genetics unit review
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Genetics Unit Review
Introduction to Genetics
GeneticsGenetics - the scientific study of heredity.
Heredity - Passing of traits from parents to offspring
Gregor Mendel was an Austrian monk. His work was important to the understanding of heredity.
Alleles and GenesGene - section of DNA which encodes for a
protein that determines a physical trait ( ie eye color).
Allele - a version of a gene. Each gene can have multiple versions, or alleles.
Alleles
Homozygous - two alleles are identical (BB, bb)Heterozygous - two alleles are different (Bb)
Trait - a specific characteristic that varies from one individual to another.
Some alleles are dominant (Capital letter) and others are recessive (lower case letter).
An organism will always exhibit the dominant trait when present.
Genotype vs Phenotype
Phenotype - physical appearance of an inherited trait.
Genotype - genetic makeup of a person.
Relationship Between Genotype and Phenotype
The genotype codes for the phenotype.
Genetics and ProbabilityProbability - the likelihood that a particular event will occur.
The principles of probability can be used to predict the outcomes of genetic crosses.
PUNNETT SQUARES!
Punnett SquaresPunnett squares can be used to predict and compare the genetic variations that will result from a cross.
Capital letter (G) = dominant allele for green
Lowercase letter (g) = recessive allele for yellow
The dominant allele will mask the recessive allele
Punnett Square ExampleFreckles (F) = DominantNo freckles (f) = Recessive
Ff - Heterozygousff - HomozygousFF - Homozygous
Ff - Frecklesff - No frecklesFF - Freckles
F f
f
f
Ff ff
Ff ff
50% freckles50% no freckles
Meiosis and Sexual Reproduction
MeiosisMaking Sperm and Eggs
Meiosis occurs in sexual reproduction when a diploid (2n) germ cell produces 4 haploid (1n) daughter cells that can mature to become gametes (sperm or egg)
Goal #1 of MeiosisGoal: Reduce genetic material by 1/2.
from mom from dad child
meiosis reducesgenetic content
toomuch!
Just right!
Why? 1n (Mom) + 1n (Dad) = 2n (offspring)
Crossing over occurs during Prophase I when parts of homologous chromosomes overlap. Crossing over increases genetic variation.
Goal #2 of Meiosis
Comparison of Mitosis and Meiosis
Mitosis Meiosis
# of divisions 1 2
# of daughter cells 2 4
Genetically identical yes no
Chromosome # Same as parent Half of parent
Where Somatic cells Sex cells
When Throughout life At sexual maturity
Role Growth and repair
Sexual reproduction
2 Phases of MeiosisMeiosis I - Homologous chromosomes separate
Meiosis II - sister chromatids separate
Phases of Meiosis
X
X
Y
Y
X
Location of Meiosis
X
X
Y
Y
X
Males - Testes Females - Ovaries
Meiosis in Males and Females
X
X
Y
Y
X
Diploid (2n) vs. Haploid (1n)
Diploid - Cells with 2 copies of each chromosome.
In humans, all cells except sex cells (gametes)
Haploid - Cells with only 1 copy of each chromosome.
In humans, only sex cells (gametes)
Chromatids vs. Homologous Chromosomes
Hom
olo
gous
chro
mos
omes
Sister chromatids are 2 duplicates of a chromosome made during DNA replication.
Homologous chromosomes are a pair of the same chromosome, one from Mom, one from Dad.
Crossing over occurs during Prophase I when parts of homologous chromosomes overlap. Crossing over increases genetic variation.
Crossing Over
8 chromosomes at the beginning of meiosis.
4 chromosomes at the end of meiosis.
Goal #1 of MeiosisGoal: Reduce genetic material by 1/2.
The Structure of DNA
NucleotidePhosphate
DeoxyriboseSugar
NitrogenousBase
One deoxyribose sugar, one phosphate and one nitrogenous base make a nucleotide.
