Genetic ENGINEERING

Passage of information from parents to offspring

• Genetic information is passed from generation to generation.
• Sexual reproduction produces genetically similar, but not identical, offspring.
• Meiosis, a cell division type, generates genetic variation.

Meiosis

• Meiosis occurs in a few cells in the testes and ovaries.
• Meiosis involves two divisions, forming four daughter cells.
• Meiosis produces four new cells with half the number of chromosomes as the parent cell and different allele combinations.
• In animals and flowering plants, meiosis produces gametes.
• Human body cells are diploid (2n), containing two complete chromosome sets.
• Meiosis produces haploid (n) gametes, containing one chromosome set.
• Meiosis is a reduction division necessary for a diploid zygote after fertilization.

Behaviour of chromosomes during meiosis

• DNA replication occurs before meiosis.
• Homologous chromosomes pair up in early meiosis stages.

Meiosis stages

• Prophase I: Centrioles divide, spindle forms, chromosomes condense, pairing occurs making bivalents.
• Metaphase I: Nuclear envelope disappears, bivalents align on the equator.
• Anaphase I: Homologous chromosomes separate to opposite poles via spindle fibres.
• Telophase I and Cytokinesis: Chromosomes unwind, spindles disappear, nuclear envelopes form, the cell divides.
• Prophase II: Centrioles divide, spindles form, chromosomes condense.
• Metaphase II: Individual chromosomes line up on the equator.
• Anaphase II: Centromeres split, chromatids separate via spindle fibres.
• Telophase II: Spindles disappear, nuclear envelopes appear, chromosomes unwind.

Genetic Variation

• Meiosis causes genetic variation through crossing over and independent assortment.
• Random gamete fusion during fertilization further increases genetic variation.

Genes and Alleles

• Homologous chromosomes in diploid cells contain the same genes in the same position (locus).
• Genes have different forms called alleles.
• An allele is one of two or more different forms of a gene that codes for a particular polypeptide or protein.

Homozygote and Heterozygote

• A homozygote has two identical alleles for a particular gene.
• A heterozygote has two different alleles for a particular gene.

Dominant and Recessive

• Letters represent alleles (e.g., F for functional and f for mutant).
• Genotypes are allele combinations (FF, Ff, ff).
• Phenotypes are observable characteristics determined by genotypes.
• Ff is a carrier: has the recessive allele but not the condition.
• Dominant alleles are expressed in heterozygotes; recessive alleles only when homozygous.
• Dominant alleles are represented by capital letters, and recessive alleles by lowercase letters.

Monohybrid inheritance

• Monohybrid inheritance is the inheritance of a single gene.
• Genetic diagrams predict offspring genotypes; always set them out clearly.
• Male gametes and sperm will contain either A allele or a allele.

Monohybrid Crosses: Skills

• Show the complete genetic diagram, not just the Punnett square.
• Indicate gamete genotypes and circle them.
• State the phenotype produced by each offspring genotype.
• Genotypes in Punnett squares show probabilities of being produced.
• A 1 in 4 chance can be written as a probability of 0.25 or 25%.
• Chance of individual child inheriting genotype is unaffected by previous children.

Test Crosses

• Test crosses determine the genotype of an organism with a dominant characteristic.
• Breed the organism with a homozygous recessive organism.
• Offspring phenotypes reveal the unknown genotype.

Codominance

• Codominant alleles both have an effect in a heterozygote.
• Use a capital letter with superscripts to represent codominant alleles.

F1 and F2 Generations

• Crossing homozygous organisms (AA and aa) produces the F1 generation (heterozygous Aa).
• Crossing two F1 individuals produces the F2 generation.

Multiple Alleles

• Some genes have more than two alleles.
• Blood group gene has three alleles: IA, IB, and I0.

Sex Linkage

• A sex-linked gene is present on the X chromosome but not the Y.
• Women (XX) have two copies; men (XY) have one copy.
• The X chromosome is longer than the Y chromosome.
• Recessive sex-linked alleles are expressed more often in males.

Sex Linked: Notice

• Superscripts on X indicate sex-linked alleles.
• Females: three possible genotypes, males: two.
• Boys inherit sex-linked genes from their mother as they receive the Y chromosome from the father.

