Download Meiosis

Meiosis Chapter 9 1 •  Each offspring in a sexually reproducing species inherits a unique combina<on of genes from its two parents – This combined set of genes contributes to a unique combina<on of traits in each individual – Gene: unit of inherited informa<on in DNA (Chromosomes contain DNA and DNA contains thousands of genes; different genes control different characteris<cs) 2 •  Sexual reproduc<on depends in part on meiosis: a type of cell division that produces four cells, each with half the number of chromosomes as the parent cell –  Duplicated Chromosome (“chromosome”): a pair of sister chroma<ds 3 4 5 •  When comparing the cells of the same species, you will see that almost all the cells have the same number and types of chromosomes – Ex. Human cells contain the same types of 46 chromosomes – A display of the human 46 chromosomes is called a karyotype 6 7 – No<ce that each of these chromosomes has a twin that resembles it in size and shape • You inherit one chromosome of each pair from your mother and the other from your father • The two chromosomes of each matching pair are called homologous chromosomes – Each homologous chromosome in a pair carries the same sequence of genes controlling the same inherited characteris<cs 8 » Ex. If a gene for eye color is located in a par<cular place on one chromosome, then a gene for eye color can be found in the same place on the homologous (matching) chromosome • However, the two genes do not have to be iden<cal. One might be for brown eyes and the other for blue eyes. All that ma\ers is that they both control eye color. 9 – Humans have 23 homologous pairs, making 46 chromosomes all together •  In males, one pair of chromosomes does not look alike: the 23rd pair of chromosomes, called the sex chromosomes, determines the persons sex. – These occur in two forms: X and Y » Males have 1 X and 1 Y chromosome » Females have 2 X chromosomes – The Y chromosome is shorter than the X chromosome 10 11 – Chromosomal abnormali<es o`en result from nondisjunc<on, the failure of chromosomes to separate properly during meiosis • This results in cells that have too many or too few chromosomes • Trisomy is an abnormality in which a cell has an extra chromosome, or sec<on of a chromosome – This means that the cell contains 47 chromosomes instead of 46 – Down syndrome or Trisomy 21, is a chromosomal abnormality that results from having an extra number 21 chromosome 12