basics conceps of genetic

8/2/2019 Basics Conceps of Genetic

1/30


2/30

Genetic Information

Gene basic unit of genetic information.Genes determine the inherited characters.

Genome the collection of geneticinformation.

Chromosomes storage units ofgenes.

DNA - is a nucleic acid that contains thegenetic instructions specifying the biologicaldevelopment of all cellular forms of life


3/30

Chromosome DNA

Gene 1

Gene 2

Telomeres

Centromere


4/30

Chromosome Logical Structure

Locus location of agene/markeron the chromosome.

Allele one variant form of agene/marker at a particular locus.

Locus1

Possible Alleles: A1,A2

Locus2Possible Alleles: B1,B2,B3


5/30

Human Genome

Most human cellscontain 46 chromosomes:

2 sex chromosomes (X,Y):XY in males.XX in females.

22 pairs of chromosomesnamed autosomes.


6/30

Genotypes Phenotypes

genotype: combination of alleles an organism

has

Example: TT, Tt, or tt

phenotype :The expression of a genotype

Example: hair color, weight, or the presence

or absence of a disease.


7/30

Genotypes Phenotypes(example)

Eb- dominantallele.

Ew- recessiveallele.

genotypes

phenotypes


8/30

Dominant vs. Recessive

A dominantallele isexpressed even if it is

paired with a recessiveallele.

A recessiveallele is

only visible when pairedwith another recessiveallele.


9/30

One Locus Inheritance

heterozygote homozygote

21A | A a | a

A | a 3 4 a | a

A | a 5 6 a | a

Male

Female

Homozygous : Both alleles for a trait are the same.Heterozygous: The organism's alleles for a trait are different.


10/30

Beyond Dominant andRecessive

Incomplete Dominance One allele is notcompletely dominant over the other. Whiteflower crosses with a red = pink flower.

Codominance Both alleles contribute to the

phenotype. Red cow X White Cow = Roan Cow. Multiple Alleles More than two alleles control

the phenotype. Coat color of rabbits. Polygenic traits Several genes control the trait.

Skin color in humans.


11/30

Laws of Inheritance

Law of Segregation: When gametes(sperm egg etc) are formed each

gamete will receive one allele or the other.

Law of independent assortment: Two ormore alleles will separate independently ofeach other when gametes are formed

This law is true only in some cases

Gene pairs on SEPARATE CHROMOSOMES

assort independently at meiosis.


12/30

Monohybrid crosses

Result :3 genotypes (TT, Tt, & tt)in a 1:2:1 genotypic ratio

3:1 Phenotypic ratio

Dihybrid crosses

Result : 9:3:3:1 phenotypic ratio. 9/16(both dominant traits), 3/16 & 3/16(one of the recessive traits), and 1/16(both recessive traits).

indicates that these alleles areseparating independently of eachother. This is evidence of Mendel's

Law of independent assortment


13/30

X-linked Inheritance

Different results obtainedfrom reciprocal crossesbetween red-eyed andwhite-eyed Drosophila.

: The geneExplanationresponsible for eye-coloris X-linked. Females have2 X-chromosomes, whilemales have 1 X-chromosomeand 1 Y-chromosome.


14/30

Human Sex Linkage

Hemophilia: Disorder of the bloodwhere clotting does notoccur properly due to afaulty protein.

Occurs on the Xchromosome, and isrecessive.

Thus a vast majority ofthose affected are

males. First known person knownto carry the disorder wasQueen Victoria ofEngland.

CarrierMother

NormalFather

NormalMale

NormalFemale

AffectedMale

AffectedFemale


15/30

Hemophilia and Royalty


16/30

Other Factors

Gene interaction: Many biological pathways are governed by

multiple enzymes, involving multiple steps. If anyone of these steps are altered. The end product

of the pathway may be disrupted.

Environmental effects: Sometimes genes will not be fully expressed

owing to external factors. Example: Humanheight may not be fully expressed if individualsexperience poor nutrition.


