CYTOGEN-MIDTERMS-LESSON-1.pdf

1 | @Pgbamms CYTOGENETICS MIDTERMS LESSON 1 SINGLE-GENE INHERITANCE ☐Joined the Augustinian order at the St. Thomas Monastery in Brno (Brünn...

1 | @Pgbamms CYTOGENETICS MIDTERMS LESSON 1 SINGLE-GENE INHERITANCE ☐Joined the Augustinian order at the St. Thomas Monastery in Brno (Brünn) in 1843 and LEARNING OUTCOMES: was given the name Gregor. 1. List the characteristics that distinguish Between 1856 and 1863, Mendel conducted single-gene diseases from other types of extensive experiments with pea plants (Pisum diseases. sativum) 2. Describe how Mendel deduced that recessive He focused on seven easily observable traits, traits seem to be disappear in hybrids such as seed shape, flower color, and plant height 3. Define and distinguish heterozygous and homozygous; dominant and recessive; His groundbreaking experiments with pea phenotype and genotype plants that revolutionized our understanding of inheritance. 4. Explain how the law of segregation reflects the events of meiosis 5. Indicate how a punnet square is used to track inheritance patterns. 6. Explain how a gene alone may not solely determine a trait 7. Distinguish between autosomal recessive and autosomal dominant inheritance 8. Explain how Mendel's experiments followed the inheritance of more than one gene His meticulous crossbreeding experiments led to the formulation of two types of inheritance: 9. Explain how the law of independent assortment reflects the events of meiosis MONOHYBRID INHERITANCE- Transfer of only ONE trait 10. Explain how pedigrees are used to show transmission of single genes. DIHYBRID INHERITANCE- Transfer of TWO traits MENDEL'S EXPERIMENTS GREGOR MENDEL GENOTYPE: ☐ Born Johann Mendel on July 20, 1822, ✓ Genetic Makeup of an organism, combination of alleles ☐Raised on a farm, he showed an aptitude for ✓ Examples: PP, pp learning and was sent to secondary school in Troppau (Opava, Czech Republic) at age 11  2 PARENTAL PHENOTYPE: GENERATION ✓ Observable characteristics (P) Example: Violet and White Mendel crossed a true-breeding HOMOZYGOUS purple-flowered ✓ Two identical alleles are present for the plant with a true- specific trait breeding ✓ Example: Violet color (PP) white-flowered plant. HETEROZYGOUS ✓ Two different alleles for the specific trait are present ✓ Example: P for violet color and p for white color DOMINANT TRAIT ✓ Expressed when an individual inherit at least one copy of the dominant allele RECESSIVE TRAIT Expressed when an individual inherit two copies of the recessive allele MONOHYBRID INHERITANCE A zygote is formed after fertilization, A monohybrid cross involves studying and it is comprised of the union of two the inheritance of a single trait. gametes from each parent. one Crossing a homozygous tall pea plant When the two gametes that formed the (TT) with a homozygous short pea plant zygote carried different alleles for a (tt). gene, the resulting zygote is a hybrid In the F2 generation (offspring of the F1 containing two different alleles and is generation), the phenotypic ratio is said to be heterozygous. typically 3:1 These progeny then form gametes, and Monohybrid crosses illustrate Mendel's the alleles again segregate. Law of Segregation During the process of meiosis, homologous chromosomes that contain the genes that codes for any given trait basically separate from one another into their identical compartment, into their identical gametes, into their identical cells  3 Punnet Square A diagram the follows and combines parental gene contributions to offspring Mendel's law of Segregation states that gametes receive only one allele of each gene. Mendel's most important discovery was that the F₁ progeny from parental strains with different traits were not true-breeders. True-breeding organisms are those that always pass down their phenotypic traits to its offspring. Mendel found that the recessive trait FIRST FILIAL GENERATION(F1) reappeared in the F₂ generation. The recessive trait always consistently appeared at a dominant: recessive ratio close to 3:1. Homozygous recessive can be used in TEST CROSS. DIHYBRID INHERITANCE This unexpected result, where all F1 plants A dihybrid cross involves studying the displayed the purple flower trait despite one inheritance of two traits simultaneously. parent having white flowers The parents differ in two characteristics, like flower color and seed shape. SECOND FILIAL GENERATION (F2) Crossing a pea plant with round, yellow seeds (RRYY) with a pea plant with wrinkled, green seeds (rryy). The offspring will all be heterozygous (RrYy) and express the dominant traits (round and yellow seeds). In the F2 generation, the phenotypic ratio is typically 9:3:3:1, representing different combinations of the two traits. Dihybrid crosses illustrate Mendel's The white flower trait reappeared in the F2 Law of Independent Assortment generation, but only in approximately one- quarter of the plants. The remaining three-quarters of the F2 plants exhibited the purple flower trait.  