Section 6 1 Chromosomes Meiosis 6 1 Chromosomes

Section 6 -1 “Chromosomes & Meiosis”

6. 1 Chromosomes and Meiosis What makes you who you are?

6. 1 Chromosomes and Meiosis The fusion of an egg cell from your mother and a sperm cell from your father resulted in the complex organism you are. The DNA that directs your cells came from your mother and father, and their DNA came from their mother and father, and so on. In this chapter, we will examine the processes that went into making you who you are.

6. 1 Chromosomes and Meiosis What traits could you predict for the child just by observing the parents?

6. 1 Chromosomes and Meiosis • How do gametes differ from body cells? • Why do gametes have only half the number of chromosomes as a body cells?

6. 1 Chromosomes and Meiosis The cells in your body can be divided into two types: • Germ cells – cells in your reproductive organs that develop into gametes Egg and Sperm • Somatic cells – body cells that make up your tissues and organs Skin, Kidneys, Muscles, Nerves

Gametes - sex cells that determine the biological sex and development of males and females • ova (eggs) in females • spermatozoa (sperm cells) in males. The DNA in your gametes is passed on to your offspring

Gametes are haploid • Haploid (n): cells that have one copy of every chromosome (1/2 of total number of chromosomes) • In humans n = 23 In this gamete, n = ?

6. 1 Chromosomes and Meiosis Body cells are diploid • Diploid (2 n): cells that have two copies of every chromosome (total number of chromosomes in the nucleus) • In humans n = 23, therefore 2 n = 46 In this body cell, 2 n = ?

6. 1 Chromosomes and Meiosis In these cells, n = ? In this cell, 2 n = ?

6. 1 Chromosomes and Meiosis If n = 4, then 2 n = ? 8 If n = 16, then 2 n = ? 32 If n = 7, then 2 n = ? 14 If n = 23, then 2 n = ? 46 If 2 n = 40, then n = ? 20 If 2 n = 18, then n = ? 9 If 2 n = 28, then n = ? 14 If 2 n = 10, then n = ? 5

• Which of the cells below are somatic cells? • Which would be gametes? Rod Cells Hair Cells Sperm Cells Muscle Cells Egg Cells Nerve Cells

Somatic Cells Gametes • Body cells • Sex cells • Make up tissues and organs • Determine the biological sex of an organism • DNA not passed on to offspring • DNA passed on to offspring

6. 1 Chromosomes and Meiosis What is a chromosome? Chromsome: Tightly coiled strands of DNA, containing many genes.

6. 1 Chromosomes and Meiosis Each species has a specific number of chromosomes per cell Strawberry: 56 (28 pairs) Snail: 24 (12 pairs) Fern: 1260 (630 pairs) Human: 46 (23 pairs) Dolphin: 44 (22 pairs) The number of chromosomes is not related to the size or complexity of an organism.

6. 1 Chromosomes and Meiosis The chromosomes in your cells can be divided into two groups: Autosomes – chromosomes that determine your body characteristics (traits), such as hair color, height, shape of your nose, etc. Sex Chromosomes – X and Y chromosomes that determine your biological sex (female/male) FEMALES: X X MALES: X Y

6. 1 Chromosomes and Meiosis In human diploid body cells (46 chromosomes) • 44 chromosomes are autosomes • 2 chromosomes are sex chromosomes. In human haploid gametes (23 chromosomes) • 22 chromosomes are autosomes • 1 chromosome is a sex chromosome (X or Y).

6. 1 Chromosomes and Meiosis Humans have two sets of chromosomes: one set from the mother; the other set from the father. Therefore, chromosomes come in pairs

6. 1 Chromosomes and Meiosis Each pair of chromosomes are called Homologous Chromosomes: pairs of chromosomes that are the same size and have the same genes.

6. 1 Chromosomes and Meiosis Mother’s Chromosome A A B B C D Father’s Chromosome Before replication a a b b C c c D d d After replication

In humans, pairs of homologous chromosomes are numbered 1 – 23, from largest to smallest. The first 1 -22 make up the autosomes. Autosomes: Chromosomes that determine physical characteristics NOT related to the biological sex of the organism

Sex Chromosomes: (23 rd pair in humans) Chromosomes that determine the biological development of sexual characteristics. Females: X X Males: X Y

Chromosomes that contain genes not directly related to sex of organisms Homologous Chromosomes pairs, one from each parent Sex Chromosomes that contain a gene that is directly related to sex of organisms

• Sexual Reproduction: the joining of two gametes that result in an offspring that are a genetic mixture of both parents. • Fertilization: the nuclei of the egg and sperm cells fuse to form a single nucleus

6. 1 Chromosomes and Meiosis

Fertilization: • 2 haploid (n) cells (egg and sperm) unite to form a single cell (zygote) that has the diploid (2 n) number of chromosomes • A zygote is a fertilized egg

6. 1 Chromosomes and Meiosis

• Mitosis makes more identical diploid cells

• Meiosis makes haploid cells from diploid cells and: – occurs in sex cells – produces gametes

6. 1 Chromosomes and Meiosis Diploid Cell: • Has two copies of each chromosome – one from each parent Haploid Cell: • Has one copy of each chromosome • Occurs in body cells • Occurs in gametes (sex cell) • Result of mitosis • Result of MEIOSIS

6. 1 Chromosomes and Meiosis How are Mitosis and Meiosis similar? • Mitosis and Meiosis are both types of cell division • They both involve the DNA coiling up to make chromosomes • The nucleus divides in both processes using many different steps

MITOSIS MEIOSIS • Create genetically identical cells • Creates genetically unique cells • Make diploid cells • Makes haploid cells • Happens throughout organisms life-time • Takes place at only certain times in life cycle • Involved in asexual reproduction • Involved in Sexual reproduction

• How are mitosis and meiosis alike? • Both involve division of the nucleus followed by the formation of new cells.