17/30

Medical Genetics

6 general patterns of inheritance areobserved:

Autosomal recessive Autosomal dominant X-linked recessive X-linked dominant Codominant Mitochondrial


18/30

Autosomalrecessive

The diseaseappears in maleand femalechildren of

unaffectedparents.

e.g., cystic

fibrosis


19/30

Autosomal dominant

Affected males andfemales appear ineach generation of

the pedigree. Affected mothers and

fathers transmit thephenotype to bothsons and daughters.

e.g., Huntingtondisease.


20/30

X-linked recessive Many more males than females show the disorder. All the daughters of an affected male are carriers.

None of the sons of an affected male show thedisorder or are carriers.

e.g., hemophilia


21/30

X-linked dominant

Affected males pass the disorder to all daughters but tonone of their sons.

Affected heterozygous females married to unaffectedmales pass the condition to half their sons and daughters

e.g. fragile X syndrome


22/30

Codominant inheritance

Two different versions(alleles) of a gene canbe expressed, and eachversion makes a slightlydifferent protein

Both alleles influencethe genetic trait ordetermine thecharacteristics of thegenetic condition.

E.g. ABO locus


23/30

Mitochondrial inheritance

This type of inheritanceapplies to genes inmitochondrial DNA

Mitochondrial disorderscan appear in everygeneration of a familyand can affect bothmales and females, butfathers do not pass

mitochondrial traits totheir children. E.g. Leber's hereditary

optic neuropathy(LHON)


24/30

Notes

Cystic fibrosis disease affecting the mucuslining of the lungs, leading to breathingproblems and other difficulties

Huntington disease - or Huntington's chorea isan inherited disorder characterized by abnormalbody movements called chorea, and loss ofmemory. There also is evidence that doctors as

far back as the Middle Ages knew of thisdevastating disease. The incidence is 5 to 8 per100,000. It takes its name from the New Yorkphysician George Huntington who first described

it precisely in 1872.


25/30

Notes

Fragile X syndrome - is agenetic condition thatcauses a range ofdevelopmental problems

including learningdisabilities and mentalretardation.

Usually males are moreseverely affected by thisdisorder than females.

learning difficulties, tend tobe restless, fidgety, andinattentive.

Prominent

characteristics of thesyndrome includean elongated face,large or protrudingears, and lowmuscle tone.


26/30

Leber's hereditary opticneuropathy (LHON)

Leber optic atrophy is a mitochondriallyinherited (mother to all offspring)

degeneration of retinal ganglion cells(RGCs) and their axons that leads to anacute or subacute loss of central vision;

this affects predominantly young adultmales


27/30

Question 1

PKU is a human hereditary disease resulting frominability of the body to process the chemicalphenylalanine (contained in protein that we eat).

It is caused by a recessive allele with simpleMendelian inheritance.

Some couple wants to have children. The man has asister with PKU and the woman has a brother with

PKU. There are no other known cases in theirfamilies.

What is the probability that their first childwill have PKU ?


28/30

Question 1-Solution Highlights

P/p P/p P/p P/p

p/p p/pP/- P/-

P the normal allelep the mutant allele


29/30

Question 2

1 2 3 4 5 6 7 8 9 10

a. What is the most likely mode of inheritance ?

b. What would be the outcomes of the cousin marriages1 x 9, 1 x 4, 2 x 3, and 2 x 8 ?

The disease is rare.


30/30

a. Observations:

After the disease is introduced into the family in generation#2, it appears in every generation dominant! Fathers do not transmit the phenotype to their sons

X-linked!

b. The outcomes: 1 x 9: 1 must be A/a

9 must beA/Y 1 x 4: 1 must be A/a

4 must be a/Y 2 x 3: 2 must be a/Y

3 must be A/a 2 x 8: 2 must be a/Y

8 must be a/a

Same

All normal

Question 2-Solution Highlights

basics conceps of genetic

Documents