Genetics Chapter on Monohybrid and Dihybrid Crosses

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Questions and Answers

What is the expected phenotypic ratio for a dihybrid cross?

1:1

3:1

1:2:1

9:3:3:1 (correct)

Which phenotype combination is represented in a dihybrid cross as recessive recessive?

Purple, Smooth

Yellow, Wrinkled (correct)

Purple, Wrinkled

Yellow, Smooth

If you observed data for phenotypes as follows: 269, 38, 96, 29, what is the first step to calculate the expected values?

Divide by 4

Multiply by 16

Sum the observed numbers (correct)

Subtract class 2 from class 1

How do you find the expected number for recessive/recessive phenotypes in a dihybrid cross?

Divide the sum by 16 Signup and view all the answers

What is represented by the one-sixteenth value in the expected phenotypic calculation for a dihybrid cross?

Expected for recessive/recessive phenotypes Signup and view all the answers

Which of the following is NOT a possible phenotype resulting from the dihybrid cross described?

Green and Smooth Signup and view all the answers

What is the expected ratio for dominant/recessive and recessive/dominant phenotypes in a dihybrid cross?

9:3 Signup and view all the answers

What is the last step in calculating expected phenotypic values from observed data?

Calculate the Chi-squared statistic Signup and view all the answers

What is the formula to calculate the expected number of recessive phenotypes in a monohybrid cross?

One fourth of the total observed phenotypes Signup and view all the answers

In the context of the Chi-squared test, what do larger Chi-squared values indicate?

Bigger differences between observed and expected values Signup and view all the answers

How many degrees of freedom should be used when analyzing two phenotypes in a Chi-squared test?

1 Signup and view all the answers

What conclusion can be drawn if the calculated Chi-square value is greater than the value at 0.05 p-value?

Deviation is significant Signup and view all the answers

What do the values in the column with your chosen p-value represent in a Chi-squared analysis?

Critical values for determining significance Signup and view all the answers

In a dihybrid cross, what traits are being investigated simultaneously?

Color and texture of kernels Signup and view all the answers

What should be done to the deviation values before calculating the Chi-squared value?

They should be squared Signup and view all the answers

What does a Chi-squared value reflect in genetic studies?

Comparison between observed and expected frequency of phenotypes Signup and view all the answers

What is the expected phenotypic ratio resulting from a typical monohybrid cross?

3:1 Signup and view all the answers

What does the Law of Independent Assortment imply about different traits?

They segregate independently of each other. Signup and view all the answers

Which generation allows for the observation of genotype from crosses according to Mendelian genetics?

F2 generation Signup and view all the answers

In a chi-squared test, when should you reject the hypothesis regarding Mendelian inheritance?

When p < 0.05 shows significant deviation Signup and view all the answers

What would be the result of a dihybrid cross for two traits that assort independently?

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

What is a common misconception about alleles in Mendelian genetics?

Alleles are identical for all individuals. Signup and view all the answers

During a monohybrid cross, what phenotype is typically expressed in the F1 generation?

Only the dominant trait Signup and view all the answers

What is the significance of producing equal gametes in heterozygotic individuals?

It illustrates the Law of Segregation. Signup and view all the answers

Study Notes

Genetics and Data Analysis

Gregor Mendel discovered genetics in 1866.
Pre-1866 understanding of genetics didn't exist in the same way as modern genetics.

Objectives

Concepts:
- Explain different phenotypes are obtained.
- Predict results of mono- and dihybrid crosses in F1 and F2 generations.
- Use Chi-Squared test to determine when data supports a hypothesis.
- Explain the immunology and genetics of the human ABO blood groups.
Outputs:
- Complete and answer tables and questions on monohybrid and dihybrid crosses, including chi-square tables.
- Complete table 10 in the lab guide and answer all questions related to blood typing, paternity, and immunology.

Roadmap of Today's Activities

Monohybrid Cross (p. 48-55): ~30 minutes; count corn kernels and compare results to expectations.
Dihybrid Cross (p. 48-55): ~30 minutes; more kernel counting.
Drosophila Salivary Gland (p. 55-56): ~5 minutes; observe chromosomal banding.
Blood Typing Exercise (p. 56-61): ~20 minutes; determine blood type based on clotting/lineage.

