Agenda To Turn In Today Homework 3 Microworlds
- Slides: 74
Agenda • To Turn In Today: – Homework 3 – Microworlds • Some of your lab reports are graded • Lecture quiz
Phases of Mitosis Identification
Meiosis Haploid gametes (n = 23) n Egg cell ANIMATION: Campbell Ch 8 - Meiosis Overview n Sperm cell Meiosis Fertilization Diploid zygote ANIMATION: Comparison of Mitosis and Meiosis (2 n = 46) Multicellular diploid adults (2 n = 46) Mitosis and development 2 n
Variation in Gametes Independent Assortment Crossing-over
Comparison of Mitosis and Meiosis MITOSIS MEIOSIS Starts with Diploid cell (2 n) Replicates DNA Once Cell divides Once Twice Pairing of homologues? No Yes Crossing over? No Yes Centromeres separate Daughter DNA Anaphase II Identical Different # of daughter cells 2 4 Daughter cell is Diploid cell (2 n) Haploid cell (1 n)
Reproduction SEXUAL • “Two” parents – Egg and Sperm – Can sometimes be one organism • Offspring’s DNA is NOT identical to parent’s DNA • Useful when organism needs to adapt to its environment
Somatic Cells • Body Cell • DIPLOID (2 n): 2 copies of each chromosome (why? ) • Produced by mitosis • Humans: 46 chromosomes
Gametes • Eggs and sperm • HAPLOID (1 n): 1 copy of each chromosome (why? ) • Produced by meiosis • Humans: 23 chromosomes
Fertilization • Fusion of two HAPLOID gametes to produce a DIPLOID ZYGOTE 23 23 46
Variation in Gametes • 23 chromosomes = ? possibilities • 2 possibilities per chromosome • 223 = 8388608
Variation in Gametes • 8388608 combinations of gametes produced by mother • 8388608 combinations of gametes produced by father • Any egg can be fertilized by any sperm
What makes chromosomes different from each other? • Carry different genes
Homologous Chromosomes • Each member of pair can carry different ALLELES of a gene at the same LOCUS – Allele = different versions of a gene – Locus (loci) = location on a chromosome
Example: eye and coat color in mice Coat-color genes Eye-color genes Brown Black C E C E c e Meiosis c e White Pink Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes
Example: eye and coat color in mice Brown coat (C); black eyes (E) White coat (c); pink eyes (e)
Patterns of Inheritance
Patterns of Inheritance • GENETICS is about how traits are passed down – Predicting inheritance of a trait – Determining probability of inheriting a disease – Purebred animals vs “mutts”
Genetics History • Hippocrates' theory of Pangenesis: “particles” from each part of the body travel to eggs or sperm and are passed on • Blending hypothesis (early 19 th century): traits from both parents mix in the offspring
Genetics History • Gregor Mendel (1822 – 1884) – – Monk University educated Studied variation in pea plants Work rejected by contemporaries, its importance was not realized until the 20 th century
Mendel’s Studies Flower color Purple White Flower position Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod color Green Yellow Tall Dwarf Stem length • Crossed pea plants that differed in certain characteristics • Could control matings • Developed true-breeding varieties • Traced traits from generation to generation
Mendel’s Studies Removed stamens from purple flower Pea flower White Stamens Petal Carpel Parents (P) Purple Transferred pollen from stamens o white flower to carpel of purple flower Pollinated carpel matured into pod Planted seeds from pod Stamen Carpel Offspring (F 1)
Mendel’s Experiments Terminology • Self-fertilization: fertilization of eggs by sperm-carrying pollen of the same flower • Cross-fertilization (cross): fertilization of one plant by pollen from a different plant • True-breeding: identical offspring from self-fertilizing parents • Hybrid: offspring of two different varieties • P (parental) generation: true-breeding parents • F 1 generation: hybrid offspring of true-breeding parents • F 2 generation: offspring of self-fertilizing F 1 parents
Mendel’s Observations P generation (true-breeding parents) Purple flowers White flowers F 1 generation All plants have purple flowers Fertilization among F 1 plants (F 1 F 1) F 2 When true-breeding parents are crossed, some traits cover up generation other traits in the F 1 generation 3 4 of plants have purple flowers 1 of 4 plants have white flowers Purple is DOMINANT over white White is RECESSIVE to purple
Mendel’s Observations P generation (true-breeding parents) Purple flowers White flowers F 1 generation All plants have purple flowers Fertilization among F 1 plants (F 1 F 1) F 2 generation 3 4 of plants have purple flowers 1 of 4 plants have white flowers Purple is DOMINANT over white White is RECESSIVE to purple Recessive traits reappear in the F 2 generation
Mendel’s Observations • An organism's appearance does not always reveal its genetic composition – Phenotype: Expressed (physical) traits – Genotype: Genetic makeup
Mendel’s Observations • Characteristics are NOT blended together like different colors of paint • Characteristics ARE determined by definite, discrete particles of inheritance (“factors” / genes) • There alternative forms of these “factors” that determine traits • For each characteristic, an organism inherits two “factors”, one from each parent
Mendel’s Law of Segregation • Describes inheritance of a single characteristic • Of a pair of alleles, only one is carried in a single gamete Homologous Chromosomes
Two Alleles • HETEROZYGOUS: Two different alleles • HOMOZYGOUS: Two identical alleles
Mendel’s Law of Independent Assortment • Describes inheritance of more than one characteristic • Genes for each characteristic are inherited independently 1 2 3 23 = 2 x 2 = 8
Monohybrid cross • P = purple flowers • p = white flowers Pp x Pp Genotype or phenotype? Homozygous or heterozygous? Dominant or recessive phenotype? What is the phenotype?
