2Background Vocabulary True-breeds: pure gene lines – offspring match parentSelf-pollination: pollen from flower fertilizes the same plantCross-pollination: pollen will fertilize a different plantHybrid: Cross between organisms with different traits (blonde hair & brown hair)Trait: Physical characteristics
3Gregor Mendel Austrian monk “Father of Modern Genetics” Famous for his work with peas
6Mendel’s Crosses TRAIT 1: Seed Shape P Cross: Round v. Wrinkled F1 Phenotype: Round
7Mendel’s Crosses TRAIT 2: Seed Color P Cross: Green v. Yellow F1 Phenotype: Yellow
8Mendel’s Crosses TRAIT 3: Flower Color P Cross: Purple v. White F1 Phenotype: Purple
9Mendel’s Crosses TRAIT 4: Pod Shape P Cross: Inflated v. Pinched F1 Phenotype: Inflated
10Mendel’s Crosses TRAIT 5: Pod Color P Cross: Green v. Yellow F1 Phenotype: Green
11Mendel’s Crosses TRAIT 6: Flower Position P Cross: Axial v. Terminal F1 Phenotype: Axial
12Mendel’s Crosses TRAIT 7: Plant Height P Cross: Tall v. Short F1 Phenotype: Tall
13Mendel’s ConclusionsBiological inheritance is determined by chemical factors passed from one generation to the next (Particulate hypothesis)Geneticists now refer to these factors as genesGenes can come in more than one form, each form is an alleleex. B or b (The “B” gene w/ 2 alleles)
14The Principle of Dominance Certain alleles will be expressed over othersThe expressed alleles are dominant to the unexpressed recessive alleles
15The F1 Cross Mendel’s experiment: The results: Allow the F1 plants to self pollinateThe results:The dominant trait was expressed 75% of the timeThe recessive trait was expressed 25% of the time
16The Explanations:1. The recessive allele was still present in the F1 plants2. Principle of Segregation: Each individual inherits two alleles for each gene.
17Probability The likelihood of an event happening How is it determined: Likelihood of rolling heads = 50% (1 of 2 possibilities)Rolling heads twice?50% x 50% = 25%To predict outcomes of genetic crosses we use punnett squares
18More genetics vocabulary… Homozygous: two identical alleles (AA or aa)Heterozygous: two different alleles (Aa)Phenotype: Physical appearanceGenotype: Genetic make-upHomozygous dominant (AA)Homozygous recessive (aa)Heterozygous (Aa)
19The Test CrossIn order to determine whether an individual expressing a dominant trait is homozygous or heterozygous, it can be crossed with an organism expressing the recessive trait.If R = round seeds and r = wrinkled seeds, show how the results of a test cross for seed shape will differ for homozgygous v. heterozgous genotypes for round seeds.
20Monohybrid (1-factor) Cross Practice KEY: G = green pods, g = yellow podsP = purple flowers, p = white flowersT = tall plants, t = short plantsShow a cross a plant heterozygous for green pods with a plants with yellow pods. What are the expected genotype and phenotype ratios?Show a cross of a homozygous tall plant with a heterozygous tall plant. What are the expected genotype and phenotype ratios?Show a cross of two heterozygous purple flowered plants. What are the expected genotype and phenotype ratios?
21Exploring Mendelian Genetics Does segregation of one set of alleles influence the segregation of another pair of alleles?Mendel’s Two Factor CrossesFollowed two traits at a time.Same method as his original single-factor crossesCross-pollinated to produce the F1 and allowed them to self-pollinate
24A Summary of Mendel’s Principles Dominance: a recessive allele will be masked by a dominant alleleSegregation: alleles for each trait segregate (separate) during gamete formationIndependent Assortment: Alleles for different traits do not influence each other’s segregation
25Mendel’s Peas were ideal for learning about inheritance, but they do not represent the norm… Traits in pea plants are determined by just two allelesIn peas, one allele is clearly dominant & the other is clearly recessiveHowever, things aren’t always this clear-cut and simple in the world of genetics.
26What if Mendel looked at mice? If a female black mouse and a male white mouse were crossed, what will the offspring look like?- 100% are GREYIf the F1 offspring were crossed, what will there offspring look like?- 25% black- 50% grey- 25% white
27Incomplete DominanceA cross between two organisms with different traits results in an offspring with a third phenotype that is a blending of the parental traits.It’s like mixing paints:Red + White = PinkRed does not totally block (dominate) white, we end up with something in-between.
29Let’s try crossing snapdragons… What will the genotype and phenotype ratios be if a red plant is crossed with a pink plant?(Use the following allele symbols: CR & CW)G:P:
30What does the prefix “Co-” mean? Consider the meaning of the following words:- Cooperate- Coexist- CohabitatWhat about “Codominance”?
