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Lecture 21

BIOL 1020 Lecture 21: Lecture 21

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Biological Sciences
BIOL 1020
Joy Stacey

Lecture 21 Sets of Chromosomes in Human Cells Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes (46) A karyotype is an ordered display of the pairs of chromosomes from a cell (sex determined) The two chromosomes in each pair are called homologous chromosomes, or homologues Chromosomes in a homologous pair are the same length and carry genes controlling the same inherited characteristics. (different because one from each parent) 22 pairs and a pair of sex chromosomes in human karyotype The sex chromosomes are called X and Y Human females have a homologous pair of X chromosomes (XX) Human males have one X and one Y chromosome (not homologousX and Y carry different genes single copy of each gene on each chromosome) The 22 pairs of chromosomes that do not determine sex are called autosomes Each pair of homologous chromosomes includes one chromosome from each parent The 46 chromosomes in a human somatic cell are two sets of 23; one from the mother and one from the father A diploid cell (2n) has two sets of chromosomes homologous pairs For humans, the diploid number is 46 (2n= 46) Still diploid in G1 (still have one from mom and one from dad) has nothing to do with double strandedness A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n) For humans, the haploid number is 23 (n= 23) Each set of 23 consists of 22 autosomes and a single sex chromosome In an unfertilized egg the sex chromosome is X In a sperm cell, the sex chromosome may be either X or Y Fertilization and meiosis alternate in sexual life cycles A life cycle is the generationtogeneration sequence of stages in the productive history of an organism Fertilization is the union of gametes The fertilized egg is called a zygote and has one set of chromosomes from each parent
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