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Mutations . Mutations get passed from one generation to the next when cells copy the mistakes in DNA. Copied mistakes go into daughter cells during cell division. To produce the next generation in sexually reproducing organisms cells experience:. Meiosis. Cell Division.

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Presentation Transcript
mutations
Mutations

Mutations get passed from one generation to the next when cells copy the mistakes in DNA

Copied mistakes go into daughter cells during cell division

To produce the next generation in sexually reproducing organisms cells experience:

Meiosis

cell division
Cell Division

Cell Division occurs in two ways:

Mitosis

produces genetically identical daughter cells

Meiosis

produces genetically different offspring

chromosome changes
Chromosome Changes

Most normal cells start with “n” number of pairs of chromosomes

n = number of kinds of chromosomes

2n = total number of chromosomes

Examples:n2n

Onion 4 8

Fly 8 16

Human 23 46

How Many Chromosomes Does It Have?

Fathers donate sex cell with half a set of chromosomes = 23

Mothers donate sex cell with half a set of chromosomes = 23

Offspring receives full set of chromosomes = 46/23 pairs

Diploid cells – 2n chromosomes

Haploid cells – n chromosomes, ½ set

meiosis
Meiosis

Only used to create sex cellscells have n number of chromosomes

Human = 23

Onion = 4

Sperm

Ovum/Egg

stages of meiosis
Stages of Meiosis

Meiosis occurs over two separate sets of stages, Meiosis 1 and Meiosis 2.

Let’s examine how this works with a cell that has 6 chromosomes

prophase i
Prophase I

Homologous chromosomes form, find each other and become tetrads

Spindle forms

Nucleus breaks up

metaphase i
Metaphase I

Tetrads line up in the middle of the cell

Spindle fibers attach to centromeres

anaphase i
Anaphase I

Tetrads split

Homologous chromosomes move to opposite ends of the cell

Cell begins cytokinesis

telophase i
Telophase I

Two haploid daughter cells are created

Meiosis 2 may begin immediately

prophase ii
Prophase II

Spindle fibers form

Nucleus breaks apart

metaphase ii
Metaphase II

Individual Chromosomes line up in the center of the cell

Spindle fibers attach to centromeres

anaphase ii
Anaphase II

Sister chromatids separate

Chromatids move to opposite ends of the cell

Spindles shorten

Cytokinesis begins

telophase ii
Telophase II

Cytokinesis ends

Four haploid cells are left

In most males, all four will become gametes

In females, only one will

gametogenesis
Gametogenesis

Gametogenesis = formation of gametes

Gametes: haploid sex cells, contain n number of chromosomes

Occurs slightly differently in males and females

Spermatogenesis = sperm

Oogenesis = egg

gametogenesis1
Gametogenesis

Spermatogenesis

Oogenesis

X X

x x

X X

x x

X

x

X

x

X

x

X

x

I

I

I

I

I

I

Gametes

I

I

I

I

I

I

I

I

I

I

3 nonfunctional polar bodies

I

I

I

I

I

I

I

I

Sperm

Egg or Ovum

I I

I I

Fertilization: sperm DNA enters egg, completing the set of chromosomes