9.2 Experimental genetics began in an abbey garden Gregor Mendel Augustinian monk who taught natural science to high school students Mendel's brilliant performance at school as a youngster encouraged his family to support his pursuit of a higher education, but their resources were limited, so Mendel entered an Augustinian monastery Gregor Mendel discovered principles of genetics in experiments with the garden pea Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes) Copyright © 2009 Pearson Education, Inc.

9.2 Experimental genetics began in an abbey garden Crosses meticulously documented Crosses numerically/statistically analyzed Scientists of 1860s did not understand and appreciate Work lost in journals for 50 years Rediscovered in 1900s independently by 3 scientists

Terms to know and understand The phenotype is the appearance or expression of a trait Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene If the alleles differ, the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect Homozygous individuals have the same allele on both homologues Heterozygous individuals have a different allele on each homologue

Mating of plants can be controlled Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels) Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another Figure14.2 Crossing pea plants

The true-breeding parents are the P generation In a typical experiment, Mendel mated two contrasting, true-breeding varieties The true-breeding parents are the P generation The hybrid offspring of the P generation are called the F1 generation When F1 individuals self-pollinate, the F2 generation is produced Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Parents (P) Offspring (F1) White 1 Removed stamens from purple flower Stamens Carpel 2 Transferred pollen from stamens of white flower to carpel of purple flower Parents (P) Purple 3 Pollinated carpel matured into pod 4 Planted seeds from pod Offspring (F1)

Mendel’s crosses led to questions When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

EXPERIMENT P Generation (true-breeding parents) Purple flowers White Fig. 14-3-1 EXPERIMENT P Generation (true-breeding parents)  Purple flowers White flowers Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation?

EXPERIMENT P Generation (true-breeding parents) Purple flowers White Fig. 14-3-2 EXPERIMENT P Generation (true-breeding parents)  Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation?

Mendel’s crosses led to questions When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

EXPERIMENT P Generation (true-breeding parents) Purple flowers White Fig. 14-3-3 EXPERIMENT P Generation (true-breeding parents)  Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation? F2 Generation 705 purple-flowered plants 224 white-flowered plants

Questions are . . . Questions that arise Answers? Questions that arise Why does one trait seemed to disappear in the F1 generation? Why does that trait reappear in one quarter of the F2 offspring? Answers?

These inherited factors are what we now call a genes Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids Mendel called the purple flower color a dominant trait and the white flower color a recessive trait These inherited factors are what we now call a genes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Table 14-1

Four related concepts make up this model Mendel’s Model Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring Four related concepts make up this model These concepts can be related to what we now know about genes and chromosomes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

The first concept is that alternative versions of genes account for variations in inherited characters For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

2. The second concept is that for each character an organism inherits two alleles, one from each parent Mendel made this deduction without knowing about the role of chromosomes The two alleles at a locus on a chromosome may be identical, as in the true-breeding plants of Mendel’s P generation - homozygous Alternatively, the two alleles at a locus may differ, as in the F1 hybrids - heterozygous Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

3. The third concept is that if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

4. The fourth concept, now known as the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Let’s look at this example again Before we were only looking at phenotype just like Gregor Mendel Let’s apply his hypotheses and look at genotype as well Draw a Punnett square that would represent true breeding purple flowers crossed with true breeding white flowers

To make a Punnett Square . . . The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Let’s look at this example again Before we were only looking at phenotype just like Gregor Mendel Let’s apply his hypotheses and look at genotype as well PP pp Pp P P p Pp Pp Pp Pp p Flowers will all be purple because of dominance

Let’s look at this example again Before we were only looking at phenotype just like Gregor Mendel Let’s apply his hypotheses and look at genotype as well Draw the Punnett square that would represent two of the F1 generation breedingt PP pp Pp This cross gives us the F1 generation P P p Pp Pp Pp Pp p

Let’s look at this example again Allow F1 generation to self-pollinate and fill out the next Punnett square PP pp Pp P p P PP Pp Pp pp p

Let’s look at this example again Allow F1 generation to self-pollinate and fill out the next Punnett square PP pp Pp P p P PP Pp PP Pp Pp pp Pp pp p ¾ of flowers will all be purple because of dominance. ¼ will be white.

Let’s look at this example again PP pp Pp P p P PP Pp PP Pp Pp pp Pp pp p Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Single trait cross

9.3 Mendel’s law of segregation describes the inheritance of a single character Four Hypotheses Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene For each characteristic, an organism inherits two alleles, one from each parent; the alleles can be the same or different A homozygous genotype has identical alleles A heterozygous genotype has two different alleles Copyright © 2009 Pearson Education, Inc.

9.3 Mendel’s law of segregation describes the inheritance of a single character Four Hypotheses If the alleles differ, the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect The phenotype is the appearance or expression of a trait The same phenotype may be determined by more than one genotype Law of segregation: Allele pairs separate (segregate) from each other during the production of gametes so that a sperm or egg carries only one allele for each gene Copyright © 2009 Pearson Education, Inc.

Humans show dominant and recessive traits Three traits that are determined by single genes with alternate alleles Dominant Traits Recessive Traits The dominant allele determines the phenotype when at least one copy is present Freckles No freckles PTC taste strips Widow’s peak Straight hairline Attached earlobe Free earlobe

Some Genetic Disorders/Anomalies Polydactyly - dominant Tay Sachs - recessive Cystic Fibrosis - recessive Huntington’s Disease - dominant Sickle Cell Anemia - recessive Cause? Single substitution of an amino acid in hemoglobin

Polydactyly Alfredo Alfonseca "The Six Shooter", former Chicago Cubs relief pitcher Six fingers and toes on each hand, all functional

9.8 Genetic traits in humans can be tracked through family pedigrees A pedigree Shows the inheritance of a trait in a family through multiple generations Demonstrates dominant or recessive inheritance Can also be used to deduce genotypes of family members Copyright © 2009 Pearson Education, Inc.

