NON-MENDELIAN GENETICS (1).pdf

NON-  MENDELIAN GENETICS LET’S  RECALL! ▪ GREGOR MENDEL ▪ Father of Genetics ▪ Mendelian Laws   MENDELIAN GENETICS ▪ Law of Segregation: Each organism has two alleles for each trait (one from each parent). When they reproduce, these allel...

NON-  MENDELIAN GENETICS LET’S  RECALL! ▪ GREGOR MENDEL ▪ Father of Genetics ▪ Mendelian Laws   MENDELIAN GENETICS ▪ Law of Segregation: Each organism has two alleles for each trait (one from each parent). When they reproduce, these alleles separate so that each parent passes only one allele to their offspring.   MENDELIAN GENETICS ▪ Law of Segregation: Each organism has two alleles for each trait (one from each parent). When they reproduce, these alleles separate so that each parent passes only one allele to their offspring.   MENDELIAN GENETICS ▪ Law of Segregation: Each organism has two alleles for each trait (one from each parent). When they reproduce, these alleles separate so that each parent passes only one allele to their offspring.   NON-MENDELIAN GENETICS ▪ Non-Mendelian inheritance is any pattern of inheritance wherein traits do not segregate following Mendel’s law. ▪ These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus.  INCOMPLETE DOMINANCE  ▪ Both alleles are present resulting in an intermediate phenotype.   EXAMPLE OF INCOMPLETE DOMINANCE ▪ When red snapdragons are crossed with white ones, the F1 hybrids have pink flowers. ▪ Segregation of alleles into gametes of the F1 plants results in an F2 generation with a 1:2:1 ratio for both genotype and phenotype. ▪ Neither allele is dominant, so rather than using upper- and lowercase letters, we use the letter C with a superscript to indicate an allele for flower color: CR for red and CW for white  The phenotype of the heterozygous genotype is a blend of the two homozygous phenotypes   The phenotype of the heterozygous genotype is a blend of the two homozygous phenotypes   CODOMINANCE  ▪ Codominance occurs when both alleles are expressed equally in the phenotype of the heterozygote.   EXAMPLE OF CODOMINANCE ▪ Example 1: A speckled chicken ▪ A cross between a black and white chicken will produce chicken with both black and white feathers. The alleles for black feathers in some varieties of chicken are codominant with the allele for white feathers.  EXAMPLE OF CODOMINANCE Another example that shows how the co-dominance pattern of inheritance is determined by genes is in the blood typing in humans. An antigen is a protein- bound to a sugar molecule found on the surface of our red blood cells. A pair of alleles (IA and IB) which controls one group of antigens, help in determining the blood types of an individual.  EXAMPLE  OF CODOMINANCE In the heterozygote condition, both IA and IB alleles are expressed in the red blood cells that will have the antigens A and B. Three alleles exist in the ABO system: A, B, and O. This result in four blood types: A, B, O, and the blended AB.      MULTIPLE  ALLELES ▪ A single gene that has more than two alleles is called multiple alleles.  EXAMPLE  OF MULTIPLE ALLELE ▪ The ABO blood groups in humans as an example of a gene that has multiple alleles is the one that controls the inheritance. There are four blood group systems A, B, AB, and O. The IA and IB are dominant over the i allele which is always recessive. However, both alleles are expressed equally when the two alleles are inherited together.  EXAMPLE  OF MULTIPLE ALLELES ▪ We know that there are three different alleles for ABO blood types, however, only two are present in an individual at a time. ▪ The IA and IB are dominant over the i allele which is always recessive. However, both alleles are expressed equally when the two alleles are inherited together. POLYGENIC  INHERITANCE ▪ An additive effect of two or more genes on a single phenotypic character   POLYGENIC INHERITANCE ▪ In this model, three separately inherited genes affect skin color. (The reported number is actually 378 genes.) ▪ The heterozygous individuals (AaBbCc) represented by the two rectangles at the top of this figure each carry three dark-skin alleles (black circles, which represent A, B, or C) and three light skin alleles (white circles, which represent a, b, or c). ▪ The Punnett square shows all possible genetic combinations in gametes and offspring of hypothetical matings between these two. The results are summarized by phenotypic frequencies (fractions) under the Punnett square. (The phenotypic ratio is 1:6:15:20:15:6:1.) SEX CHROMOSOME  AND SEX DETERMINATION ▪ In each cell, humans have 46 chromosomes or 23 pairs of chromosomes for both males and females. Twenty-two pairs are somatic chromosomes (any