6/11/13 LIVING ENV.1. Attendance2. Test Information3. Review powerpoints 4. Time to work on owed work.
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
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 II
Meiosis I results in two haploid (N) cells. Each cell has half the number of
chromosomes as the original cell.
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!
Meiosis Cell Division - Makes Gametes
4 functional (all 4 work) sperm
Humans have 46 chromosomes, so gametes have HALF that number -23
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
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
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
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
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
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.
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.
DNA: Deoxyribonucleic Acid
• Made up of nucleotides• Building block of DNA• Contains:
–Phosphate–Sugar–Nitrogen Base
There is approximately 6.5 feet of DNA in one single human cell and 10 – 20 billion miles of DNA in the whole body!!!
DNA vs. RNA
DNA RNA
Sugar Deoxyribose
Ribose
Nitrogen Base
Thymine Uracil
Structure Double Stranded
Single Strande
d
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
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
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.
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
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”.
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.
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