Genetics Lecture (3) PDF

Genetics Principles Of Heredity LECTURE (3) DR. El-Sawy 1  Genetics Principles Of Heredity...

Genetics Principles Of Heredity LECTURE (3) DR. El-Sawy 1  Genetics Principles Of Heredity Genetics Heredity  The science of heredity.  Transmission of genetic information from parent to offspring. Gene Genome Chromosome  Segment of DNA carry specific  The entire set of genes in an  Molecule of DNA packed with sequence of nucleotide encoding organism. histone protein. a single specific protein located  Humans contain 46 chromosomes on chromosome (23 pairs):  Functional units of DNA = One inherited from father & One Hereditary unit. inherited from mother. 44 somatic chromosomes. 2 sex chromosomes (X +Y). DR. El-Sawy 2  Genetics Principles Of Heredity Locus Alleles (alternative form) Homozygous Heterozygous  Each gene has a specific  Forms of gene found at  Both alleles of a pair site on a certain particular locus  Both alleles of a pair are the same TT, tt chromosome (fixed  One allele is inherited from are not the same Tt positions). father & the other from mother. Dominant Recessive  The allele of a gene that masks or suppresses  The allele that is masked by dominant allele. expression of an alternate allele.  Appears in heterozygous condition.  Appears only in homozygous condition. DR. El-Sawy 3  Genetics Principles Of Heredity Trait Genotype Phenotype (external appearance)  Any genetically determined  Genetic makeup of organisms.  Physical appearance of organism characteristics of the individual  Alleles carried by an individual eg. (Genotype + environment). RR, Rr, rr. (internal information)  Physical characteristic or appearance of an individual. Example Trait Genotype Phenotype Dominant allele Recessive allele Eye colour BB. Bb, bb Brown or blue B b DR. El-Sawy 4  Genetics Principles Of Heredity  One allele masked another; one allele was dominant over the other. Principle of  Each trait is controlled by 2 factors (alleles), one factor Dominance: (dominant) may mask other factor (recessive) preventing it from having an effect.  When gametes are formed, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. Principle of Segregation: Principle of  The alleles for one trait separate independently of the Independent alleles for other traits during gamete formation Assortment:  It is a chart that allows to easily determine the expected ratios of possible genotypes in the offspring of two parents. Punnett square: DR. El-Sawy 5  Genetics Principles Of Heredity  A family pedigree shows how a trait is passed from generation to generation within a family.  A pedigree can show\whether a Mendelian trait is Autosomal or x-linked trait & Dominant or recessive. 1. Incomplete Inheritance. 2. Co-dominance. 3. Multiple Alleles. 4. Polygenic Traits. 5. Sex-linked. DR. El-Sawy 6  Genetics Principles Of Heredity A. Incomplete Inheritance (Incomplete Dominance)  The heterozygous offspring displays a third Phenotype Def (intermediate in phenotype).  Hair Type → There are genes for straight & curly hair  If an individual is heterozygous , they will typically have the phenotype of wavy hair. Example B. Multiple Alleles Def  Genes often exist in several different forms.  Human Blood group (A, B, O, or AB) : Multiple allele Example A, B, and O A and B dominant / O recessive [3 alleles & 4 phenotypes] DR. El-Sawy 7  Genetics Principles Of Heredity C. Co-Dominance  Both traits are dominant and show up in the phenotype together.  They both influence the phenotype.  Both alleles of a gene are expressed in the phenotype.  In human: AB blood group. D. Polygenic Inheritance (Polygenic Traits)  Traits controlled by interaction of two or more genes (multiple Def genes). Example  Skin color is governed by 6 genes and at least 12 alleles. E. Sex-Linked Genetics  Sex is determined by sex chromosomes X and Y : Male Female XY XX Receives ALL of his X-linked genes Receives her X-linked genes from from his mother. both parents.  X chromosome contains many important genes unrelated to sex determination DR. El-Sawy 8  Genetics Principles Of Heredity Sex-linked Inheritance  Genes for some traits are found on the sex chromosomes (X)  Most of these traits are recessive. Heterozygous Are carriers. XXC Females Not show the trait, but carry a gene for the trait. Homozygous XcXc Have the trait. Females Have the trait. Males with gene XcY Not have another X to counterbalance the affected gene. X-Linked Recessive Disorder Males will show this trait if they have the recessive allele Male on X chromosome Females will show this trait if they have the recessive Female allele on both X chromosomes. Hemophilia: Inability to have clotting of blood, Xh Examples Color blindness: Xc DR. El-Sawy 9  Genetics Principles Of Heredity  Individuals 6 and 7, children of unaffected parents, are affected. Four individuals are definitely unaffected carriers. Which ones are they? Partial Pedigree for Albinism DR. El-Sawy 10