Genetics and Heredity Lab Exercise 40 BI 233

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

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.

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

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

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 heterozygous.

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 dominant

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

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 traits.

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 square