Genetic Definitions: Genotype, Phenotype and Alleles

Key Genetic Definitions

• Genotype refers to an organism's genetic constitution, including all alleles present in its DNA
• Internal genetic makeup determines inherited traits
• Genotypes can be homozygous (two identical alleles) or heterozygous (two different alleles)
• Phenotype refers to observable traits resulting from genotype-environment interaction
• Phenotypic traits include hair color and susceptibility to diseases
• Environmental factors like nutrition and climate can influence phenotype
• Alleles are alternative forms of a gene at the same locus on a chromosome
• Alleles can be dominant or recessive
• Eye color alleles can be brown (dominant) or blue (recessive)
• Alleles are inherited from both parents
• Homozygous organisms possess two identical alleles (AA or aa) at a gene's locus
• Homozygous individuals always pass on the same allele to offspring
• Heterozygous organisms possess two different alleles (Aa) at a gene's locus
• In heterozygous individuals, the dominant allele typically determines the phenotype
• A dominant allele expresses its phenotype with only one copy present (Aa)
• Dominant alleles, such as "A", mask the effect of recessive alleles like "a" and are represented by capital letters
• Recessive alleles only express their phenotype with two copies present (aa)
• Individuals with dominant alleles (Aa or AA) mask recessive allele effects
• Recessive alleles are represented by lowercase letters
• Codominance occurs when both alleles are fully expressed in a heterozygous individual
• Neither allele is dominant or recessive in codominance
• Blood type AB is a codominance example, where both A and B alleles are equally expressed, yielding both A and B antigens
• Incomplete dominance occurs when neither allele is fully dominant, blending traits
• Crossing red (RR) and white (WW) flowers results in pink (RW) flowers as an example of incomplete dominance
• Epistasis involves one gene masking or modifying another's expression
• In coat color, one gene determines pigment production, overriding the color gene
• Polygenic inheritance is when multiple genes contribute to a trait's phenotype
• Polygenic traits include human height and skin color, showing continuous variation
• A Punnett square predicts genetic outcomes by showing allele combinations in offspring, based on parental genotypes
• Punnett squares visualize trait inheritance probabilities

Mendel's Laws

• Law of Segregation states that allele pairs separate during gamete formation, with each gamete carrying one allele per gene
• Genetic diversity is ensured, with each parent donating one allele
• The Law of Independent Assortment states that alleles for different traits are inherited independently during gamete formation
• The inheritance of one trait does not affect another if genes are on different chromosomes

Cell Division: Meiosis & Mitosis

• Meiosis is a cell division producing four non-identical daughter cells with half the chromosomes of the parent cell
• Meiosis is necessary for sexual reproduction and includes meiosis I and meiosis II
• Mitosis is a cell division producing two genetically identical daughter cells with the same chromosome number as the parent cell
• Mitosis is used for growth, repair, and asexual reproduction, producing two diploid cells
• Crossing over occurs during meiosis I where homologous chromosomes exchange chromatid segments
• This process creates new allele combinations and increases genetic variation, occurring in prophase I
• Independent assortment is the random distribution of different chromosomes into gametes during meiosis
• Independent assortment contributes to genetic variation in offspring

Genes & Inheritance

• X-linked inheritance refers to traits determined by genes on the X chromosome
• Males are more likely to express X-linked traits because they are XY, whereas females are XX
• Autosomal dominant inheritance involves traits or disorders expressed with one copy of a dominant allele, such as Huntington’s disease
• Autosomal recessive inheritance involves traits/disorders that are expressed with two copies of a recessive allele, such as cystic fibrosis
• A carrier has one recessive allele for a genetic condition but does not show symptoms and can pass the allele to offspring
• The Probability Product Rule (Multiplication Rule) says that the probability of two independent events both occurring is the product of their individual probabilities
• The Probability Sum Rule (Addition Rule) says that the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities
• A pedigree traces the inheritance of specific traits or disorders across family generations
• Pedigrees determine if a trait is dominant or recessive and identify carrier individuals

Chromosomes

• A karyotype is an organized profile of an individuals chromosomes that identifies chromosomal abnormalities
• Human karyotypes consist of 46 chromosomes, with 22 pairs of autosomes and two sex chromosomes (XX or XY)
• Mutations are changes in the DNA sequence of a gene or chromosome and can be spontaneous or caused by environmental factors
• Some mutations lead to genetic disorders, while others are neutral or beneficial
• Epigenetics is the study of gene expression changes without DNA sequence alterations
• Epigenetic changes are influenced by environmental factors, affecting gene activation and can be inherited
• Blood type inheritance is governed by the ABO system (A, B, O alleles) and the Rh factor with A and B and Rh+ being dominant
• Gametes are reproductive cells (sperm or egg) carrying half of the genetic information for fertilization
• During fertilization, gametes fuse to form a zygote with a full set of chromosomes
• A zygote is a fertilized egg containing a complete set of chromosomes, half from each parent, that develops into an embryo
• Chromosomes are thread-like structures of DNA and proteins containing genetic instructions, with humans having 23 pairs (46 total)
• Sex-linked traits are determined by genes on sex chromosomes, especially the X chromosome
• Males are more likely to express X-linked traits like color blindness with only one X chromosome
• Heredity is the transmission of genetic information from one generation to the next, facilitated via genes

