Fundamentals of Genetics Chapter 9 Table of Contents Section 1 Mendel’s Legacy Section 2 Genetic Crosses

Section 1 Mendel’s Legacy Chapter 9 Objectives Describe how Mendel was able to control how his pea plants were pollinated. Describe the steps in Mendel’s experiments on true-breeding garden peas. Distinguish between dominant and recessive traits. State two laws of heredity that were developed from Mendel’s work. Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes.

Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel The study of how characteristics are transmitted from parents to offspring is called genetics.

Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued Mendel’s Garden Peas –Mendel observed characteristics of pea plants. –Traits are genetically determined variants of a characteristic. –Each characteristic occurred in two contrasting traits.

Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued Mendel’s Methods –Mendel used cross-pollination techniques in which pollen is transferred between flowers of two different plants.

Section 1 Mendel’s Legacy Chapter 9 Mendel’s Experiments Mendel bred plants for several generations that were true-breeding for specific traits and called these the P (Parental) generation. Offspring of the P generation were called the F 1 (First Filial ) generation. Offspring of the F 1 generation were called the F 2 (Second Filial) generation.

Chapter 9 Three Steps of Mendel’s Experiments Section 1 Mendel’s Legacy

Chapter 9 Click below to watch the Visual Concept. Visual Concept Mendel’s Experiments Section 1 Mendel’s Legacy

Chapter 9 Mendel’s Results and Conclusions Recessive and Dominant Traits –Mendel concluded that inherited characteristics are controlled by factors that occur in pairs. –In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.

Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued The Law of Segregation –The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes.

Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued The Law of Independent Assortment –The law of independent assortment states that factors for individual characteristics are distributed to gametes independent of one another. –The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.

Section 1 Mendel’s Legacy Chapter 9 Support for Mendel’s Conclusions We now know that the factors that Mendel studied are alleles, or alternative forms of a gene. One allele for each trait is passed from each parent to the offspring.

Chapter 9 Click below to watch the Visual Concept. Visual Concept Mendel’s Conclusions Section 1 Mendel’s Legacy

Section 2 Genetic Crosses Chapter 9 Objectives Differentiate between the genotype and the phenotype of an organism. Explain how probability is used to predict the results of genetic crosses. Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses. Differentiate a monohybrid cross from a dihybrid cross.

Section 2 Genetic Crosses Chapter 9 Genotype and Phenotype The genotype is the genetic makeup of an organism. The phenotype is the appearance of an organism.

Section 2 Genetic Crosses Chapter 9 Probability Probability is the likelihood that a specific event will occur. A probability may be expressed as a decimal, a percentage, or a fraction.

Chapter 9 Click below to watch the Visual Concept. Visual Concept Calculating Probability Section 2 Genetic Crosses

Chapter 9 Predicting Results of Monohybrid Crosses A Punnett square can be used to predict the outcome of genetic crosses. A cross in which one characteristic is tracked is a monohybrid cross.

Chapter 9 Click below to watch the Visual Concept. Visual Concept Punnett Square with Homozygous Cross Section 2 Genetic Crosses

Chapter 9 Monohybrid Cross of Heterozygous Plants Section 2 Genetic Crosses

Chapter 9 Predicting Results of Monohybrid Crosses, continued Complete dominance occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype. TT (Homozygous Dominant)---Tall Tt (Heterozygous)---Tall tt (Homozygous Recessive)---Short

Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Incomplete dominance occurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait. Intermediate Color is a blend of Parental Traits

Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring. Both Parental Traits appear together. Example: Roan Cow or Horse. There are equal amounts of white hair and red hair blending together to give a color that is a combination of the two.

Section 2 Genetic Crosses Chapter 9 Predicting Results of Dihybrid Crosses A cross in which two characteristics are tracked is a dihybrid cross.

Chapter 9 Dihybrid Crosses Section 2 Genetic Crosses

Dihybrid Punnett Square Homozygous round and yellow with a heterozygous yellow and round RRYY with RrYy Offspring are all round and yellow RY Ry rY ry RRYY RRYy RrYY RrYy

Dihybrid Punnett Square Homozygous wrinkled and green with a heterozygous yellow and round rryy with RrYy 4 round yellow, 4 round green, 4 wrinkled yellow, 4 wrinkled, green ry RY Ry rY ry RrYy Rryy rrYy rryy

Gene Linkage Gene Linkage- genes that are located on the same chromosome are inherited together. These genes travel together during gamete formation. This is an exception to the Mendelian Principle of Independent Assortment because linked genes do not segregate independently. Chapter 9 Section 3 Genetics

