genetics
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Gene, chromosome,DNA
DNA
Patterns of Inheritance• Complete Dominance• Incomplete Dominance• Codominance• Pleitrophy• Epistasis• Multiple Alleles• Polygenic• Sex Linked• Sex influenced• multifactorial
Blending theory
• Genetic materials are like liquids
Particulate theory
Hereditary units are discrete units or genes
Mendel
• Made genetics quantifiable
• Experimental crosses
• Character- detectable inherited feature
• Trait-variation of a character
• True breeding or pure bred- always produced the same trait
• Hybrids produced different variants
WHY
Nature vs Nurture
• What role is played by genetics?
• What role is played by the environment?
A a
AA aa
a aAA
aaAA
Gametes (A,a) segregate
Principles of Heredity• Alternative versions of genes (alleles)
account for variations in a trait.• For each character, an organism inherits
two alleles, one from each parent.• If alleles differ, then the dominant will be
fully expressed over the recessive.• The two alleles segregate (separate)
during gamete formation.• Alleles on different chromosomes
segregate independently of one another
•A •a
•B •b
•Independent Assortment and Segregation
•For an organism of the genotype AaBb
•Meiosis results in the following:
•a •A
•b •B
•Independent Assortment and Segregation
•For an organism of the genotype AaBb
•ab •AB
•A •a
•B •b
•Independent Assortment and Segregation
•For an organism of the genotype AaBb
•AB •ab
•a •A
•B •b
•Independent Assortment and Segregation
•For an organism of the genotype AaBb
•aB •Ab
•a •A
•b •B
•Independent Assortment and Segregation
•For an organism of the genotype AaBb
•ab •AB
Calculate the posssible gametes from the following crossesBbHh, DDHh, BbDd, bbhh
•BH, Bh, bH, bh
•DH,Dh
•BD, Bd, bD, bd
•bh
Genetic Crosses and Problems
• Monohybrid
• Dihybrid
• Pedigree
Monohybrid Cross-consider onlyone trait
B B
b Bb Bb
b Bb BbOffspring F1Gametes
Gametes
Monohybrid Cross-consider onlyone trait
B b
B BB Bb
b Bb bbOffspring F2Gametes
Gametes
Genotypic ratio 1 : 2 : 1Phenotypic ratio 3 : 1
Law of Multiplication of Probabilities
• Bb ½ B or ½ b
XBb ½ B or ½ b
1/4BB + 1/2Bb + ¼ bb
• BB ½ B or ½ B
XBb ½ B or ½ b
½ BB + ½ Bb
Gametes BW Bw bW bwBW BBWW BBWw BbWW BbWwBw BBWw BBww BbWw BbwwbW BbWW BbWw bbWW bbWwbw BbWw Bbww bbWw bbww
Dihybrid cross-cross two traitsheterozygous black wings
BbWw X BbWwPhenotypic Ratio 9:3:3:1
Crossing over
During prophase of meiosis homologous pairs may exchange
genetic material.
•TETRAD or synapsis
New Genetic Combinations
• Recombination during fertilization brings together two sets of genetic instructions
• Meiosis-crossing over brings about new combinations
• Random genetic mutation can result in random genetic change
Autosomal Complete Dominance
• One gene is able to dominate the other recessive allele
• Example all offspring express B as black fur over b white
B
B
b b
Bb Bb
Bb Bb
All black offspring
Autosomal Dominant
•Huntingtons Disease
•Achondroplasia
•Certain Form of Breast Cancer
•Galactosemia, Albinism
•Sickle cell Anemia
•Cystic Fibrosis
•Tay-Sachs
•PKU-phenylketonuria
Autosomal Dominant Patterns
Autosomal Recessive Pattern
Gene is unable to express itself unless it is in a homozygous condition.
? ?
C
C
c
c c cCc
CCCc
• Incomplete dominance-
both genes are expressed as intermediate forms
R R
W
W
RW
RR-red, WW-white
RW-pink
RW
RWRW
R R
R’
R’
RR’ RR’
RR’ RR’
Red crossed with whiteresults in pink flowers
Incomplete dominance
• Both genes are unable to be expressed ,the heterozygote is intermediate in expression
R’ R’
R’
R’
R’
R’
R
R R R R
R
CODOMINANCE- each gene of the allele is expressed
The A,B, O Blood typeshows Codominance
genotypes
iAiA, iBiB, iOiO,iAiB, iAiO ,and iBiO
iA iA
iB
iB
iAiB
iAiB
iAiB
iAiB
Blood Groups
A B O AB
iAiA iAiO
iBiB iBiO
iOiO iAiB
Type
Genotypes
Multiple Alleles
• In this pattern more than two alleles are possible for a trait.
• Blood Groups or types are an example of this also.
