6/11/13 LIVING ENV.1. Attendance2. Test Information3. Review powerpoints 4. Time to work on owed work.

MEIOSISDivision of Sex Cells

Meiosis

A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

Diploid – 2 sets of chromosomes Haploid – 1 set of chromosomes Homologous – chromosomes that each

have a corresponding chromosome from the opposite sex parent

Meiosis

Meiosis Stages

Meiosis usually involves 2 distinct stages Meiosis I Meiosis II

Prophase I

Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

There are 4 chromosomes in a tetrad. The pairing of homologous chromosomes

is the key to understanding meiosis. Crossing-over may occur here Crossing-over is when chromosomes

overlap and exchange portions of their chromatids.

Prophase I

Metaphase I

Spindle fibers attach to the chromosomes

Metaphase I

Anaphase I

The fibers pull the homologous chromosomes toward opposite ends of the cell.

Anaphase I

Telophase I & Cytokinesis

Nuclear membranes form. The cell separates into 2 cells.

Telophase I

Prophase II

Meiosis I results in two haploid (N) cells. Each cell has half the number of

chromosomes as the original cell.

Prophase II

Metaphase II

The chromosomes line up similar to metaphase in mitosis.

Metaphase II

Anaphase II

Sister chromatids separate and move to opposite ends of the cell.

Anaphase II

Telophase II

Meiosis II results in 4 haploid cells.

Telophase II

Gamete Formation

In males, meiosis results in 4 sperm cells In females, meiosis results in 1 egg cell

and three polar bodies, which are not used in reproduction.

Mitosis vs Meiosis

Mitosis MeiosisResults in 2 Diploid Cells

(2N)4 Haploid Cells (N)

Cells are Genetically Identical

Genetically Different

Occurs in Somatic (Body) Cells

Sex Cells

Name That Whatzitdoing!Getting ready to divide

Separating to the poles

Lining up on the equator

Mitosis! Now there are 2 cells!

Mitosis in Onion Cells Right Before Your Eyes in the Microscope

Is This Mitosis or Meiosis?

Meiosis! Of course! End up with 4 cells, not 2 as in mitosis

Mitosis or Meiosis?

Mitosis or Meiosis?

Meiosis Cell Division - Makes Gametes

4 functional (all 4 work) sperm

Humans have 46 chromosomes, so gametes have HALF that number -23

Meiosis Makes Ova (Eggs) Too, Of Course, But How Many are Functional?

Right!Only one!

Ready to Quiz Yourself?Mitosis Meiosis

Cell division for what kind of cells?

All cells EXCEPT for gametes

ONLY gametes

Ends up with this many chromosomes compared to the species number of chromosomes

Identical number as the

species number (46 for

humans)

1/2 the number as the

species number(23 for

humans)

Ends up with this many cells 2 4Ends up with this many FUNCTIONAL cells

24 for sperm

but only1 for eggs

(ovum)

Impacts, Issues: The Color of Skin

Skin color comes from the pigment melanin Produced by melanocytes in skin cells More than 100 genes directly or indirectly

influence amount of melanin in an individual’s skin Lead to many variations in skin color

Video: ABC News: All in the family: Mixed race twins

19.1 Basic Concepts of Heredity

Genes provide the instructions for all human traits, including physical features and how body parts function

Each person inherits a particular mix of maternal and paternal genes

Basic Concepts of Heredity (1)

Genes Humans have ~21,500 Chemical instructions for building proteins Locus: specific location on a chromosome

Diploid cells contain two copies of each gene on pairs of homologous chromosomes

Allele: each version of a gene

A Few Basic Genetic Terms

Many Genetic Traits Have Dominant and Recessive Forms

Basic Concepts of Heredity (2)

Homozygous condition: identical alleles

Heterozygous condition: different alleles

Dominant allele Effect masks recessive allele paired with it

Basic Concepts of Heredity (3)

Genetic representations Homozygous dominant (AA) Homozygous recessive (aa) Heterozygous (Aa)

Genotype Inherited alleles

Phenotype Observable functional or physical traits

Genotype and Phenotype Compared

DNAStructur

e

DNA Structure

DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix.

A molecule of DNA is made up of millions of tiny subunits called Nucleotides.

Each nucleotide consists of:1. Phosphate group2. Pentose sugar3. Nitrogenous base

Nucleotides

Phosphate

Pentose

Sugar

Nitrogenous

Base

Nucleotides

The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.

There are four types of nitrogenous bases.

Nucleotides

A

Adenine

T

Thymine

G

Guanine

C

Cytosine

Nucleotides

Each base will only bond with one other specific base.

Adenine (A) Thymine (T)

Cytosine (C) Guanine (G)

Form a base pair.