Monohybrid cross • P = purple flowers • p = white flowers P p Pp x Pp P p What gametes can these parental flowers make?
Monohybrid cross • P = purple flowers • p = white flowers Pp x Pp P P P p p What combinations of gametes will be in the offspring?
Punnett Square • Shows possible • Purple flower allele: P combinations of alleles • White flower allele: p • Demonstrates Mendel’s Laws P p P PP Pp pp
Punnett Square Problems 1. Heterozygous x white 2. Homozygous yellow (Y) x homozygous green (y)
Human Inheritance Dominant Traits Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe
More than one trait? Hypothesis: Independent assortment Hypothesis: Dependent assortment P generation rryy RRYY ry Gametes RY Rr. Yy F 1 generation Sperm 1 2 F 2 generation 1 2 RY 1 2 ry RY rryy Gametes RY ry Will the F 1 and F 2 generations Rr. Yy maintain the same combinations Sperm of traits as the parental plants? RY r. Y Ry ry 1 4 RY RRYY 1 4 Rr. YY 1 4 RRYy 1 4 Rr. Yy r. Y Will yellow always be round and Rr. YY rr. YY Rr. Yy rr. Yy Eggs Yellow green wrinkled? Ry round Eggs 1 2 RRYY 1 4 ry 1 4 Actual results contradict hypothesis 1 4 ry RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy Actual results support hypothesis 9 16 3 16 1 16 Green round Yellow wrinkled Green wrinkled
More than one trait? Hypothesis: Independent assortment Hypothesis: Dependent assortment P generation rryy RRYY ry Gametes RY rryy Gametes RY Rr. Yy F 1 generation Rr. Yy Sperm 1 2 F 2 generation ry 1 2 RY 1 2 1 4 ry RY Eggs 1 2 ry 1 4 RY 1 4 r. Y 1 4 Ry Eggs Actual results contradict hypothesis 1 4 ry RY 1 4 r. Y 1 4 Ry 1 4 ry RRYY Rr. YY RRYy Rr. YY rr. YY Rr. Yy rr. Yy RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy Actual results support hypothesis 9 16 3 16 1 16 Yellow round Green round Yellow wrinkled Green wrinkled
Dihybrid Cross 1. Determine the gametes that can be produced Rr. Yy RRYY RY Ry r. Y ry RY RY
Dihybrid Cross 2. Fill in the Punnett Square RY Ry r. Y ry RY RRYy Rr. YY Rr. Yy Ry RRYy RRyy Rr. Yy Rryy r. Y Rr. Yy rr. YY rr. Yy ry Rr. Yy Rryy rr. Yy rryy
Rules of Probability • Mendel’s Laws follow the rules of probability 1. Events that follow rules of probability are independent events – If you flip a coin once, the probability of getting heads is ½. – If you flip a coin a second time, the probability of getting heads is ½ regardless of what you got the first time. – If you already have two girls, the probability of a third baby being a girl is still ½.
Rules of Probability • Rule of multiplication: The probability of two events occurring together is the product of the separate probabilities of the independent events F 1 genotypes Bb male Formation of sperm Bb female Formation of eggs 1 2 B 1 2 b 1 2 B B B b B 1 4 F 2 genotypes b 1 4 B 1 4 b b b 1 4
Test Cross • Used to determine unknown genotypes Black is dominant over brown What are the possible GENOTYPES for a black lab?