Multiple Allele Multiple Alleles- exist for a particular trait even though only two alleles are inherited. Ex. Three alleles exist for blood type (A, B, and O), which result in four different blood groups. Blood Type ( Phenotype ) Genotype Type A AA and AO I A I A or I A i Type B BB and BO I B I B or I B i Type AB AB I A I B Type O OO ii Chapter 9 Section 3 Genetics

Blood Type Crosses Type O mother and Type AB father IAIA i IAiIAi 50% blood type A 50% blood type B 100% type AB i IBiIBi IBiIBi IAiIAi IBIB IAIA IAIBIAIB IAIA Homozygous Type A mother and Homozygous Type B father IBIB IBIB IAIBIAIB IAIBIAIB IAIBIAIB

Blood Type Frequencies in the US ABO Type Rh Type How Many Have It Opositive 37.4% 44% Onegative6.6% Apositive35.7% 42% Anegative6.3% Bpositive8.5% 10% Bnegative1.5% ABpositive3.4% 4% ABnegative.6% ABO and Rh Blood Type Frequencies in the United States

Polygenic Traits Polygenic Traits are traits that are controlled by two or more genes. These traits often show a great variety of phenotypes. Ex. Skin Color Mendel’s principles of genetics did not explain that many traits are controlled by more than one gene. Chapter 9 Section 3 Genetics

Sex Determination Remember that humans have 22 pairs of autosomes and 1 pair of sex chromosomes These sex chromosomes determine the gender of the offspring –XX is a female –XY is a male Each offspring gets an X from the mother and either an X or a Y from the father----Male determines the sex of the offspring

Sex Determination Predicting the sex of the offspring can be done using a Punnett Square Each time a male gamete fertilizes a female gamete, there is a 50% chance for either sex

Sex-Linked Traits Sex-Linked Traits result of genes that are carried on either the X or the Y chromosome. This is an exception to Mendel’s principle of independent assortment, which does not explain sex-linked traits. Males: XY Females: XX In humans, the Y chromosome carries very few genes, the X chromosome contains a number of genes that affect many traits. Sex-linked genes are expressed differently form an autosomal gene. Chapter 9 Section 3 Genetics

Sex-Linked Traits (continued) If a gene is linked on the X chromosome (X-linked): Female offspring will inherit the gene as they do all other chromosomes X from the father and X from the mother). Male offspring will inherit the gene on their X chromosome, but no on the Y chromosome. Since males have on X chromosome, they express the allele whether it is dominant or recessive, there is no second allele to mask the effects of the other allele. Chapter 9 Section 3 Genetics

Predicting Sex-Linked Traits The chances that an offspring will have a sex-linked trait can be predicted using a Punnett Square

Sex-Linked Traits (continued) Chapter 9 Section 3 Genetics

Sex-Linked Crosses Colorblind mother and Normal father XNXN Y XnXn XNXnXNXn Normal daughters (carriers) Colorblind sons 50% Normal daughters and sons 50% colorblind daughters and sons Colorblindness is a recessive sex-linked trait. Use X N for the normal allele and X n for the colorblind allele Heterozygous Normal mother and Colorblind father XnXn XnYXnY XnYXnY XNXnXNXn XnXn Y XNXN XNXnXNXn XnXn XnYXnY XNYXNY XnXnXnXn

DOMINANT TRAITSRECESSIVE TRAITS eye coloringbrown eyesgrey, green, hazel, blue eyes visionfarsightedness normal vision normal vision normal vision normal vision nearsightedness night blindness color blindness* hairdark hair non-red hair curly hair full head of hair widow's peak blonde, light, red hair red hair straight hair baldness* normal hairline facial featuresdimples unattached earlobes freckles broad lips no dimples attached earlobes no freckles thin lips appendagesextra digits fused digits short digits fingers lack 1 joint limb dwarfing clubbed thumb double-jointedness normal number normal digits normal digits normal joints normal proportion normal thumb normal joints otherimmunity to poison ivy normal pigmented skin normal blood clotting normal hearing normal hearing and speaking normal- no PKU susceptibility to poison ivy albinism hemophilia* congenital deafness deaf mutism phenylketonuria (PKU) DOMINANT AND RECESSIVE CHARACTERISTICS Characteristics in the left-hand column dominate over those characteristics listed in the right-hand column.

Pedigree- is a chart constructed to show an inheritance pattern (trait, disease, disorder) within a family through multiple generations. Through the use of a pedigree chart and key, the genotype and phenotype of the family members and the genetic characteristics (dominant recessive, sex-linked) of the trait can be tracked. Chapter 9 Section 3 Genetics

Chapter 9 Section 3 Genetics

Chapter 9 Section 3 Genetics