GCD 3022 1st Edition Lecture 9 Outline of Last Lecture I Incomplete Penetrance a Two explanations II Blood types a Example 1 III Types of dominance a Loss of function recessive allele b Dominant negative c Incomplete dominance i Example 1 loss of function allele ii Example 2 probability d Overdominance e Complementation IV Environmental Effects V Penetrance VI Chromosomes a Homologous Chromosome b Chromatids c Sister Chromatids These 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 Bivalents e Karyotype VII X linked recessive inheritance a Example 1 b Example 2 c Example 3 Outline of Current Lecture I Introduction a Maternal effect and epigenetic inheritance b Extranuclear inheritance II Maternal Effect a Definition b Explanation c Example water snail III Epigenetic Inheritance a Definition b Explanation of Causes c Dosage Compensation i Definition d X inactivation i Barr body 1 Table ii Lyon hypothesis iii Mechanism Current Lecture I Introduction a Maternal effect and epigenetic inheritance i Involve genes only in the nucleus ii Genotype of offspring does not directly govern phenotype as predicted by Mendel b Extranuclear inheritance i Involves genes in organelles other than the nucleus ii The main extracellular source of genetic inheritance is the mitochondria II Maternal Effect a 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 offspring c 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 development ii If the mother was DD then all of the offspring will be dextral regardless of the father s genotype iii If the mother was dd then all of the offspring will be sinistral regardless of the father s genotype III Epigenetic Inheritance a 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 of many generations because the DNA sequence does not change b Epigenetic changes are caused by DNA and chromosomal modifications during oogenesis spermatogenesis or early embryonic development c Dosage compensation i 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 inactivation i Barr body inactive copy of the X chromosome discovered by Mary Lyon in 1961 1 Normal Female XX 1 barr body 2 Normal Male XY 0 barr bodies 3 Turner syndrome female X0 0 barr bodies 4 Triple X syndrome female XXX 2 barr bodies 5 Klinefelter syndrome male XXY 1 barr body ii Lyon Hypothesis named after Mary Lyon describes the mechanism of Xinactivation iii 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 multicolored coat pattern
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