Genetics

• Genetics is the study of genes, heredity, and genetic variation in living organisms, examining trait inheritance and genetic information encoding
• Mutatations, inheritance patterns, and genetic disorders are all studied in genetics
• Genetics is not the study of purely phenotypic traits or environmental factors alone, not ecology, physiology, or behaviorism
• A gene is a DNA segment carrying instructions for a specific protein or RNA molecule
• Genes are basic heredity units determining traits like eye color and susceptibility to diseases with nucleotide sequences encoding information
• A genome is the entire set of genetic material in an organism, including all genes, non-coding sequences, regulatory elements, and other genetic components
• Bioethics studies ethical issues from advances in biology and medicine related to genetics, biotechnology, cloning, and gene editing

Genetics In Practice

• Evoluation depends on genetics as it is through genetic variation that species evolve over time, from genetic changes like mutations, recombination, and natural selection
• Mutations lead to new traits and can provide advantages, mutations increasing organism fitness are more likely to be passed on
• Natural selection leads to genetic variations accumulating or can genetic drift and gene flow influence genetic diversity during evolutionary changes
• Genetic drift and gene flow can also influence genetic diversity.
• Practical uses of DNA information in medicine includes genetic testing to diagnose genetic disorders, determine disease risk, and personalize treatment
• DNA profiling in forensic science is used to identify individuals in criminal investigations or for paternity tests
• Genetically Modified Organisms(GMOs) are developed to improve crop yields, pest resistance, and nutritional content
• DNA analysis can be used to trace ancestral origins and trace genetic relationships with ancestry testing
• Pharmacogenomics is the study of how genetic variation affects an individuals response to drugs, leading to personalized medicine
• DNA info combined with environmental factors, clinical data, and epigenetic information helps maintain health and treat diseases
• Studying other species' genomes teaches of evolution and ecology- helps conservation, agriculture, and veterinary medicine
• Genomics can extend to plants and microorganisms, improving ecosystems and making crops more resilient
• Genomic data helps trace evolutionary history identifying biomarkers and preventing disease with lifestyle change medication or genetic screening
• Personalized medicine targets an individuals make up reducing side effects genetic and cellular

The Cell cycle

• Somatic cells, not involved in reproduction, have a full set of chromosomes and are diploid
• Somatic cells are skin cells, muscle cells, and nerve cells
• Germ cells (sperm and eggs) are involved in sexual reproduction and are haploid
• When germ cells fuse, they form a diploid zygote
• Diploid cells have two chromosome sets (46 chromosomes) and haploid cells just have one (23 chromosomes)
• Cell differentiation is when less specialized cells become more specialized with structure and function
• Cell fate is controlled with gene expression, environmental signals stem cells- unspecialized, can differentiate
• The cell cycle is the series of stages that a cell goes through to grow and divide with two sections: Interphase and Mitosis.
• Interphase, before division, has subphases G1, S, and G2, where the cell grows, replicates its DNA, and prepares for mitosis
• Mitosis involves prophase, metaphase, anaphase and telophase

Events and control of the cell cycle

• During mitosis, cells condense sister chromatids and attach centromeres to spindle fibers
• Cell chromosomes go to the equator with sister chromatids pulled to opposite poles
• New membranes reform, and cells uncoil
• Tight regulation ensures timely cell division during the cell cycle where Cylins and Cyclin Dependent kinases(CDKs)
• Checkpoints in the cell assess correctness and Tumor supressors act as brakes stopping the cell from moving
• Genetic diversity and meiosis is due to crossing over and independent assortment

Meoisis I and II

• In meiosis I, crossing over in prophase I, pairs homologues and splits
• In meiosis II sister chromatids are separated and replicated, yielding four haploid gametes

Production of sex cells

• Spermatogenesis occurs in the testes and happens when Stem cells undergo mitosis to produce primary spermatocytes
• Primary spermatocytes undergo meiosis I and meiosis2 to form secondary spermatocytes, then spermatids before forming into spermatozoa
• Oogonia undergoes mitosis but enter miosis i until completed

Understanding Scientific Research

• Scientific literature help with advancing knowledge, evidence-based decisions, innovation, and ciritcal thinking to help with design experimental understanding
• Heterozygote are organisms which different alleles for a particular gene and homozygotes do not.
• Dominant Alleles and Dominant Alles express when a pheno types shows in a heterozygote, else its recessive.
• Interactions between the Pheno Types and environments interact to form genotypes.
• Each individual has two alleles with the laws of segregation.
• Heterozygotes are only dominant if they have one affected parent with an affected trait.

Traits

• If recessive, two carriers are needed to express a trait.
• Mendel's laws is when chromosomes are inherited dependently of one another as long as its on a different chromosome
• Pedigrees show dominants traits from every generation and recessive skipping the generations.
• The dominant alelle masks the effect of a recesive one
• Mitochondrial DNA is solely inherited from the mother, and nuclear is both parents.
• Genese located close to eachother mean they are less likely to be separated.