Reproduction and Genetic Variability PDF

Reproduction and Genetic Variability Learning Objectives Identify two ways that organisms reproduce and how this impact the genetics of their offspring Explain how and when genetic diversity is introduced during meiosis. Explain the contribution of mutation, crossing over, and independent assortment...

Reproduction and Genetic Variability Learning Objectives Identify two ways that organisms reproduce and how this impact the genetics of their offspring Explain how and when genetic diversity is introduced during meiosis. Explain the contribution of mutation, crossing over, and independent assortment to the generation of genetic variability. Explain the difference between a somatic mutation and a germ line mutation and the potential effect each might have on subsequent generations. Explain how different alleles of the same gene originally came to be and how this relates to genetic variation. Explain the concept of genetic variation and describe how it can impact DNA sequences and traits Identify and describe five different inheritance patterns for heritable traits and identify them in examples Describe the types of traits that can be genetically encoded Explain what is meant by allele frequency in a population. Explain the concept of Hardy Weinberg Equilibrium Identify and describe the conditions that must be met under Hardy Weinberg Equilibrium Explain what allele frequencies, genotypic frequencies, and phenotypic frequencies are and how they are represented using the variables ‘p’ and ‘q’ Calculate allele frequencies based on the genetic makeup of a population and on given values for ‘p’ or ‘q’ Write and explain the terms of the Hardy Weinberg Equation Announcements Tuesday 2/13 Homework 7 Thursday 2/15 Homework 8 Monday 2/19 Canvas Quiz 4 Organisms can Reproduction Asexually or Sexually Asexual Reproduction Accomplished through Cell Division Offspring are genetic clones of parents Sexual Reproduction Accomplished with Gametes Offspring are genetically unique Sexually reproducing organisms cycle between haploid and diploid states The somatic cells of organisms are diploid, and the germ cells used for reproduction are haploid cells called gametes 5 Meiosis gives rise to gametes Meiosis: A series of two cell divisions that create haploid gamete cells with a unique complement of genes The gametes produced by meiosis are genetically unique relative to each other and to the parents that produce them. Offspring produced by sexual reproduction are genetically unique 6 The gametes produced by Meiosis are Genetically Unique Driven by Three Main Processes During Meiosis: Random Assortment of Homologous Chromosomes Crossing Over/Recombination Random Mutations 7 Random Assortment of Homologous Chromosomes Maternal and paternal chromosomes are divided up at random between daughter cells during meiosis Each gamete produced contains a unique and random combination of chromosomes from each grandparent 8 Meiosis rearranges DNA between homologous chromosomes Homologous chromosomes swap DNA in a process called “Crossing over” or “Recombination 9 Meiosis rearranges DNA between homologous chromosomes Parental Germline Cell Recombination creates new combinations of alleles on a chromosome After recombination, the chromosomes in gametes contain different sets of alleles than: The chromosomes in the parent The chromosomes in other gametes A B C D A B C D a b c d a b c d Gametes A B c D a B C d A b c D a b C d 10 https://www.youtube.com/watch?v=GoJCer_acIQ Genetic Errors during Meiosis Impact Offspring Mistakes during meiosis can create new mutations These are called germline mutations Germline mutations can be as small as a single base or impact entire chromosomes 12 Germline Mutations Create Genetic Variation in Populations Only mutations present in the germline can be passed to offspring New mutations in somatic cells die with the individual who possess them 13 Mutations and Black Golden Retrievers? https://www.youtube.com/watch?v=chRSMA1IgjE Look for examples of traits that might come from: Somatic mutations Germline mutations 14 Mutations and Black Golden Retrievers? Which of the following likely result from somatic mutations? A. B. C. D. E. True all-black golden retrievers Having two different colored eyes Black fur in Lab/Retriever mixes Black spots on golden retrievers The flat coated retriever breed 15 Mutations and Black Golden Retrievers? Which of the following likely result from germline mutations? A. B. C. D. E. True all-black golden retrievers Having two different colored eyes Black fur in Lab/Retriever mixes Black spots on golden retrievers The flat coated retriever breed 16 Mutations and Black Golden Retrievers? Would a golden retriever with a black spot on its ear be likely to have black-coated offspring? A. Yes B. No 17 Genetic Variation: How similar are individuals of the same species? 6 billion base pairs in a diploid human genome. ~20,000 genes, with only 2% encoding Humans are 99.6 - 99.9% similar to one another at the genetic level. 