HMB265H1 Lecture Notes - Lecture 7: Walter Sutton, Homologous Chromosome, Allosome

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Lecture 7: Meiosis and the Chromosomal Theory of Inheritance
Analysis of Chromosomes
Walter Sutton Studied great lubber grasshopper
Body cells contained 22 chromosomes + X & Y chromosomes
Gametes contained 11 chromosomes and X or Y in equal numbers
o After fertilization
Females were XX
Males were XY
Homologous chromosomes are the same size and have similar banding
patterns, they also carry the same genes
Metaphase chromosomes are classified by the position of the centromere
o Centromere near the middle Metacentric
o Centromere near the end Acrocentric
Microscopy provided a means to follow movement of chromosomes
during cell division
o Mitosis: two daughter cells (somatic cells) contain same number
of chromosomes as parent cell
o Meiosis: daughter cells (sperm and egg) contained half the
number of chromosomes as the parents
Gamete contains ½ the number of chromosomes as the zygote
Haploid: cells that carry only a single chromosome set
Diploid: cells that carry two matching chromosome sets
n: the number of chromosomes in a haploid cell
2n: the number of chromosomes in a diploid cell
Meiosis produces haploid gametes
Somatic Cells: divide mitotically and make up cast majority of organism’s tissues
Germ Cells: specialized role in the production of gametes
o Arise during embryonic development in animals and floral development in plants
o Undergo meiosis to produce haploid gametes
o Gametes unite with gamete from opposite sex to produce diploid offspring
Karyotype
Karyotypes can be produced by cutting micrograph images of stained chromosomes and arranging them in
matched pairs
o The sex chromosomes and autosomes are arranged in homologous pairs of
decreasing size
Autosomes- pairs of non sex chromosomes arranged in homologous pairs
Sex chromosome
o Provides bassi for sex determination
o One sex has matching pair
o Other sex has non-matching sex chromosomes
o Variation in sex determination between species
Chromosome
Female
Male
Organism
XX-XY
XX
XY
Mammals, Drosophila
XX-XO
XX
XO
Some grasshoppers
ZZ_ZW
ZW
ZZ
Fish, Birds, Moths
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HMB265H1 Full Course Notes
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Document Summary

Lecture 7: meiosis and the chromosomal theory of inheritance. Chromosome theory correlates with mendel"s laws of inheritance. Each cell contains 2 copies of each chromosome. Chromosome complements appear unchanged during transmission from parent to offspring. Each cell contains 2 copies of each gene. Genes appear unchanged during transmission from parent to offspring. Alternative alleles segregate to different gametes to different gametes. Alternative alleles of unrelated genes assort pairs separate without regard to the assortment of other homologous chromosome pairs. At fertilization an egg"s set of chromosomes unite randomly with encountered sperm"s chromosomes. In all cells derived from a fertilized egg, chromosomes are of maternal origin, and other is paternal independently. Alleles obtained from one parent unite at random with those of another parent. In all cells derived from a fertilized gamete, of genes are maternal, and are paternal. X-linkage using drosophila: observed true-breeding sex ratios, observed sex:trait ratios.

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