Genetics Fundamentals

• Understanding trait inheritance is key to genetics.
• The monohybrid cross focuses on single-trait inheritance with dominant and recessive alleles.
• Segregation of two or more genes explores how genes on different chromosomes segregate independently.
• Mendelian Inheritance uses Mendel's laws of segregation and independent assortment, guiding the understanding of genetic transmission.
• Probability principles allow predicting genetic outcomes mathematically.
• Segregation in human pedigrees tracks genetic traits/disorders across generations, revealing inheritance patterns.
• Genetic analysis and modified dihybrid ratios show how gene interactions alter inheritance patterns.
• Epistasis, where one gene masks another's expression, complicates Mendelian expectations.
• Mendelian genetics includes segregation and independent assortment.

The Monohybrid Crosses

• Genes are unit factors.
• Alleles are alternative forms of a single gene (e.g., tall [D] vs. dwarf [d]).
• Phenotype is the appearance of an individual (e.g., tall vs. dwarf plant).
• Genotype is indicated by two unit factors (alleles present): DD vs. Dd vs. dd, representing genetic makeup.
• Homozygous individuals possess two identical alleles for a trait (DD or dd).
• Heterozygous individuals possess two different alleles for a trait (Dd).
• Gregor Mendel, an Austrian monk, studied inheritance using garden peas beginning in 1865.
• Mendel crossed pea plants with contrasting phenotypes, observing traits across generations.
• Mendel's monohybrid crosses with true-breeding pea plants differing in a single trait (tall vs. short).
• F1 generation exhibited one parental trait, showing no blending.
• Self-pollinating F1 produced F2, generation, showing a 3:1 dominant-to-recessive trait ratio.
• Traits are inherited as discrete units (genes), with one allele dominant over another.
• Mendel's experiments were key principles of inheritance, including dominance, segregation, and the 3:1 phenotypic ratio in F2 generation.

Segregation of Two or More Genes

• Homologous chromosomes pair during the first meiotic division (one from each parent).
• Heterozygous offspring (Aa) form if parents are homozygous, but for different alleles (A and a).
• In anaphase I, paired chromosomes separate, moving to opposite cell poles, carrying either A or a allele.
• Physical separation of chromosomes segregates alleles into different daughter cells.
• Mendel's Principle of Segregation relies on homologous chromosome separation during anaphase I.

Mendelian Laws

• Mendel's experiments showed one characteristic disappears in F1 plants, reappearing in F2.
• In F2, 75% of plants had one characteristic value, 25% had the other, creating a 3:1 ratio.
• Mendel's Principle of Segregation states that two factors control traits, separating into different gametes during reproduction.

Principles of Uniformity and Principle of Independent Assortment - "Second Law"

• Mendel's second experiment set uniformity and independent assortment establishment.
• Mendel's principles of uniformity were two-trait crosses, establishing that if plants are crossed and are different with one characteristic, future generations would all be the same.
• Heterozygotes share a common phenotype.
• Mendel's second principle is independent assortment, which are factors independently inherited.

Genetics of Inheritance

• Characteristics are controlled by genes on chromosomes
• The position of a gene on a chromosome is called its locus.
• Copies of the same gene, one from each parent are in each individual
• Versions of genes are called alleles
• Alleles account for variation in organisms' characteristics

Principles of Dominance - "Third Law"

• The expressed allele is called the dominant allele
• The unexpressed allele is called the recessive allele
• An uppercase letter typically represents dominant alleles
• Lowercase letters represent the recessive alleles
• The principle of dominance states each gamete carriers a single gene allele: Some alleles being dominant and some recessive

Mendelian Inheritance

• Mendel's laws can be used to develop a more useful plant variety
• One must know how to predict offspring genotype, phenotype and what probability is at play

Predicting Offspring Genotypes

• A PP genotype will show 25% offspring
• A pp genotype will show 25% offspring
• An Pp genotype will show 50% offspring

Predicting Offspring Phenotypes

• Phenotypes in offspring are determined by the offsprings' genotypes
• Offspring with the PP or Pp genotype will have a dominate phenotype
• Offspring with the pp genotype will have a recessive phenotype

