Mitosis: occurs in somatic cells

• One diploid parent produces two diploid daughter cells

Meiosis: Occurs to produce gametes (sex) cells

• Sperm or egg cells

• One diploid parent cell produces four haploid daughter Cells

Essential Vocabulary

Homologous chromosomes: members of the same pair (one from each parent)

Sister chromatids: Identical replicated chromatids joined by the centromere

Replicated chromosomes: Contains 2 sister chromatids (after S phase)

Non-replicated chromosomes: Contains one chromatid after division

Haploid: cell containing one set of chromosomes (half of normal)

Diploid: Cell containing two sets of chromosomes

Meiosis I: homologous pairs separated

Meiosis II: sister chromatids separated

Genetic recombination during meiosis is a result of:

1) Crossing over/exchange of homologous chromosome segments during prophase I

2) Independent assortment: Chromosomes are selected randomly to be pulled to each side of the cell during Anaphase I

Fraternal: Two separate egg cells

• Same genetic variation as other siblings

Identical: embryo splits

• Genetically identical

Mendelian Genetics Definitions

Gene: Codes for a trait

Allele: Version of a gene

Dominant: Masks recessive

Recessive: Is masked by a dominant trait

Homozygous: two of the same allele for a trait

Heterozygous: Two different alleles for a trait

Genotype: Genes possessed by an organism

Phenotype: Physical expression of genes

Biological Females: XX

Biological Male: XY

Other Systems

• Insect Female: XX

• Insect Male: XO

• Birds, some reptiles, some insects Female: ZW

• Birds, some reptiles, some insects Male: ZZ

• Ants & Bees Haploid: Male

• Ants & Bees Diploid: Female

Sex-linked traits - carried on sex chromosomes

• Usually X chromosome

X-linked recessive: Females can be carriers

• Ex. Hemophilia

XY: normal male

X’Y: has trait

XX: Normal female

X’X’: has trait

X’X: carrier

Incomplete dominance

• The dominant allele only partially masks the recessive allele