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: jlarkin@lsu.edu

Teaching Assistants:

See syllabus for your TA and locationof 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 points400 points

Make-up Exam:

The third exam is an in class make-up exam for students who missed an exam due to anexcused 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.

Homework

Problems 2.4, 2.5, 2.9, 2.10, 2.11, 2.12, 2.13, 2.15.

Due: Wednesday, Jan 23 (Sec 5,6,7 &10)

or Friday, January 25 (Sec 8,9,11,12)

(Along with additional problems).

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 forwomen, 2.0% increase for men).

Genetics: The Science of

InheritanceGenotype(Inherited traits)

Environment

Phenotype(Actual characteristicsof organism)

Genetic Variation in Chickens

Gold-lacedWyandotte

BlackWyandotte

White-crested Polands

Genetically-engineered resistance to the European Corn Borer

Fig. 1.14

Structure of Eukaryotic Cells

Fig. 2.2

DNA is found in:

Nucleus

Mitochondria and chloroplasts

Mito. and chloro. derived from prokaryotic symbionts

Fig. 1.4

DNA Structure (Simplified)

Hydrogen-bonded base-pairs (G-C, A-T)

Covalently-bonded sequence of base-pairs(deoxyribose-phosphodiester backbone)

Functions of DNA:

Replication (preserves genetic information)

Gene expression (information in genes expressed as proteinfor cell functions)

(Fig. 1.6)

DNA replication depends on base-pairingand 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 O2 and CO2 in the blood

Consequences of mutation

Changes in the DNA sequence of agene (mutations) change the sequence of the encoded protein.

Therefore, mutations can alter proteinstructure and function.

Example: Hemoglobin sickle-cellmutation.

Mutations in genes change proteinsand phenotypes

Normal gene

Normal protein

Normalphenotype

Mutant gene

Mutant protein

Mutantphenotype

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

Replicatedchromosomes

Chr. #preserved

Meiosis

Four haploid gametes

Meiosis

Diploid cell

Human Life Cycle

Mitosismakes mytoes

Meiosismakes 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

Aftercytokinesis

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 toopposite poles as independentchromosomes.

MeiosisFig. 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:Reductiondivision

Tetrad

Two copies ofsamechromosome

Meiosis, continued

1n,2c

1n,2c

Meiosis II

Four haploid gametes, all1n, 1c.

Fig. 2.14. Crossingover

Occurs during prophase I

Chiasma (pl. chiasmata)indicate where chromosomes have exchanged geneticmaterial.

Crossing over (Recombination)

Synapsis(pairing)

Prophase I

Metaphase I

Genes in Meiosis

Meiosis I:Reductiondivision

Two copies ofchromosome,with -globin alleles

H hLet 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.

Mendel’s Conclusions

• 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

PunnettSquare

Mendel’s Principles

• 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.