chromosome that is not a sex chromosome) The 23rd pair consists of sex chromosomes. ▪ Somatic contains our genetic information or all the traits that we inherit from our parents the 23rd contains the gametes that determine our gender. ▪ Male Chromosomes – XY non-identical sex chromosomes ▪ Female Chromosome XX identical sex chromosomes SEX CHROMOSOME  AND SEX DETERMINATION ▪ A male offspring will be produced when an egg fertilized by a sperm passing on a Y chromosome. ▪ A female offspring will be a result of a fertilized egg through a sperm carrying an X chromosome. Therefore, there is a fifty-percent probability of having a male and female 50% chance of female child 50% chance of male child offspring. 3 KINDS  OF SEX-RELATED INHERITANCE 1. Sex-Linked Traits – these are inherited through the X chromosomes 2. Sex-Influence Traits – occur when phenotypes are different between males and females with the same genotype 3. Sex-Limited Traits – traits that can only be expressed in one sex or the other. 3 KINDS OF SEX-RELATED INHERITANCE  1. SEX-LINKED TRAITS ▪ Sex-linked genes are genes found either on X or Y chromosomes which are inherited differences among male and a female. Sex-linked traits determined by an X-linked gene when an X chromosome takes control. On the other hand, the so called Y-linked genes are those located on the Y chromosome. ▪ Genetically determined by alleles located on sex chromosomes.   HEMOPHILIA ▪ Hemophilia, an example of an X-linked trait is a rare genetic disorder in which a person lacks enough blood- clotting proteins caused by a change in one of the genes.   HEMOPHILIA ▪ Since this phenomenon is sited on the X chromosome, females identified to have affected two X chromosomes cause the disorder. But if there is only one chromosome affected, the female individual is referred to as “carrier” of the disorder.   A Punnett square showing the probability of the offspring carrying the X-linked recessive trait for hemophilia. XY genotypes are affected by hemophilia, whereas XX genotypes are carriers of the trait.   HEMOPHILIA   HEMOPHILIA   HEMOPHILIA   HEMOPHILIA   HEMOPHILIA   HEMOPHILIA   HEMOPHILIA   HEMOPHILIA   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   COLORBLINDNESS Another example. These traits will be manifested in females who have two genes of color-blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   Hypertrichosis pinnae auris These traits will be manifested in females who have two genes of color- blindness. Meanwhile, in males, there is only one gene of the disorder needed to express the phenomenon.   2. SEX-INFLUENCED TRAITS ▪ Are autosomal traits that are influenced by sex hormones ▪ It is a recessive trait   BALDNESS ▪ Influenced by the hormone testosterone   2. SEX-INFLUENCED TRAITS ▪ The gene has two alleles, “bald” (b) and “non-bald” (B), and these genes are highly influenced by the hormones individually. We know that all humans have testosterone, but males have higher levels of testosterone than females do.   BALDNESS ▪ Influenced by the hormone testosterone   BALDNESS ▪ Influenced by the hormone testosterone   BALDNESS ▪ Influenced by the hormone testosterone   BALDNESS ▪ Influenced by the hormone testosterone   BALDNESS ▪ Influenced by the hormone testosterone   BALDNESS ▪ Influenced by the hormone testosterone   2. SEX-LIMITED TRAITS ▪ Sex-limited traits are those traits limited to only one sex. Lactation is a good example of a sex-limited trait that is exclusively exhibited among females. ▪ Lactating gene (L) is a dominant gene over the non-lactating recessive gene (l). In female cattle carrying one dominant gene (XXLl), or two dominant genes (XXLL) lactation will be shown. Nevertheless, neither male cattle having dominant genes nor in male cattle that have recessive genes will lactate.  2. SEX-LIMITED TRAITS Mutation & Genetic Disorders   Mutations A mutation may be defined as a permanent change in the DNA. Mutations that affect the germ cells are transputted to the progeny and may give rise to inherited diseases. Mutations thar aries in somatic cells are important in the genesis of cancers and some congeital malformations. Mutations  may be classified into three catagories: Genome mutations – involve loss or gain of whole chromosomes (giving rise to monosomy or trisomy) Chromosome mutations – result from rearrangement of genetic material and give rise to visible structural changes in the chromosome. Gene mutations – may result in partial or complete deletion of a gene or, more often, affect a single base. For example, a single nucleotide base may be substituted by a different base, resulting in a point mutation. Autosomal dominant disorders