 Chromosomes contain genes.  A chromosome is an organized structure of DNA and protein found in cells.  Different forms of the same gene are called alleles  Human cells have 23 pairs of large linear nuclear chromosomes (22 pairs of autosomes and one pair of sex chromosomes), giving a total of 46 per cell

 Dominant-when one allele covers up another  B  Recessive- the allele that gets covered up or disappears.  b

GENOTYPE  Genotype- the letters used to represent the alleles  Bb PHENOTYPE  Phenotype- the way the organism looks  Black

HETEROZYGOUS  Heterozygous-  Homozygous-  2 different alleles (1 dominant & 1 recessive)  Bb HOMOZYGOUSE  Homozygous-  2 different alleles (1 dominant & 1 recessive)  2 of the same alleles (either 2 dominant or 2 recessive  BB or bb

 1. They are made of CELLS 2. They RESPOND to stimuli 3. They use ENERGY 4. They GROW and DEVELOP 5. They can REPRODUCE

 One way to remember the characteristics of living things is to remember “MRS. GREN”  – M-movement  – Rrespiration  S-stimuli – G-growth  – R-reproduction – E-elimination of wastes –  N-nutrition

PROKARYOTICEUKARYOTIC

PROKARYOTIC  No nucleus  No organelles  Most bacteria  1 st kind of cell  Very simple  EUKARYOTIC  Plants and animals  Organelles  Nucleus  Last to evolve

 AsexualReproduction  – 1 parent needed  – All offspring are identical  – Advantage-faster than sexual reproduction  – Also called budding  – Looks like mitosis  – Ex: bacteria  Sexual Reproduction  – Advantage-All offspring are different (genetic variation)  2 parents needed  Most animals

 Egg: female sex cell  Sperm: male sex cell  After fertilization, zygote  Body cells> sex cells

DIPLOID  Skin, blood, mucus  Mitosis  2 sets of chromosomes  46 chromosomes HAPLOID  Sperm and egg  Meiosis  1 set of chromosomes  23 chromosomes