BIOL2107 Week 9 Study Guide

Midterm #2
- Rescheduled to March 19
- 77% of the class voted on the change
- Same format, slightly shorter
Inheritance Practice Problems
- Posted; students are encouraged to try them out
Final Exam
- Scheduled for April 16 at 2:00 PM

Given a pedigree, determine genotype/phenotype of individuals
Compare and contrast three types of dominance
Given a genotype or phenotype ratio, determine dominance types; and vice versa, given dominance types, determine genotype/phenotype ratios/numbers
Given epistatic interactions (recessive/dominant), predict genotype and phenotype ratios
Provide examples where the environment can interact with genotype to influence phenotype
Identify situations where dihybrid crosses result in non-Mendelian ratios because of gene interactions
Considering the mechanisms of epigenetics, predict the effects of methylation/demethylation of genes
Provide examples of epigenetically regulated phenotypes

PKD is an autosomal dominant disease in humans caused by a genetic mutation.
Results in the formation of cysts on the kidneys, which is eventually fatal.
Pedigree Analysis: Individuals confirmed with the disease are marked in black.
- Probability Questions:
- Given that three of his brothers have the disease, what is the probability that the fourth son will also have it?
- What is the probability the third daughter will have the disease?

Mendel's Assumptions:
- Many traits are not Mendelian, either due to luck in trait selection or multiple observations.
- Conditions assumed by Mendel were:
- Clear phenotype with only two options
- One allele completely dominant over the other
- No selection affecting progeny viability
- One gene associated with the trait
- No significant gene x environment interactions

Types of Dominance
- Complete Dominance:
- The phenotype of the heterozygote is the same as one of the homozygotes.
- Incomplete Dominance:
- The phenotype of the heterozygote is intermediate between the two homozygotes.
- Codominance:
- The phenotype of the heterozygote includes the phenotypes of both homozygotes.

Human Hair Texture:
- An individual inherits one allele for curly hair and one for straight hair, resulting in wavy hair.
Plant Flower Color:
- Crossing red flowers with white flowers produces pink flowers.

Blood Types
- Type A (AA or AO) produces A sugars
- Type B (BB or BO) produces B sugars
- Type AB (AB) produces both A and B sugars

HLA Genes in Humans:
- Responsible for immune response, with between 400 and 1,200 alleles, including HLA-A, HLA-B, and HLA-C
Allele Frequencies:
- The frequency of an allele is the percentage of total copies of one allele in a population.
- Most common allele is often referred to as the wildtype (+) allele, though exceptions exist.
- Polymorphic genes have multiple alleles, with high-frequency ones termed common variants or major alleles and less common variants termed mutations or minor alleles.

Definition:
- A single gene can affect multiple traits.
Example:
- In cats, one gene influences both fur color and eye color with allele A yielding black fur/green eyes and allele a resulting in white fur/blue eyes.
Statistics on Pleiotropy:
- 40% of white cats with blue eyes are deaf due to genetic mutations affecting pigmentation.
Other Examples:
- Coat color in mice, bobtail in cats (Manx)

Condition: Autosomal recessive; a loss of function allele affects the conversion of phenylalanine to tyrosine.
Environmental modification (diet) allows management of the phenotype.
Testing Protocol: Shortly after birth, newborns are screened for PKU using a heel prick blood test.

Normal Range for Phenylalanine: 0.5 to 2 mg/dL
Case Study: Baby's Phenylalanine Level is 8 mg/dL
1. What can be inferred about the baby's condition?
2. Why is early testing for PKU critical for diagnosis and treatment?

Definition: An allele of one gene masks or affects the expression of another gene's allele; the masking allele is termed epistatic, while the masked allele is hypostatic.

Recessive Epistasis: Results where one gene's recessive alleles mask effects of another gene.
Dominant Epistasis: A dominant allele masks the effects of another gene's alleles.
Duplicate Recessive Epistasis: Two genes need to have recessive alleles present to show a particular phenotype.

Many traits influenced by multiple genes, e.g., human hearing loss has over 50 implicated genes.
- Complementation Tests: Used to determine if mutations are in the same or different genes.

Definitions:
- Penetrance: The percentage of a population with a specific genotype that displays the expected phenotype
- Expressivity: The degree or intensity of expression of a specific genotype in a phenotype

Mechanism: Changes to DNA that do not alter the sequence but can affect gene regulation, often involving DNA methylation.
Example: Honeybee development influenced by royal jelly intake alters DNA methylation patterns, affecting phenotype outcomes.

Epigenetic Reprogramming: Adult cells can be turned into induced pluripotent stem cells (iPSCs) through exposure to specific transcription factors, enabling them to differentiate into various cell types depending on epigenetic modifications.