Understanding Inheritance Concepts

Understanding Inheritance

Definitions:
- Trait: A specific characteristic of an organism.
- True-breeding: Organisms that consistently produce offspring with the same trait when self-fertilized.
- Cross: The mating of two organisms.
- Parental generation (P generation): The original pair of organisms in a cross.
- First filial generation (F1 generation): The offspring of the parental generation.
- Second filial generation (F2 generation): The offspring of the F1 generation.
- Monohybrid cross: A cross between two organisms that differ in only one trait.
- Dominant trait/allele: A trait that masks the expression of another trait.
- Recessive trait/allele: A trait that is only expressed when two copies of the allele are present.
- Genotype: The genetic makeup of an organism.
- Homozygous: Having two identical alleles for a trait.
- Heterozygous: Having two different alleles for a trait.
- Phenotype: The observable characteristics of an organism.
Mendel's Experiments:
- Mendel chose garden pea plants for his experiments due to their ease of cultivation, short generation time, and distinct, easily identifiable traits.
- His monohybrid crosses demonstrated the principles of dominance and segregation.
Law of Segregation:
- During gamete formation, the two alleles for each trait separate, so that each gamete receives only one allele.

Studying Genetic Crosses

Definitions:
- Punnett square: A diagram used to predict the possible genotypes and phenotypes of offspring from a cross.
- Test cross: A cross between an individual with an unknown genotype and a homozygous recessive individual.
- Dihybrid cross: A cross between two organisms that differ in two traits.
- Chromosome theory of inheritance: The theory that genes are located on chromosomes.
Test Crosses:
- Used to determine if an individual with a dominant phenotype is homozygous or heterozygous.
Mendel's Dihybrid Crosses:
- Showed that alleles for different traits separate independently of each other during gamete formation.
Law of Independent Assortment:
- During gamete formation, the alleles for different traits separate independently of each other.
Predicting Offspring:
- Punnett squares can be used to predict the probability of specific genotypes and phenotypes in offspring.
- You can determine the genotypic ratio (the ratio of different genotypes) and the phenotypic ratio (the ratio of different phenotypes) for a given cross.

Following Patterns of Inheritance in Humans

Definitions:
- Pedigree: A diagram that shows the inheritance of a trait within a family.
- Autosomal inheritance: Inheritance of traits located on autosomes (non-sex chromosomes).
- Autosomal dominant disorder: A disorder that is expressed when only one copy of the dominant allele is present.
- Autosomal recessive disorder: A disorder that is only expressed when two copies of the recessive allele are present.
- Genetic tests: Tests that analyze DNA, chromosomes, or proteins to detect genetic conditions.
- Gene therapy: The use of genes to treat or prevent disease.
Pedigrees:
- Symbols in pedigrees indicate the sex of individuals, their relationships, and whether they have the trait in question.
- Pedigrees can be used to track traits through generations, identify potential carriers, and determine the pattern of inheritance.
Determining Genotype from Phenotype:
- You can deduce the genotypes of individuals in a pedigree by analyzing their phenotypes and the phenotypes of their relatives.
Pattern of Inheritance:
- The pattern of inheritance for a specific trait can be determined by observing how it is passed through generations in a pedigree.
Genetic Disorders:
- Huntington's disease: A dominant neurological disorder that causes progressive deterioration of brain cells.
- Cystic fibrosis: A recessive disorder that affects the lungs, digestive system, and other organs.
Types of Genetic Tests:
- Karyotype: Analyzes the number and structure of chromosomes.
- FISH (fluorescence in situ hybridization): Uses fluorescent probes to detect specific DNA sequences on chromosomes.
- Gene testing: Analyzes specific genes for mutations or variations.
- Biochemical testing: Measures the levels of specific proteins and enzymes in the body.
Gene Therapy:
- Aims to replace or modify defective genes with healthy ones.
- Challenges include delivering the gene to the target cells, ensuring that the gene is expressed correctly, and avoiding unwanted side effects.

Beyond Mendel's Observations of Inheritance

Definitions:
- Incomplete dominance: A pattern of inheritance where the heterozygote phenotype is intermediate between the two homozygous phenotypes.
- Codominance: A pattern of inheritance where both alleles are expressed equally in the heterozygote.
- Multiple alleles: When more than two alleles exist for a trait.
- Polygenic inheritance: When a trait is controlled by multiple genes.
- Heterozygous advantage: When the heterozygous genotype has a higher fitness than either homozygous genotype.
Environmental Effects:
- Environmental conditions can affect the expression of traits.
ABO Blood Types:
- An example of codominance and dominance.
- The A and B alleles are codominant, and the O allele is recessive.
Blood Transfusions:
- Blood transfusions are only compatible between individuals with matching blood types.
- Individuals with type O blood are universal donors, while those with type AB blood are universal recipients.

Inheritance of Linked Genes

Definitions:
- Linked genes: Genes that are located on the same chromosome and tend to be inherited together.
- Linkage group: A group of linked genes.
- Chromosome mapping: The process of determining the relative positions of genes on a chromosome.
- Sex-linked trait: A trait that is located on a sex chromosome.
- X-linked genes: Genes located on the X chromosome.
- Y-linked genes: Genes located on the Y chromosome.
- X-linked dominant: A dominant trait that is located on the X chromosome.
- X-linked recessive: A recessive trait that is located on the X chromosome.
- Barr body: An inactive X chromosome in female cells.
Crossing Over:
- Can "unlink" genes by exchanging segments of chromosomes.
- The frequency of crossing over can be used to determine the distance between linked gens.
Chromosome Mapping:
- Crossing over frequency is used to create chromosome maps, which show the relative positions of genes on chromosomes.

The Future of Genetic Research

Definitions:
- Human genome: The complete set of DNA within a human cell.
- Bioinformatics: The application of computer science and statistics to biological data.
- Genomics: The study of genomes.
- Single nucleotide polymorphism (SNP): A variation in a single nucleotide in DNA.
- Haplotype: A set of linked alleles inherited together.
- HapMap Project: A project that mapped common haplotypes in human populations.
- Microarray: A tool that allows researchers to analyze the expression of thousands of genes simultaneously.
- Genetic profile: A summary of an individual's genetic makeup.
Human Genome Project (HGP):
- Sequenced the entire human genome.
- Identified genes associated with various diseases.
Microarrays:
- Can be used to study gene expression, identify mutations, and diagnose diseases.
Genetic Profiles:
- Offer potential benefits for personalized medicine and disease prediction.
- Raise ethical concerns about privacy, discrimination, and the potential for misuse of genetic information.