Bio Exam 3 - Meiosis and Mendelian Inheritance

Meiosis

Cell division in which haploid cells are produced from diploid cells; takes place in germ cells in humans; produces sperm and egg cells (gametes); produces genetic variability

2 divisions of meiosis

Meiosis 1 - the reduction division, reduces number of chromosomes from 46 to 23, produces 2 cells, separates homologous pairs, Meiosis 2 - the equational division, produces 4 cells from the 2 produced in meiosis 1, separates sister chromatids; each division consists of prophase, metaphase, anaphase, and telophase

Meiosis 1

Mendel’s Law of Segregation

At the end of meiosis, each gamete carries one copy of an allele

Prophase 1

Homologs pair up and undergo crossing over; spindle forms, nuclear envelope breaks down

Crossing over

Homologous pairs interact and swap information; increases genetic variation

Metaphase 1

Homologous pairs align along the equator

Independent assortment (Mendel’s 2nd law)

Random alignment of chromosomes; maternal and paternal line up but it doesn’t matter what side

Anaphase 1 and Telophase 1

Homologs separate; move to opposite poles

Meiosis 2

Meiosis 2

Same as meiosis 1, except sister chromatids line up and are separated

Mitosis - # of divisions, # of daughter cells, genetics, chromosome #, what kind of cells does it occur in, purpose

One division, two daughter cells per cycle, daughter cells genetically identical, chromosome number of daughter cells same as that of parent cell, occurs in somatic cells, used for growth, repair, and asexual reproduction

Meiosis - # of divisions, # of daughter cells, genetics, chromosome #, what kind of cells does it occur in, purpose

Two divisions, four daughter cells per cycle, daughter cells genetically different, chromosome number of daughter cells half that of parent cell, occurs in germline cells, used for sexual reproduction, producing new gene combinations

Cytoplasmic division in males vs females

Females - one oocyte and three polar bodies; males - cytoplasmic division is equal among the resulting cells

First and Second nondisjunction

First nondisjunction - homologous pairs don’t separate properly, all of the gametes have an incorrect number of chromosomes; second nondisjunction - sister chromatids don’t separate properly, two of the gametes have an incorrect number of chromosomes

Results of meiosis

4 haploid cells; each carry a new assortment of genes and chromosomes that hold one copy of the genome, diverse