G Chapter 4 - Chapter 4 Humans carry 23 pairs of...

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Chapter 4 Humans carry 23 pairs of chromosomes for a total of 46 Children with Down’s syndrome contain 47 chromosomes in each cell nucleus Chromosomes are cellular structures responsible for transmitting genetic information Two cycles of cell division: mitosis (for somatic or body cells) & meiosis (for gametes - eggs & sperm) When these cycles don’t work properly, it leads to errors in chromosome distribution, which leads to repercussions to an individual’s health and survival. Ex: Down’s Syndrome – failure of chromosome segregation during meiosis 4.1 Chromosomes: The Carriers of Genes Genes Reside in Chromosomes Chromosomes are long, threadlike bodies within the nucleus Mitosis results in two daughter cells containing the same number and type of chromosomes as the original parent cell Meiosis generates in egg or sperm cells containing half the number of chromosomes found in other cells within the same organism Chromosomes consist of two matching sets: one by the maternal gamete and the other by the parental gamete Haploid – gametes and other cells that carry a single set of chromosomes Diploid – zygotes and other cells carrying two matching sets n – the number of chromosomes in a normal haploid cell 2n – the number of chromosomes in a normal diploid cell In humans, 2n = 46; n = 23 Metaphase – chromosomes have duplicated and condensed Sister chromatids – two identical halves that each chromosome consists of Centromere – a specific location where the sister chromatids are attached Homologous chromosomes (or homologs) – chromosomes that match in size, shape and banding Homologous chromosomes carry the same genes but vary in the identity of particular alleles Nonhomologous chromosomes carry completely unrelated sets of genetic information Karyotype – micrographs of stained chromosomes in homologous pairs of decreasing size Sex chromosomes – determine the sex of an individual 4.2 Sex Chromosomes and Sex Determination A male contains one half a set of 11 autosomes plus an X chromosome, while the other half have a set of 11 autosomes plus a Y.
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