Observable Patterns of Inheritance

Can you do this?

Terms to Know Probability True-breeding Hybrid Segregation Traits Genes Homozygous Heterozygous Phenotype Genotype Dominant Recessive

Genes Chemical factors that determine traits (units of information) Analogy: Genes are like a combination of ingredients in a recipe. They code for a specific food. Passed from parents to offspring Each has a specific location (locus) on a chromosome

Alleles Different forms of a gene (back to analogy…replacing jiffy p.b. with skippy p.b.) Dominant allele (Uppercase letter) overrules a recessive allele (lowercase letter) that it is paired with

Allele Combinations Homozygous =purebred Heterozygous =hybrid having two identical alleles at a locus AA (dominant expressed) or aa (recessive expressed) Heterozygous =hybrid having two different alleles at a locus Aa (dominant expressed)

Genotype & Phenotype Genotype refers to particular genes an individual carries Phenotype refers to an individual’s observable traits Cannot always determine genotype by observing phenotype

Tracking Generations Parental generation P mates to produce First-generation offspring F1 mate to produce Second-generation offspring F2

Earlobe Variation Whether a person is born with attached or detached earlobes depends on a single gene Gene has two molecular forms (alleles)

Earlobe Variation You inherited one allele for this gene from each parent Dominant allele specifies detached earlobes (E) Recessive allele specifies attached earlobes (e)

Dominant & Recessive Alleles If you have attached earlobes, you inherited two copies of the recessive allele If you have detached earlobes, you may have either one or two copies of the dominant allele

Early Ideas About Heredity People knew that sperm and eggs transmitted information about traits Blending theory Problem: Would expect variation to disappear Variation in traits persists

Gregor Mendel Strong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

Mendel was born in1822 Austrian monk Studied at the Univ. of Vienna Teacher (High School)

Figure 24–5 The Structure of a Flower Section 24-1 Filament Anther Stigma Style Ovary Carpel Petal Sepal Ovule Stamen

The Garden Pea Plant Self-pollinating True breeding (different alleles not normally introduced) Can be experimentally cross-pollinated

How did Mendel fertilize the plants?

F1 Results of One Monohybrid Cross

Dominant trait is expressed F M Dominant trait is expressed Recessive appears

Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall

F1 Results of Mendel’s Dihybrid Crosses All plants displayed the dominant form of both traits We now know: All plants inherited one allele for each trait from each parent All plants were heterozygous (AaBb)

Principle of Dominance Some alleles are dominant and others are recessive.

Mendel wanted to know if the recessive alleles disappeared or are they still in the f1,just hidden.

Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

Mendel’s Theory of Segregation An individual inherits a unit of information (allele) about a trait from each parent During gamete formation, the alleles segregate from each other

Independent Assortment Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis

Independent Assortment Metaphase I OR A A a a A A a a B B b b b b B B Metaphase II: A A a a A A a a B B b b b b B B Gametes: B B b b b b B B A A a a A A a a 1/4 AB 1/4 ab 1/4 Ab 1/4 aB

F2 Results of Monohybrid Cross

The physical characteristic Type of alleles

Impact of Mendel’s Work Mendel presented his results in 1865 Paper received little notice Mendel discontinued his experiments in 1871 Paper rediscovered in 1900 and finally appreciated

Probability The likelihood that a particular event will occur. Flip a coin. We use Punnett Squares

D 38- Deduce the probable mode of inheritance of traits (e.g.,

Homozygous recessive a a A a aa Aa Homozygous recessive a a A Aa Punnett Squares of Test Crosses Homozygous recessive a a A a aa Aa Homozygous recessive a a A Aa Two phenotypes All dominant phenotype

Punnett Square of a Monohybrid Cross Female gametes Male gametes A a A a Aa AA aa Dominant phenotype can arise 3 ways, recessive only one

Test Cross Individual that shows dominant phenotype is crossed with individual with recessive phenotype Examining offspring allows you to determine the genotype of the dominant individual

Tt X Tt Cross

Tt X Tt Cross

Tt X Tt Cross

Genetics Practice Problem 1 What occurs when a purple plant that is heterozygous is fertilized by a white plant? Identify generations Punnett Square Genotypes % Phenotype %

Principle of Independent Assortment The genes for different traits separate independently of one another during the formation of gametes.

