5. The state in which there are two copies of each chromosome present is known as diploid (2n). H Haploid (n)– only one copy of a chromosome is present All of the somatic cells in our bodies are diploid cells The only cells in our bodies that are haploid are our gametes – eggs and sperm
6. Human somatic cells have 46 chromosomes diploid number (2n) = 46 23 from mom - 23 from dad 22 pairs are autosomes –true homologous pairs 1 pair is not necessarily homologous - sex chromosomes females are XX males are XY – a non homologous pair.
7. Meiosis – form of cell division where there are two successive rounds of cell division following DNA replication - produces haploid cells (n) - start with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) - occurs in our germ cells – cells that produce our gametes - egg and sperm
9. Cell division All complex organisms originated from a single fertilized egg. Every cell in your body started here, through cell division the numbers are increased Cell then specialize and change into their various roles
13. 2 daughter cells identical to original Parent cell Chromosomes are copied and double in number Chromosomes now split
14. Reproduction presents a major problem for cells and organisms: (how can information be transmitted faithfully to progeny) I II III IV = one bit of genetic information
15. = one bit of genetic information The information transfer problem becomes more challenging as more bits of information are incorporated into the organism
16. One of life’s solutions to this challenge: “Package” the bits of information into single units called chromosomes = one bit of genetic information
20. C Chromosome basics . T The number of chromosomes present within the nucleus is a characteristic of the species. Chromosomes of humans and most other eukaryotic species occurs in pairs. Members of a chromosome pair are known as homologues.
21. Mitosis/Cell division mitosis is the process of cell division in which one cell becomes two identical daughter cells development renewal regeneration
22. The cell cycle is the mechanism by which a cell duplicates its contents and then divides in two cell grows and duplicates its contents cell contents cell divides in two Each parental cell gives rise to two daughter cells on completion of each cell cycle parental cell daughter cell 1 daughter cell 2
58. Meiosis – A Source of Distinction Why do you share some but not all characters of each parent? What are the rules of this sharing game? At one level, the answers lie in meiosis.
59. Meiosis does two things - 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number. In meiosis, one diploid cells produces four haploid cells.
61. 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. This makes for a lot of genetic diversity . This trick is accomplished through independent assortment and crossing-over . Genetic diversity is important for the evolution of populations and species .
62. Meiosis Parent cell – chromosome pair Chromosomes copied 1 st division - pairs split 2 nd division – produces 4 gamete cells with ½ the original no. of chromosomes
71. Figure 13.7 The stages of meiotic cell division: Meiosis I
77. Figure 13.7 The stages of meiotic cell division: Meiosis II
78. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2 n distinct gametes, where n = the number of unique chromosomes. That’s a lot of diversity by this mechanism alone. In humans, n = 23 and 2 23 = 6,000,0000.
80. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.
87. Meiosis error - fertilization Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. In humans this often occurs with the 21 st pair – producing a child with Downs Syndrome
88. 21 trisomy – Downs Syndrome Can you see the extra 21 st chromosome? Is this person male or female?