Introduction Meiosis Sexual Reproduction Sexual Reproduction Involves two

Introduction: Meiosis & Sexual Reproduction

Sexual Reproduction • Involves two parents • Offspring receive ½ DNA from each parent • Offspring not identical to parents…. they are a mix of the parents.

Meiosis • Cell division that produces sex cells called. . . gametes (sperm and egg cells) • Takes place in testes of males and ovaries of females • Reduces the chromosome number by half • Fertilization restores chromosome number:

Human Chromosomes

Human Chromosomes

Human Chromosomes 5 of 9 • A human zygote contains 46 chromosomes. • 23 chromosomes came from the mother through the egg and 23 chromosomes came from the father through the sperm. • Each chromosome from the sperm corresponds to a chromosome from the egg creating a pair. • These pairs are called homologous chromosomes • Homologous chromosomes are similar in size, shape and etc control the same traits.

A. Diploid Number of Chromosomes • Found in body cells… Like skin, bone & muscle cells • These cells contain all homologous pairs of chromosomes or full set of chromosomes. • Symbol = 2 n B. Monoploid/Haploid Number of Chromosomes • Found in gametes (sperm & eggs) • These cells contain… only one chromosome from each homologous pair • Symbol = n

Diploid (2 n) Human Fruit Fly Onion Goldfish Monoploid (n)

Questions 1. What does meiosis do to the chromosome number of cells & what type of cells does meiosis make? • Reduces the chromosome # by half and makes gametes.

2. Name two ways in which mitosis and meiosis are different. • Mitosis keeps the chromosome number the same, while meiosis reduces it by half • Mitosis is for growth or repair of tissue, while meiosis is used to make gametes.

3. Humans have 46 chromosomes…why are they arranged in pairs of 23? • The chromosomes you got from your dad correspond to the chromosomes you got from your mom. They pair and control the same traits. 4. What are these chromosomes called? • Homologous Chromosomes

5. In humans, what is the diploid number of chromosomes? What is the monoploid number? • Diploid number is 46, while the monoploid number is 23

6. How many pairs of homologous chromosomes do diploid cells have…. How many pairs of homologous chromosomes do monoploid/haploid cells have? • Diploid cells have all the homologous pairs, while monoploid cells only contain one member of each homologous pair.

Non-disjunction

Trisomy 21