Figure 11-10 Independent Assortment in Peas

Yellow round 9/16 Green round 3/16 Yellow wrinkled 3/16 Green wrinkled 1/16 9 : 3 : 3 : 1 Ratio

Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits

Straight Pinky (Dominant) Bent Pinky (Recessive) Straight Thumb (Dominant) Curved Thumb (Recessive)

Achondroplastic Dwarfism More Dominant Traits Polydactylism Achondroplastic Dwarfism Tay-Sachs Disease - One Wrong Letter

Dominance Relations Complete dominance Incomplete dominance Heterozygote phenotype is somewhere between that of two homozyotes Codominance Non-identical alleles specify two phenotypes that are both expressed in heterozygotes

Flower Color in Snapdragons: Incomplete Dominance Red-flowered plant X White-flowered plant Pink-flowered F1 plants (homozygote) (homozygote) (heterozygotes)

Flower Color in Snapdragons: Incomplete Dominance Red flowers - two alleles allow them to make a red pigment White flowers - two mutant alleles; can’t make red pigment Pink flowers have one normal and one mutant allele; make a smaller amount of red pigment

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

Flower Color in Snapdragons: Incomplete Dominance Pink-flowered plant X Pink-flowered plant White-, pink-, and red-flowered plants in a 1:2:1 ratio (heterozygote) (heterozygote)

Incomplete Dominance Neither allele is dominant over the other Combination of red and white flowers

Codominant Sickle Cell Disease ABO Blood Types

Pleitropy Alleles at a single locus may have effects on two or more traits Classic example is the effects of the mutant allele at the beta-globin locus that gives rise to sickle-cell anemia

Teachers Domain - A Mutation Story

Genetics of Sickle-Cell Anemia Two alleles 1) HbA Encodes normal beta hemoglobin chain 2) HbS Mutant allele encodes defective chain HbS homozygotes produce only the defective hemoglobin; suffer from sickle-cell anemia

Pleiotrophic Effects of HbS/HbS At low oxygen levels, cells with only HbS hemoglobin “sickle” and stick together This impedes oxygen delivery and blood flow Over time, it causes damage throughout the body

Blood Typing Karl Landsteiner 1897 Worked at the Univ. of Vienna, Vienna Austria (Sound familiar?) Wanted to find out which red blood cells would clot

First found two different groups, A and B Third group would not clot when exposed to A or B What do you think this was? What about the forth group?

Genetics of ABO Blood Types: Three Alleles Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Two alleles (IA and IB) are codominant when paired Third allele (i) is recessive to others

ABO Blood Type: Glycolipids on Red Cells Type A - Glycolipid A on cell surface Type B - Glycolipid B on cell surface Type AB - Both glyocolipids A & B Type O - Neither glyocolipid A nor B

ABO Blood Type: Allele Combinations Type A - IAIA or IAi Type B - IBIB or IBi Type AB - IAIB Type O - ii

ABO and Transfusions Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface Type O is universal donor because it has neither type A nor type B glycolipid

Codominance and Multiple Alleles - AB or NOT AB Codominance - both alleles are dominant IA and IB Multiple Alleles - genes have more than two alleles IA, IB, Ia

Figure 14-4 Blood Groups Safe Transfusions Phenotype Antigen on (Blood Type Antigen on Red Blood Cell Genotype To From

Universal Acceptor Universal Donor

Rh factor - Another Blood Trait Pregnancy complications Rh is a type of protein in the blood If an Rh- man reproduces with an Rh + woman complications can occur.

