Genetics Lecture 4: Gene Segregation

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Questions and Answers

What term describes two or more alternative forms of a gene?

  • Dominant
  • Homozygous
  • Genotype
  • Alleles (correct)

Which of the following correctly defines a recessive trait?

  • A trait that appears in the first filial generation
  • A trait that occurs in all offspring
  • A trait that is always expressed
  • A trait that does not appear in the first filial generation (correct)

An individual with the genotype RR for seed shape is described as:

  • Heterozygous
  • Homozygous (correct)
  • Genotypically recessive
  • Phenotypically dominant

Which term describes the genetic constitution inherited from the parents?

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

Which of the following statements about dominant traits is true?

<p>They are expressed in the presence of recessive alleles. (C)</p> Signup and view all the answers

What defines a heterozygous individual?

<p>Possessing two different alleles for a trait (A)</p> Signup and view all the answers

What is the phenotype of a plant with the genotypes Rr?

<p>Only round (D)</p> Signup and view all the answers

Which of the following describes the role of a gene?

<p>It is a segment of DNA that influences traits. (D)</p> Signup and view all the answers

What does the F1 generation represent in a genetic cross?

<p>The progeny produced from a cross between two parents (C)</p> Signup and view all the answers

Which term describes the mating of closely related individuals in genetic studies?

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

What phenotype ratio is observed in the F2 generation from a typical monohybrid cross?

<p>3 dominant : 1 recessive (D)</p> Signup and view all the answers

In a dihybrid cross, how many character pairs are studied simultaneously?

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

What describes the relationship between the parental plants used in Mendel's experiments?

<p>They were homozygous from pure breeding lines. (D)</p> Signup and view all the answers

What is the F2 generation produced from inbreeding of the F1 generation called?

<p>Second Filial generation (D)</p> Signup and view all the answers

Which of the following best describes a monohybrid cross?

<p>A cross between parents differing in a single pair of contrasting characters (C)</p> Signup and view all the answers

If the phenotypic ratio obtained from a monohybrid cross is approximately 3:1, what does this imply?

<p>One allele is completely dominant over the other. (A)</p> Signup and view all the answers

In Mendel's experiments, what trait was shown in the F1 generation?

<p>The dominant trait (D)</p> Signup and view all the answers

What ratio was observed in the phenotypic expression in the F2 generation?

<p>3:1 (C)</p> Signup and view all the answers

How do gametes carry the alleles during the formation?

<p>Each allele is carried equally in every gamete (C)</p> Signup and view all the answers

What does self-fertilization of the F1 generation result in concerning genotypes?

<p>Offspring have a 1:2:1 genotypic ratio (C)</p> Signup and view all the answers

What conclusion can be drawn about allele contributions from parents based on the given observations?

<p>Each parent must have contributed equally to the progeny (D)</p> Signup and view all the answers

Why do reciprocal crosses yield the same results in Mendel's experiments?

<p>They involve the same types of gametes regardless of the parent (B)</p> Signup and view all the answers

What genotypes exhibit the same phenotype in Mendelian inheritance?

<p>Homozygous dominant (RR) and heterozygous (Rr) (B)</p> Signup and view all the answers

What occurs to a trait that did not appear in the F1 generation?

<p>It reappears in the F2 generation (B)</p> Signup and view all the answers

What is the primary concept of the Law of Segregation?

<p>Alleles remain together without altering each other. (A)</p> Signup and view all the answers

What ratio was observed in F2 generation of round and wrinkled seeds?

<p>2.96:1 (B)</p> Signup and view all the answers

In the context of Mendel's crosses, what did the F1 generation of yellow and green seeds display?

<p>All yellow seeds (B)</p> Signup and view all the answers

Which of the following results was reported from the F2 generation of purple and white petals?

<p>75.89% purple; 24.11% white (D)</p> Signup and view all the answers

What does the Law of Independent Assortment describe?

<p>The separation of alleles for different traits. (B)</p> Signup and view all the answers

What was the total number of long and short flowers in the F2 generation?

<p>787 long; 277 short (D)</p> Signup and view all the answers

Which pair of parental phenotypes produced an F2 ratio of approximately 3:1?

<p>Round and wrinkled seeds (A)</p> Signup and view all the answers

What percentage of offspring in the F2 generation of green and yellow pods were green?

