Lab Exercise 40BI 233

Genetics and Heredity

DefinitionsHeredity = 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

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 autosomes

The remaining pair are called sex chromosomes.

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

GenomeAll 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 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.

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.

Hitchhiker’s 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.

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 typesThere 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 TypeThe presence of

the Rh antigen is dominant

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 square