Chpt. 14 Mendel's Experiments in Genetics

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Questions and Answers

What is the result of a gene at one locus affecting the expression of another gene at a different locus known as?

Phenotypic variation

Epistasis (correct)

Genetic drift

Mutation

What term describes inheritance when two or more genes influence a single phenotype?

Recessive inheritance

Epistatic inheritance

Monogenic inheritance

Polygenic inheritance (correct)

In a cross between two BbEe labradors, what is the expected phenotypic ratio of offspring considering epistasis for coat color?

9:3:4 (correct)

9:3:3

3:1:4

1:1:1

What was a key characteristic of the parental plants in Mendel's experiments?

They were true-breeding. (C) Signup and view all the answers

What was the observed ratio of purple to white flowers in the F2 generation?

3:1 (B) Signup and view all the answers

Which statement correctly describes the results of the F1 generation in Mendel's experiments?

All plants had purple flowers. (B) Signup and view all the answers

What term is used to describe the variants of a heritable feature?

Traits (B) Signup and view all the answers

What does the modern explanation of inheritance state regarding alleles?

An organism inherits two alleles, one from each parent. (A) Signup and view all the answers

What does the term 'particulate inheritance' refer to in Mendel's findings?

Inheritance where traits are passed in discrete units. (D) Signup and view all the answers

Which of the following traits did Mendel choose for his experiments?

Plants showing distinct forms like purple or white flowers. (A) Signup and view all the answers

How did Mendel control fertilization in his pea plants?

He removed the male organs from some plants. (C) Signup and view all the answers

Which technology or method did Mendel NOT utilize in his experiments?

Cross-breeding different species. (A) Signup and view all the answers

What did Mendel conclude about the white trait in the F2 generation?

It was masked but still present. (C) Signup and view all the answers

What is the probability of obtaining hybrid offspring (Rr) from a cross between two Rr parents?

1/2 (C) Signup and view all the answers

Which rule states that the probability of two independent events occurring together is the product of their individual probabilities?

Multiplication rule (B) Signup and view all the answers

During the cross of YyRr with YyRr, what is the probability of producing offspring with genotype yyRr?

1/16 (C) Signup and view all the answers

What is the phenotypic ratio observed in a dihybrid cross of YyRr parents?

9:3:3:1 (C) Signup and view all the answers

What does the term 'mutually exclusive events' refer to in probability?

Events that cannot occur at the same time (B) Signup and view all the answers

In a pedigree analysis, what does a filled symbol represent?

Individual with the trait (B) Signup and view all the answers

What is the probability of obtaining a phenotype with round seeds (R) in a cross PP x Pp?

3/4 (B) Signup and view all the answers

From a cross of YYrr and Yyrr parents, what is the probability of offspring with genotype Yyrr?

1/2 (A) Signup and view all the answers

What type of inheritance is indicated when traits follow Mendelian rules?

Simple dominant and recessive inheritance (D) Signup and view all the answers

In the context of genetics, what does the term 'segregation' refer to?

The separation of alleles during gamete formation (A) Signup and view all the answers

What is the correct interpretation of a genotype of rr in a genetic cross?

Homozygous recessive (A) Signup and view all the answers

If a trait is dominant, how would its frequency compare to its recessive counterpart in the population?

It would be more frequent (B) Signup and view all the answers

When applying the addition rule in probability, what must be true about the events being summed?

They must be mutually exclusive events (A) Signup and view all the answers

What is the probability of offspring with the genotype YYrr from a YyRr x YyRr cross?

1/16 (A) Signup and view all the answers

What does the law of independent assortment state about alleles during meiosis?

Alleles assort independently of each other on nonhomologous chromosomes. (A) Signup and view all the answers

In a dihybrid cross, what phenotypic ratio is typically observed in the F2 generation when independent assortment occurs?

9:3:3:1 (D) Signup and view all the answers

How do the laws of segregation and independent assortment differ?

Segregation applies to single gene traits, while assortment applies to multiple gene traits. (B) Signup and view all the answers

What can affect the expression of dominant and recessive alleles?

Environmental factors alongside genetic factors. (A) Signup and view all the answers

During which phase of meiosis does the independent assortment of alleles occur?

Metaphase I (A) Signup and view all the answers

Given the genotype YyRr, which gametes could be produced according to the law of independent assortment?

YR, Yr, yR, and yr (D) Signup and view all the answers

What does the term 'phenotypic ratio' refer to?

The observable characteristics of offspring. (A) Signup and view all the answers

Which of the following statements about dominant and recessive genes is not true?

A recessive gene can become dominant under certain conditions. (C) Signup and view all the answers

What is the primary outcome of the law of segregation during meiosis?

Each allele of a gene separates into different gametes. (D) Signup and view all the answers

What is the general implication of alleles being on nonhomologous chromosomes?

They will segregate independently during meiosis. (C) Signup and view all the answers

In the results showing a 9:3:3:1 ratio, what does this specifically refer to?

The distribution of phenotypes in the offspring. (B) Signup and view all the answers

What is demonstrated by the hypothesis of independent assortment?

Genes are inherited independently of each other under certain conditions. (C) Signup and view all the answers

Which gametic outcome would not be expected from a YyRr cross?

yyR (B) Signup and view all the answers

If an organism has two different alleles for a given trait, it is considered to be:

Heterozygous (B) Signup and view all the answers

What does pleiotropy refer to in genetics?

