Genetics Chapter 1 And 2 ClassPresentation Transcript
Principles of Genetics Book: Snustad and Simmons, 4th ed. (new edition) Professor: John C. Larkin
Contact Information: John C. Larkin Office: 316 Life Sciences Office Hours: Wed. 10:00am-12:00am Phone: 578-8552 Email: [email_address]
Teaching Assistants: See syllabus for your TA and location of your Discussion Section
Discussion Sections (“Labs”) Discussion of homework problems Quizzes Turn in homework Discussion sections will meet this week!
Grading: Two lecture exams 200 points Final exam ( Comprehensive!) 100 points Homework (best 5 of 6) 50 points Quizzes (best 5 of 6) 50 points 400 points
Make-up Exam: The third exam is an in class make-up exam for students who missed an exam due to an excused absence. There will be no other make-up exams. The make-up may not substitute for the final. Students may also take the make-up exam to replace a lecture exam score but in this case the make-up exam must count toward the final grade.
Incarceration rate by gender (from http://www.ojp.usdoj.gov/bjs/prisons.htm ) : Men are ten times as likely as women to be in prison. But, incarceration rate is increasing faster among women than among men (from 2003 to 2004, 2.9% increase for women, 2.0% increase for men).
Genetics: The Science of Inheritance Genotype (Inherited traits) Environment Phenotype (Actual characteristics of organism)
Genetic Variation in Chickens Gold-laced Wyandotte Black Wyandotte
Genetically-engineered resistance to the European Corn Borer Fig. 1.14
Structure of Eukaryotic Cells Fig. 2.2
DNA is found in:
Mitochondria and chloroplasts
Mito. and chloro. derived from
Fig. 1.4 DNA Structure (Simplified)
Hydrogen-bonded base-pairs (G-C, A-T)
Covalently-bonded sequence of base-pairs
Functions of DNA: Replication (preserves genetic information) Gene expression (information in genes expressed as protein for cell functions)
(Fig. 1.6) DNA replication depends on base-pairing and preserves the sequence of bases
Gene Expression: The process by which genes affect the phenotype. Converts sequence of nucleotides to sequence of amino acids in a protein, via transcription and translation.
Human beta-globin gene expression FIG. 1.7
Protein Structure and Function
. The amino acid sequence of a protein determines its structure and function.
Much of an organism’s phenotype results from protein function.
Example: Hemoglobin carries O 2 and CO 2 in the blood
Consequences of mutation
Changes in the DNA sequence of a
gene (mutations) change the sequence
of the encoded protein.
Therefore, mutations can alter protein
structure and function.
Example: Hemoglobin sickle-cell
Mutations in genes change proteins and phenotypes Normal gene Normal protein Normal phenotype Mutant gene Mutant protein Mutant phenotype
Mitosis and Meiosis
The Cell Cycle
Mitosis: Purpose is to preserve chromosome number.
Meiosis: Purpose is to create haploid gametes, and to create new genotype combinations.
Replication of a chromosome during mitosis (in a diploid) Diploid cell Replicated chromosomes Chr. # preserved
Meiosis Four haploid gametes Meiosis Diploid cell
Human Life Cycle Mitosis makes my toes Meiosis makes my gametes (From Campbell)
The Cell Cycle (Fig. 2.4) G1 S G2 Mitosis & cytokinesis
Structure of a replicated chromosome
Counting chromosomes and chromatids
n = haploid number of chromosomes
Example: the humans have 23 different chromosomes (n=23).
Diploid cells have 2n chromosome #. Human diploid cells, have 46 chromosomes (2n=46).
c = number of chromatids in unreplicated (G1) haploid state.
Replication of a chromosome in a diploid (n=1) during mitosis (see Fig.2.10) G1 S G2 After cytokinesis Both daughter cells still diploid! 2n 2c 2n 4c 2n 2c
Stages of mitosis (Fig. 2.6)
Stages of mitosis
Note! At metaphase in mitosis, all chromosomes line up individually on the metaphase plate, and the chromatids separate and move to opposite poles as independent chromosomes.
Meiosis Fig. 2.11
Meiosis overview: Meiosis I
Prophase of Meiosis I is longer than mitotic prophase.
In Metaphase I, the two copies of each replicated chromosome pair at the metaphase plate (a tetrad ), unlike mitosis.
In Anaphase I, each chromosome moves to pole without chromatid separation.
At the end of Meiosis I, the chromosome # has been reduced, but each chromosome still has two chromatids.
Meiosis overview: Meiosis II
The chromosomes are not replicated in the interphase between Meiosis I & Meiosis II.
The chromatids finally separate in Anaphase II.
The final result is four haploid gametes, each with half the number of chromosomes present in the diploid cells.
Chromosomes in Meiosis (in a diploid, see Fig. 2.10) 2n, 2c 2n, 4c 1n, 2c 1n, 2c Meiosis I: Reduction division Tetrad Two copies of same chromosome
Meiosis, continued 1n, 2c 1n, 2c Meiosis II Four haploid gametes, all 1n, 1c.
Fig. 2.14. Crossing over Occurs during prophase I Chiasma (pl. chiasmata) indicate where chromosomes have exchanged genetic material.
Crossing over (Recombination) Synapsis (pairing) Prophase I Metaphase I
Genes in Meiosis Meiosis I: Reduction division Two copies of chromosome, with -globin alleles H h Let H= normal -globin Let h=sickle cell -globin
Meiosis, continued Meiosis II Four haploid gametes, 2 H and 2 h H H h h
Fig 3.1 Let D = tall Let d = dwarf P F1 F2 D_ = DD or Dd DD dd Dd 787 Tall (D_ ) 277 Dwarf (dd)
Mendel’s Initial Observations from Monohybrid Cross
The dwarf trait is hidden in the F1, but reappears unchanged in the F2. This contradicts “blending inheritance”.
In the F2, tall and dwarf plants appear in a ratio of about 3 tall : 1 dwarf.
Each trait is controlled by an inherited factor, now called a “gene”.
Two copies of each gene are present in the organism. These copies are called “alleles”.
The alleles are usually transmitted unchanged through crosses.
Fig. 3.2. Symbolic representation of Mendel’s cross Punnett Square
Principle of Dominance: In a heterozygote, one allele may conceal another.
Principle of Segregation: In a heterozygote, the alleles segregate from each other during gamete formation.
Molecular basis of Mendel’s cross
Gibberellin (GA) is a plant growth hormone, synthesized by specific enzymes.
Dwarf plants (dd homozygotes) have a mutation a gene that codes for a GA biosynthesis enzyme.
Tall plants have at least one functional copy of the enzyme.