Genetics

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



•ab •AB

•A •a

•B •b



•AB •ab

•a •A

•B •b



•aB •Ab

•a •A

•b •B



•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




• Vector


Recombinant DNA

• Plasmid DNA




• Vector


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

Documents

Genetics