One gene affecting multiple phenotypic traits (A) Signup and view all the answers

Which of the following describes codominance?

Both alleles expressed in the phenotype of heterozygotes (A) Signup and view all the answers

What characterizes polygenic inheritance?

A single phenotypic trait affected by multiple genes (C) Signup and view all the answers

How is incomplete dominance different from complete dominance?

It results in an intermediate phenotype rather than one resembling either parent (C) Signup and view all the answers

In the presence of multiple alleles, how do they affect phenotypic expression?

More than two variations of a gene influencing a single trait (B) Signup and view all the answers

What is epistasis in genetic terms?

One gene modifying the expression of another gene (C) Signup and view all the answers

What determines how a given gene is expressed according to the nurture concept?

The environment and external factors affecting the individual (A) Signup and view all the answers

Which of the following best describes complete dominance?

The phenotype of the heterozygote is indistinguishable from that of the homozygous dominant (C) Signup and view all the answers

Study Notes

Mendel's Experiments

Mendel studied pea plants because they have a short generation time, allowing him to observe several generations in a single growing season.
He could control mating in pea plants by removing the male organs to prevent self-fertilization.
He meticulously recorded data and kept track of thousands of plants throughout his experiments.
He only studied traits with distinct forms, such as purple or white flowers, green or yellow seeds, eliminating ambiguity in observation.

Terminology Used

Character: A heritable feature, such as flower color.
Trait: A variant of a character, such as purple or white flowers.
Parental generation (P): The original plants used for crossing.
First filial generation (F1): The offspring of the parental generation.
Second filial generation (F2): The offspring of the F1 generation.

Parental Generation (P)

The parental plants were true-breeding, meaning they consistently produced offspring with the same traits.
For example, a purple-flowered plant only produced purple-flowered offspring, and a white-flowered plant only produced white-flowered offspring.
Mendel crossed a purple-flowered plant with a white-flowered plant.

Results of Crossing

All F1 generation plants had purple flowers, demonstrating that the white trait was not lost but masked.
No light purple flowers were observed, contradicting the blending hypothesis.
In the F2 generation, some plants exhibited white flowers again, indicating that the white "particle" was present but masked in the F1.
The F2 generation had a 3:1 ratio of purple to white flowers, suggesting that the white trait was not lost but recessive.
This pattern was consistent across six other characters.

Key Concepts from Mendel's Experiments and Observations

Particulate inheritance: Traits are determined by discrete units of inheritance, now known as genes.
Alleles: Different versions of a gene, accounting for variations in a character.
Law of Segregation: Each organism inherits two alleles for each character, one from each parent, which are separated during gamete formation.
Law of Independent Assortment: Alleles for different genes assort independently of each other during gamete formation.

Polygenic Inheritance

When the phenotype is influenced by multiple genes.
Examples include height, skin color, and weight.

Probability and Genetics

The multiplication rule calculates the probability of two independent events occurring together.
The addition rule calculates the probability of one event occurring given two or more mutually exclusive events.

Epistasis

A gene at one locus can affect the expression of a gene at another locus.
For example, in Labrador Retrievers, the "B" gene controls black (B) or brown (bb) coat color, however, a separate gene (C) determines if pigment is deposited in the hair. If the "C" gene is homozygous recessive (cc), the dog will be albino regardless of its genotype for the "B" gene.

Mendelian Inheritance in Humans

Many human traits follow Mendelian inheritance patterns.
Studying pedigrees can help determine the mode of inheritance for human traits.

Genes and the Environment

Genes play a major role in our lives, but we are not simply products of our genes.
The environment can influence how a gene is expressed.
Example: Hydrangeas of the same genetic variety grown in acidic soil with free aluminum will have blue flowers, while hydrangeas grown in basic soil will have pink flowers.

Alleles and Genetic Expression

Complete dominance: One allele completely masks the effect of another allele.
- Example: In pea plants, the allele for purple flowers (P) is dominant over the allele for white flowers (p). A plant with the genotype PP or Pp will have purple flowers.
Incomplete dominance: The heterozygous phenotype is intermediate between the two homozygous phenotypes.
- Example: Snapdragon flowers with the genotype CRCR are red, CWCW are white, and CRCW are pink.
Codominance: Both alleles are expressed in the heterozygote.
- Example: In humans, the ABO blood group is determined by three alleles: IA, IB, and i. Individuals with the genotype IAIB have both A and B antigens on their red blood cells.
Multiple alleles: Some genes have more than two alleles in the population.
- Example: The ABO blood group system is an example of multiple alleles.
Pleiotropy: One gene affects multiple phenotypic characters.
- Example: Sickle-cell disease, which affects red blood cell shape, can also cause anemia, joint pain, and organ damage.

Interactions Between Genes

Epistasis: The phenotypic expression of one gene affects the expression of another gene.
- Example: In Labrador retrievers, the gene for coat color (B) is epistatic to the gene for pigment deposition (E). A dog with the genotype BbEe will have black fur if it inherits at least one dominant E allele, but will have brown fur if it inherits two recessive e alleles.
Polygenic inheritance: A single phenotypic character is affected by two or more genes.
- Example: Skin color, height, and eye color are examples of polygenic inheritance.

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Description

Explore the groundbreaking experiments conducted by Gregor Mendel on pea plants, which laid the foundation for modern genetics. This quiz covers key terminology, important generations, and the meticulous methods Mendel employed to study inheritance patterns. Test your understanding of Mendel's work and its significance in the field of genetics.