)</p> Signup and view all the answers

In genetic terminology, what does homozygote mean?

<p>An individual with two of the same alleles at a locus (B)</p> Signup and view all the answers

Which factor did Mendel not utilize in his genetic experiments?

<p>Studying complex characteristics of animals (B)</p> Signup and view all the answers

What is the correct binomial expansion for $n = 3$?

<p>$a^3 + 3a^2b + 3ab^2 + b^3$ (B)</p> Signup and view all the answers

Which of the following ratios represents the expected genotypic ratio for a monohybrid cross between Aa and Aa?

<p>1:2:1 (C)</p> Signup and view all the answers

In a dihybrid cross examining two traits, what is the principle that states gametes located on different chromosomes will sort independently?

<p>Principle of Independent Assortment (A)</p> Signup and view all the answers

What phenotypic ratio would you expect from a cross between Aa and aa?

<p>1:1 (D)</p> Signup and view all the answers

Which of the following is NOT a part of the binomial expansion for $p + q$?

<p>$qp$ (C)</p> Signup and view all the answers

How are the principles of segregation and independent assortment similar?

<p>Both involve the formation of gametes. (C)</p> Signup and view all the answers

What is the expected progeny ratio for a cross between AA and aa?

<p>All Aa (C)</p> Signup and view all the answers

What is the correct expansion for the binomial expression $(p + q)^4$?

<p>$p^4 + 4p^3q + 6p^2q^2 + 4pq^3 + q^4$ (D)</p> Signup and view all the answers

What does a monohybrid cross examine?

<p>Cross between two parents that differ in a single characteristic (A)</p> Signup and view all the answers

What is the principle of segregation?

<p>Alleles separate when forming gametes, with one allele going to each gamete (C)</p> Signup and view all the answers

Which statement about dominant and recessive alleles is true?

<p>Only the trait indicated by the dominant allele is observed (A)</p> Signup and view all the answers

During which phase of meiosis do alleles segregate into gametes?

<p>Anaphase I (A)</p> Signup and view all the answers

What is true regarding two alleles in an individual organism?

<p>They segregate, with one allele in each gamete (A)</p> Signup and view all the answers

What does the concept of independent assortment state?

<p>Different characteristics are inherited independently of each other (C)</p> Signup and view all the answers

What happens to alleles during gamete formation?

<p>They separate into different gametes with equal probability (A)</p> Signup and view all the answers

According to Mendel’s theory, which statement about gametes is correct?

<p>Gametes are haploid and carry only one allele (C)</p> Signup and view all the answers

How did Mendel determine that each of his pea plants carried two alleles for a characteristic?

<p>He noted that the traits encoded by both alleles appeared in the F2 progeny. (D)</p> Signup and view all the answers

What is the probability of obtaining an offspring with winkled seeds when an F1 plant is backcrossed with a parent having round seeds?

<p>1/4 (A)</p> Signup and view all the answers

Which rule is used to calculate the probability of a specific genetic outcome in a cross?

<p>Multiplication rule (A)</p> Signup and view all the answers

If the probability of blood-type A is 1/8 and the probability of blood-type O is 1/2, what is the correct calculation for the probability of being either blood-type A or O?

<p>5/8 (A)</p> Signup and view all the answers

Which of the following best describes the binomial expansion in a genetic context?

<p>Expressed as (p + q)n, with n being the total possible outcomes. (D)</p> Signup and view all the answers

In which scenario would the multiplication rule of probability apply?

<p>Determining the occurrence of two independent traits in offspring. (A)</p> Signup and view all the answers

Which concept is crucial for understanding the outcomes of Mendelian crosses?

<p>Principle of Segregation (A)</p> Signup and view all the answers

How do backcrosses contribute to understanding dominant traits?

<p>They help predict the ratio of dominant to recessive traits in progeny. (A)</p> Signup and view all the answers

Flashcards

Locus

A specific location on a chromosome where a gene is found.

Allele

One of two or more alternative forms of a gene.

Genotype

The set of alleles possessed by an individual organism.

Phenotype

The observable characteristics of an organism, determined by its genotype and environmental factors.

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Heterozygote

An individual organism possessing two different alleles at a specific locus.

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Homozygote

An individual organism possessing two of the same alleles at a specific locus.

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Gene

An inherited factor that helps determine a characteristic, encoded in DNA.

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Genetics

The study of heredity and the variation of inherited characteristics.

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Monohybrid cross

A cross between two parents that differ in a single characteristic.

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Principle of Segregation

The principle that states that each individual diploid organism possesses two alleles for a specific trait, and these alleles separate during gamete formation.

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Concept of Dominance

When two different alleles are present in a genotype, only the trait encoded by the dominant allele is observed in the phenotype.

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Chromosomal theory of heredity

The theory proposed by Sutton that chromosomes carry the genetic material and are responsible for heredity.

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Gamete formation

The formation of gametes, involving the process of meiosis.

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F1 generation

The offspring of a cross between two individuals that differ in one or more traits.

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F2 generation

The offspring of a cross between two individuals from the F1 generation.

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Backcross

A cross between an individual with an unknown genotype and a homozygous recessive individual.

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Punnett square

A diagram used to predict the possible genotypes and phenotypes of the offspring of a genetic cross.

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Probability

The likelihood of a particular event occurring.

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Multiplication rule

The probability of two independent events occurring is the product of their individual probabilities.