Test Cross • How can we figure out if the dog is BB or Bb? Testcross: Genotypes bb B_ Two possibilities for the black dog: BB B Gametes b Offspring Bb or Bb All black b Bb bb 1 black : 1 chocolate
When it’s not so simple • GENE LINKAGE: genes on the same chromosome are likely to be inherited together Tetrad A B a b A b a B Crossing over Gametes
When it’s not so simple • GENE LINKAGE: genes on the same chromosome are likely to be inherited together UNLESS crossing over occurs between the linked genes Tetrad A B a b A b a B Crossing over Gametes
When it’s not so simple • Genes that are further apart will recombine more frequently Chromosome g c l 17% 9% 9. 5% Recombination frequencies
When it’s not so simple • INCOMPLETE DOMINANCE: heterozygotes have a unique or intermediate phenotype
When it’s not so simple • INCOMPLETE DOMINANCE: heterozygotes have a unique or intermediate phenotype Genotypes: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors Phenotypes: LDL receptor Cell Normal Mild disease Severe disease
Incomplete Dominance Problem • The color of fruit for a certain plant is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants?
When it’s not so simple • CODOMINANCE: both alleles are expressed equally in the phenotype of a heterozygote • RR = red hair • rr = white hair • Rr = red hairs and white hairs
Codominant Alleles - Bloodtype • Three alleles for blood type –A –B –O • This allele is for a protein (blood antigen) on the outer surface of red blood cells
Codominant Alleles - Bloodtype ANTIGENS ANTIBODIES • A gene A protein • B gene B protein • O gene no protein • Your body produces antibodies to any protein that you don’t have the gene for
Codominant Alleles - Bloodtype
Blood Type & Multiple Alleles
Blood Type Problem • Mary wants to know who the father of her baby is. She has blood type A and the baby has blood type AB. The potential fathers have: – Father #1 is type A – Father #2 is type B – Father #3 is type O
Pleiotropy A single gene influences multiple characteristics • Example: sickle cell disease – Allele causes production of abnormal hemoglobin in homozygotes – Many severe physical effects – Heterozygotes generally healthy
Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Clumping of cells and clogging of small blood vessels Breakdown of red blood cells Physical weakness Impaired mental function Anemia 5, 555 Sickle-cells Heart failure Paralysis Pain and fever Pneumonia and other infections Accumulation of sickled cells in spleen Brain damage Damage to other organs Rheumatism Spleen damage Kidney failure
Polygenic the additive effects of two or more genes on a single phenotypic characteristic • Example: human skin color – controlled by at least three genes
Epistasis The action of one gene is modified by the expression of another gene • Coat color in mice is controlled by B gene – B = black; b = brown • Presence or lack of pigment is controlled by C gene – C = presence; c = albino • If mouse has cc and can produce no pigment, the color of pigment doesn’t matter
Epistasis The action of one gene is modified by the expression of another gene • Albinism also found in other organisms
Epistasis The action of one gene is modified by the expression of another gene
Environmental Affects Nature vs nurture • Many characteristics are a result of genetic AND environmental factors • Only genetic characteristics are inherited
Sex Linkage • Sex Chromosomes = X and Y • What do you notice about the X and the Y chromosomes? X chromosome has many genes Y chromosome has few
Sex Linkage • Female = ? • Male = ? X X Y X
Riddle me this… • Hemophilia is a recessive sex-linked disease. Are boys or girls more likely to suffer from hemophilia? WHY?
Sex Determination in other Animals 32 16 22 + XX 22 + X 76 + ZW 76 + ZZ
Pedigrees • Used to trace inheritance Dd Joshua Lambert Dd Abigail Linnell D? Abigail Lambert D? John Eddy dd Jonathan Lambert Dd Dd dd D? Hepzibah Daggett Dd Elizabeth Eddy Dd Dd Dd dd Female Male Deaf Hearing
Hemophilia in the Royal Families of Europe
Human Inheritance
Inbreeding • Does not create mutant monster offspring • Increases the likelihood that both parents will have the same recessive genes that will be expressed in offspring
Inbreeding vs hybrid vigor Purebred animals Hip Dysplasia
Inbreeding vs hybrid vigor Hybrid animals Less likelihood of being homozygous recessive
Inbreeding among endangered animals Cheetahs • • 99% same genes poor sperm viability poor survival entire population susceptible to diseases
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