<p>73.79% (A)</p> Signup and view all the answers

What does the Law of Independent Assortment state regarding alleles of different gene pairs during meiosis?

<p>They separate independently and randomly combine. (C)</p> Signup and view all the answers

Which of the following best describes Mendel's basis for the Law of Independent Assortment?

<p>Dihybrid crosses involving multiple traits. (D)</p> Signup and view all the answers

In Mendel's experiments with parents RRYY and rryy, what genotype will the F1 generation exhibit?

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

What is referred to as Mendel’s third law of heredity?

<p>Law of Independent Assortment (D)</p> Signup and view all the answers

When forming gametes, each gamete receives which of the following?

<p>One allele from each allelic pair. (D)</p> Signup and view all the answers

Which term describes the process where the assortment of alleles of different traits occurs randomly?

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

What happens to alleles of different traits when gametes are formed?

<p>They assort independently of one another. (A)</p> Signup and view all the answers

In the context of the Law of Independent Assortment, what is the outcome when gametes combine?

<p>They produce combinations not represented in the parental genotypes. (C)</p> Signup and view all the answers

What is the process called when a plant's pollen fertilizes its own stigma?

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

What is the outcome of selfing or sib-mating in terms of generating the F2 generation?

<p>Gametes will segregate and combine randomly (D)</p> Signup and view all the answers

Which of the following represents the gametes produced by parents with genotypes RrYy?

<p>RY, Ry, rY, ry (D)</p> Signup and view all the answers

What does the Punnett square illustrate during fertilization of RrYy parents?

<p>Possible genotypic combinations of the offspring (B)</p> Signup and view all the answers

In the F2 generation, what is the expected ratio of the genotype RrYy?

<p>2:4:2 (A)</p> Signup and view all the answers

How do the alleles of two gene pairs separate during meiosis according to the law of independent assortment?

<p>Randomly and independently from each other (C)</p> Signup and view all the answers

What is the total number of distinct genotypes observed in the F2 generation from a dihybrid cross?

<p>6 (C)</p> Signup and view all the answers

Which alleles result from the combinations of gametes RY, Ry, rY, and ry in a Punnett square?

<p>RRYY, RRYy, RrYY, RrYy, rrYY, rryy (B)</p> Signup and view all the answers

Flashcards

Factor

A unit in an organism responsible for inheriting and expressing a specific trait.

Gene

A specific part of DNA that determines inheritable traits.

Alleles

Different forms of a gene.

Dominant Allele

The trait that shows up in a hybrid generation.

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Recessive Allele

A trait masked in a hybrid generation.

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Genotype

The genetic makeup of an individual.

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Phenotype

An organism's observable characteristics.

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Homozygous

Having two identical alleles for a trait.

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Parent generation

The first generation of parents used in a genetic cross.

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F1 generation

The offspring resulting from a cross between two parent generations.

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Monohybrid cross

A cross between two organisms that are heterozygous for one specific trait.

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Monohybrid ratio

The expected phenotypic ratio (3 dominant : 1 recessive) in an F2 from a monohybrid cross.

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Dihybrid cross

A cross between two organisms that are heterozygous for two different traits.

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Inbreeding

Mating closely related individuals.

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F2 generation

The offspring resulting from a cross between two F1 organisms.

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Heterozygous

An organism with two different alleles for a particular gene.

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Law of Segregation

During gamete formation, allele pairs separate and each gamete receives only one allele from each pair.

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Allele Pair

Two versions of a gene, one from each parent, responsible for a specific trait.

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Hybrid Union

The combination of two different alleles for a trait, one from each parent.

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Punnett Square

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

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Law of Independent Assortment

During gamete formation, alleles for different traits separate independently of each other.

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Single Gene

A specific segment of DNA responsible for a particular trait.

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Dominant Trait

The trait that appears in the first filial (F1) generation, masking the other trait. It's the trait that is expressed, even when the organism has two different alleles for that trait.

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Recessive Trait

The trait that is hidden in the F1 generation but reappears in the F2 generation. It's the trait that only shows up if the organism has two copies of the same allele for that trait.

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Reciprocal Cross

A cross where the parents' roles are reversed. For example, if the first cross has a female with a dominant trait and a male with a recessive trait, the reciprocal cross would have a male with the dominant trait and a female with the recessive trait.

