Ch15WordLectureOutline - CHAPTER 15 THE CHROMOSOMAL BASIS...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
CHAPTER 15 THE CHROMOSOMAL BASIS OF INHERITANCE Introduction It was not until 1900 that biology finally caught up with Gregor Mendel. Independently, Karl Correns, Erich von Tschermak, and Hugo de Vries all found that Mendel had explained the same results 35 years before. Still, resistance remained about Mendel’s laws of segregation and independent assortment until evidence had mounted that they had a physical basis in the behavior of chromosomes. Mendel’s hereditary factors are the genes located on chromosomes. A. Relating Mendelism to Chromosomes 1. Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles Around 1900, cytologists and geneticists began to see parallels between the behavior of chromosomes and the behavior of Mendel’s factors. Chromosomes and genes are both present in pairs in diploid cells. Homologous chromosomes separate and alleles segregate during meiosis. Fertilization restores the paired condition for both chromosomes and genes. Around 1902, Walter Sutton, Theodor Boveri, and others noted these parallels and a chromosome theory of inheritance began to take form. 2. Morgan traced a gene to a specific chromosome Thomas Hunt Morgan was the first to associate a specific gene with a
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Like Mendel, Morgan made an insightful choice as an experimental animal, Drosophila melanogaster , a fruit fly species that eats fungi on fruit. Fruit flies are prolific breeders and have a generation time of two weeks. Fruit flies have three pairs of autosomes and a pair of sex chromosomes (XX in females, XY in males). Morgan spent a year looking for variant individuals among the flies he was breeding. He discovered a single male fly with white eyes instead of the usual red. The normal character phenotype is the wild type . Alternative traits are mutant phenotypes . When Morgan crossed his white-eyed male with a red-eyed female, all the F 1 offspring had red eyes, The red allele appeared dominant to the white allele. Crosses between the F 1 offspring produced the classic 3:1 phenotypic ratio in the F 2 offspring. Surprisingly, the white-eyed trait appeared only in males. All the females and half the males had red eyes. Morgan concluded that a fly’s eye color was linked to its sex. Morgan deduced that the gene with the white-eyed mutation is on the X chromosome alone, a sex-linked gene . Females (XX) may have two red-eyed alleles and have red eyes or may be heterozygous and have red eyes. Males (XY) have only a single allele and will be red eyed if they have a red-eyed allele or white-eyed if they have a white-eyed allele. 3. Linked genes tend to be inherited together
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 08/28/2010 for the course SCIENCE 101 taught by Professor Wong during the Spring '10 term at Rutgers.

Page1 / 17

Ch15WordLectureOutline - CHAPTER 15 THE CHROMOSOMAL BASIS...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online