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