Bio 150, Week 4 notes
Bio 150, Week 4 notes Bio 150
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This 3 page Class Notes was uploaded by Morgan Bell on Tuesday October 11, 2016. The Class Notes belongs to Bio 150 at Converse College taught by Dr. Steele in Fall 2016. Since its upload, it has received 4 views. For similar materials see Biology of Sexuality in Biology at Converse College.
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Date Created: 10/11/16
Bio 150Week 4 9/199/23 Cellular Reproduction and Sex inheritance Mitosis vs. Meiosis Autosome vs. Sex Chromosome Homologous Autosomes (22 prs = 44) identical in length, size, shape, and gene sequence Sex chromosomes (1 pr= 2) XX XY nonidentical but still homologous Sex Determination The X Chromosome Carries more than 2,000 genes Most genes deal with nonsexual traits Genes on X chromosome can be expressed in both males and females The Y Chromosome Small, with few genes Master gene for male sex determination SRY gene (sexdetermining region of Y) SRY present, testes form SRY absent, ovaries form Sex Determination Primary Sex Determination Bipotential gonads ovary or testes? Chromosomal (not environmental) Y chromosome SRY gene TDF – testis determining factor XY, XXY, XXXY – males XX, XO – female Secondary Sex Determination Affects phenotype outside gonads Reproductive ducts, external genitalia Determined by hormones Other What causes changes in chromosome number? Most changes in chromosome number are due to nondisjunction (failure of chromosomes to separate) Aneuploidy Individuals have one extra or one less chromosome (2n + 1 or 2n 1) Major cause of human reproductive failure Most human miscarriages are aneuploids Down Syndrome Trisomy of chromosome 21 Mental impairment and a variety of additional defects Can be detected before birth Risk of Down syndrome increases dramatically when mothers are over age 35 Turner Syndrome Inheritance of only one X (XO) 98% spontaneously aborted Survivors are short, infertile females No functional ovaries Secondary sexual traits reduced May be treated with hormones, surgery Klinefelter Syndrome XXY condition Results mainly from nondisjunction in mother (67%) Phenotype is tall males Sterile or nearly so Feminized traits (sparse facial hair, somewhat enlarged breasts) Treated with testosterone injections
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