Dihybrid inheritance

• Dihybrid inheritance involves two genes.

Notice: dihybrid cross

• Always write alleles for the same gene together and in the same order.

Dihybrid Cross

• The genetic diagram shows offspring from a cross between two heterozygous dogs with both genes showing dominance.
• 9:3:3:1 ratio is typical for dihybrid crosses between heterozygotes with dominance.

Epistasis

• Epistasis occurs when two genes at different loci interact to produce a phenotype.

Using Statistics in Genetics

• Genetic diagrams predict probabilities; phenotypic ratios are rarely exact.
• Statistics determine if observed results differ significantly from expected results.

Null Hypothesis and Probability Level

• Null hypothesis: observed results are not significantly different from expected results.
• Statistics test determines the probability of the null hypothesis.
• If the probability is ≥0.05, accept the null hypothesis.
• If the probability is <0.05, reject the null hypothesis.

The Chi-Squared Test

• Chi-squared test (x²) is used to test the probability of the null hypothesis.
• Construct a results table.

Genes, proteins and phenotypes

• Genes code for amino acid sequences of polypeptides and proteins.

The TYR Gene and Albinism

• Melanin is the pigment for fur, skin, and iris color.
• TYR gene codes for tyrosinase, an enzyme needed for melanin production.
• Mutations in TYR mean non-functional tyrosinase.
• Two copies of a non-functional TYR gene cause albinism.
• At least one functinal TYR may produce enough tyrosinase for function.

The HBB Gene, Haemoglobin and Sickle-Cell Anaemia

• HBB gene codes for a polypeptide in haemoglobin.
• Sickle-cell anaemia: base T instead of A.
• HbA: normal allele
• Hbs: sickle allele
• Normal sequence: GTG CAC CTG ACT CCT GAG GAG AAG TCT.
• Amino acid sequence: Val-His-Leu-Thr-Pro-Glu-Glu-Lys-Ser.
• Abnormal: GTG CAC CTG ACT CCT GTG GAG AAG TCT.
• Change: one base pair.
• Amino acid sequence: Val-His-Leu-Thr-Pro-Val-Glu-Lys-Ser.
• Glutamic acids are outside and hydrophilic and interact with water to make molecules soluable.
• Valine is hydrophobic and does not.
• Causes molecules to stick and pull red block cells otu of shapd when oxygen concentrtion is low.
• Sicle cells do not move easily through blod.

The F8 Gene, Factor VIII and Haemophilia

• Clotting factors are plasma proteins for blood clotting.
• F8 codes for factor VIII clotting protein.
• If injured the protein activates as factor VIII which stops blood.
• Mutation causes and abnormality or reduciton.
• The F8 is located on the X chromosome so the condition is sex-linked.

The HTT Gene, Huntingtin and Huntington's Disease

• Harmful conditions are the result of receissive allelles.
• Huntingtons is an example of dominant allele.
• The HTT gene codes for a huntington protein.
• HTT gene has a repeating the CAG triplicate sequence. A mutut allele with 40 copies can caue damage.
• Huntington diseases is usually causes by a dominant allele where the possession of one one copy of mutut allele will result in the disease.

Genetic Control of Stem Elongation

• The amount of gibberellin stimulates stem elongation in the planys.
• The plants dont have to stem enzymes which make gibberellinl which causes plants to remaisn small.
• If Le is the domiant is will code for the enzyme.
• If the plant id hoozygous it wil not produce enymes where Applying gibberellin is these plants make them grow taller.

Control of gene expression

• All cells in a person conatins a full set of genes.
• Gene expression is is the reult of transacription and Translation that result in the productiion of a polypetide or protein in for what it codes.

The Lac Operon

• Lac is an example of best studied controle gene.
• The bacterium makes lactase only if lactase is present where this is located for the gene is closely with seveal gene.
• Each structural gene code for a protein where involveds the enyme and protien.
• Alllowing for transcribes

Trancriptions Factors in Eukaryotes

• A molecule that causes and prevent trascription by coding for enzymes.
• If present, enzymes will break down DELLA protiens where the PIF from free that bind to amylase to produced.