Genetics Unit Review

Introduction to Genetics

Genetics Genetics - 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 Genes Gene - 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 Probability Probability - 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 Squares Punnett 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 Example Freckles (F) = Dominant No freckles (f) = Recessive F f f Ff ff Ff - Heterozygous ff - Homozygous FF - Homozygous Ff ff Ff - Freckles ff - No freckles FF - Freckles 50% freckles 50% no freckles

Meiosis and Sexual Reproduction

Meiosis Making 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 Meiosis Goal: Reduce genetic material by 1/2. from mom from dad child meiosis reduces genetic content too much! Just right! Why? 1n (Mom) + 1n (Dad) = 2n (offspring)

Goal #2 of Meiosis Crossing over occurs during Prophase I when parts of homologous chromosomes overlap. Crossing over increases genetic variation.

Comparison of Mitosis and Meiosis # of divisions 1 2 # of daughter cells 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 Meiosis Meiosis 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 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. Homologous chromosomes

Crossing Over Crossing over occurs during Prophase I when parts of homologous chromosomes overlap. Crossing over increases genetic variation.

Goal #1 of Meiosis Goal: Reduce genetic material by 1/2. 8 chromosomes at the beginning of meiosis. 4 chromosomes at the end of meiosis.

The Structure of DNA

Nucleotide Phosphate Nitrogenous Base Deoxyribose Sugar 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 Dogma DNA Transcription RNA Translation Protein (Nucleus) (Cytoplasm) DNA Transcription RNA Translation Protein

DNA Replication 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 Transcription 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 Translation DNA Translation occurs in the cytoplasm. Amino acids are produced. Conversion of mRNA into an amino acid sequence that makes protein.

Central Dogma DNA Transcription RNA Translation Protein (Nucleus) (Cytoplasm) DNA Transcription RNA Translation Protein

Semi-Conservative Replication Parent DNA Strand DNA Replication Two identical Daughter DNA 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) Sugar Phosphate Backbone Nitrogenous Base Nitrogenous Base Sugar Phosphate Backbone

Protein Synthesis Requires Three Types of RNA 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 - mRNA B - DNA template F,G,H - tRNA L - Amino acid chain C - mRNA I - Anticodon M - Amino acid D - 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) codon anticodon The anticodon is complementary to the 3 bases of the codon on the mRNA molecule.

Practice A T C G A C T T A G C T G A A T C G A C T U A G C U G A Original DNA Replication Comp. DNA T A G C T G A A T C G A C T Original DNA Transcription mRNA U A G C U G A

Mutations TAC GCC AGC CCG Original TAC CCA GCC CG Deletion Mutation 2 TAC GCC AGC CCG Original TAA CGC CAG CCC G Insertion

Mutations TAC GCC AGC CCG Original TAC GCC TGC CCG Substitution Which mutations are frameshift mutations? Deletion and Insertion