Nitrogenous Bases
Purines:Adenine (A)Guanine (G)
Pyrimidines:Cytosine (C)Thymine (T)
Purines are double ring bases and Pyrimidines are single ring bases
Hydrogen Bonds
• Two strands of DNA are held together by hydrogen bonds
• RNA only has one strand. No hydrogen bonds
Base Pairing Rule
Guanine Cytosine Adenine Thymine
Structure of DNA
Sides of ladder = sugars (S) and phosphates (P)Rungs of ladder = nitrogenous base (A,T,G,C)
The Shape of the DNA Molecule
• DNA is a very long polymer
• The basic shape is like a twisted ladder
• This is called a double helix
• The DNA double helix has two strands twisted together
Components of DNA
• Nucleotide - C• Deoxyribose
sugar - E• All nitrogenous bases - A, B, D, F• Phosphate - G• Hydrogen bond - H
Structure of DNA
• The backbone of DNA is repeating phosphates and deoxyribose sugar
•The rungs are nitrogenase bases
Central DogmaDNA Transcription RNA Translation Protein
(Nucleus) (Cytoplasm)
• DNA Replication occurs in the nucleus.
• Two strands of DNA identical to the parent DNA are produced.
• DNA has to be copied before the cell divides.
DNA Replication
• DNA Transcription occurs in the nucleus.
• Messenger RNA (mRNA) is produced.
• mRNA carries copies of the instructions for making proteins from the nucleus to the ribosome.
DNA Transcription
• DNA Translation occurs in the cytoplasm.
• Amino acids are produced.
• Conversion of mRNA into an amino acid sequence that makes protein.
DNA Translation
Central DogmaDNA Transcription RNA Translation Protein
(Nucleus) (Cytoplasm)
Semi-Conservative Replication
Parent DNAStrand
DNAReplication
Two identical DaughterDNA Strands
Replication - DNA to DNA
DNA Replication• DNA molecule untwists and unzips into
two strands
• Free nucleotides attach and 2 new strands are produced using the old strand as a template
• DNA replication is semi-conservative: one DNA strand is conserved, other is new
Replication Bubbles
In eukaryotes, DNA replication occurs at hundreds of sites. Replication proceeds in both directions until each chromosome is completely copied. The sites where replication occurs are called replication forks.
Replication Fork
• DNA replication begins at the Origins of Replication• Two strands open forming Replication Forks• New strands grow at the forks
DNA Replication
• Parent strands - D & E• New strands - A & B• Enzyme at C - DNA Polymerase
RNA vs DNA
RNA DNA
• single stranded• short ( 1 gene)• ribose sugar• uracil (U)
• double stranded• long (many genes)• deoxyribose sugar• thymine (T)
NitrogenousBase
SugarPhosphateBackbone
NitrogenousBase
SugarPhosphateBackbone
Protein Synthesis Requires Three Types of RNA
1. mRNA - Messenger RNA
2. tRNA - Transfer RNA
3. rRNA - Ribosomal RNA
DNA Transcription• mRNA is formed from DNA in the nucleus by a process called DNA transcription
• mRNA goes from the nucleus to the ribosome in the cytoplasm
• mRNA is translated into amino acids to make a protein
Parts of Transcription/Translation
A - DNA E - Codon K - mRNAB - DNA template F,G,H - tRNA L - Amino acid chainC - mRNA I - Anticodon M - Amino acidD - Nuclear Memb. J - Ribosome
Central Dogma Summary
Translation of mRNA into Amino Acids
• The “words” of the DNA “language” are triplets of bases called CODONS
3 bases = 1 triplet = 1 codon - located on mRNA
Transfer RNA (tRNA)
The anticodon is complementary to the 3 bases of the codon on the mRNA molecule.
codon
anticodon
anticodon
PracticeA T C G A C T
T A G C T G A
Original DNAReplication
Comp. DNA
A T C G A C TOriginal DNATranscription
mRNA U A G C U G A
Mutations
TAC GCC AGC CCG Original
TAC CCA GCC CG
TAC GCC AGC CCG Original
TAA CGC CAG CCC G
Mutation 1
Mutation 2
Deletion
Insertion
Mutations
TAC GCC AGC CCG Original
TAC GCC TGC CCG
Mutation 3
Substitution
Which mutations are frameshift mutations?
Deletion and Insertion
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