Sexual Reproduction and Meiosis

Sexual Reproduction Overview

• Requires the union of a sperm cell (male) and an egg cell (female) from separate parents.

• This union is called fertilization.

• Fertilization creates a zygote.

• A zygote has a full set of chromosomes. It is diploid in number.

Sexual Reproduction Overview

• Diploid = 2n [ex. humans, n=23. 2(23)]

• Haploid means that a cell has half the number of chromosomes in a cell.

• Haploid = n [ex. Human n = 23]

• Each chromosome has a match in the nucleus that is very similar.

Meiosis Overview

• This creates pairs of matching chromosomes for each cell.

• Meiosis is cell division in sex cells.

• Two divisions occur.

• Start with one sex cell, end up with four.

• A full set of chromosomes will be reduced to half the number in each sex cell.

• Diploid cell to 4 haploid cells.

Sexual Reproduction Overview

Each chromosomes has a match. These are homologous chromosomes.

Each parent must only contribute half of the required chromosomes.

Meiosis meets this requirement creating haploid cells.

One duplicated chromosomes

Homologous chromosomes

Draw this Venn Diagram

Mitosis and Meiosis Compared

Mitosis Meiosis

Mitosis and Meiosis Compared

Mitosis

•Diploid cell

•2 new cells

•1 division

•Anaphase – sister chromatids separate

Mitosis and Meiosis Compared

Meiosis

•Haploid cell

•4 new cells

•2 division

•Anaphase I – sister chromatids stay together

Only the pairs are separating

Mitosis and Meiosis Compared

Mitosis Meiosis

•Nucleus breaks up

•Chromosomes line up in the center

•Chromosomes separate

•Cytokinesis occurs

Common to both

Mitosis and Meiosis Compared

Mitosis Meiosis

•Nucleus breaks up

•Chromosomes line up in the center

•Chromosomes separate

•Cytokinesis occurs

•Haploid cell

•2 new cells

•1 division

•Anaphase I – sister chromatids stay together

•Diploid cell

•2 new cells

•1 division

•Anaphase – sister chromatids separate

Common to both

What is it?• DNA is:

– A molecule

– Deoxyribonucleic acid

– Stores hereditary material

– A code of instructions

• For an organisms growth

• For normal functions

• For creating proteins

What is it?

• DNA is:

– Found in the chromosomes of a cell’s nucleus

– Is copied and passed to new cells

– The key to biological life

Structure of DNA

• Each molecule consists of:

– A five carbon sugar (deoxyribose)

– A phosphate group

– A nitrogen containing base (4 total)• Thymine• Guanine• Cytosine • Adenine

Structure of DNA

• Each molecule is:

– A double helix (spiral structure)

• Think of a ladder that has been twisted

Copying of DNA

• Before a cell divides the DNA found in chromosomes must duplicate.

• Here’s how:

• Nitrogen bases separate (like unzipping a zipper).

• This creates 2 halves of DNA that serve as a pattern.

Copying of DNA

• An enzyme synthesizes the matching halves of DNA.

• The 2 new DNA halves match up to the original DNA.

• The cell is now ready to divide.

• Now look at the board and let’s illustrate.

Functions of DNA • Purposes of DNA

– Stores information for making you like you are (eye color, hair color, etc)

– Provides the code for making proteins• Proteins build cells and tissues in

your body• Proteins also act as enzymes that

trigger many chemical reactions in your cells

Functions of DNA

• Making proteins

– Proteins:

• Are made of amino acids

• Instructions for each protein are found on a GENE.

–A gene is a section of DNA on a chromosome

»Look at figure 16 on page 112.

Functions of DNA • Making proteins

• Genes provide the code and are in the nucleus

• Proteins are made in ribosomes in the cytoplasm

• The codes for making proteins are carried from the nucleus to the ribosomes by another nucleic acid called RNA.

Functions of RNA– Three types

1. messenger RNA (mRNA)

2. transfer RNA (tRNA)

3. ribosomal RNA (rRNA)

Look at page 113. We will discuss figure 17 to learn about RNA and making proteins.