Genetics Basics Introduction to Mendelian Genetics In the

Genetics Basics

Introduction to Mendelian Genetics �In the 1800, Gregor Mendel studied garden peas in an Austrian monastery. He knew the male part produced the sperm and the female part produced the egg. �During sexual reproduction, sperm and egg unite in a process called fertilization. Fertilization produces a new cell. �Mendel was observing inheritance of traits. �Gregor Mendel is called the father of Genetics.

Seven Traits Mendel Studied �Seed texture – round, wrinkled �Seed color –yellow, green �Seed coat color – gray, white �Pod Appearance – inflated (smooth), constricted �Pod Color – green, yellow �Position of flowers along stem – axial (side), terminal (tip) �Stem length – tall, short

Key Genetic Terminology �An organism that has the same genes for a particular trait is known as a pure bred. �An organism that has different genes for a particular trait is known as a hybrid. �P generation refers to the parental generation. �F 1 generation represents the first offspring or first filial. �F 2 Generation stands for the second set of offspring or the second filial.

Key Genetic Terminology �Factors that control traits (occur in pairs) are called genes. �A genes that masks or hides the other factor of a trait is known as dominant. �A gene that is masked if a stronger factor is present is known as recessive. �Dominant will always overpower recessive traits. �Different forms of a gene are called alleles (usually represented by letters).

Alleles �The genetic make-up of an organism is known as its genotype. Example: GG, Gg, gg �The physical appearance of an organism is known as the phenotype. Example: green or yellow. �When both alleles are the same, they are homozygous. Example: GG, gg �When the alleles are different, they are heterozygous. Example: Gg �A cross between individuals that involve one pair of contrasting traits is known as a monohybrid cross. �A diagram used to aid in predicting possibilities is known as Punnett Square

Mendel’s Laws �Law of Dominance: A dominant gene will express itself over a recessive gene, and the recessive trait will only be expressed if the individual has two recessive alleles �Law of Segregation: 2 factors (alleles) for a trait segregate (separate) during the formation of eggs and sperm. They do not mix to form a new trait. �Law of Independent Assortment: traits are inherited independently of other traits (unless they genes are found on the same chromosome, then they may be inherited together).

Complete Dominance �Complete Dominance : one gene is dominant, one is recessive, and the dominant gene will always be seen �Dominant traits are indicated by a capital letter.

Example 2 of Complete Dominance �In guinea pigs, rough coat (R) is dominant to smooth coat (r), what are the expected percentages of the offspring when a heterozygous rough coat guinea pig is crossed with a smooth coat guinea pig?

Example 2 of Complete Dominance 1. Heterozygous rough x smooth Rr x rr 2. R r r Rr rr 3. There are two genotypes for the cross. 50% are Rr which are hybrid dominant. The purebred recessive alleles, rr, are also 50%. Phenotypes seen in the offspring are 50% rough coat guinea pigs and 50% smooth coat guinea pigs.

Other Forms of Dominance �Incomplete Dominance: Neither gene is dominant so you will see a blending of the trait (Blends Traits) �Codominance: Both alleles are dominant and both will be seen at the same time (Co – Both Show).

Incomplete Dominance Example 3 (Blending in plant fruit color) Genotype RR R’R’ RR’ Phenotype Red Yellow Orange What are the expected percentages of the offspring resulting from parent plants that are orange and yellow? *Important difference: the letters in incomplete dominance are the same and only the prime signifies different traits. *

Incomplete Dominance Example 3 1. 2. Red x white RR x R’R’ R R R’ RR’ RR’ 3. There is only one genotype for the cross. 100% are RR’ which are heterozygous. The only phenotype seen in this cross will be pink.

Incomplete Dominance Example 4 (Blending in Snapdragons) Genotype RR R’R’ RR’ Phenotype Red White Pink What are the expected percentages of the offspring resulting from red and white snapdragon parents?

Incomplete Dominance Example 4 1. 2. Red x white RR x R’R’ R R R’ RR’ RR’ 3. There is only one genotype for the cross. 100% are RR’ which are heterozygous. The only phenotype seen in this cross will be pink.

Codominance Example 5 �The phenotypes and genotypes for feather color in a certain chicken species are shown in the chart below. Genotype Phenotype WW White feathers BW Speckled feathers BB Black feathers �What are the possible outcomes of the offspring produced when a rooster with black feathers is crossed with a hen of speckled feathers? * Important difference: the letters are both capitalized and different letters

Codominance Example 5 1. 2. Black x speckled BB x BW B BB BB W BW BW 3. There are two genotypes for the cross. 50% are BB which are purebred. The remaining 50% are heterozygous, BW. The phenotype seen in this cross will be 50% black feathers and 50% speckled feathers.

Codominance Example 6 The genotypes and phenotypes for cows are listed below. Genotype Phenotype RR Red WW White RW Roan What are the possible outcomes of the offspring produced when a roan cow is crossed with a roan bull?