First generation (grandparents) Ff Ff ff Ff Second generation Ff Ff ff Ff Second generation (parents, aunts, and uncles) FF ff ff Ff Ff ff or Ff Third generation (two sisters) ff FF Figure 9.8B Pedigree showing inheritance of attached versus free earlobe in a hypothetical family. or Female Male Ff Affected Marriage Unaffected Siblings Pedigree for a family inheritance of a recessive trait such as deafness

Recessive disease Rr rr ? rr rr

Dominant disease

Dominant disease dd dd dd Dd dd

Huntington’s Disease - handout

Huntington’s Disease Questions Questions What are the chances of a parent with HD passing with HD passing the gene on to any one of his or her children? Thinking of all the ways in which the number of repeats may be passed on to children, discuss the possibility that John may get an HD gene from his mother from his father From which parent did Dink get the gene for HD? Explain how you can tell. Do you expect John's mother to show symptoms of HD? Why or why not.

Huntington’s Disease Questions Questions John's Aunt Barbara refused to have the test for HD. Discuss some reasons that she may have had for coming to that decision. When she applied for a job as an airline pilot, the company, knowing of the occurrence of HD in the family, insisted that she be tested. Does the company have the right to require the test? Explain why or why not. When John reaches the age of 18, he may make the decision of whether or not to be tested for the HD gene. Consider this question from the perspective of John, John's future children, John's future wife, John's employer, John's medical insurer. Explain to John why he should have the test done. Explain to John why he should not have the test done.

VARIATIONS ON MENDEL’S LAWS Copyright © 2009 Pearson Education, Inc.

9.11 Incomplete dominance results in intermediate phenotypes Incomplete dominance Neither allele is dominant over the other Expression of both alleles is observed as an intermediate phenotype in the heterozygous individual Copyright © 2009 Pearson Education, Inc.

P generation Red RR White rr Gametes R r F1 generation Pink Rr Gametes Red RR White rr Gametes R r F1 generation Pink Rr Gametes 1 – 2 R 1 – 2 r Sperm 1 – 2 R 1 – 2 r F2 generation RR rR 1 – 2 R Eggs Rr rr 1 – 2 r

Genotypes: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors Phenotypes: LDL LDL receptor Cell Normal Mild disease Severe disease

9.12 Many genes have more than two alleles in the population Multiple alleles More than two alleles are found in the population A diploid individual can carry any two of these alleles The ABO blood group has three alleles, leading to four phenotypes: type A, type B, type AB, and type O blood Copyright © 2009 Pearson Education, Inc.

9.12 Many genes have more than two alleles in the population Codominance Neither allele is dominant over the other Expression of both alleles is observed as a distinct phenotype in the heterozygous individual Observed for type AB blood Copyright © 2009 Pearson Education, Inc.

Blood Group (Phenotype) Genotypes Red Blood Cells O ii IAIA or IAi A Carbohydrate A IBIB or IBi B Carbohydrate B AB IAIB

Phenotype Genotype A IA IA , IA i B IB IB , IB i AB IA IB O i i Blood Type Phenotype Genotype A IA IA , IA i B IB IB , IB i AB IA IB O i i

Blood Genetics IA i IA IB IB i IA i i i IB i

Blood Typing Questions Given a mom with blood type AB and child with blood type A, what are the possible blood types of the father? IA IB IAIA IA i IA ? ____ i IAIA ? ____ IA

Dominance Worksheet Copyright © 2009 Pearson Education, Inc.

9.13 A single gene may affect many phenotypic characters Pleiotropy One gene influencing many characteristics The gene for sickle cell disease Affects the type of hemoglobin produced Affects the shape of red blood cells Causes anemia Causes organ damage Is related to susceptibility to malaria Copyright © 2009 Pearson Education, Inc.

Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle cells Clumping of cells and clogging of small blood vessels Breakdown of red blood cells Accumulation of sickled cells in spleen Fi Physical weakness Heart failure Pain and fever Brain damage Damage to other organs Spleen damage Anemia Impaired mental function Pneumonia and other infections Kidney failure Paralysis Rheumatism

9.14 A single character may be influenced by many genes Polygenic inheritance Many genes influence one trait Skin color is affected by at least three genes Copyright © 2009 Pearson Education, Inc.

aabbcc (very light) AABBCC (very dark) AaBbCc AaBbCc P generation aabbcc (very light) AABBCC (very dark) F1 generation AaBbCc AaBbCc Sperm 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 8 – 1 F2 generation 8 – 1 8 – 1 8 – 1 64 –– 20 8 – 1 Eggs 8 – 1 64 –– 15 8 – 1 8 – 1 Fraction of population 8 – 1 64 –– 6 64 –– 1 64 –– 1 64 –– 6 64 –– 15 64 –– 20 64 –– 15 64 –– 6 64 –– 1 Skin color

9.15 The environment affects many characters Phenotypic variations are influenced by the environment Skin color is affected by exposure to sunlight Susceptibility to diseases, such as cancer, has hereditary and environmental components Copyright © 2009 Pearson Education, Inc.

Environment—It can fool you

Environment—It can fool you ! The hydrangea flower color is controlled first by flower color genes similar to those in the pea. Purple vs. white has complete dominance. But, pink vs. blue is controlled by the acidity of the soil

Environment—It can fool you ! The hydrangea flower color is controlled first by flower color genes similar to those in the pea. Purple vs. white has complete dominance. But, pink vs. blue is controlled by the acidity of the soil