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Division of Sex Cells

 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 usually involves 2 distinct stages  Meiosis I  Meiosis II

 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.

 Spindle fibers attach to the chromosomes

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

 Nuclear membranes form.  The cell separates into 2 cells.

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

 The chromosomes line up similar to metaphase in mitosis.

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

 Meiosis II results in 4 haploid cells.

 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.

MitosisMeiosis Results 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!

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

4 functional (all 4 work) sperm Humans have 46 chromosome s, so gametes have HALF that number - 23

Right! Only one!

MitosisMeiosis 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 24 Ends up with this many FUNCTIONAL cells 2 4 for sperm but only 1 for eggs (ovum)

 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

 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

 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

 Homozygous condition: identical alleles  Heterozygous condition: different alleles  Dominant allele  Effect masks recessive allele paired with it

 Genetic representations  Homozygous dominant ( AA )  Homozygous recessive ( aa )  Heterozygous ( Aa )  Genotype  Inherited alleles  Phenotype  Observable functional or physical traits

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 group 2. Pentose sugar 3. Nitrogenous base

Phosphate Pentose Sugar Nitrogenous Base

The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.

A Adenine T Thymine G Guanine C Cytosine

Each base will only bond with one other specific base. Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair.

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

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

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 DNARNA SugarDeoxyriboseRibose Nitrogen Base ThymineUracil StructureDouble Stranded Single Stranded

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.