UNIT IV

UNIT IV

Genetics

I. GeneticsA. Mendel – father of genetics

• Inheritance – traits carried on chromosomes

• Genes – code for certain traits• Alleles – same gene,

different trait

B. Principle of dominance – dominant trait will express itself1.Dominant traits –

expresses , shows up2.Recessive traits – will

only show up if both recessive alleles are present

C. Genotype – gene, “code” R = red & r = white

1. Homozygous dominant – 2 dominant alleles (RR = purebred)

2. Homozygous recessive – 2 recessive alleles (rr = purebred)

3. Heterozygous – one dominant and one recessive allele (Rr = hybrid)

D. Phenotype – how genotype expresses itself , “looks like

C.Punnett square – prediction of pairing• R = red, r = white• Genotypes all Rr• Phenotypes all redRR x rr

R R

Rr Rr

Rr Rr

r

r

• R = red, r = white• Genotypes 1 RR, 2 Rr, 1 rr• Phenotypes 3 red, 1 white• Rr x Rr RR Rr

Rr rr

R r

R

r

Heterozygous(hybrid) cross

D. Incomplete dominance – heterozygous “blending” of dominant and recessive trait• Genotypes all Rr phenotypes all pinkRR x rr

• 1RR = red, 2Rr = pink, 1 rr = white

• 2 pink and 2 white

Rr Rr

Rr Rr

R R r

r

RR Rr

Rr rr

R rR

r

Rr rrRr rr

R r r r

E. Codominance – if heterozygous, both traits are expressed

Blood types : antigens A, B, AB, OAB blood - both A and B antigens are presentPositive blood is a separate gene Rh d antigen

F.Multiple alleles – traits expressed on more than two alleles

1. 3 or more alleles – combinations of alleles genotype AABBCCDD whats the phenotype

2. Human examples• Hair color – 3 alleles (9)• Eye color – 3 alleles (9)• Skin color – 8 alleles (64)

G.Polygenic system – interaction of multiple genes, determines phenotype

1. Continuous variation – full range of phenotypes –2. Discontinuous variation – phenotype fall into a few

well separated categories

H. Environmental Influence on gene expression1. sun exposure, coldexample: siamese cat and himalayan darker color on ears, face and paws

I. Principle of segregation1. Gametes – separation of alleles – occurs

during meiosis2. Parental – purebreds homozygous,

dominant or recessive (RR x RR or rr x rr) P generation = RR x rr

3. First filial – F1 generation, offspring of P generation, hybrids – heterozygous Rr

4. Second filial – F2 offspring of hybrid cross, phenotype ratio 3:1

J. Independent assortment• Dihybrid cross –TtGg x TtGg• predicted phenotypes 9:3:3:1• T = tall• t = dwarf fill this in • G = green• g = albino

Punnett Square for BbEe sire bred to BbEe dam

* Dam can contribute

BE bE Be be

Sire

can

contribute

BE BBEE BbEE BBEe BbEe

bE BbEE bbEE BbEe bbEe

Be BBEe BbEe BBee Bbee

be BbEe bbEe Bbee bbee

Being black, sire and dam must both be B-E-; having produced yellow and chocolate pups, each must also have the b and e alleles, so in each case the genotype is BbEe. A BbEe parent can contribute the four combinations of alleles BE, bE, Be, and be to various pups.

BBEE (1 pup in sixteen or 6.25%) blackBbEE (2/16 or 12.5%) blackBBEe (2/16 or 12.5%) blackBbEe (4/16 or 25%) blackbbEE (1/16 or 6.25%) chocolatebbEe (2/16 or 12.5%) chocolateBBee (1/16 or 6.25%) yellowBbee (2/16 or 12.5%) yellowbbee (1/16 or 6.25%) yellow with brown nose and light eyes

II. Human geneticsA. Karyotyping – human chromosomes

1. Autosomal – 22 pairs of somatic2. Sex chromosomes – 1 pair XX or XY

B. Pedigree – genetic relationship in familieshttp://www.zerobio.com/drag_gr11/pedigree/

pedigree1.htm

C. Abnormalities – different from the normD. Disease – serious disorders or abnormalities caused by genes

III. Human genesA. Autosomal recessive inheritance – must have both recessive alleles

1. Albinism – aa , can’t make melanin2. Tay-sachs disease – at 6 months

develops spot on retina blindness, death

3. Cystic fibrosis – most common 1/2500 children

4. Lactose intolerance – don’t have lactase5. Sickle cell anemia – red blood cells,

sickle shaped – so can’t carry O2 well and get stuck in capillaries

B. Autosomal dominant inheritance – two dominant alleles or heterozygous

1. Darwin tubercle – thickened rim of cartilage in ear

2. Achondroplasia – dwarfism3. Huntington’s disease – manifests in 30’s or

40’s, loss of muscle control, loss of brain tissue

4. Polydactyly – 6 fingers or toes

IV. Sex-linked human inheritance – traits carried on the x chromosome

A. Sex – linked disorders XX normal female, X-X female carrier,

X-X- afflicted female, X-Y afflicted male,

XY normal male1. Hemophilia – bleeding disorder X-Y

or X-X-

2. Colorblindness – red- green –blue , X-Y or X-X-

V. Incorrect chromosome number – any number but 46 in humans (Down syndrome- 47) trisomy on the 21st chromosome

A. Disjunction abnormalities – extra or too few, occurs in meiosis, can also result in some degree of mental retardation and increased risk of diseases and defects1. Turners syndrome: XO2. Klinefelter syndrome: XXY3. Meta or super female: XXX4. Jacob syndrome: XYY

