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Chapter 12.1. Human Chromosomes . AP Biology Fall 2010. Chapter12.1 Objectives. Differentiate between sex chromosomes and autosomes . Chromosomes. Genes : are units of information about heritable traits

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chapter 12 1

Chapter 12.1

Human Chromosomes

AP Biology

Fall 2010

chapter12 1 objectives
Chapter12.1 Objectives
  • Differentiate between sex chromosomes and autosomes
  • Genes: are units of information about heritable traits
  • Diploid organisms possess pairs of homologous chromosomes, which are alike in length, shape, and gene sequence
  • Alleles: are slightly different molecular forms of the same gene, which are shuffled during meiosis
  • A wild-type allele: is a gene’s most common form
    • A less common form of the gene is the mutant allele
  • Genes on the same chromosome are physically connected, but genes from one homolog may exchange places with those on the other homolog in crossing over, which produces genetic recombination
  • A chromosome’s structure may change during mitosis or meiosis, as can the parental chromosome number (quantity)
autosomes and sex chromosomes
Autosomes and Sex Chromosomes
  • Sex chromosomes determine gender
    • Human females have 2 X chromosomes
    • Human males have one X and one Y
    • 2 present in humans
  • Do you think all mammals

have similar sex chromosomes?

autosomes and sex chromosomes6
Autosomes and Sex Chromosomes
  • Most of the chromosomes are of the same quantity and type in both sexes and are called autosomes
    • 44 present in humans
  • Total human chromosome number is 46
sex determination in humans
Sex Determination in Humans
  • Each human egg with contain 22 autosomes, plus one X
  • Sperm will carry 22 autosomes, plus either one X or one Y
  • An X-bearing egg plus a X-bearing sperm produces female offspring
  • An X-bearing egg plus a Y-bearing sperm produces male offspring
sex determination in humans8
Sex Determination in Humans
  • The Y chromosome carries a male-determining (SRY) gene, which leads to the formation of the testes, which secrete testosterone
  • Absence of the male gene in females leads to the formation of ovaries
  • The X chromosome obviously codes for sexual traits, but it also carries many genes for nonsexual traits
    • Which genes do you think are sex linked?
  • What is the difference between sex chromosomes and autosomes?
  • What chromosomes code for the different sexes in humans?
  • Autosomes are pairs of chromosomes that are the same in males and females of a species. Sex chromosomes differ between males and females of a species.
  • In humans XX codes for females, and XY codes for males.