31This is called ‘roan’ fur; red & white fur together. Let’s look at cattle….This cow resulted from a cross between a cow with red fur and a cow with white fur.This is called ‘roan’ fur; red & white fur together.
32CodominanceSimilar to incomplete dominance in that there is a 3rd phenotypeIn COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms.Red x White = red & white
33Let’s try crossing cattle…. What will the gentype and phenotype ratios be if a red cow is crossed with a white cow?G:P:
34Polygenic (Multifactorial) Traits Phenotype is determine by more than one geneOften results in gradations, where each gene has an additive effectEx) If 10 gene loci are turned on plant will be20cm tall, if only 5 loci are turned on plantwill be 10cm tallResults in a bell-shaped curveSkin color & Height are examples in humans
37ABO Blood TypesIn addition to having multiple alleles, ABO blood type also exhibits codominance‘IA’ & ‘IB’ are codominant‘i’ is recessive
38ABO Blood Typing Genotype Blood Type IA IA or IA i IB IB or IB i IAIB
39What does your ABO blood type mean? Remember the ‘flags’ on our cell membranes? They help cells to recognize each other.Some of those flags ‘announce’ your blood type. We call these flags antigensBloodTypeAntigenABABO
44Rh Disease Mother's antibodies cross the placenta to fight the Rh positive cells in the baby's body.As the antibodies destroy the red blood cells, the baby canbecome anemic.The anemia can lead to other complications including jaundice and organ enlargementWith amniocentesis, the amniotic fluid may have a yellow coloring and contain bilirubin.Ultrasound of the fetus shows enlarged liver, spleen, or heart and fluid build up in the fetus' abdomen.
45Gene Linkage & Mapping Chromosomes Genes on the same chromosome are more likely to be inherited togetherCrossing over helps to increased variation, but the closer two genes are on a chromosome the more likely they are to be “linked”
46Sex Chromosomes & Autosomes Two of the 46 human chromosomes are known as sex chromosomes, because they determine the individual’s sex.Females have two copies of an X chromosome.Males have one X chromosome and one Y chromosome.The remaining 44 chromosomes are known as autosomal chromosomes or autosomes.
47Sex-Linked Genes Located on one of the sex chromosomes (X or Y) Since the X chromosome is longer, it has many genes not found on the Y chromosome.Most sex-linked genes are X-linked genes.
50Calico/Tortioseshell Cats There is a fur color gene located on the X chromosome in cats.For tortoiseshell there are two possible alleles, orange and black, which are codominant in a heterozygoteFor calico there are also codominant black and orange alleles, but they code for blotches on a white background.Are these cats male or female? Explain.
51Complete the following sex-linked crosses: Laura and Steve are expecting their first child. They are concerned about the chances their child might be hemophiliac because both Steve and Laura’s father are hemophiliac. What is the probability of Laura and Steve having a hemophiliac child?Eva and Paul just had a son, Michael. Paul is has normal color vision, but Eva’s father was colorblind. What is the likelihood that Michael is colorblind?
54Complete the following pedigrees. Which is for a sex-linked trait Complete the following pedigrees. Which is for a sex-linked trait? How do you know?
55Chromosomal Disorders The most common error in meiosis occurs when homologous chromosomes fail to separate.This is known as nondisjunction, which means “not coming apart”If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes and a disorder of chromosome numbers may occur.A monosomy results if an entire chromosome is missing and a trisomy results if there is an additional copy of a chromosome
57Jumping GenesIn the 1940’s, while studying corn, Barbara McClintock discovered that sometimes genes could move from one location to another in a chromosome or even to other chromosomes.The movement could result in the genes landing in the middle of another gene and disrupting them.These “jumping genes” are now called transposons.
60Down Syndrome Trisomy 21 Produces mild to severe mental retardation Characterized by:Increased susceptibility to many diseasesHigher frequency of some birth defects.
61Turner Syndrome Monosomy X Result of nondisjunction in females Characteristic physical abnormalities, such as short stature, broad chest, low hairline, low-set ears, and webbed neck
62Klinefelter Syndrome Karyotype 47, XXY Extra X chromosome interferes with meiosis and usually prevents these individuals from reproducingMost common sex chromosome disorder, second most common disorder due to the presence of an extra chromosome
63Genes & The Environment Many of your personal traits are only partially governed by genetics.Environmental factors can have an effect on gene expression.Epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence.
65The Genetic Basis of Cancer You already know that cancer results when controls on the cell cycle do not work properly and cells grow and divide too quickly.Two classes of genes direct the production of proteins that regulate cell growth and division:one produces growth factors to initiate cell division (can mutate to an oncogene & result in too much growth factor)the other produces proteins to stop cell division (tumor suppressor genes)Cancer is always a genetic disease in that it results from changes in DNA:Since the mutations do not usually arise in gametes, cancer is not usually passed from parent to childHowever some mutations do arise in the ovaries or testes which can give rise to gametes and result in the inheritance of cancer genes.