Introduction to Genetics Genetics = the scientific study of heredity

The Work of Gregor Mendel Austrian monk studied heredity heredity—the passing on of characteristics from parents to offspring Characteristics that are inherited are called traits. First person to successfully predict how traits are transferred from generation to generation Used garden peas in his experiments The Father of Genetics

Why pea plants? Reproduce sexually, which means that they produce male and female sex cells, called gametes. In a process called fertilization, the male gamete unites with the female gamete. The resulting fertilized cell, called a zygote, then develops into a seed.

Mendel’s Experiment He took pollen from a male plant and dusted it onto a female plant. Female part Transfer pollen Pollen grains Male parts Cross-pollination Parental generation (p) = the original pair of plants Offspring (f1) = first filial generation (f2) = second filial generation The original parents, the true-breeding plants, are known as the P1 generation. The offspring of the parent plants are known as the F1 generation. When you cross two F1 plants with each other, their offspring are the F2 generation.

His first experiments are called monohybrid crosses because they only deal with ONE single trait (height, color) mono means “one” He studied only one trait at a time to control variables, and he analyzed his data mathematically. The tall pea plants he worked with were from populations of plants that had been tall for many generations and had always produced tall offspring. Such plants are said to be true breeding for tallness. Likewise, the short plants he worked with were true breeding for shortness.

Concluded: Each organism has two factors that control each of its traits. These factors are genes and that they are located on chromosomes. Genes exist in different forms called alleles. P1 Short pea plant Tall pea plant F1 An organism’s two alleles are located on different copies of a chromosome—one inherited from the female parent and one from the male parent. All tall pea plants F2 3 tall: 1 short

T t Tall plant Short plant All tall plants F1 Mendel called the observed trait dominant and the trait that disappeared recessive. Mendel concluded that the allele for tall plants is dominant to the allele for short plants. When recording the results of crosses, it is customary to use the same letter for different alleles of the same gene. An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. The dominant allele is always written first.

An organism’s genotype can’t always be determined by its phenotype. The way an organism looks and behaves is called its phenotype. Ex. Tall, yellow The allele combination an organism contains is known as its genotype. Ex. TT, Tt An organism’s genotype can’t always be determined by its phenotype. Law of segregation Tt xTt cross F1 Tall plant T t 3 Tall Short 1 F2

An organism is homozygous for a trait if its two alleles for the trait are the same. (True-breeding) Exp. TT or tt An organism is heterozygous for a trait if its two alleles for the trait differ from each other. (Hybrid) Exp. Tt

Genetics & Probability probability = the likelihood that a particular event will occur Ex. Coin flipping: 1/2 probability that coin will flip head/tail If you flip the coin 3 times what's the probability of flipping 3 heads? 1/2 x 1/2 x 1/2 = 1/8 *Past outcomes do not affect future ones!!* The principles of probability can be used to predict the outcomes of genetic crosses. What is the probability of parents having two male offspring in a row? (1/2*1/2=1/4)

Punnett Squares: Are used to predict and compare the genetic variations that will result from a cross. The types of gametes go on the top and left sides of the square The possible gene combinations appear in the four boxes

If you know the genotypes of the parents, you can use a Punnett square to predict the possible genotypes of their offspring. T t T T T t t t

You try this one: A a

Question 1 The passing on of characteristics from parents to offspring is __________. A. genetics B. heredity C. pollination D. allelic frequency Section 1 Check

The answer is B. Genetics is the branch of biology that studies heredity.

Question 2 Answer What are traits? Traits are characteristics that are inherited. Height, hair color and eye color are examples of traits in humans. Section 1 Check

Question 3 Gametes are __________. A. male sex cells B. female sex cells C. both male and female sex cells D. fertilized cells that develop into adult organisms Section 1 Check

The answer is C. Organisms that reproduce sexually produce male and female sex cells, called gametes. Section 1 Check

Question 4 Which of the following genotypes represents a animal that is homozygous dominant for a trait? a. KK b. Kk c. kk Section 1 Check

Question 5 Which of the following genotypes represents a plant that is homozygous recessive for height? A. TT B. Tt C. tt Section 1 Check

Mendel’s Dihybrid Crosses round yellow x wrinkled green Round yellow Wrinkled green All round yellow Round green Wrinkled yellow 9 3 1 P1 F1 F2 Mendel performed another set of crosses in which he used peas that differed from each other in two traits rather than only one. Such a cross involving two different traits is called a dihybrid cross.

He found they appeared in a definite ratio of phenotypes 9:3:3:1— 9 round yellow: 3 round green: 3 wrinkled yellow: 1 wrinkled green. He concluded that the seed shape and seed color—are inherited independently of each other. This conclusion is known as the law of independent assortment.

Dihybrid Punnett square Gametes from RrYy parent RY Ry rY ry RRYY RRYy RrYY RrYy Rryy rrYY rrYy rryy Dihybrid crosses A Punnett square for a dihybrid cross will need to be four boxes on each side for a total of 16 boxes. Dihybrid Punnett square

Exceptions to Mendel To be continued on the next exciting adventure of BIOLOGY…….

Exceptions to Mendel Not all genes show simple patterns of dominant and recessive alleles. Because the majority of traits are controlled by more then one gene/alleles.

Incomplete dominance Cases in which one allele is not completely dominant over another. Neither allele is dominant Ex. Red flower x White flower = Pink flower

Codominance Cases in which both alleles are expressed. Ex. White chicken x Black chicken = Speckled (white and black) chicken

Multiple Alleles when a gene has more than two alleles Ex. Mice coat color is determined by one gene with four different alleles. Three different colors result from the combinations of these alleles.

Blood Types - Multiple Alleles and Codominance In humans, there are four blood types (phenotypes): A, B, AB, and O Blood type is controlled by three alleles. A, B, O O is recessive, two O alleles must be present for the person to have type O blood A and B are codominant. If a person receives an A allele and a B allele, their blood type is type AB Crosses involving blood type often use an I to denote the alleles - see chart.

Type O's are automatically OO and type AB is automatically AB Type O's are automatically OO and type AB is automatically AB. Type A and B can be homozygous or heterozygous.

The blood type determines what antibodies are located within the blood The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death. Type AB blood has no antibodies, any blood can be donated to them - they are called the "universal acceptors" Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, they are called the "universal donors"

Polygenic traits traits controlled by two or more genes Ex. At least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies. Different combinations of alleles for these genes yield different eye colors.

Sex Linked Some genes are located on the X chromosome. Females receive two alleles (XX) for these genes, but males only receive one (XY). When doing a punnet square, use large X's and Y's to denote male and female, use superscript letters to designate the alleles. Ex. hemophilia (bleeding) and color blindness are recessive sex-linked traits (XcXc or XcY) If the parent is a male, the genotype is automatically known. A colorblind male has to be b (recessive), since he only has one allele and colorblindness is recessive. A normal male must then be B (dominant) Females can be heterozygous for the colorblindness trait - they are called carriers. A female can be XBXB - normal, XBXb - carrier, or XbXb - colorblind

The following shows a cross between a normal man and a woman who is a carrier.

What more practice problems?

1 codominance In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding (homozygous) one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines, some are two-pronged, some are one-pronged. Is this an example of codominance or incomplete dominance?

2 A nurse at a hospital removed the wrist tags of three babies in the maternity ward. She needs to figure out which baby belongs to which parents, so she checks their blood types. Using the chart below, match the baby to its correct parents. Parents Blood Types Mr. Hartzel O Mrs. Hartzel A Mr. Simon AB Mrs. Simon Mr. Peach Mrs. Peach Baby Blood type Jennifer O Rebecca A Holly B