Genetics 3000 GEN 3000
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This 0 page Class Notes was uploaded by Jomary Arias on Wednesday February 3, 2016. The Class Notes belongs to GEN 3000 at Clemson University taught by Dr. Kate Tsai in Spring 2016. Since its upload, it has received 48 views. For similar materials see Genetics in Biomedical Sciences at Clemson University.
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Date Created: 02/03/16
GEN 3000 Genetics Dr Kate Tsai Chapter 5 Lecture Notes Topic Sex Determination Key Terms 0 formation of offspring that are genetically different from the parent Offspring must have 2 different types of gametes male and female 0 defined by the PHENOTYPE of an individual not their genotype genes are located on chromosomes and chromosomes are substrates for gene segregation 0 the sex that produces IDENTICAL gametes All gametes end up the same as far as the number of chromosomes 0 the sex that produces two DIFFERENT gametes All gametes end up With different number of chromosomes 0 have 1 set of chromosomes 0 have 2 sets of chromosomes 0 When chromosomes or chromatids pull apart and divide during Anaphase o When chromosomes fail to seperate 0 discovered that Male insects has a strange chromosomal X body in the nuclei 0 discovered that Female grasshopper cells had 1 more chromosome than males discovered that Female grasshoppers have 2 X chromosomes Also that the X chromosome in males was paired With a smaller Y chromosome These X and Y chromosomes separate into different sperm cells While egg cells all get a single X chromosome 2 Types of Organisms ONE house TWO house has BOTH female and male reproductive Individual has EITHER female or male structures reproductive structures Plants because they can selffertilize Mammalians GEN 3000 Genetics Dr Kate Tsai Chapter 5 Lecture Notes 1 Chromosomal Sex Determining System 2 Genetic Sex Determining System 3 Environmental Sex Determining System Chromosomal and Environmental Sex Determining systems trigger differences between sex males and females Genetic Sex Determining system over laps with the other mechanisms 1 Chromosomal Sex Determining System 0 some plants insects reptiles and mammals Female XX Homogametic Male XY Heterogametic 1mm is a more simple system At meiosis half of the sperm receive an X chromosome and the other half get no sex chromosome Female XX Homogametic Male X0 O place holder 0 1 In this system the Female produces 2 Different games so the offspring will receive half Z and the other half W Female ZW Heterogametic Male 22 Homogametic Ex Birds moths some fish 2 Genetic Sex Determining System No obvious difference in chromosomes because there is no sex chromosome Genes determine the sex of an individual Similar to chromosomal sexdetermining 3 Environmental Sex Determining System Environmental factors such as temperature determine the sex of the organism Alligator Warm temperature during embryonic development produces males while cool temperatures produce females studied 1237 ies the F1 generation produces all but 3 of the ies had red eyes The 3 ies were males with white eyes Why was this Nondisjunction and not a random mutation This phenotype occurred too frequently therefore it was hypothesized that the cause for the mutation is that the X chromosome fails to separate in Anaphase I of Meiosis GEN 3000 Genetics Dr Kate Tsai Chapter 5 Lecture Notes Nondisjunction I 2 copies of the X chromosome going to some eggs while other get none Can occur in any stage of Anaphase during meiosis or mitosis Flies With just a Y chromosome or XXX extra X chromosome is lethal In Drosophila ies Sex is not determined by the presence of absence of the Y chromosome instead sex is based on a ratio 0 X0 females receive only 1 X 0 XXXY XXXXY or XXYY Males chromosome so they have 45 instead have one or more Y chromosomes of the normal 46 chromosomes and multiple X chromosomes Do not undergo puberty 0 47 chromosomes 0 Low hairline extra folds of skin on 0 Males have small testes enlarged neck breast and reduced facial hair 0 normal female anatomy fertility and intelligence May have some cognitive impairment severity and phenotypic differences increase With increasing number of X chromosomes 1 X contains genetic information that is essential for BOTH sexes at least 1 X chromosome is required 2 Maledetermining gene is located on the Y chromosomes Klinefelter Syndrome 3 The absence of Y chromosome I defaults to female development 4 Genes required for fertility are on BOTH X and Y chromosomes Females need at least 2 X chromosomes to be fertile Turner Syndrome 5 Addition X chromosomes are detrimental sometimes lethal All humans have neutral undifferentiated gonads early in development Males have a which triggers teste development they then secrete testosterone expressing the male characteristics GEN 3000 Genetics Dr Kate Tsai Chapter 5 Lecture Notes In male With XX chromosomes they lack the Y chromosome and therefore do not have the SRY gene During meiosis homologous chromosomes line up at pseudoautosomal regions When crossing over takes place the SRY could accidentally be transferred to an X chromosome Women With Androgen insensitivity syndrome These women have a functional SRY gene triggers teste developments but they lack the receptors DOSAGE COMPENSATION since females have 2 copies of every Xlinked gene they should produce twice the amount of the gene produce as males inactive X chromosomes heterozygous females at the X loci Will express only 1 allele or the other in a given cell Females are mosaic for expression of a Xlinked gene
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