Introduction to Genetics Genetics = the scientific study of heredity

The Work of Gregor Mendel Gregor Medel 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

His first experiments are called monohybrid crosses because they only deal with ONE single trait (height, color) mono means “one”

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. Short pea plant Tall pea plant All tall pea plants 3 tall: 1 short P1P1 F1F1 F2F2

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. TT T T tt t t Tall plant Short plant All tall plants F1F1

Law of Segregation the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring which allele in a parent's pair of alleles is inherited is a matter of chance segregation of alleles occurs during the process of gamete formation (meiosis) randomly unite at fertilization

Law of segregation Tt xTt cross F1F1 Tall plant TTT T t Tt tT t t t 3 Tall Short 1 Tall F2F2 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.

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. Tt T t T T t t

You try this one: AA A a

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

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

Section 1 Check Question 2 What are traits? Answer 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 __________. D. fertilized cells that develop into adult organisms C. both male and female sex cells B. female sex cells A. male sex cells

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? C. tt B. Tt A. TT

Mendel’s Dihybrid Crosses Dihybrid Cross round yellow x wrinkled green Round yellow Wrinkled green All round yellow Round yellow Round greenWrinkled yellow Wrinkled green 9331 P1P1 F1F1 F2F2

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

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 than 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

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 A and B can be homozygous or heterozygous.

Sex Linked Some genes are located on the X chromosome. Females receive two alleles (XX) for these genes, but males only receive one (y). 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 (dominate) 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 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? codominance

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. ParentsBlood Types Mr. HartzelO Mrs. HartzelA Mr. SimonAB Mrs. SimonAB Mr. PeachO Mrs. PeachO BabyBlood type JenniferO RebeccaA HollyB