is one of many ways that a trait or disorder can be passed down through families. In an autosomal dominant disease, if you get the abnormal gene from only one parent, you can get the disease. (neurofibromatosis, tuberous sclerosis, polycystic kidney disease, familiar polyposis coli, hereditary spherocytosis, Marfan syndrome, osteogenesis imperfecta, achondroplasia, familiar hypercholesterolemia) Autosomal recessive disorders you inherit two mutated genes, one from each parent. These disorders are usually passed on by two carriers. Their health is rarely affected, but they have one mutated gene (recessive gene) and one normal gene (dominant gene) for the condition. (cystic fibrosis, phenylketonuria, homocystinuria, hemochromatosis, sickle cell anemia, thalassemias, alkaptonuria, neurogenic muscular atrophies) X-linked disorders traits located in X chromosome. (glucose-6- phosphate dehydrogenase deficiency)   Genetic Testing - Amniocentesis and Chronic Villi Sampling, Sample of amniotic fluid or placenta Karyotyping - Taking a picture of the chromosomes in a cell   What Can Go Wrong? Nondisjunction (most deadly) - Improper separation of homologous chromosomes in meiosis I or chromatids in meiosis II or mitosis (at an early embryonic stage) Results in too many or too few chromosomes in daughter cells 🠶 D N A mutations - M o r e specific letter changes in code - Results in the inability to make certain proteins   Nondisjunction Causes: Aneuploidy: cells that have too many or too few chromosomes are aneuploid. Monosomy: only 1 of a pair present Trisomy: 3 instead of 2 present  Disorders  associated with defects in structural proteins Marfan syndrome A disorder of the connective tissues of the body, manifested principally by changes in the skeleton, eyes, and cardiovascular system. Ehlers-Danlos syndromes A clinically and genetically heterogeneous group of disorders that result from some defect in collagen synthesis or structure (other disorders resulting from mutations affecting collagen synthesis include osteogenesis imperfecta, Alport syndrome, epidermolysis bullosa) Disorders  associated with defects in receptor proteins Familiar hypercholesterolemia A disease that is the consequence of a mutation in the gene encoding the receptor for low-density lipoprotein (LDL), which is involved in the transport and metabolism cholesterol..  Disorders with multifactorial inheritance DOWNSYNDROME – caused by Trisomy 21 Symptoms: Mental retardation Flattened face Sparse, straight hair Short stature Average life expectancy: 55 years (much longer than it used to be even just recently) EDWARD SYNDROME – caused by Trisomy 18 Symptoms: Mental and physical retardation Skull and facial abnormalities Defects in all organ systems Poor muscle tone Average life expectancy: 2-4 months   KLINEFELTER SYNDROME (XXY) – 2 or more chromosomes and 1 more Y chromosome genetic condition that results when a boy is born with an extra copy of the X chromosome. JACOB’S SYNDROME – also known as XYY syndrome. an aneuploid genetic condition in which a male has an extra Y chromosome.   TURNER SYNDROME – a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing.. PATAU SYNDROME Caused by Trisomy 13 a serious, rare genetic disorder caused by having an additional copy of chromosome 13 in some or all of the body's cells.   CRI-DU-CHAT SYNDROME – Deletion on part of chromosome 5 Infants with this condition often have a high-pitched cry that sounds like that of a cat. Autosomal Recessive Disorders  Cystic Fibrosis (CF) Mutation on chromosome Thick mucous develops in the lungs and digestive tract Tay Sachs Disease Fatty substance builds up in neurons Gradual paralysis and loss of nervous function by age 4-5 Single defective enzyme Heterozygote carriers (Hh) do not have the disorder, but are resistant to Tuberculosis Autosomal Recessive Disorders  PKU (Phenylketonuria a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body. Phenylalanine builds up and interferes with the nervous system leading to mental retardation and even death Sickle-Cell Anemia Abnormality in hemoglobin (carries oxygen in our red blood cells) Cells become sickle-shaped and clog blood vessels (painful) Autosomal Dominant Disorders  Neurofibromatosis (NF) Could be “Elephant Man’s” disorder Mutation on chromosome 17 Huntington’s Disease an inherited condition that affects cells in your brain. causing involuntary muscle jerks, slurred speach, loss of balance, mood swings, memory loss, incapacitation X-Linked or Sex-Linked Traits  Colorblindness (3 types – Red/Green most common) Hemophilia Lack a blood clotting factor Can bleed to death from wounds or bruises (internal bleeding)