Edpuzzle Notes Meiosis+Mitosis (Unit 4)

Mitosis

Makes identical body cells like skin and stomach cells

Meiosis

Makes sperm and egg cells known as gametes

Body cells

Have 46 chromosomes

Sperm and egg cells

Each have 23 chromosomes

Interphase

Occurs before mitosis and meiosis; includes growth, DNA replication, and normal cell processes

Meiosis type

Reduction division that reduces chromosome number by half

PMAT

Stands for prophase, metaphase, anaphase, and telophase

Number of divisions in meiosis

Two divisions occur

Prophase I

Chromosomes condense and thicken, homologous pairs line up, and crossing over occurs

Homologous chromosomes

Chromosomes that are about the same size and contain the same types of genes in the same locations

Crossing over

Exchange of genetic information between homologous chromosomes; increases genetic variation

Metaphase I

Chromosomes line up in the middle of the cell

Anaphase I

Chromosomes are pulled away by spindle fibers

Telophase I

Two different nuclei form

Genetic variety in meiosis

Caused by independent assortment and crossing over

Chromosome number change

Starting cells have 46 chromosomes; ending cells have 23

Nondisjunction

Error where a cell receives too many or too few chromosomes; can lead to genetic disorders

Importance of meiosis

Creates genetic diversity so offspring are different and more resistant to disease

Diploid

Two complete sets of chromosomes (2n)

Haploid

One complete set of chromosomes (n)

Somatic cells

All body cells except gametes

Gametes

Egg and sperm cells

Fertilization

When haploid cells combine to form a diploid zygote

Zygote

Fertilized egg that is diploid

Mitosis purpose

Used for growth and repair; makes identical cells

DNA replication

Occurs during interphase

Crossing over in mitosis

Does not occur in mitosis

Cell division in meiosis

One cell divides twice (homologous pairs separate, then chromatids separate)

Independent assortment

Random alignment and separation of homologous pairs; contributes to genetic variation

Genetic variation sources

Independent assortment, crossing over, and random fertilization

Zygotes and organisms

Diploid

Gametes

Haploid

Homologous pairs

Also called homologous chromosomes or homologs