Genetics Chapter on Monohybrid and Dihybrid Crosses

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.

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.