Download - Basics Conceps of Genetic
-
8/2/2019 Basics Conceps of Genetic
1/30
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
3/30
Chromosome DNA
Gene 1
Gene 2
Telomeres
Centromere
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
7/30
Genotypes Phenotypes(example)
Eb- dominantallele.
Ew- recessiveallele.
genotypes
phenotypes
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
15/30
Hemophilia and Royalty
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
17/30
Medical Genetics
6 general patterns of inheritance areobserved:
Autosomal recessive Autosomal dominant X-linked recessive X-linked dominant Codominant Mitochondrial
-
8/2/2019 Basics Conceps of Genetic
18/30
Autosomalrecessive
The diseaseappears in maleand femalechildren of
unaffectedparents.
e.g., cystic
fibrosis
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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)
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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 ?
-
8/2/2019 Basics Conceps of Genetic
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
-
8/2/2019 Basics Conceps of Genetic
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.
-
8/2/2019 Basics Conceps of Genetic
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