Polygenic Traits: Desiree’s Baby Case Study More than one gene controls a trait Skin color more than one gene, incomplete dominance

A,B and C are dark a,b and c are light

Sex Linked Traits - traits that are carried on the either the x or y chromosome

Figure 14-13 Colorblindness Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

Figure 14-13 Colorblindness Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

Colorblindness

Cystic Fibrosis - Finding Cures is Hard Sex-Linked Disorder Cystic Fibrosis - Finding Cures is Hard

Hairy Pinna - long hair on ears Male Pattern Baldness (X chromosome) Hairy Pinna - long hair on ears

Recessive Disorder Figure 14-8 The Cause of Cystic Fibrosis Chromosome # 7 CFTR gene The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

Albinism Phenotype results when pathway for melanin production is completely blocked Genotype - Homozygous recessive at the gene locus that codes for tyrosinase, an enzyme in the melanin-synthesizing pathway

Human Genetics

Tracing Genes Through Families - Human Pedigrees Female Partner Male Brothers and Sisters

Figure 14-3 A Pedigree A circle represents a female. A square represents a male. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A half-shaded circle or square indicates that a person is a carrier of the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait.

Ability to roll the tongue in the Senator Family Tongue Roller - dominant, Non-Tongue Roller - recessive White = tongue roller, Purple = non-roller What are the genotypes of everyone? R = roller, r = non roller

George, Sam, Ann, Michael, Daniel and Alan are Rr Arlene, Tom, Wilma, and Carla are rr Sandra, Tina and Christopher are either RR or Rr

Case Study - Hemophilia and the Royal Family

1. First, let’s take a look at Queen Victoria’s son Leopold’s family 1. First, let’s take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice of Athlone, had one hemophilic son (Rupert) and two other children—a boy and a girl—whose status is unknown. a) What is the probability that her other son was hemophilic? b) What is the probability that her daughter was a carrier? Hemophilic? c) What is the probability that both children were normal?

2. Now for the Spanish connection: Victoria’s youngest child, Beatrice, gave birth to one daughter, one normal son, and two hemophilic sons. Looking at the pedigree of the royal family, identify which of Beatrice’s children received the hemophilic gene; why can you make this conclusion? Notice that Beatrice’s daughter, Eugenie, married King Alfonso XIII of Spain and had six children, one of whom was the father of Juan Carlos, the current King of Spain. Would you predict that Juan Carlos was normal, a carrier, or a hemophilic?

3. Alexis did not die from hemophilia 3. Alexis did not die from hemophilia. At the age of fourteen he was executed with the rest of the family. His four oldest sisters were also young and didn’t have children, so we don’t know whether any of them was a carrier. But we can make an estimate. a) What are the probabilities that all four of the girls were carriers of the allele hemophilia? b) Supposing Alexis had lived and married a normal woman, what are the chances that his daughter would be a hemophiliac? c) What are the chances his daughters would be carriers? d) What are the chances that his sons would be hemophiliacs?

Homologous chromosomes fail to separate Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

Homologous chromosomes fail to separate Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

Homologous chromosomes fail to separate Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

Epistasis Interaction between the products of gene pairs Common among genes for hair color in mammals

Genetics of Coat Color in Labrador Retrievers Two genes involved - One gene influences melanin production Two alleles - B (black) is dominant over b (brown) - Other gene influences melanin deposition Two alleles - E promotes pigment deposition and is dominant over e

Allele Combinations and Coat Color Black coat - Must have at least one dominant allele at both loci BBEE, BbEe, BBEe, or BbEE Brown coat - bbEE, bbEe Yellow coat - Bbee, BbEE, bbee

Alleles at two loci (R and P) interact Comb Shape in Poultry Alleles at two loci (R and P) interact Walnut comb - RRPP, RRPp, RrPP, RrPp Rose comb - RRpp, Rrpp Pea comb - rrPP, rrPp Single comb - rrpp

Campodactyly: Unexpected Phenotypes Effect of allele varies: Bent fingers on both hands Bent fingers on one hand No effect Many factors affect gene expression

Continuous Variation A more or less continuous range of small differences in a given trait among individuals The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait

Human Variation Some human traits occur as a few discrete types Attached or detached earlobes Many genetic disorders Other traits show continuous variation Height Weight Eye color

Temperature Effects on Phenotype Himalayan rabbits are Homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathway Melanin is produced in cooler areas of body

Environmental Effects on Plant Phenotype Hydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue