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?

Section 10.2 Summary – pages Genes do not exist free in the nucleus of a cell; they are lined up on chromosomes.

Section 10.2 Summary – pages 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. Diploid Cells From Mom From Dad

Section 10.2 Summary – pages The two chromosomes of a pair are called homologous chromosomes. Each pair of homologous chromosomes has genes for the same traits. Homologous Chromosomes

Section 10.2 Summary – pages A cell with two of each kind of chromosome is called a diploid cell. All of your body cells are diploid. Diploid Cells

Section 10.2 Summary – pages 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.

Section 10.2 Summary – pages So, sex cells CANNOT be diploid. A cell containing only one of each kind of chromosome is called a haploid cell. Haploid Cells

Section 10.2 Summary – pages Sexual Reproduction Zygote

Section 10.2 Summary – pages Chromosome Numbers of Common Organisms OrganismBody Cell Fruit fly 8 Garden pea14 Corn20 Tomato24 Leopard Frog Apple34 Human46 Chimpanzee48 Dog78 Adder’s tongue fern 1260 Sex Cell Diploid and Haploid Cells

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. It starts with a DIPLOID cell 46 Chromosomes Replicate It ends with TWO IDENTICAL DIPLOID cells

Meiosis I Meiosis II The kind of cell division that produces sex cells (haploid) containing half the number of chromosomes as a body cell, is called meiosis.

Meiosis: cell division that makes SEX CELLS. It starts with a DIPLOID cell 46 Chromosomes Replicate 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.

FROM MOM FROM DAD This chromosome inherited by mom could code for straight hair, brown hair, and green eyes… This chromosome inherited by dad could code for curly hair, black hair, and brown eyes… After crossing-over 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 These haploid cells are called sex cells— gametes. Male gametes are called sperm. Female gametes are called eggs. Meiosis

Section 10.2 Summary – pages When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes. Meiosis

Section 12.3 Summary – pages 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 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. Nondisjunction

Section 12.3 Summary – pages Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood. Down syndrome: Trisomy 21

Section 12.3 Summary – pages Down syndrome: Trisomy 21 The incidence of Down syndrome births is higher in older mothers, especially those over 40. Extra chromosome on 21 1 in every 1100 live births Range from mild to severe physical and mental disabilities

Section 2 Check A cell with two of each kind of chromosome is __________. Question 1 D. polyploid C. biploid B. haploid A. diploid

Section 2 Check 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. Homologous Chromosome 4 aA Terminal Axial Inflated D Constricted d Tall T Short t

Section 2 Check Why do organisms need meiosis for reproduction? Question 2 Meiosis Sperm Cell Egg Cell Haploid gametes (n=23) Fertilization Diploid zygote (2n=46) Mitosis and Development Multicellular diploid adults (2n=46)

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 Sperm Cell Egg Cell Haploid gametes (n=23) Fertilization Diploid zygote (2n=46) Mitosis and Development Multicellular diploid adults (2n=46)

Section 3 Check Trisomy usually results from _______. (TX Obj 2; 6C) Question 2 D. twenty-two pairs of chromosomes C. nondisjunction B. incomplete dominance A. polygenic inheritance The answer is C.