Review 4: Heredity & Molecular Genetics

AP Biology

Heredity & Molecular Genetics• Meiosis produces haploid gametes.• Different versions of same gene are called

alleles.• Mendelian inheritance• Non-Mendelian inheritance• Chi-square analysis• DNA & RNA• Central Dogma• Regulation of Genes• Mutations• Biotechnology

Meiosis Produces Haploid Gametes

• Meiosis 1 separates homologous pairs: reduction division

• Meiosis 2 separates sister chromatids: produces 4 sex cells

Different Versions of Same Gene are Called Alleles

• Dominant vs. Recessive• Homozygous vs. Heterozygous• Phenotype vs. Genotype

Mendelian Inheritance• Monohybrid Crosses

-Aa x Az = 3:1 ratio-Law of SegregationAlternative alleles of a character segregate and remain distinct.• Dihybrid Crosses

-AaBb x AaBb = 9:3:3:1 ratio-Law of Independent AssortmentGenes that are located on different chromosomes assort independently during meiosis.• Test Cross

-Determine genotype of individual showing dominant phenotype.-Unknown (A_) x aa (homozygous recessive)

Non-Mendelian Inheritance

• Incomplete Dominance (pink flower color)• Co-dominance (blood type)• Sex linked (mainly X-linked: color

blindness, hemophilia)• Epistasis (coat color)• Pleiotrophy (dwarfism, giantism)• Polygenic (skin color)

Epistasis• The effects of one gene are modified by one or

several other genes

Pleiotropy & Polygenic• A single gene influences multiple phenotypic

traits• Examples: Dwarfism, Gigantism

• Polygenic

Chi-square analysis

• Determining if observed results are significantly different from expected results

• Know how to use formula when given & how to interpret results

-degrees freedom (1 less than number of classes of results)-less than p=.05, then difference can be due to random chance alone & null hypothesis is accepted

DNA & RNA• DNA: ACTG nitrogen bases, double helix

- A:T, C:G• RNA: ACUG nitrogen bases, single helix

Central Dogma• DNA -> RNA -> protein -> trait• Transcription (DNA -> mRNA)• Translation (mRNA -> protein)

Transcription• Production of RNA copy of DNA sequence• In nucleus• RNA polymerase copies coding strand & produces

mRNA

Translation

• mRNA -> protein• In cytoplasm• Codons on mRNA read by ribosome• Matched to anticodons of tRNA• tRNA carries amino acids to mRNA &

ribosome assembles polypeptide chain• Start codon (Met) & stop codons, redundancy

in code• Universal code (single common ancestor)

Regulation of Genes• Operons

-Prokaryotes-Cluster of genes for enzymes in a pathway-Controlled by repressor protein-Repressible operon (synthesis pathway = tryp operon) vs. inducible operon (digestive pathway = lac operon)• Transcription Factors

-Proteins which enable bonding of RNA polymerase to gene

Operons• Functioning unit of genomic material containing a

cluster of genes under the control of a single regulatory signal or promoter

Mutations• Fuel for evolution = variation, genetic

change• Gene duplication, point mutation,

insertions, deletion

Biotechnology

• Scientists can modify an organism’s genome by inserting foreign DNA.

• Techniques

Modify Organism’s Genome

• Bacterial Transformation (human insulin gene in E. coli)

• Possible because of universal genetic code

Techniques• Restriction digest: Restriction enzymes,

sticky ends• Transformation: Restriction enzymes,

sticky ends, ligase, amp selection, lacZ screening

• Gel electrophoresis: DNA moves in an electrical field (negative -> positive), small pieces move further

• PCR: DNA amplification• RFLP: DNA fingerprinting• Sanger sequencing: Human Genome

Project