Genetic Terms

Genes: units of information about specific traits passed from parents to offspring (hereditary). Located at a specific location on the chromosome.
Locus: a specific location on a chromosome where a gene is found.
Alleles: different molecular forms of a gene; usually two alleles for each trait; arise by mutation.

Allele Combinations

Alleles: can be homozygous (identical alleles at a locus) or heterozygous (different alleles at a locus).
Dominant alleles: mask the expression of recessive alleles and are expressed in heterozygotes.Recessive alleles are only expressed if in a homozygous state.
Meiosis: during meiosis, alleles/genes on different chromosomes sort independently during metaphase I, and separate during anaphase I. New alleles/genes are recombined in the offspring.

Genotypes and Phenotypes

Genotype: refers to the particular genes an individual carries.
Phenotype: refers to an individual's observable traits in relation to a particular characteristic.
Not all genotypes can be determined by observing the phenotype. In a monohybrid or dihybrid cross, the first generation of offspring (F1) won't always show the genotype but the second generation of offspring (F2) will.

Mendelian Genetics

Assumptions:
- Characteristics are discrete.
- Genetic characteristics have alternate forms (alleles) inherited from one of two parents.
- One allele is dominant over another and determines the phenotype.
- Heterozygous individuals produce gametes with equal frequency of the two alleles (Law of Segregation).
- Different traits have independent assortment; genes are unlinked (Law of Independent Assortment).

Monohybrid Crosses

Typically involving a homozygous recessive genotype and a homozygous dominant genotype.
All offspring in the F1 generation will have the dominant phenotype.
In the F2 generation, the more abundant phenotype indicates the dominant allele (may be homozygous dominant or heterozygous). The ratio of expected phenotypes is 3:1 of dominant to recessive.

Chi Squared Test

Purpose: a statistical test to see if observed values differ significantly from expected values. Often used to test if observed Mendelian ratios follow a Mendelian pattern.
Rejection/Acceptance of Hypothesis: If there's a significant difference (p < 0.05) between observed and expected values, reject the hypothesis; otherwise, "fail to reject". The larger the difference, the larger the Chi-Squared value. Larger sample sizes lead to smaller chi squared values.
Calculate Expected Values: sum the observed phenotypes for a dihybrid cross, divide by 16 (to get the one-sixteenth expected number). Multiply by 3 for recessive/dominant and multiply by 9 for dominant/dominant phenotypes

Observing the Giant Salivary Gland Chromosomes of Drosophila

Flies have very large salivary gland chromosomes.
During development, chromosomes replicate but don't divide leading to very large structures with copies of DNA and banded appearance.
Banded patterns can be correlated with specific genes expressed during development.

Human Blood Groups (A, B, O)

ABO blood groups in humans are determined by three alleles for an enzyme (I) that attaches A or B carbohydrates to red blood cells (IA, IB, i).
A and B are dominant over O
A and B are co-expressed when both alleles present (AB blood type)
The type O blood group is recessive and represented by ii

Immunology and Human Blood Groups

Antigens: substances recognized as foreign. When the immune system recognizes an antigen, it produces antibodies.
Antibodies: bind to and inactivate antigens, marking them for destruction. - Type A has A carbohydrate, anti-B antibody. - Type B has B carbohydrate, anti-A antibody. - Type AB has both A and B carbohydrates, no antibodies. - Type O has neither A or B carbohydrate but both anti-A and anti-B antibodies.

Blood Typing Exercise

The exercise describes the procedure for blood typing several fictional people.

Blood Transfusions

Blood type compatibility is vital for successful transfusions.
- Type A can receive A or O
- Type B can receive B or O
- Type AB can receive any blood type
- Type O can only receive type O

Blood Typing and Paternity Exercise

Information about phenotypes of mother and child may be used to deduce possible genotypes of the father.
Phenotype O means genotype ii for child, which helps to ascertain the genotype of the mother that child inherits from in cases involving parentage.

Outputs (Notebook Check)

Complete tables and Chi-square tests for both two and four data classes.
Complete anonymous blood typing exercise.
Complete all questions related to immunology and blood typing.

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Description

This quiz covers essential concepts of genetics, particularly focusing on monohybrid and dihybrid crosses as pioneered by Gregor Mendel. Participants will apply the Chi-Squared test to analyze data and explore the genetics of human ABO blood groups. Complete tables and answer questions pertaining to these genetic principles and their real-world applications.