The Probability Method

• Mendelian segregation is like a coin toss: When a heterozygote produces gametes, half carry one type of allele
• A particular dominant allele probability is 1/2, and a recessive allele probability is 1/2
• Aa x Aa is a example of a cross with two heterozygotes
• A zygote AA probability would simply be the probability each uniting gamete contains A: (1/2)*(1/2) = 1/4
• Aa heterozygotes: 1/2

The Rules of Probability

• Mutually exclusive events will equal the total of likelihoods of individual events
• One gene can be found as an allele designated de, which is a recessive allele that causes droopy ears; the normal allele is De
• Probability that mice (Dede Ctct), and that the offspring is 9 with normal ears and normal tails, 3 with normal ears and crinkly tails, 3 with droopy ears and normal tails, and 1 with droopy ears and a crinkly tail. Four mutually exclusive phenotypes.

Applying the Multiplicative Rule

• The multiplicative rule can determine the likelihood of two or more independent outcomes originating from a genetic cross.
• Independent events means the occurrence of one trait has zero effect on another
• An example is rare, recessive a human trait known as congenital analgesia. In which someone can't perceive sensation
• What's likelihood that a non-affect couple first three offspring would have congenital analgesia?
• To answer the "product rule" is a way to do it.

The Binomial Expansion Equation

• The binomial expansion can predict unordered combinations of traits
• To calculate the individual probabilities of an individual offspring one must consider the blue-eye and brown-eye phenotypes.
• Determine events in a single "blue" or "brown", category versus events total number

The Rules of Probability

Calculating the individual trait likelihood(each phenotype) can be used through a Punnett square

Pedigree Analysis

• Researchers study human inheritance by reviewing family trees in a pedigree analysis
• Pedigree Analysis is aimed at determining the type of inheritance pattern the gene will follow
• Pedigree Analyses give important clues concerning the pattern of inheritance of traits within human families
• Roman Numerals show generations
• In pedigrees, affected individuals are shown through blacked out symbols; unaffected, blanked Individuals I-1 and 1-2 are the grandparents of III-1, III-2, III-3, III-4, III-5, III-6, and III-7
• Individuals III-1, III-2, and III-3 are brother and sisters
• Individual III-4 is affected by a genetic disease
• Individuals are shown through the symbols 1-1, 1-2, II-4, and II-5, are presumed heterozygous and are not affected with the disease; produce homozygous off spring that are

Pedigree Analysis and Genetic Diseases

• If a genetic disease is caused by a recessive allele, with the recessive allele producing a disease, the individual has to inherit two copies to exhibit the disease
• Two "heterozygous normal" will produce 1/4 of the offspring to show the disease
• alternatively a dominant trait inherited traits will at least garner one parent from an affected family

Cystic Fibrosis (CF)

• A human genetic disease- Among Caucasians 3% are heterozygous carriers of this recessive allele
• In homozygotes, disease abnormalities that can take place in the pancreas, sweat glands, and lungs
• An imbalance can also affect the plasma membrane

Genetic Analysis

• Genetic (DNA or RNA interpretation to understanding structure, function, and variation through a gene)

Classical Genetics

• Pre-dates study and structure of DNA
• Examines inheritance through crosses of offspring and organisms
• Identifying gene variation in phenotype and mapping gene areas to specific chromosomes

Molecular genetics

• With the invention of DNA allowed scientist at a molecular-level to study genes
• This can sequence DNA to determine what define genes chemical composition + regulatory sequences

Population genetics

• Examines genetic variation through entire populations
• Can trace allele frequencies and changes overtime to study traits, evolution, disease, and medical characteristics

Modified Dihybrid Ratios Caused by Epistasis

• Dihybrid crosses can produce phenotypic ratio of modified versions like 9:3:4; 12:3:1, 9:7, or 15:1.

Epistasis

• "standing upon"
• Epistasis is what causes Mendel's law to not always appear when operating with masked genes -Refers to interactions genes, not alleles

Explore fundamental concepts in genetics, including the differences between alleles and genes, genotype and phenotype, and homozygous and heterozygous individuals. Understand Mendel's principles of inheritance, segregation, and phenotypic ratios in monohybrid crosses. Learn about the role of meiosis in genetic diversity.