Genetics and Heredity

Lab Exercise 40BI 233Genetics and HeredityGenomeAll of the genes in all of the chromosomes together are called the genomeThe study of all the genes in the human species is called genomics

Human Genome map was completed in 2003 2DefinitionsHeredity = the inheritance of traitsGenetics = the study of mechanisms of heredity.Genes: A portion of a DNA strand that functions as a hereditary unit, is located at a particular site on a specific chromosome, and codes for a specific protein or polypeptide

Gene ExpressionA person has two genes for every inherited characteristic.If one gene is always expressed, geneticists call that gene dominant.A gene that is not expressed when its mate is different is termed a recessive gene

Gene expressionCodominance is the condition in which an individual heterozygous for a gene exhibits the phenotypes of both homozygote's (example AB blood)Incomplete dominance is when neither of two alleles is completely dominant.(example: sickle cell anemia at organism level)

Gene ExpressionPolygenic inheritance occurs when two or more genes whose additive effects determine a particular trait.(skin color)Multi allelic inheritance: refers to different versions of one trait on the same gene (Blood types)

Inherited characteristicsThe characteristic actually expressed in an individual is called a phenotype.The genetic constitution of an individual, along with environmental influences is called the genotype.If both genes for a trait are the same the individual is homozygous.If genes are not the same they are heterozygous.

Genes and ChromosomesThe position of a gene on a chromosome is called a locus.Genetic maps show the relative locations of genes along the chromosome.There can be alternate versions of genes called alleles which produce different phenotypes

CentromereEach chromosome often has a constriction along its length called a centromere.The shorter arm is placed on top in a karyotype and is called the p arm, the longer arm is on the bottom and is called the q arm. Numbered regions and subregions are then assigned from the centromere outwardThe breast cancer gene BRCA1 is located at 17q21 meaning that it is on the long arm of chromosome 17 in the region of 21Used for gene mapping

ChromosomesWe inherit 23 DNA molecules from our mothers and 23 DNA molecules from our fathers for a total of 46.22 pairs of these chromosomes are called autosomesThe remaining pair are called sex chromosomes.

Taste differencesSodium benzoate test The ability to taste something sweet, salty, or bitter in the paper is dominant.PTC (phenylthiocarbamide) test The ability to sense a bitter taste is dominant.Thiourea test the ability to taste something bitter is dominant

Anatomical characteristics of handBent little finger If distal phalanx of the little finger bends toward the fourth finger, you have dominant trait.Middigital hair hair on middle phalanges is dominant.Hitchhikers thumb- If you can hyperextend the distal joint of the thumb noticeable, you have the recessive trait.

Facial FeaturesPigmented anterior of the iris If you have pigment on the anterior and posterior of the iris, your eyes are green, brown, black and hazel.If you lack pigment on the anterior aspect of the iris, yours eyes are blue or grey.Pigmentation is dominant

Phenotypes of facial featuresAttached earlobes Lobe of the ear is attached rather than free, you have the recessive trait.Widows peak hairline straight across forehead is recessive traitTongue roll curling tongue is dominantFreckles if your face is free of freckles you have the recessive form of this characteristic

ABO blood typesThere are two dominant genes for ABO blood typesType A (IA):signifies the A antigenType B (IB): signifies the B antigen.Type O (i): is recessive to both Type A and Type BA person with Type A blood can have IAIA or IAiType B blood can have IBIB or IBi

Rh Blood TypeThe presence of the Rh antigen is dominant

KaryotypesStandard chromosome chartMajor clinical genetic toolChromosomes are presented by size and physical landmarks that appear during mitotic metaphase when DNA is coiled tightlyKaryotypes can be used to diagnose many genetic conditions as well as reveal effects of environmental toxins.

Non-disjunction problemsWhen the homologous chromosomes or sister chromatids fail to separate at anaphase An extra chromosome is called trisomy and a missing chromosome is called monosomyTrisomy 21 (Downs syndrome)Signs include impaired physical development; short stature; relatively flat face with a flat nasal bridge and mental retardationTrisomy 13 & 18 are other chromosomal trisomies but fetuses do not usually survive until birth.

Turners SyndromeXOHave only one sex chromosome Designated as 45,X indicating they have 45 chromosomes and one X chromosome.Not noticeable until puberty when they fail to develop secondary sex characteristics and are usually infertile.Webbed neckAbout 97% of fetuses with Turner syndrome die before birth.

Klinefelters SyndromeIf an XX egg is fertilized by a Y-bearing sperm the result is an XXY combination.Sterile males with usually average intelligence with undeveloped testes, sparse body hair, usually long arms and legs and enlarged breasts.Often goes undetected until puberty.

Chromosome DuplicationsFragile X syndromeCaused by repeats on the X chromosomesMost people have about 29 repeats but persons with Fragile X have over 700 repeats due to duplication.A major cause of mental retardation and is found in more males because of the single X chromosomes

Translocation defectDifferent chromosomes exchange or combine partsExposure to certain viruses, drugs and radiation can cause translocations, but they often arise for no apparent reason.No gain or loss of genetic material is involvedCan be a cause of Downs syndrome when a Robertson translocation produces 3 copies of the long arm of chromosome 21

PedigreeThe study of a family tree and the careful compilation of phenotypic records of both families over a number of generations.By studying human families for affected and unaffected members over several generations we can usually tell whether a trait is autosomal recessive or is carried on a sex chromosome.

Autosomal Recessive TraitsCharacteristics:Most affected individuals have unaffected parentsAll children of two affected individuals are affectedThe risk of an affected child from a mating of two heterozygotes is 25%Expressed in both males and femalesExamples: albinism, cystic fibrosis, PKU, etc.

Autosomal DominantCharacteristics:Every affected individual should have at least one affected parentAffects males and females equallyTwo affected individuals may have an unaffected child because most affected individuals are heterozygous.Examples: Huntington disease, Marfan syndrome

X-linked recessive Characteristics:Phenotypic expression is much more common in males than femalesAffect males get the mutant allele from their mothers and transmit it to all their daughters but not to any sons.Examples: colorblindness, hemophilia, muscular dystrophy (some forms)

Hemophilia in Royal Family

Is this trait autosomal recessive, autosomal dominant or sex linked? How can you tell?ProbabilityIs the likelihood of a the offspring of a particular set of parents will have a certain inherited condition.Genetic counselors work with prospective parents to determine their possible genotypes for a variety of traits and then predict the probability of their children having those traits.

ActivitiesFollow the instructions in your lab manual to determine your phenotype for the listed traits.After you have determined your phenotype then determine your possible genotypes.Answer the questions in your lab manual using the Punnett squares and pedigreesBe able to answer questions concerning both karyotypes and pedigrees