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Genotypic Ratio

The ratio of different genotypes in a population. It shows the proportion of individuals with each combination of alleles.

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Selfing

The process where a plant pollinates its own stigma with its pollen.

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Sib-mating

The mating of siblings, like brothers and sisters, in the case of F1 generation.

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Independent Assortment

The principle that alleles of different genes separate and recombine independently during gamete formation.

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Gametes

Sex cells (sperm or egg) that carry genetic information.

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Random Combination

The unpredictable way that alleles combine during fertilization, leading to diversity.

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Gamete Formation

The process of creating sex cells (sperm or egg) with half the number of chromosomes from the parent cell.

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Allele Separation

During gamete formation, the two alleles of a gene pair separate into different gametes.

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Genotype of F1 generation

The genotype of the offspring resulting from a cross between two homozygous parents, one dominant and one recessive, is heterozygous for both traits.

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Third Law of Heredity

Another name for the Law of Independent Assortment, often referred to as Mendel's third law.

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Study Notes

Gene Segregation and Interaction

  • Genetics lecture 4 covers gene segregation and interaction
  • Prepared by Helen LV. Ebuña, Department of Agronomy & Plant Breeding, College of Agriculture, Central Mindanao University
  • Lecture references Bio 31 (Principles of Genetics)

Terminologies

  • Factor: A particle in an organism responsible for inheritance and expressing traits
  • Gene: A segment of DNA determining inheritance and expression of a trait; previously called a "factor" by Mendel
  • Alleles/Allelomorphs: Alternative forms of a gene (e.g., round or wrinkled seed shape in peas)
  • Dominant: Trait appearing in the 1st filial (F1) generation; dominant allele
  • Recessive: Trait hidden in the 1st filial (F1) generation; recessive allele
  • Genotype: The genetic makeup of an individual (inherited from parents)
  • Phenotype: The observable traits (morphology, physiology, behavior) of an organism for a specific trait (eg, seed shape)
  • Homozygous: Individual with identical alleles for a trait (e.g., RR or rr)
  • Heterozygous: Individual with dissimilar alleles for a trait (e.g., Rr)
  • Parent (P) generation: The original parents of a cross
  • F1 generation: The progeny produced from the parent (P) generation
  • F2 generation: The progeny from self-hybridization or inbreeding of the F1 generation individuals
  • Inbreeding: Mating of closely related individuals in a progeny (e.g., F1)
  • Monohybrid cross: Cross between parents differing in a single pair of contrasting characters
  • Monohybrid ratio: The phenotypic ratio of dominant to recessive traits obtained from a monohybrid cross in the F2 generation (e.g., 3:1)

Dihybrid cross

  • Cross that simultaneously studies two pairs of contrasting characters

Mendel's Hybridization Experiments

  • Involved testing 7 individual characters by hybridizing 2 varieties with alternative traits (e.g., tall x short, green-seeded x yellow-seeded)
  • 1st generation (F1) plants showed only one of the traits.
  • The hidden trait reappeared in the 2nd generation (F2)

Law of Dominance

  • In a hybrid union, the allele expressing itself phenotypically is dominant
  • while the other allele(s) is recessive.

Pea Traits Studied by Mendel

  • Provided a summary table of various pea traits, their dominant and recessive forms and their ratio values in the F2 generation.

Dominant and Recessive Characters in Plants and Animals

  • Displays examples of dominant and recessive characters in plants (e.g. sorghum) and animals (e.g., mice)

Law of Segregation

  • Each parent contributes equally to the progeny
  • Factors/alleles separate during gametes formation.

Law of Independent Assortment

  • Alleles of different gene pairs separate independently, combining randomly during meiosis.
  • Mendel based this on dihybrid cross results

Chi-Square test

  • Statistical test for determining if observed data fits expected Mendelian ratios
  • Formula: χ² = Σ [(Observed Value - Expected Value)² / Expected Value] (for n > 2)
  • Degrees of freedom (df) = n − 1

Chromosomal Basis of Mendelian Laws

  • Sutton and Boveri (1900) linked Mendelian laws with chromosomes behavior.
  • Chromosomes exist in pairs
  • Alleles of a gene pair separate during meiosis
  • Allele pairs are in pairs immediately after fertilization

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