Genetics and Heredity Lab Exercise 40 BI 233

Genome �All of the genes in all of the chromosomes together are called the genome �The study of all the genes in the human species is called genomics

Definitions �Heredity = the inheritance of traits �Genetics = 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 Expression �A 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 expression � Codominance 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 Expression �Polygenic 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 characteristics � The 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

Genes and Chromosomes �The 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

Centromere � Each 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 outward � The breast cancer gene BRCA 1 is located at 17 q 21 meaning that it is on the long arm of chromosome 17 in the region of 21 � Used for gene mapping

Chromosomes �We 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 autosomes �The remaining pair are called sex chromosomes.

Taste differences �Sodium 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

Anatomical characteristics of hand � Bent 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. � Hitchhiker’s thumb- If you can hyperextend the distal joint of the thumb noticeable, you have the recessive trait.

Facial Features �Pigmented 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 features � Attached earlobes – Lobe of the ear is attached rather than free, you have the recessive trait. � Widow’s peak – hairline straight across forehead is recessive trait � Tongue roll – curling tongue is dominant � Freckles – if your face is free of freckles you have the recessive form of this characteristic

ABO blood types � There are two dominant genes for ABO blood types � Type A (IA): signifies the A antigen � Type B (IB): signifies the B antigen. � Type O (i): is recessive to both Type A and Type B � A person with Type A blood can have IAIA or IAi � Type B blood can have IBIB or IBi

Rh Blood Type �The presence of the Rh antigen is dominant

Karyotypes � Standard chromosome chart � Major clinical genetic tool � Chromosomes are presented by size and physical landmarks that appear during mitotic metaphase when DNA is coiled tightly � Karyotypes can be used to diagnose many genetic conditions as well as reveal effects of environmental toxins.

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

Turner’s Syndrome � XO � Have 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 neck � About 97% of fetuses with Turner syndrome die before birth.

Klinefelter’s Syndrome �If an XX egg is fertilized by a Ybearing 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

Chromosome Duplications �Fragile X syndrome �Caused by repeats on the X chromosomes �Most 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 defect � Different chromosomes exchange or combine parts � Exposure to certain viruses, drugs and radiation cause translocations, but they often arise for no apparent reason. � No gain or loss of genetic material is involved � Can be a cause of Down’s syndrome when a Robertson translocation produces 3 copies of the long arm

Pedigree � The 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 Traits � Characteristics: � Most affected individuals have unaffected parents � All children of two affected individuals are affected � The risk of an affected child from a mating of two heterozygotes is 25% � Expressed in both males and females � Examples: albinism, cystic fibrosis, PKU, etc.

Autosomal Dominant � Characteristics: � Every affected individual should have at least one affected parent � Affects males and females equally � Two 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 females � Affect 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?

Probability �Is 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

Activities �Follow 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 pedigrees �Be able to answer questions concerning both karyotypes and pedigrees