Presentation on theme: "Background Vocabulary True-breeds: pure gene lines – offspring match parent Self-pollination: pollen from flower fertilizes the same plant Cross-pollination:"— Presentation transcript:
Background Vocabulary True-breeds: pure gene lines – offspring match parent Self-pollination: pollen from flower fertilizes the same plant Cross-pollination: pollen will fertilize a different plant Hybrid: Cross between organisms with different traits (blonde hair & brown hair) Trait: Physical characteristics
Gregor Mendel Austrian monk “Father of Modern Genetics” Famous for his work with peas
Mendel’s Crosses TRAIT 1: Seed Shape P Cross: Round v. Wrinkled F1 Phenotype: Round
Mendel’s Crosses TRAIT 2: Seed Color P Cross: Green v. Yellow F1 Phenotype: Yellow
Mendel’s Crosses TRAIT 3: Flower Color P Cross: Purple v. White F1 Phenotype: Purple
Mendel’s Crosses TRAIT 4: Pod Shape P Cross: Inflated v. Pinched F1 Phenotype: Inflated
Mendel’s Crosses TRAIT 5: Pod Color P Cross: Green v. Yellow F1 Phenotype: Green
Mendel’s Crosses TRAIT 6: Flower Position P Cross: Axial v. Terminal F1 Phenotype: Axial
Mendel’s Crosses TRAIT 7: Plant Height P Cross: Tall v. Short F1 Phenotype: Tall
Mendel’s Conclusions Biological inheritance is determined by chemical factors passed from one generation to the next (Particulate hypothesis)Biological inheritance is determined by chemical factors passed from one generation to the next (Particulate hypothesis) –Geneticists now refer to these factors as genes –Genes can come in more than one form, each form is an allele ex. B or b (The “B” gene w/ 2 alleles)
The Principle of Dominance 1.Certain alleles will be expressed over others 2.The expressed alleles are dominant to the unexpressed recessive alleles
The F 1 Cross Mendel’s experiment: –Allow the F1 plants to self pollinate The results: –The dominant trait was expressed 75% of the time –The recessive trait was expressed 25% of the time
The Explanations: 1. The recessive allele was still present in the F1 plants 2. Principle of Segregation: Each individual inherits two alleles for each gene.
Probability 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% punnett squaresTo predict outcomes of genetic crosses we use punnett squares
More genetics vocabulary… Homozygous: two identical alleles (AA or aa) Heterozygous: two different alleles (Aa) Phenotype: Physical appearance Genotype: Genetic make-up –Homozygous dominant (AA) –Homozygous recessive (aa) –Heterozygous (Aa)
The Test Cross In 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.
Monohybrid (1-factor) Cross Practice KEY: G = green pods, g = yellow pods P = purple flowers, p = white flowers T = tall plants, t = short plants Show 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?
Exploring Mendelian Genetics Does segregation of one set of alleles influence the segregation of another pair of alleles? Mendel’s Two Factor Crosses –Followed two traits at a time. –Same method as his original single-factor crosses –Cross-pollinated to produce the F1 and allowed them to self-pollinate
The Parental Cross _________________________________
A Summary of Mendel’s Principles Dominance: a recessive allele will be masked by a dominant allele Segregation: alleles for each trait segregate (separate) during gamete formation Independent Assortment: Alleles for different traits do not influence each other’s segregation
Mendel’s Peas were ideal for learning about inheritance, but they do not represent the norm… Traits in pea plants are determined by just two alleles In peas, one allele is clearly dominant & the other is clearly recessive However, things aren’t always this clear- cut and simple in the world of genetics.
What if Mendel looked at mice? If a female black mouse and a male white mouse were crossed, what will the offspring look like? GREY - 100% are GREY If the F1 offspring were crossed, what will there offspring look like? - 25% black - 50% grey - 25% white
Incomplete Dominance A 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 = Pink –Red does not totally block (dominate) white, we end up with something in-between.
Let’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: C R & C W ) G: P:
What does the prefix “Co-” mean? Consider the meaning of the following words: - Cooperate - Coexist - Cohabitat What about “Codominance”?
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.
Codominance Similar to incomplete dominance in that there is a 3 rd phenotype In COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms. Red x White = red & white
Let’s try crossing cattle…. What will the gentype and phenotype ratios be if a red cow is crossed with a white cow? G: P:
Polygenic (Multifactorial) Traits Phenotype is determine by more than one gene Often results in gradations, where each gene has an additive effect Ex) If 10 gene loci are turned on plant will be 20cm tall, if only 5 loci are turned on plant will be 10cm tall Results in a bell-shaped curve –Skin color & Height are examples in humans
Full color: CC, Cc ch, Cc h, or Cc Chinchilla: c ch c h, c ch c ch, or c ch cHimalayan: c h c, or c h c h AIbino: cc KEY C = full color; dominant to all other alleles c ch = chinchilla; partial defect in pigmentation; dominant to c h and c alleles c h = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Multiple Alleles More than 2 alleles for a particular trait
ABO Blood Types In addition to having multiple alleles, ABO blood type also exhibits codominance ‘I A’ & ‘I B’ are codominant ‘i’ is recessive
ABO Blood Typing GenotypeBlood Type I A I A or I A i I B I B or I B i IAIBIAIB ii
What 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 antigens Blood Type Antigen A B AB O
ABO Blood Transfusions Blood Type Can receive: A B AB* O*
Rh 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 can become anemic. The anemia can lead to other complications including jaundice and organ enlargement With 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.
Gene Linkage & Mapping Chromosomes Genes on the same chromosome are more likely to be inherited together Crossing over helps to increased variation, but the closer two genes are on a chromosome the more likely they are to be “linked”
Sex 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.
Sex-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.
Calico/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 heterozygote For 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 Are these cats male or female? Explain.
Complete the following sex-linked crosses: 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? 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?
Complete the following pedigrees. Which is for a sex-linked trait? How do you know?
Chromosomal 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
Jumping Genes In 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.
Down Syndrome Trisomy 21 Produces mild to severe mental retardation Characterized by: –Increased susceptibility to many diseases –Higher frequency of some birth defects.
Turner 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
Klinefelter Syndrome Karyotype 47, XXY Extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing Most common sex chromosome disorder, second most common disorder due to the presence of an extra chromosome
Genes & 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.
The 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 child –However some mutations do arise in the ovaries or testes which can give rise to gametes and result in the inheritance of cancer genes.