Meiosis Diploid (2N) – 2 sets of chromosomes 1) In humans what is the diploid chromosome number? Haploid (N) – 1 set of chromosomes 2) In humans what is the haploid chromosome number? Homologous – a pair of chromosomes (1 from each parent) that 3)___________, 4)__________ and 5)______________

Meiosis and sexual reproduction significantly contribute to genetic variation among offspring Some steps closely resemble Mitosis Like Mitosis, Meiosis is preceded by chromosome replication Meiosis is different because a single chromosome replication is followed by two rounds of cell division Meiosis I and Meiosis II.

Chromosome Genes Chromosome: A bundle of DNA containing many genes B A C

B a c d A C E A C B A C 6) Which is the homologous chromosome to 1? How do you know? 1234

B a c B a c B A C B A C 1 2 7) What is the relationship between 1 and 2? 34 8) What is the relationship between 3 and 4?

A cell which contains two copies of each chromosome is… 9) ____________ Normal body cells are 9)_____

A cell which contains one copy of each chromosome is… 10)________ Gametes (sex cells) are 10)________ Sperm Ovum

Sperm cells are produced by … 11)_________ The chromosomes in the nucleus are copied 12)______ haploid daughter cells are produced Each daughter cell contains only one of the homologous chromosomes from the diploid parent cell Diploid parent cell

Eggs are also produced by 13)_________ Haploid Diploid parent cell

14) So why would we want to create haploid gametes? 15) What would happen if the sperm and egg cells generated were diploid cells?

Generation 1

Generation 2 Generation 3=16 Generation 4=32 Generation 5=64 Generation 6=128 Generation 7=256

Replication of DNA must occur before cell division. 16) When does this occur?

17) In Meiosis I the _____________split and the chromosome number goes from ____ to _____

Meiosis II looks a lot like 18)_______________

Crossing Over-when homologoues chromosomes exchange pieces with each other. This occurs during Prophase I I need 4 volunteers. Results in genetic variation

Summary of Meiosis 2 cell divisions. Start with 2 copies of each chromosome (homologues), each with 2 chromatids. In meiosis 1, crossing over in prophase mixes alleles between the homologues. In metaphase of meiosis 1, homologues pair up, and in anaphase the homologues are separated into 2 cells. Meiosis 2 is just like mitosis. The centromeres divide in anaphase, giving rise to a total of 4 cells, each with 1 copy of each chromosome, and each chromosome with only 1 chromatid.

MitosisMeiosis DNA replication During _________ Divisions___________ Crossing overDoes not occur Can occur in prophase I Role in animal body Produces cells for growth and tissue repair Produces gametes Results in___ Diploid Cells (2N) ___ Haploid Cells (N) Cells areGenetically __________ Occurs in________Cells_______ Cells

MitosisMeiosis DNA replicationDuring interphase Divisions12 Crossing overDoes not occur Can occur in prophase I Role in animal body Produces cells for growth and tissue repair Produces gametes Results in2 Diploid Cells (2N) 4 Haploid Cells (N) Cells areGenetically identical Genetically different Occurs inBody CellsSex Cells

19) Where are sex cells found in your body?

20)Which process is this? Provides for growth, repair, and asexual reproduction Produces TWO daughter cells that are genetically identical to the parent cell Involves one division of the DNA Diploid parent cells produce diploid daughter cells Happens in most cells of the body…

21) Which process is this? Yields haploid daughter cells with only ONE member of the homologous chromosome pair Produces FOUR daughter cells that are genetically different from the parent cell Involves TWO divisions of the DNA Exchange of genetic material occurs between homologous chromosomes

22) What are similarities between Mitosis and Meiosis?

Similarities? Chromosomes duplicate only once before each stage Both make it possible for cells to inherit genetic information in the form of chromosome copies

23) What are the differences between Meiosis and Mitosis?

Meiosis Consists of 2 cycles Results in a reduction of the chromosome # Is a division of sex cells Results in 4 daughter cells

Random assortment of chromosomes

24) How does meiosis contribute to genetic diversity?

Random assortment of chromosomes Crossing Over How does meiosis contribute to genetic diversity? This is important because the greater the genetic diversity the greater the probability that a population will survive an epidemic.

Fertilization: An ova and a sperm fuse to form a diploid zygote Ova Sperm Zygote The zygote contains one allele from each parent This process is random

The same rules apply to inheritance in plants as apply to inheritance in animals. The male gamete or sex cell is … … pollen The female gamete is… … the egg cell