Population Genetics I. Basic Principles II. X-linked Genes III. Modeling Selection
Basic Principles of Genetics
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Transcript of Basic Principles of Genetics
BASIC PRINCIPLES OF GENETICS
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Coiling of DNA1ry coiling of the duplex itself.2ry coiling around histone beads (nucleosome).3ry coiling of nucleosomes (chromatin fibers).4ry coiling forming loops.
Structure of DNATwo polynucleotide strandsTwo chains run in opposite directionSugar backbone Bases inside helix in Complementary base pairing (A=T & C=G)Strands bonded by weak hydrogen bonds
Definitions
Genome
the total number of genes
contained in one cell
Genotype
complete genetic constitution
of an individual
Phenotype
the physical appearance of
an individual that is
produced by the interaction
of his genes & environment
Trait
variation of an expressed
characteristic
Karyotype
systematic arrangement of
images of chromosomes
into homologous pairs
Autosomal chromosome
in humans, the 22 pairs of
chromosomes that are not
the sex chromosomes (XX or
XY)
Sex chromosomes
pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes
Allele
alternative forms of a gene that occupy a specific locus on a specific gene
Homozygous
having two identical alleles
for a given gene
Heterozygous
having two different alleles
for a given gene
Carrier
heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to his or her offspring
Dominant
describes a trait that is expressed both in homozygous & heterozygous form
Dominant lethal
inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span
Recessive
describes a trait that is only expressed in homozygous form and is masked in heterozygous form
Recessive lethal
inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span
Incomplete dominance
pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes
X-linked
pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair
X-linked dominant
pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd
pair
X-linked recessive
pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd
pair
Transcription
copying of DNA
sequences into mRNA
Translation
copying of mRNA
sequences into protein
Gene
Gene
the unit of heredity that occupies a specific locus on the chromosome. It is a DNA sequence that directs synthesis of a specific polypeptide chain
Genes
Structural
Regulatory
Operator
Structural Gene
directs synthesis of a
specific polypeptide chain
Regulatory Gene
repressor substance
secretion
Operator Gene
switches on structural
gene
The Genetic Code
This is the language of
mRNA
Based on the 4 bases of
mRNA
“Words” are 3 RNA
nucleotide sequences
called codons
Gene Mutation
Mutation
change in the nucleotide
sequence of DNA
A- Spontaneous Mutations(molecular decay)
B- Induced Mutations (mutagens)
- Chemicals
- Radiation
- Viral
Types of mutations
Types of Mutations
Chromosomal mutations involve changes in the whole chromosome.
Gene mutations result from changes in a single gene.
Effects of Gene Mutations
A- Neutral Effect (Silent mutation)
B- Harmful Effect
C- Beneficial Effect
Silent mutation
Another triplet for the
same AA
Harmful Effects
1.Errors in protein sequence partly or completely non-functioning proteins.
Harmful Effects
2.Germ cell mutations hereditary diseases/teratogenecity(heterozygous/homozygous)
Harmful Effects
3.
Somatic cell mutations
cancers
Regulation of gene expression
Not all genes are transcribed all the time.
Controlling mechanisms in the cell regulate the flow of enzymes & other proteins, determining which genes are turned on.
Some genes are needed for short periods of life cycle, others such as those involved in energy production may be operating all time.
DNA Functions
DNA functions
REPLICATION
METABOLISM
Replication
From one generation to another inheritance.
From cell to cell division.
Metabolism
gene expression & protein
synthesis (transcription &
translation)
Replication
DNA replication
it is the process by which
genetic information is
transmitted from one cell to
another
DNA replication
it starts by separation of the
2 strands. Each acts as a
template for a new strand
(semi-conservative)
DNA replication
DNA polymerase proceeds in
only one direction along the
helix (from the 5’ to 3’ end of
DNA) but starts in many sites.
Transcription
Transcription
the process whereby genetic information is transmitted from DNA to mRNA by RNA polymerase into complementary single-stranded copies of RNA
mRNA
are the processed transcripts of genes that code for polypeptides
Codon
a triplet of adjacent nucleotides in the mRNA chain that codes for a specific AA in the synthesis of a protein molecule
Exons
nucleotide sequences that is found in a gene, code information for protein synthesis, & is transcribed to mRNA
Introns
segments of a gene situated between exons that is removed before translation of mRNA & does not function in coding for protein synthesis
Promoterthe place where RNA polymerase 1st attaches. They vary from gene to another but contain sequences in common of 7 base sequence of all T’s & A’s
Termination
certain sequence that terminates gene transcription (downstream beyond the 5’ end)
Sense strand
the strand that is actually transcribed is the one with specific promoter sequence. The other non-sense strand is not used in transcription
ProcessingCAPPING: addition of a chemical cap to the 5’ end (attach RNA to the ribosome).SPLICING: excision of introns.POLYTAIL: addition of poly A tail (AAAA) to the 3’ end (it aids in transporting RNA molecule into the cytoplasm).
Translation
Translation
it is the process by which mRNA is translated into protein synthesis. It involves tRNA & rRNA
tRNA
one end binds a particular AA (all are 20), the other end has a 3-base sequence, the anticodon, that pairs with a particular codon on mRNA
rRNA
structural elements of ribosomes. They are the benches on which protein synthesis occurs
Steps of translation
mRNA moves along ribosomes
tRNA adapts
Starting codon= ATG
Stop codon= UGA, UAG, UAA
Summary
DNA transcription at chromosomes mRNA movement across NM rRNA translation at ribosomes protein
Patterns Of Inheritance
Patterns of inheritance
Autosomal Recessive Inheritance
Autosomal Dominant Inheritance
X-Linked Recessive Inheritance
X-Linked Dominant Inheritance
Autosomal Recessive Inheritance
Autosomal recessive
pattern of recessive
inheritance that corresponds
to a gene on one of the 22
autosomal chromosomes
Autosomal Dominant Inheritance
Autosomal dominant
pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
X-Linked Recessive Inheritance
X-Linked Dominant Inheritance
Referencescnx.org
Basics Of Human Genetics Prof. Dr. RandaYoussef Kasr El Aini (Presentation)
All about genes. Maha Adel Shaheen, MD Professor of Dermatology & Venereology AinShams University (Presentation)
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