Genetics Lecture 4: Gene Segregation

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the number of different gametes produced by an organism with two gene pairs?

4 (correct)

How many phenotypes are expected from a genetic cross involving four gene pairs?

16 (correct)

In a Chi-Square test, what does the degree of freedom represent?

The total count of phenotypes

The total number of observations

The expected ratio

The number of classes minus one (correct)

Which ratio corresponds to the expected phenotypic ratio for a dihybrid cross according to Mendel's law of independent assortment?

9:3:3:1 Signup and view all the answers

What Chi-Square value would indicate a good fit for observed data to a 9:3:3:1 ratio if the expected values were significantly different from the observed values?

3.84 Signup and view all the answers

If an organism has three gene pairs, how many different genotypes can arise from those alleles?

27 Signup and view all the answers

Which of the following represents the expected number of gametes for an organism with four gene pairs?

16 Signup and view all the answers

In using the Chi-Square test, what is the formula used to calculate the degrees of freedom?

n - 1 Signup and view all the answers

What does the Law of Segregation state about alleles during gamete formation?

Each allele maintains its identity and separates during gamete formation. Signup and view all the answers

In Mendel's experiments with round and wrinkled seeds, what was the resulting F2 phenotypic ratio?

2.96:1 Signup and view all the answers

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

Genes segregate independently of each other during gamete formation. Signup and view all the answers

What is the primary purpose of using a Punnett square in genetics?

To forecast potential genotypes and phenotypes of offspring. Signup and view all the answers

What ratio was observed in Mendel's crosses involving axial and terminal flowers?

3.14:1 Signup and view all the answers

What characteristic do all traits Mendel studied have in common regarding F1 generation offspring?

All expressed only the dominant trait. Signup and view all the answers

Which of the following plant traits did Mendel NOT examine in his experiments?

Root length Signup and view all the answers

Which statement most accurately reflects the outcome of Mendel's F2 generation when crossing yellow and green seeds?

The observed ratio was approximately 3:1 yellow to green. Signup and view all the answers

What does the Law of Independent Assortment state regarding alleles during gamete formation?

Alleles of different genes segregate independently. Signup and view all the answers

In the context of dihybrid crosses, what is the significance of the Law of Independent Assortment?

It allows for the independent inheritance of multiple traits. Signup and view all the answers

Which of the following best describes the function during meiosis as stated by the Law of Independent Assortment?

Alleles assort independently, allowing for diverse genetic combinations. Signup and view all the answers

How does the Law of Independent Assortment relate to Mendel's experiments?

It was derived from observations of dihybrid crosses. Signup and view all the answers

Which statement is true regarding the inheritance of traits under the Law of Independent Assortment?

The inheritance of one trait does not influence another. Signup and view all the answers

What is the expected phenotypic ratio for a dihybrid cross that follows Mendel's Law of Independent Assortment?

9:3:3:1 Signup and view all the answers

What happens to alleles from different gene pairs during the formation of gametes according to the Law of Independent Assortment?

They partition equally into gametes irrespective of parental combination. Signup and view all the answers

What aspect of Mendel's experiments supports the principle of independent assortment?

The random combination of alleles from dihybrid crosses. Signup and view all the answers

Study Notes

Lecture 4: Gene Segregation and Interaction

Factor: A particle or unit in an organism responsible for inheritance and expression of a characteristic.
Gene: Mendel's factor, a segment of DNA determining inheritance and expression of a characteristic.
Alleles/Allelomorphs: Two or more alternative forms of a gene. Examples include round (R) and wrinkled (r) seed shapes in pea plants. Alleles occupy the same locus on homologous chromosomes.
Dominant: The trait that appears in the F1 generation.
Recessive: The trait suppressed in the F1 generation.
Genotype: The genetic makeup (e.g., RR or Rr) of an individual.
Phenotype: The observable characteristics (e.g., round or wrinkled seeds).
Homozygous: An individual with identical alleles (e.g., RR or rr).
Heterozygous: An individual with dissimilar alleles (e.g., Rr). Also referred to as a hybrid.
Parent Generation (P): The initial parents involved in a cross.
F1 Generation: The offspring from the P generation cross.
Inbreeding: When F1 individuals cross.
F2 Generation: The offspring from the self-hybridization or inbreeding of F1 individuals.

Monohybrid Cross

Monohybrid cross: The cross between two parents differing in a single pair of contrasting characteristics. Offspring in the F1 generation are heterozygous for one trait only.
Monohybrid ratio: The phenotypic ratio of 3 dominant to 1 recessive, obtained in the F2 generation, from a monohybrid cross. This ratio is 3:1.

Dihybrid Cross

Dihybrid Cross: The cross between two parents differing in two pairs of contrasting characteristics. The F1 offspring are described as dihybrid or double heterozygous.

Mendel's Hybridization Experiments

Mendel tested seven characteristics with pea plants by hybridizing different varieties showing contrasting traits. (e.g., tall x short; green-seeded x yellow-seeded).
Parental plants were pure-breeding (homozygous) line.
F1 generation produced all round seeds.
Self-fertilization of F1 plants gave a mix of round and wrinkled seeds in F2 generation.

Results of Mendel's Crosses

Details of characteristic traits, observed ratio in F2 offspring. (e.g., round seeds:wrinkled seeds, 2.96:1)

Law of Dominance

In a hybrid union, the allele expressing itself phenotypically is the dominant allele. The other allele is recessive.
The hybrid individual shows only the dominant characteristic.
This is Mendel's first law of inheritance

Law of Segregation

The law states that the unit of hereditary characteristics occur in pairs. During meiosis, these separate, and only one member of the pair goes to each gamete.
The combination of the male and female gametes during fertilization restores the diploid chromosome number.
The inheritance process depends on chance - whether a particular gamete gets the dominant or recessive allele. (Example: 3:1 ratio of yellow to green seeds).

Law of Independent Assortment

This law applies when considering two or more genes simultaneously.
Genes for different characteristics are inherited independently.
Alleles from different gene pairs separate independently and combine randomly during meiosis.
Results of dihybrid crosses support this law.

Formulas

Used in calculating probabilities based on the number of gene pairs

Chi-Square Test

Statistical test to check if the observed data fits a predicted Mendelian ratio.
A formula for calculating the chi-square value.
Degrees of freedom calculation
The decision to accept or reject the hypothesis (null hypothesis) based on comparing the calculated chi squared value to a critical chi squared value.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the principles of gene segregation and interaction in this quiz based on Lecture 4. Learn about key concepts such as alleles, dominant and recessive traits, and the differences between genotype and phenotype. Test your understanding of genetic inheritance through Mendel's framework.