Codominance Example 6 1. 2. Roan x roan RW x RW R RR RW WW 3. There are three genotypes for the cross. 25% are RR which are homozygous. 25% are WW which are also homozygous. The remaining 50% are heterozygous, RW. The three phenotypes are seen in this cross. 25% are red, 50% are roan, and 25% are white.

Multiple Alleles �Multiple Alleles: Genes have 3 or more alleles �When working with multiple alleles, follow alphabetical, capital letter, then lower case rule �Sex linked and Blood Types are examples of multiple alleles

Sex-Linked � XX = alleles for female, XY = alleles for male � Because the X chromosome has more genes on it, most sex- linked genes are X-linked (Sex-linked is X linked). � There is no dominant or recessive on the Y chromosome � A recessive (lower case) sex-linked disorder carried on the X chromosomes � Possible male genotypes for colorblindness: XBY, Xb. Y � Possible female genotypes for colorblindness: X BXB, X BX b , X b � Males are more likely to inherit color blindness because he only receives on X chromosome. If a male inherits the gene from his mother, he has colorblindness. � Heterozygous females are carriers.

Sex-Linked Colorblindness Example 7 �A colorblind man marries a carrier female with normal vision. What are the possible outcomes of their children?

Sex-Linked Example 7 1. Colorblind male x carrier female Xb Y 2. XB x X B Xb Xb XBXb Y XBY Xb X b Xb Y 3. There are four genotypes for the cross all with 25% probability. XBXb will be a carrier. Xb is the only homozygous allele combination. Phenotypes vary. Of the two daughters, 50%, XBXb , will have normal vision and be carriers. The other 50% will be Xb. Xb which are colorblind daughter. Of the sons, XBY will have normal vision and Xb Y will be colorblind.

Sex-Linked Colorblindness Example 8 �A man with normal vision marries a colorblind woman. What are the possible outcomes of their children?

Sex-Linked Example 8 1. Normal male x colorblind female X B Y x X b Xb 2. XB Y Xb XBXb X b. Y Xb XBXb Xb Y 3. There are two genotypes for the cross and both are heterozygous. The carrier trait of XBXb will occur in 100% of the daughters. Xb Y will occur in 100% of the daughters. Phenotypes vary. 100% of the daughters will have normal vision. 100% of the sons will be colorblind.

Multiple Alleles (Blood Type) �Each person has 2 alleles – one from the mother and one from the father �There are 3 alleles for blood type: IA, IB, and i �Follow rules alphabetical, capital, lower case �IA and IB are dominant over i, which is recessive �IA and IB are codominant to each other � 1. type A = IAIA or IAi 2. type B = IBIB or IBi 3. type AB = I AI B 4. type O = ii

Blood Donor Information

Blood Type Example 9 �A heterozygous type A man has children with a heterozygous type B woman. What are the results of their offspring?

Blood Type Example 9 1. Heterozygous type A x heterozygous type B IA i 2. x IB i IB IA IAIB i i IA i ii 3. There are four genotypes for the cross. 75 % are heterozygous. There are four phenotypes. 25% is homozygous. 25% will have type AB. 25% will have type A. 25% will have type B. 25% will have type O.

Blood Type Example 10 �A man with type O blood has children with a woman with type AB blood. What are the results of their offspring?

Blood Type Example 10 1. Type O x Type AB ii x I AIB 2. i i IA IA i IB IB i 3. There are two genotypes for the cross and both are heterozygous. 50% are IA i. 50% are IB i. There are two phenotypes 50% will have type A. 50% will have type B.

Dihybrid Crosses �Dihybrid crosses are for the inheritance of TWO traits. �The problem will be set up like TTRR x ttrr. To figure out the alleles to be given to the offspring we use the FOIL method. �FOIL stands for First, Outer, Inner, Last. We pair the first two letters of each trait, the outer two letters of each trait, the inner two letters of each trait and the last two letters of each trait.

Dihybrid FOIL Example If we are looking at the two traits for height and seed shape, Tall is dominant to short and Round is dominant to wrinkled. What are the possible alleles that each parent could give? Tt. Rr x Tt. Rr

Dihybrid FOIL example If we are looking at the two traits for height and seed shape, Tall is dominant to short and Round is dominant to wrinkled. What are the possible alleles that each parent could give? Tt. Rr x Tt. Rr The parents could each give TR, Tr, t. R, and tr.

Dihybrid cross example �Using the alleles from the FOIL example, complete the cross. TR TR Tr t. R tr

Dihybrid cross example �Using the alleles from the FOIL example, complete the cross. TR Tr t. R tr TR TTRr Tt. RR Tt. Rr Tr TTRr TTrr Tt. Rr Ttrr t. R Tt. Rr tt. RR tt. Rr tr Tt. Rr Ttrr tt. Rr ttrr