Form a base pair.

DNA Structure

Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

G

G

A

T

T

A

A

C

T

G

C

A

T

C

DNA Structure

To crack the genetic code found in DNA we need to look at the sequence of bases.

The bases are arranged in triplets called codons.

A G G - C T C - A A G - T C C - T A GT C C - G A G - T T C - A G G - A T C

DNA Structure

A gene is a section of DNA that codes for a protein.

Each unique gene has a unique sequence of bases.

This unique sequence of bases will code for the production of a unique protein.

It is these proteins and combination of proteins that give us a unique phenotype.

Protein

DNA

Gene

Trait

DNA and RNA

Unified Science

DNA: Deoxyribonucleic Acid

• Made up of nucleotides• Building block of DNA• Contains:

–Phosphate–Sugar–Nitrogen Base

DNA: Deoxyribonucleic Acid •Adenine

•Thymine

•Guanine

•Cytosine

Deoxyribose

Base Pairing RULE

• Adenine pairs with Thymine

A T• Guanine pairs with

Cytosine G C

Each base pair is connected by a hydrogen bond

Backbone has covalent bonds

DNA Founders

• James Watson• Francis Crick• Rosalind Franklin• Maurice Wilkins

1962 Noble Prize

Double Helix

There is approximately 6.5 feet of DNA in one single human cell and 10 – 20 billion miles of DNA in the whole body!!!

RNA: Ribonucleic Acid•Adenine

•URACIL

•Guanine

•Cytosine

RIBOSE

DNA vs. RNA

DNA RNA

Sugar Deoxyribose

Ribose

Nitrogen Base

Thymine Uracil

Structure Double Stranded

Single Strande

d

DNA RNA Protein

3 Types of RNA:• Messenger RNA (mRNA) –

carries genetic information from nucleus to cytoplasm

• Transfer RNA (tRNA) – carries amino acids from cytoplasm to ribosomes

• Ribosomal RNA (rRNA) – consists of RNA nucleotides in globular form

Transcription

• Process of genetic information being copied from DNA to RNA

Translation• Process of genetic information

being changed from RNA into amino acids

• Codon - 3 mRNA nucleotides that code for amino acids

• Anticodon - 3 tRNA nucleotides that complement mRNA codon

Translation & Transcription

RNA

Ribonucleic Acid

Structure of RNA

Single stranded Ribose Sugar 5 carbon sugar Phosphate group Adenine, Uracil, Cytosine, Guanine

Types of RNA

Three main types Messenger RNA (mRNA) – transfers

DNA code to ribosomes for translation. Transfer RNA (tRNA) – brings amino

acids to ribosomes for protein synthesis. Ribosomal RNA (rRNA) – Ribosomes are

made of rRNA and protein.

Transcription

RNA molecules are produced by copying part of the nucleotide sequence of DNA into complementary sequence in RNA, a process called transcription.

During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA.

mRNA

How Does it Work?

RNA Polymerase looks for a region on the DNA known as a promoter, where it binds and begins transcription.

RNA strands are then edited. Some parts are removed (introns) - which are not expressed – and other that are left are called exons or expressed genes.

The Genetic Code

This is the language of mRNA. Based on the 4 bases of mRNA. “Words” are 3 RNA sequences called

codons. The strand aaacguucgccc would be

separated as aaa-cgu-ucg-ccc the amino acids would then be Lysine – Arginine – Serine - Proline

Genetic Codes

Translation

During translation, the cell uses information from messenger RNA to produce proteins.

A – Transcription occurs in nucleus. B – mRNA moves to the cytoplasm then to the

ribosomes. tRNA “read” the mRNA and obtain the amino acid coded for.

C – Ribosomes attach amino acids together forming a polypeptide chain.

D – Polypeptide chain keeps growing until a stop codon is reached.

Mutations

Gene mutations result from changes in a single gene. Chromosomal mutations involve changes whole chromosomes.

Gene Mutation

Point Mutation – Affect one nucleotide thus occurring at a single point on the gene. Usually one nucleotide is substituted for another nucleotide.

Frameshift Mutation – Inserting an extra nucleotide or deleting a nucleotide causes the entire code to “shift”.

Gene Mutation

Chromosomal Mutations

Deletion – Part of a chromosome is deleted Duplication – part of a chromosome is

duplicated Inversion – chromosome twists and inverts the

code. Translocation – Genetic information is traded

between nonhomologous chromosomes.

Chromosomal Mutations

Gene Regulation

In simple cells (prokaryotic) lac genes which are controlled by stimuli, turn genes on and off.

In complex cells (eukaryotic) this process is not as simple. Promoter sequences regulate gene operation.