Theoretical Genetics

Theoretical Genetics

Genetics • Gregor Mendel – The Father of Genetics • High School teacher and minister • One of side jobs was as a gardener • While gardening he completed the work that changed biology forever. • Pea plants!!! • LUCKY LUCKY LUCKY MAN!

Mendel’s Peas • During sexual reproduction, male and female reproductive cells join in a process called Fertilization • Pea plants in most gardens are self-pollinating which results in offspring identical to itself. • Mendel knew this and used this information to “mix it up” a bit

Pass the peas please Mendel looked at 7 traits that he observed in the plants which included: Height – Tall or short Seed Color – Yellow or Green Seed Shape – Round or wrinkled Pod shape – Smooth or constricted Seed Coat color – Gray or white Pod Color – Green or yellow Flower Position – Axial or Terminal

Lets talk about Sex (Pea style) • Mendel crossed the plants by removing the male portions of the plants and controlling pollination of the plants. • Mendel crossed plants with each of the seven contrasting characteristics and studied their offspring. • The offspring of crosses between parents of different traits are called hybrids.

What He Saw! • After studying the offspring he came up with two conclusions: • Biological inheritance is determined by factors that are passed from one generation to the next. Today scientists call them genes. • Principle of Dominance: some alleles are dominant(CAPITAL LETTER) and others are recessive(lower case letter). • Dominant alleles will always exhibit that form of the trait. Recessive alleles are only seen when there is no dominant allele present

Important terms ·Genotype = the alleles of an organism (e.g. one brown eyed allele and one blue eyed allele, Tt, tt, TT) ·Phenotype = the physical characteristics of an organism (e.g. brown eyes, tall, short, tall) ·Homozygous = having two identical alleles for the same gene (TT, tt) ·Heterozygous = having two different alleles for the same gene(Tt)

·Dominant allele = an allele that has the same affect on the phenotype whether it is present in the homozygous or heterozygous state (e.g. brown eye allele, Tall gene in pea plants Tt and Tt are both tall) - Represented by a capital letter in the genotype ·Recessive allele = an allele that only has an affect on the phenotype when present in the homozygous state (e.g. blue eye allele) - Represented by a lowercase letter in the genotype

Carrier = an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele (e.g. carriers for sickle cell have a resistance to malaria but can pass on the sickle cell disease to their children) ·Test cross = testing a suspected heterozygote by crossing with a known homozygous recessive

Punnett Squares ·Can be used to determine the offspring of a monohybrid (one trait) cross ·Male gametes go on one side of the square while female gametes go on the other side ·Potential offspring are inside the square ·In the example R is the dominant allele and codes for Red petals while r is the recessive allele and codes for white petals What percent of offspring will be red? What percent will be white?

·Some genes have multiple alleles While multiple alleles may exist in the population, an individual can still only have two ·Multiple alleles increase the variety of phenotypes in the population ·Alleles may be dominant, recessive, or codominant to each other

·For example, rabbit coat color has four alleles: C, cch, ch, and c ·These dominance of these alleles follows the order in which they are listed ·Produces several possible phenotypes. C > cch > ch > c Full color C_ Albino cc Chinchilla cchcch, cchch, cchc Himalayan chch, chc

·Codominant alleles = pairs of alleles that both affect the phenotype when present in a heterozygote ·E.g. A cow with the allele for white hair and the allele for brown hair will be roan (white with brown spots)

Human blood type: gene with multiple alleles that are codominant ·Three alleles and four phenotypes ·The ‘I’ in the genotype stands for immunoglobin ·i represents the recessive allele that codes for type O blood ·IA and IB are codominant to each other ·The allele hierarchy is IA = IB > i

Sex Chromosomes ·Chromosome pair number 23 are referred to as the sex chromosomes and determine gender - the only pair that might not match in size/shape - X chromosome is longer and contains many more genes.

·X is always donated to the offspring by the mother while the sperm may donate either an X or a Y ·An embryo with XX genotype will be female while an embryo with XY genotype will be male

·Some genes are present on the X chromosome but absent from the Y - Y chromosomes have fewer loci and therefore fewer genes than X ·Sex Linked Gene: any gene with its locus on the X or Y chromosome - often affect one gender more than the other.

·Color blindness as an example of recessive sex linked gene 4 Sex-Linked Traits: Normal Color Vision: A: 29, B: 45, C: --, D: 26 Red-Green Color-Blind: A: 70, B: --, C: 5, D: -- Red Color-blind: A: 70, B: --, C: 5, D: 6 Green Color-Blind: A: 70, B: --, C: 5, D: 2

·The dominant allele is XB while the recessive allele is Xb · A female with the genotype Xb, Xb will be color blind A female with the genotype XB, Xb is a carrier(not color blind herself but can pass the recessive gene to her children) ·Any male children who receive the Xb allele from their mother will be color blind because there is no allele on the Y chromosome to dominate over it (their genotype will be Xb,Y)

·Hemophilia as another example of recessive sex linked gene Research on your own: - Characteristics of disease: - Inheritance pattern:

Pedigrees ·Often geneticists will carry out planned experiments in which breeding pairs are selected and the offspring phenotypes counted. ·However this is not acceptable or possible when working with humans. ·Instead geneticists have to collect information about individuals and relatives within a family and construct diagrams of inheritance (family trees) called pedigrees. ·Pedigrees are often used to track the inheritance of a disease in a family

·In pedigrees circles represent females while squares represent males ·Shaded individuals are affected with the condition ·Individuals who are half shaded are carriers (some pedigrees don’t do the half shading and you have to figure out whether or not they are carriers by looking at the individuals parents and offspring) ·Horizontal lines connect two people who have mated ·Vertical lines connect parents with children

Trait: Colorblindness ID the genotype of each family member.

Phenylketonuria (PKU) is a metabolic disorder and a recessive genetic condition. ·Which individuals can we be sure about their genotype? ·

Since it was not possible to identify the condition of 12 and 13 suggest their genotype and phenotype and how the diagram may need modifying?

Theoretical Genetics