4 Single-Gene Inheritance Also known as Mendelian inheritance, refers to traits that are determined by a single gene. Single gene inheritance may be more difficult to interpret than a pea plant having green or yellow peas because many phenotypes associated with single genes are influenced by other genes as well as by environmental factors Single gene controls transmission, but other genes and the environment affect the degree of the trait or severity of the It occurs during Metaphase I illness encapsulates a fundamental concept in genetics known as polygenic Random Alignment: The orientation of inheritance. each homologous pair is completely random. This means that the maternal POLYGENIC INHERITANCE: and paternal chromosomes can be Multiple genes arranged in any order along the ✓ Numerous genes can contribute to a trait metaphase plate. ✓These genes may interact by adding and New Combinations: As the subtracting from the overall expression of the homologous pairs separate during trait Anaphase I, each daughter cell receives ☐ Environmental factor a random mix of maternal and paternal ✓ Plays a crucial role in shaping how genes are chromosomes. This shuffling of expressed. chromosomes ensures that each gamete ✓Diet, lifestyle, toxin exposure can influence receives a unique combination of genes. the severity or manifestation of traits. Examples of Polygenic inheritance: Height ✓ Genes is responsible in determining the height of an individual ✓ Nutrition and overall health can also influence final height Cystic fibrosis ✓Single gene mutation causes CF ✓Severity of the disease can vary widely among individuals with the same mutation ✓Exposure to infection and access to healthcare can influence the progression of the disease.  5 MODE OF INHERITANCE Genetic Basis: The cause of single-gene The mode of inheritance describes how diseases is a mutation in a specific gene, leading a trait is passed from parents to to a change in the protein product of that gene. offspring. It depends whether the gene determines: ☐ Environmental Influence: Single-gene Autosome or Sex chromosome diseases are not typically influenced by (X-linked) environmental factors such as smoking or Dominant or Recessive exposure to toxins. Single-Gene Diseases? Characteristics of Single-Gene Disease? Single-Gene disease is defined as Prevalence: Single-gene diseases are generally diseases that occur due to the mutations less common than other types of diseases. in the single gene that ultimately form non-functional gene. Potential for Gene Therapy: Due to the It is also named as Mendelian relatively simple genetic basis of single-gene disorders, unifactorial or monogenetic diseases, they are considered good candidates disorders. for gene therapy. Thousands of diseases in human are result of single gene mutations. As they AUTOSOMAL DOMINANT are genetic disorders, it means they pass from parents to offspring. A dominant allele means that only one copy of the disease- causing gene is needed for the disorder to be expressed. Characteristics: Affected individuals usually have an affected parent. The disorder appears in every generation. Both males and females are equally affected. Examples: Huntington's disease, achondroplasia (dwarfism), neurofibromatosis. Huntington's disease ✓ The mutation responsible for HD occurs in Characteristics of Single-Gene Disease? the HTT gene, located on chromosome 4 ✓ Caused by a dominant mutation in the HTT Inheritance Pattern: Single-gene diseases are gene typically inherited, meaning they are present at birth. It is also named as Mendelian disorders, unifactorial or monogenetic disorders.  6 Two copies of the altered gene are required for an individual to express the trait. Characteristics: They each carry one copy of the recessive allele, but they don't express the trait themselves (Carriers). The trait can be hidden in a family for Marfan Syndrome: Caused by a mutation in the generations if carriers don't have children with FBN1 gene on chromosome 15. This gene other carriers. provides instructions for making a protein called both genders have an equal chance of fibrillin-1, which is essential for connective inheriting it. tissue. Mutations in FBN1 can lead to a variety Examples: Cystic fibrosis, sickle cell anemia, of symptoms, including tall stature, long limbs, Tay-Sachs disease, phenylketonuria (PKU). and heart problems Cystic fibrosis Achondroplasia: The most common form of ✓ needs two copies of the mutated CFTR