Chapter 8 Cell ReproductionIntroduction to Chromosomes
Important Words Chromosomes – tightly coiled Strands of DNA wrap packages of DNA; they are rod around proteins called shaped and proteins hold them Histones. together.
Important Words Chromatid – each half of a chromosome; forms as DNA copies itself before cell division Centromere – holds the chromatids together until they separate
Important Words How many chromosomes do humans have? Each species has a unique number of chromosomes. 46 chromosomes or 23 pairs.
Types of Chromosomes 2 Types of Chromosomes: 1. Sex Chromosomes – are the chromosomes that determine the sex of an organism. Female: XX Male: XY 2. Autosomes – all other chromosomes Humans: 44 autosomal chromosomes
Karyotype: Picture ofChromosomes. What do younotice about the arrangement?
Chromosomes Karyotype – is a picture of the chromosomes in a somatic (body) cell. 22 homologous pairs of autosomes. 2 sex chromosomes Is this person male or female? Male: XY Normal or abnormal Normal: 23 pairs
Chromosomes Homologous chromosomes – two copies of each autosome (maternal and paternal) Homologous chromosomes are the same size, shape, and carry genes for the same trait. Final pair is not numbered: Sex Chromosomes.
Compare the karyotypes. Record your observationsKaryotype A Karyotype B
ComparisonsKaryotype A Karyotype B 19 pairs: Not Human 23 pairs: Human Sex: Male (XY) Sex: Female (XX) Sister chromatids are still Single Copy of each attached at their chromosome. centromeres (these are This picture was taken double copies of each AFTER the cell divided! chromosome). Be prepared to analyze a This is a picture karyotype regardless of BEFORE the cell divided! when the picture of the chromosomes was taken.
Chromosomes Diploid – cells have two sets (maternal and paternal) of chromosomes. Have all 46 chromosomes. Represented by 2n (means a full set of DNA) Somatic Cells (cells making up the body) Haploid – cells have one set of chromosomes. Have 23 chromosomes. Represented by n (means a half set of DNA) Gametes (reproductive cells : egg and sperm)
Haploid Cells Reproductive Cells Gametes - sperm and egg cells; they have 23 chromosomes Fertilization 23 in sperm + 23 in egg = 46 in zygote Gametes are produced through Meiosis (cell division results in 4 genetically different cells)
Diploid Cells Somatic Cells Cells that make up the body of organisms. Somatic Cells are produced through Mitosis (cell division results in 2 genetically identical cells).