VI. Gene Regulation in Eukaryotes

• Female cat cells inactivate one of two X chromosomes in every cell (producing a Barr body)– Different patches of skin cells in a cat inactivate

different X chromosomes– Patches of fur growing from skin cells may differ in

color if fur genes on X chromosomes differ

VII. Structural abberrationsA. Deletions – part of chromosome is missing,

cri-du-chat syndrome #5, leukemia #21B. Inversions –part of chromosome is reversedC. Translocation – part of one chromosome

breaks off and attaches to another chromosome

D. Duplications – chromosome replicates genetic material it already has

VIII.Genetic screening • Ethical issues• insurance

I. Chemical nature of genesA. Coding capacity – genes carry codes produces traits

in the organismB. Transformation – A T G C Adenine Thymine Guanine Cytosinenucleotide code for all traits

II. DNA – deoxyribonucleic acidA. Base composition

• Chargaff’s rule – • A – T, T – A, G – C, C - G

B. Double helix model – 1953 by Watson and Crick – nucleotides form rungs of ladder, phosphate and ribose (sides)

1. Purines – 2 carbon ring, adenine and guanine2. Pyrimidines – single carbon ring, thymine and cytosine3. Base pairing – A T, G C

III. DNA replicationA. Template – bases need to form a complimentary strandB. DNA polymerase – enzyme which separates the base pairs –

separates the DNA molecules

IV. Mutations• Alteration of the bases

I. RNA – ribonucleic acid – one strandA. Composition – CG, AU , cytosine, guanine, adenine,

uracilB. Function – carry DNA instructions to various cell partsC. Protein synthesis – code for amino acid sequences

D. Messenger RNA – mRNA, carries DNA instructions “codons”

E. Transfer RNA – tRNA, translate the code “anticodons”

F. Ribosomal RNA – rRNA, from code puts amino acids together to form proteins

G. RNAi- interference RNA- destroys “suspect” codes such as viruses

RNA Intermediaries

• There are three types of RNA involved in protein synthesis– Messenger RNA (mRNA) carries DNA gene

information to the ribosome– Transfer RNA (tRNA) brings amino acids to the

ribosome– Ribosomal RNA (rRNA) is part of the structure of

ribosomes

II. Transcription – mRNA carries the code

DNA mRNA tRNA amino acidrRNA

C – G C G assemble

T – A U A aspartic acid amino

G – C G C acids

A – T A U make

C – G C G cysteine the

G – C G C protein

(transcription) (translation)(codons) anticodons

III. Translation – tRNA translates the codeIV. Protein synthesis – rRNA makes the protein

I. Genetic engineeringA. Recombination in nature

1. Mutations2. Crossing over3. Selective breeding

B. Plasmids – DNA bearing units (rings) that lie outside of bacterial chromosomes used to incorporate DNA sequences – then clone

B.Restrictive Fragments1.Restriction enzymes – cut

DNA at specific places – looks for recognition sequence

2.Gel electrophoresis – sizing DNA fragments

D. DNA sequencing – PCR polymerase chain reaction – make millions of copies of DNA sequence

II. Gene manipulation – patented mice, genes inserted into eggs of organisms

A. Gene insertion – edit the code, frost resistance, drought resistance, BT corn

B. Genetic engineering of bacteria – insert human DNA into bacteria, human insulin, HGH

C. Cloning – make an exact genetic copy, reproductive cloning = Dolly

1. Recombination DNA – Polly, human DNA for factor IX inserted into sheep donor cell

2. Xenotransplantation – transplanting of organs from one species to another

From bacteria (E. coli) and fungus, fruits and vegetables to animals, genetic manipulation is becoming more and more common in our society. In the US market now, 60-70% of the processed foods are genetically modified. In 2006, United States GMO crops reached just shy of 135 million acres, with the total global area exceeding 250 million acres!¹This is a short list of the genetically modified food crops that are grown in the US today:CornSoy beanSugar caneTomatoesPotatoesSweet peppersBananasStrawberriesZucchiniPineapplesCocoa beansYellow squash

III. New human genetics – human genome project, 20,000genes –30,000 genes, 3 billion base pairs

A. Genetic disease – 1,112 disease related genes, 400 base pairs identified

B. Genetic testing: ethical issues – C. cloning vs. variety, D. diagnostics vs. treatment

IV. Genetically modified foods• Golden rice, bacteria + daffodil genes, makes beta

carotene Vitamin A• Bt corn & cotton bacteria produces insecticide• Herbicide resistant soybeansConcerns: allergies, hybridize

V. Stem Cells