Lab Exercise 40 BI 233 Genetics and Heredity

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

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

Chromosomes We inherit 23 DNA molecules from our mothers and 23 DNA molecules from our fathers for a total of pairs of these chromosomes are called autosomes The remaining pair are called sex chromosomes.

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

Gene Expression A person has two genes for every inherited characteristic. If one allele is always expressed, geneticists call that gene dominant. A allele that is not expressed when its mate is different is termed a recessive gene Example: Genotype ‘Aa’ and ‘A’ is the phenotype, then ‘A’ is dominant, ‘a’ is recessive.

Gene Expression Incomplete dominance: the phenotype of two heterozygous alleles is intermediate between the phenotype. (sickle cell trait): Aa – bit of each allele Codominant inheritance: Both alleles are expressed in the phenotype: AB – both alleles - making up AB blood type

Gene Expression Most human traits are the result of polygenic inheritance, which occurs when multiple genes interact to produce a phenotype. Eye color was believed to be a strict dominant-recessive trait but we now know that it is the result of interactions of many genes- polygenic. (other examples include height and skin color)

Sex Linked Traits Traits expressed by genes on the X or Y Chromosome (Sex Chromosomes). Not as many genes on the Y chromosome so X-linked traits much more common. X-linked recessive trait is always expressed in a male, because he has only one X chromosome. Females are called carriers if she has one allele and must have 2 recessive alleles to express trait. Examples: color blindness and hemophilia X-linked dominant traits are rare

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 = Codominance Type A (I A ):signifies the A antigen. A person with Type A blood can have I A I A or I a i Type B (I B ): signifies the B antigen. Type B blood can have I B I B or I b i Type O (i): is recessive to both Type A and Type B. Type O blood must be ii

Rh Blood Type The presence of the Rh antigen is dominant – 85% Rh negative does not have Rh antibodies without exposure.

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. Use Punnett squares to answer questions in your packet.

Karyotype Graphical representation of pairs of homologous chromosomes as they appear in metaphase of the cell cycle. They are arranged from largest to smallest. The number and structures are then evaluated. Many chromosomal abnormalities can be discovered this way Male Female

Abnormal Chromosome Numbers = Aneuploidy Monosomy: missing a chromosome (Turner’s syndrome – 45, missing one X) Trisomy: extra chromosomes (46). Most autosomal aneuploids are spontaneously aborted. Mental retardation is common if individual survives. Some that do survive are Trisomy 13 (<5%), Trisomy 18 (<5%) and Trisomy 21(85%)

Sex Chromosome Aneuploids Sex chromosome aneuploidy is less severe than autosomal aneuploidy. Examples include: Turner syndrome (X,O) Triple X females (XXX) Klinefelter syndrome (XXY) XYY syndrome in males

Pedigrees Geneticists use charts called pedigrees to display family relationships and to follow which relatives have specific phenotypes and, sometimes genotypes. They help keep tract of relationships and traits. Important for helping families identify the risk of transmitting an inherited illness Queen Victoria’s Pedigree

Pedigree Key Dominant or Recessive Autosomal or X-linked

Pedigree Examples Albinism: autosomal recessive Try to figure out the genotypes Autosomal dominance Try to figure out the genotypes

Red-Green Color Blindness X linked recessive

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