GCD 3022 1st Edition Lecture 9Outline of Last Lecture I. Incomplete Penetrancea. Two explanationsII. Blood typesa. Example 1III. Types of dominancea. Loss-of-function recessive alleleb. Dominant negative c. Incomplete dominancei. Example 1: loss-of-function alleleii. Example 2: probabilityd. Overdominancee. ComplementationIV. Environmental EffectsV. PenetranceVI. Chromosomesa. Homologous Chromosomeb. Chromatids c. Sister ChromatidsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.d. Bivalentse. Karyotype VII. X-linked recessive inheritancea. Example 1b. Example 2c. Example 3Outline of Current Lecture I. Introductiona. Maternal effect and epigenetic inheritanceb. Extranuclear inheritanceII. Maternal Effecta. Definitionb. Explanationc. Example: water snailIII. Epigenetic Inheritancea. Definitionb. Explanation of Causesc. Dosage Compensationi. Definitiond. X-inactivationi. Barr body1. Tableii. Lyon hypothesisiii. MechanismCurrent LectureI. Introductiona. Maternal effect and epigenetic inheritancei. Involve genes only in the nucleusii. Genotype of offspring does not directly govern phenotype as predicted byMendelb. Extranuclear inheritancei. Involves genes in organelles other than the nucleusii. The main extracellular source of genetic inheritance is the mitochondriaII. Maternal Effecta. An inheritance pattern for nuclear genes in which the genotype of the mother directly determines the phenotype of her offspring (genotypes of father and offspring do not affect the phenotype of the offspring)b. Due to accumulation of gene products that the mother provides to her developing eggs (oogenesis). Maternal (nurse) cells concentrate the gene products in the egg, which has an overdominance-like effect on the offspringc. Example: in the water snail (Limnaeaperegra), the shell and organs can be oriented in two directions- right handed (dextral): dominant, and left-handed (sinistral): recessive. In this species, the genotype of the mother determines the phenotype of the offspring. i. For example: if the mother is Dd, the offspring are either sinistral or dextral depending on which allele was emphasized in egg developmentii. If the mother was DD then all of the offspring will be dextral, regardless ofthe father’s genotypeiii. If the mother was dd then all of the offspring will be sinistral, regardless of the father’s genotypeIII. Epigenetic Inheritancea. A pattern in which a modification occurs to a nuclear gene or chromosome that alters gene expression. Expression is not permanently changed over the course ofmany generations (because the DNA sequence does not change). b. Epigenetic changes are caused by DNA and chromosomal modifications during oogenesis, spermatogenesis, or early embryonic developmentc. Dosage compensationi. Used to compensate for differences in number of active sex chromosomes (XX in females and XY in males). Can occur using different mechanisms depending on the species but has been studied extensively in mammals. Can also be referred to as X inactivation.d. X-inactivationi. Barr body: inactive copy of the X chromosome, discovered by Mary Lyon in 19611. Normal Female: XX, 1 barr body2. Normal Male: XY, 0 barr bodies3. Turner syndrome (female): X0, 0 barr bodies4. Triple X syndrome (female): XXX, 2 barr bodies5. Klinefelter syndrome (male): XXY, 1 barr bodyii. Lyon Hypothesis: named after Mary Lyon, describes the mechanism of X-inactivationiii. Mechanism: during X chromosome inactivation, the DNA becomes highly compacted and cannot be expressed, this inactivation is passed on to all future somatic cells. An example of this pattern of inheritance is calico cats—some X chromosomes are inactivated randomly, producing a multi-colored coat
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