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Addition rule

The probability of either one or the other of two mutually exclusive events occurring is the sum of their individual probabilities.

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Binomial expansion

A mathematical formula used to calculate the probabilities of different outcomes in a series of events.

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Dihybrid Cross

A cross involving two individuals that differ in two traits.

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Principle of Independent Assortment

The principle that states that alleles for different traits (located on different chromosomes) segregate independently during gamete formation, meaning that the inheritance of one trait does not influence the inheritance of another.

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Uniform Progeny

When a homozygous dominant individual is crossed with a heterozygous individual, the offspring will have the dominant phenotype.

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Segregation vs. Independent Assortment

The principle of segregation states that during gamete formation, two alleles for a specific trait separate from each other, with only one allele being passed on to each offspring. The principle of independent assortment states that the separation of alleles for different traits is independent of one another. Both principles are related as they occur during anaphase I of meiosis, resulting in gametes with a unique combination of alleles. However, they differ in their focus: segregation emphasizes the separation of alleles for a specific trait, while independent assortment highlights the independent separation of alleles for different traits.

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Dihybrid Testcross

A dihybrid testcross is used to determine the genotype of an unknown individual with regard to two traits. It involves crossing the unknown individual with a homozygous recessive individual for both traits. The resulting offspring phenotypes can then be analyzed to deduce the unknown individual's genotype. This method is based on the expected phenotypic ratios produced by different genotype combinations.

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Chi-Square Goodness-of-Fit Test

The chi-square goodness-of-fit test is a statistical method used to determine if the observed phenotypic ratios in a genetic experiment deviate significantly from the expected ratios. It calculates a chi-square value based on the difference between observed and expected numbers of progeny. The probability associated with this chi-square value represents the likelihood that the observed deviation is due to chance. If the probability is low (e.g., less than 0.05), the deviation is considered significant, suggesting that the observed results may not be due to chance.

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Chi-square Test Interpretation

A probability of 0.72 in a chi-square test indicates that there is a 72% chance that the difference between observed and expected numbers of progeny could be due to chance. In other words, the deviation from the expected ratios is not statistically significant and the observed results are likely not due to a specific genetic mechanism.

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Study Notes

Basic Principles of Heredity

  • Gregor Mendel's success in genetics stemmed from a proper experimental design and mathematical analysis of results, focusing on easily discernible characteristics.

  • Mendel's study of pea plants (Pisum sativum) revealed traits like seed color (yellow/green), seed shape (round/wrinkled), pod color (yellow/green), pod shape (inflated/constricted), flower position (axial/terminal), and stem length (short/tall).

Mendelian Experiments and Success

  • Mendel's controlled experiments involved hybridizing pea plants through cross-pollination.

  • He tracked traits through generations, observing consistent patterns. Analysis of these patterns mathematically led to conclusions about inheritance.

  • His detailed approach contributed to the principles of inheritance.

Genetic Terminology

  • Gene: An inherited factor (within DNA) influencing a characteristic.

  • Allele: One of multiple forms of a gene at a specific locus.

  • Locus: The specific location of a gene on a chromosome.

  • Genotype: The genetic makeup (allele combination) of an organism.

  • Heterozygote: An organism with two different alleles at a locus.

  • Homozygote: An organism with two identical alleles at a locus.

  • Phenotype: The observable characteristic or trait resulting from the genotype.

  • Characteristic/Character: An attribute or feature of an organism.

Monohybrid Crosses

  • A monohybrid cross investigates a single trait, revealing the concept of dominance (one allele masks another) and segregation (alleles separate during gamete formation, each gamete receiving only one allele).

  • Mendel's experiments illustrated these principles using pea plant traits, leading to significant conclusions and observations.

  • The Punnett square is a tool for predicting the genetic outcomes of crosses.

Principle of Segregation

  • Each diploid organism has two alleles for a trait. This is due to the fact that each gamete, during meiosis, receives only one copy.

  • The alleles separate during gamete formation.

  • During fertilization, each offspring inherits one allele from each parent.

  • When determining the genetic outcome of a cross, the alleles should be treated as separate entities.

Principle of Independent Assortment

  • Alleles on different pairs of chromosomes sort independently during meiosis.

  • This means that the inheritance of one trait doesn't influence the inheritance of another trait.

  • Mendel's experiments demonstrated independent assortment using pea plant traits, leading to the observation of distinct ratios in offspring traits.

Probability in Genetics

  • Probability is the likelihood of a specific event occurring.

  • The multiplication rule calculates probabilities of independent events.

  • The addition rule calculates probabilities of mutually exclusive events.

  • These methods (multiplication and addition rule) are helpful for predicting outcomes of genetic crosses.

Chi-square Goodness-of-Fit Test

  • This test is used to assess the difference between predicted and observed results in genetic experiments.

  • It evaluates the probability that observed deviations are due to random chance.

Dihybrid Crosses

  • These experiments examine inheritance patterns of two traits simultaneously.

  • They confirm the principle of independent assortment, where alleles of different traits sort independently during meiosis and are passed on to the offspring.

  • The use of branch diagrams can be used to illustrate the possible results of a dihybrid cross

  • The dihybrid testcross is a tool for verifying inheritance patterns.

Testcross

  • A testcross involves crossing an individual of unknown genotype with a homozygous recessive individual (for the trait in question).
  • Analysing the offspring phenotypes reveals the unknown genotype.

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