gene dwarfism, caused by a mutation in the FGFR3 ✓ Carriers have one normal CFTR gene and gene on chromosome 4. This gene plays a role one mutated CFTR gene. in bone growth. Mutations in FGFR3 can lead to ✓ They don't have cystic fibrosis, but they can short stature, disproportionately short limbs, and pass the mutated gene to their children. other skeletal abnormalities. Neurofibromatosis Type 1 (NF1): Caused by a mutation in the NF1 gene on chromosome 17 This gene produces a protein that helps regulate cell growth. Mutations in NF1 can lead to the development of tumors on nerve tissue, which can cause a variety of symptoms, including skin lesions, bone deformities, and learning disabilities. Sickle Cell Disease: Caused by a Familial Hypercholesterolemia: Caused by a mutation in the HBB gene on mutation on chromosome 19. This gene provides chromosome 11. This gene produces a instructions for making a protein called the protein called beta-globin, which is part low-density lipoprotein (LDL) receptor, which of hemoglobin, the protein that carries helps remove cholesterol from the bloodstream. oxygen in red blood cells. Mutations in Mutations in LDLR can lead to high levels of HBB can lead to sickle-shaped red LDL cholesterol, increasing the risk of heart blood cells, which can block blood flow disease. and cause pain, damage to organs, and other complications. AUTOSOMAL RECESSIVE  7 Tay-Sachs Disease: Caused by a Observing the Expression of the Trait mutation in the HEXA gene on chromosome 15. This gene produces an enzyme called hexosaminidase A, which helps break down a fatty substance called GM2 ganglioside in the brain. Mutations in HEXA cari lead to a buildup of GM2 ganglioside, which can damage nerve cells and cause severe neurological problems. Punnett Squares They help determine the probability of a Phenylketonuria (PKU): Caused by a child inheriting a particular allele. mutation in the PAH gene on chromosome 12. This gene produces an enzyme called phenylalanine hydroxylase, which helps break down the amino acid phenylalanine. Mutations in PAH can lead to a buildup of phenylalanine in the body, which can damage the brain and nervous system. ☐ Physical Examination and Phenotype Observing the trait: Sometimes, a trait Albinism: A group of genetic disorders is directly observable, like eye color, characterized by a deficiency or absence hair color, or certain physical features. of melanin, the pigment that gives color Dominant traits: Dominant traits are to skin, hair, and eyes. Several genes can often expressed even if only one copy of be involved, including TYR, OCA2, the dominant allele is present. and SLC45A2. Recessive traits: Recessive traits only show up if an individual inherits two copies of the recessive allele. Genetic Testing DNA analysis: Genetic testing directly examines a person's DNA to identify specific genes and alleles. This can provide definitive information about whether a person has a dominant or ☐ Scientists and doctors use a combination of recessive allele for a particular trait or methods to figure out if a person has a dominant disease. or recessive allele for a particular trait or Direct Gene Sequencing, SNP disease. Analysis (Single Nucleotide Family History (Pedigree Analysis) Polymorphisms), Microsatellite Physical Examination and Phenotype Analysis Genetic Testing Punnett Squares  8 Family History (Pedigree Analysis) Tracing the pattern: Doctors and geneticists carefully study a family's medical history, creating a family tree called a pedigree. This shows how a trait or disease has been passed down through generations. Autosomal recessive inheritance Importance of Pedigree Analysis They provide a powerful tool for understanding how these traits are passed down through generations, helping to determine the mode of inheritance and identify individuals at Trait often skips generations. risk. An almost equal number of affected males and By analyzing the pedigree, geneticists females. can predict the likelihood of a trait If both parents are affected, all children should appearing in future generations. be affected. In most cases of unaffected people mating with affected individuals, all children produced are unaffected. When at least one child is affected (indicating that the unaffected parent is heterozygous), then  9 approximately half the children should be affected. Most affected individuals have unaffected parents Autosomal dominant inheritance Trait should not skip generations. An affected person mating with an unaffected person should produce approximately 50% affected offspring (indicating also that the affected individual is heterozygous). The distribution of the trait among sexes should be almost equal. Transmitted by either sex.