Blood Groups
A B O AB
iAiA iAiO
iBiB iBiO
iOiO iAiB
Type
Genotypes
What about RH Factor
• Single dominant gene produces an RH antigen labeled +
• RH negative individuals are homozygous recessive - -
Polygenic• More than one pair of genes
control the trait
• Genes working together
• Expression is varied
• Race is an example
• Most common form of inheritance
Pleitrophy
• A gene which affects an organism in many ways
• Multiple phenotypic effects
• Ex. Sickle-cell anemia, albinism
Epistasis
• A gene at one location alters the phenotypic expression of another gene
• Coat color in some mammals
Polygenic Inheritance
• Additive effect of two or more genes on phenotypic expression
• Phenotypic expression varies along a continuum
• Skin and eye pigmentation
Multifactorial
• Influenced by both environment and heredity
Sex or X linked
Inheritance- genes that are carried on the X
chromosome
Barr Bodies
• When multiple X chromosomes are present one or more will be inactivated leaving only one
• The inactive X forms a dark staining Barr body
• Random inactivation can result in mosaics
Sex-Linked Disorders
• Genes carried on the X chromsome
• Males only have one- more likely to have trait
• Females can be carriers
• Most important diseases are recessive
Red-green color blindness, hemophilia
Sex linked Patterns
Sex influenced• Genomic imprinting-gene
expression is dependent on the sex of the individual in which the gene originated
Prader-Willi- deletion of paternal chromosome 15
Angelman syndrome- if inherited from mother
Fragile X syndrome- fragment on X caused by triplet repeats
•PPLL X ppll
•F1 all PpLl
•F2 PpLl X PpLl
•From 500 offspring
•281 purple long
•93 purple round
•93 red long
•31 red round
•Should yield a
•9:3:3:1 ratio
•F2 hybrid crosses
Linkage Maps
• Map units or centimorgans = cross over or recombination frequencies
Based on crossover frequencies or the
frequencies that genes are recombined in ways that suggest they are linked
together.Measured in linkage units or
Morgan Units
C
18%
13%
5%
•6 %
AB D
C----7----A----6----B---5--D
*If the ratios deviate from the expected ratio
they could indicate that genes are linked.
*If genes are linked they are inherited together
unless they are separated as a result of crossing
over. Resulting in 1:1:1:1 ratios
*The frequency that these genes are then separated represents the relative distance they are from each other.
Klinefelter’s Syndrome
Karyotype- a picture or arrangement of metaphase chromosomes.
Can be taken from- amniocentesis -chorionic vili biopsy
Can be taken from any cells capturedin metaphase of mitosis.
Chromsomes are stained and photographed and then arranged by pairs according to size and banding patterns.
Chromosome Karyotypes
Mutations-any sudden change in genetic
material that can be passed on to the next generation
Albinismrecessive disorderlack of
pigmentation
Deletion
A fragment of a chromosome is missing
ex. Cri-du-chat syndrome or deletion of the short arm of the b group
chromosome results in a sever form of autism
Translocation- exchange of genetic material from one location on a chromosome to another non-homologous chromosome.
Ex. D_G translocation causes a form of Down’sSyndrome
Recombinant DNA
• Plasmid DNA
• Ligase enzyme Bacterial Cell
• Restriction Enzyme Bacterial cell wall
• Host cell Sticky ends
• Vector
• DNA fragment desired gene to be cloned
Recombinant DNA
• Plasmid DNA
• Ligase enzyme Bacterial Cell
• Restriction Enzyme Bacterial cell wall
• Host cell Sticky ends
• Vector
• DNA fragment desired gene to be cloned
Recombinant DNA
• Plasmid DNA
• Ligase enzyme Bacterial Cell
• Restriction Enzyme Bacterial cell wall
• Host cell Sticky ends
• Vector
• DNA fragment desired gene to be cloned
Gene Therapy- insertion of genes to correct defects
Mapping a chromosome
Linkage maps- measured in centimorgansa unit derived from analysis of cross-overstatistics. Measures the frequerncies ofcrossing over for genes on the samechromosomes.
T
T
T TT
t t t t
t
T t
pg102
• 1. I 2. A, 3. F, 4. E, 5. L, 6.J 7. H, 8. M, 9. C, 10. K
• 1.b, 2, d, 3. b, 4. c, 5.b, 6. c, 7.c, 8 c 9. b, 10. d, ( pg 104) 11. b, 12. d, 13. b, 14. d, 15. c, 16. d, 17 a, 18. c
104
• None exonerated
• A or O
• A or O
• AB
• B. or O.
Pg 111
• 3. b, 4. d, 5. d, 6. b, 7. d, 8. a, 9. a, 10 a, 11. d, 12. b, 13. c, 14. d, 15. a, 16. c, 17. b, 18. c, 19. a
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