I told you before that we categorize human cells in two categories: body cells and sex cells, what do you THINK makes them so different? HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?
Genes do not exist free in the nucleus of a cell; they are lined up on chromosomes. Section 10.2 Summary – pages 263-273
Diploid Cells Section 10.2 Summary – pages 263-273 • In the body cells of animals and most plants, chromosomes occur in pairs. • In each pair, one you inherited from your mom, the other from your dad. From Mom From Dad
Homologous Chromosomes Section 10.2 Summary – pages 263-273 • The two chromosomes of a pair are called homologous chromosomes. • Each pair of homologous chromosomes has genes for the same traits.
Diploid Cells Section 10.2 Summary – pages 263-273 • A cell with two of each kind of chromosome is called a diploid cell. • All of your body cells are diploid.
Section 10.2 Summary – pages 263-273 • Body cells (diploid) are different from sex cells. • Each person can only pass on ONE of their homologous chromosomes to their young. HUMANS = 46 CHROMOSOMES IN THEIR BODY CELLS Each parent passes 23 to their young, so that when the sperm and egg combine- it will equal 46 Chromosomes.
Haploid Cells Section 10.2 Summary – pages 263-273 • So, sex cells CANNOT be diploid. • A cell containing only one of each kind of chromosome is called a haploid cell.
Sexual Reproduction Section 10.2 Summary – pages 263-273 Zygote
Section 10.2 Summary – pages 263-273 Diploid and Haploid Cells Chromosome Numbers of Common Organisms Organism Body Cell Sex Cell 8 Fruit fly 4 Garden pea 14 7 Corn 20 10 Tomato 24 12 26 Leopard Frog 13 17 Apple 34 Human 46 23 Chimpanzee 48 24 Dog 78 39 1260 630 Adder’s tongue fern
In Humans, how many chromosomes would each of these cells have….. CHEEK CELL 46 SPERM CELL 23 EGG CELL 23 NERVE CELL 46
Since they have different amounts of chromosomes, the way they are made differ. ● Body cells are made by the division process MITOSIS. ● Sex cells are made by the division process MEIOSIS.
Before a cell can divide by either method, it must first prepare for cell division. The cell cycle (or entire life cycle of the cell) consists of: INTERPHASE: The longest/busiest stage in a cell’s life 1. Chromosomes (DNA) replicates 2. Cell grows bigger CELL DIVISION: Mitosis or Meiosis CYTOKINESIS: When the cytoplasm divides and the cell completely separates.
Mitosis: cell division that makes BODY CELLS. 46 It starts with a DIPLOID cell Chromosomes Replicate 92 46 46 It ends with TWO IDENTICAL DIPLOID cells
The kind of cell division that produces sex cells (haploid) containing half the number of chromosomes as a body cell, is called meiosis. Meiosis I MeiosisII
Meiosis: cell division that makes SEX CELLS. 46 It starts with a DIPLOID cell Chromosomes Replicate 92 46 46 23 23 23 23 It ends with FOUR HAPLOID cells (not identical)
Crossing-Over In Meiosis: Before the sex cells are created, Homologous chromosomes actually break and exchange traits- in a process known as crossing over.
After crossing-over FROM MOM FROM DAD This chromosome inherited by dad could code for curly hair, black hair, and brown eyes… This chromosome inherited by mom could code for straight hair, brown hair, and green eyes… Now one chromosome passed on to offspring could have traits from both homologous… curly hair, brown hair, and green eyes…
Crossing-Over Crossing over can occur at any location on a chromosome, and it can occur at several locations at the same time. This causes the traits found in each gamete varied. This is why siblings of the same parents can look so different from each other.
Section 10.2 Summary – pages 263-273 Meiosis • These haploid cells are called sex cells— gametes. • Male gametes are called sperm. • Female gametes are called eggs.
Section 10.2 Summary – pages 263-273 Meiosis • When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.
Section 12.3 Summary – pages 323 - 329 • This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome numbers in cells.
Section 10.2 Summary – pages 263-273 Nondisjunction • The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction. • This would occur when homologous chromosomes are suppose to separate from each other.
Down syndrome: Trisomy 21 Section 12.3 Summary – pages 323 - 329 • Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood.
Section 12.3 Summary – pages 323 - 329 Down syndrome: Trisomy 21 • Extra chromosome on 21 • 1 in every 1100 live births • Range from mild to severe physical and mental disabilities • The incidence of Down syndrome births is higher in older mothers, especially those over 40.
Section 2 Check Question 1 A cell with two of each kind of chromosome is __________. A. diploid B. haploid C. biploid D. polyploid
Section 2 Check Homologous Chromosome 4 The answer is A. The two chromosomes of each pair in a diploid cell are called homologous chromosomes. Each has genes for the same traits. a A Terminal Axial Inflated D d Constricted T t Short Tall
Section 2 Check Question 2 Meiosis Haploid gametes (n=23) Sperm Cell Why do organisms need meiosis for reproduction? Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Multicellular diploid adults (2n=46) Mitosis and Development
Section 2 Check Meiosis is cell division that produces haploid gametes. If meiosis did not occur, each generation would have twice as many chromosomes as the preceding generation. Meiosis Haploid gametes (n=23) Sperm Cell Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Multicellular diploid adults (2n=46) Mitosis and Development
Section 3 Check Question 2 Trisomy usually results from _______. (TX Obj 2; 6C) A. polygenic inheritance B. incomplete dominance C. nondisjunction D. twenty-two pairs of chromosomes The answer is C.