1. Genes, Chromosomes & Numbers
Chapter 10.2

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

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

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

5. 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

6. 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

7. 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.
= 92
Egg + sperm = zygote (fertilized egg)

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

9. 23 + 23 = 46 2 separate divisions: Meiosis I & Meiosis II
Begin with 1 diploid (2n) cell.
End with 4 haploid (n) gametes
= 46
Egg + sperm = zygote (fertilized egg)

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