Genes, Chromosomes & Numbers Chapter 10.2

Genes & Chromosomes Genes Sequences of DNA that code for traits Found on chromosomes 1000 or more genes

Diploid Cell Body cells (except for sperm and egg= sex cells) Contain two of each chromosome (2n) one chromosome from each parent during fertilization

Haploid Cell Gametes (sex cells)- sperm and egg Contain one of each kind of chromosome Said to contain n number of chromosomes

Practice Questions: Humans contain 46 chromosomes in their body cells. How many chromosomes are in the gametes? 23 A fruit fly has 4 chromosomes in its gamete cells. How many chromosomes are in the diploid cell? 8

Homologous Chromosomes Paired chromosomes genes for the same traits in the same order Not always identical to each other heterozygous different alleles for the same gene homozygous Contain same alleles for a trait F A B F a B

Why Meiosis? If mitosis was only type of cell division, 46 + 46 = 92 gametes would have same number of chromosomes as the body cells During fertilization, gametes would have twice the number of chromosomes as each of its parents. 46 + 46 = 92 Egg + sperm = zygote (fertilized egg)

Meiosis produce gametes contain half the number of chromosomes as a parent’s body cell

23 + 23 = 46 2 separate divisions: Meiosis I & Meiosis II Begin with 1 diploid (2n) cell. End with 4 haploid (n) gametes 23 + 23 = 46 Egg + sperm = zygote (fertilized egg)

Sexual Reproduction Production and fusion of haploid cells to form a diploid zygote (fertilized egg)