Meiosis

Sex cell production

Meiosis - Sex Cell Reproduction

• Requires two parents

• Parent cells produce sex cells– Male (sperm)– Females (egg)

• Sex cells have ½ the number of chromosomes– Humans have 46

chromosomes– So human sex cells have how

many chromosomes?• 23

• When sex cells combine the offspring will have a full set of chromosomes

Sexual Reproduction

• Advantages of sexual reproduction– Chromosomes from 2 parents– offspring are different than

the parent– Offspring are likely more

adaptable

• Different from asexual reproduction which

ALWAYS produces offspring that are the SAME.

Homologous Chromosomes• Chromosomes that carry

the same set of instructions.

• One from mother and one from father• Remember – these replicate during interphase!

Meiosi

s

• Produces sex cells and

• Parent cells divide twice producing4 daughter cells

• Daughter cells (sex cells) have ½ the number of chromosomes as the parent cell

Growing quadruplets

Meiosis I Contains all the steps of

mitosisIs like mitosis except…– Homologous

chromosomes pair up– Sister chromatids don’t

separate– Produces TWO cells

Meiosis occurs in two steps…..

Meiosis II Contains all steps of

mitosisIs like mitosis except:• No DNA replication• 4 daughter cells

with ½ number of chromosomes as parent

• Diploid (2n) – full set of chromosomes–Parent cell

• Haploid (n) – half a set of chromosomes

–Daughter cells

Additional Vocabulary

Sex Cell

s

Sperm Cells

Egg Cells

http://www.mwit.ac.th/~bio/assets/meiosis%5B1%5D.swf

Mitosis & Meiosis on the Table• Objective: Discover critical differences between mitosis and

meiosis, and the main functions of meiosis.

• Assumptions: copy from handout• Table: Distinguishing features• Summary: Copy from handout

• Questions: 1. What are the 2 main functions of meiosis?2. If you were to model an organism with six chromosomes how

many more pipe cleaners will you need? Will you need to use a third color? Why or why not?

3. Adder’s fern has 1,400 chromosomes. How many chromosomes do its sex cells have?