18 What does genetic variability look like at the level of DNA sequences? Many small differences: Single nucleotide polymorphisms (SNPs) Small INDELs 19 What does genetic variability look like at the level of DNA sequences? Some large differences: Chromosomal rearrangements Aneuploidy: monosomy and trisomy Genetic Variation may or may not impact genes Only ~1% of the human genome codes for proteins. Many SNPs are found in DNA sequences that don’t code for anything, and this variation has no impact on traits. Some genetic variation is found in genes or the sequences that regulate them. This variation impacts traits. 21 Genetic Variation can have various impacts on organisms Neutral Alleles: have no effect on organism’s ability to survive and reproduce Negative Alleles: decrease an organism’s ability to survive and reproduce Positive Alleles: increase an organism’s ability to survive and reproduce 22 Genes and Traits: Mendelian Traits Mendelian Traits 1 gene -> 1 trait Dominant Allele Recessive Allele Homozygous Heterozygous 23 Genes and Traits: Partial Dominance Partial Dominance: the “dominant” allele does not fully control the trait when combined with a second allele Incomplete Dominance 1 gene -> 1 trait Traits blend in heterozygotes Codominance 1 gene -> 1 trait Both Traits Expressed in heterozygotes 24 Genes and Traits: Non-Mendelian Traits Polygenic Traits Multiple Genes -> 1 trait Pleotropic Genes One Gene -> Many traits 25 Phenotypic Variation in Populations Widely observable and often genetically encoded (at least in part). Anatomical Traits Physiological Traits Behavioral Traits Perceptual Traits Most traits are polygenic and impacted by environmental factors. 26 Phenotypic Variation in Populations Most traits have no impact on survival and reproduction (neutral traits) Some traits can be beneficial (positive traits) and others can be detrimental (negative traits) Whether traits are neutral, positive, or negative depends on the environment that an organism lives in. ACE and ACE2 Receptor Proteins https://www.youtube.com/watch?v=xIlaQuRaZmk Angiotensin Converting Enzymes Cleave Angiotensin proteins to modify their functions Regulate blood pressure, inflammation, cell division Clicker Question Given that both the ACE and ACE2 genes impact blood pressure, you could say this trait is: A. Codominant B. Mendelian C. Polygenic D. Incomplete dominance E. Pleiotropic Clicker Question How many alleles for the ACE2 gene would you guess are found in human populations? A. Two B. Five C. Dozens D. Hundreds E. Thousands ACE2 Receptor Alleles and COVID-19 Susceptibility There are thousands of alleles for ACE2 in the human population. The ACE2 Protein is the main receptor for SARS-CoV-2 https://www.youtube.com/watch?v=Xuc9D4LVJdg Some ACE2 Receptor Alleles may impact COVID-19 Susceptibility https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7314689/ Clicker Question Given that ACE2 impact several traits, you could say this gene is: A. Codominant B. Mendelian C. Polygenic D. Incomplete dominance E. Pleiotropic Measuring Genetic Variability Allele Frequency: the incidence of an allele in a population Genotypic Frequency: the incidence of a genotype in a population Phenotypic Frequency: the incidence of a phenotype in a population 34 Genetic Variability in a Controlled System Hardy-Weinberg Equilibrium: Conditions in which allele frequency remains constant in a population Individuals don’t leave or join the population Alleles are passed down to progeny at random (No Selection or Drift) No new mutations occur 35 Real Populations often deviate from Hardy-Weinberg Conditions 36 Allele Frequency in Hardy Weinberg Equilibrium Assumes only two alleles for a trait, one dominant and the other recessive (classic Mendelian trait) Allele frequencies are represented by “p” and “q” - p is the frequency of the dominant allele - q is the frequency of the recessive allele 37 Allele Frequency in Hardy Weinberg Equilibrium p is the frequency of the dominant allele q is the frequency of the recessive allele If the genotypes for all individuals is know, determining allele frequency is straight forward. bb Bb BB BB Bb 38 Allele Frequency in Hardy Weinberg Equilibrium bb How many total copies of this gene are there in this population? Bb BB BB Bb A. B. C. D. E. 1 2 5 6 10 How many copies are the dominant ‘B’ allele? How many copies are the recessive ‘b’ allele? 39 Allele Frequency in Hardy Weinberg Equilibrium bb Bb BB BB Bb What is the value for ‘p’ for this population A. 0.2 B. 0.6 C. 1 D. 6 E. 10 40 Allele Frequency in Hardy Weinberg Equilibrium bb Bb BB BB Bb What is the value for ‘q’ for this population A. 0.2 B. 0.4 C. 0.6 D. 0.8 E. 1 41 Allele Frequency in Hardy Weinberg Equilibrium p is the frequency of the dominant allele q is the frequency of the recessive allele p + q = 1 for a population in Hardy Weinberg Equilibrium bb Bb BB BB Bb 42 Genotypic Frequency in Hardy Weinberg Equilibrium The probability of having a specific genotype depends on each allele’s frequency in the population. Probability of being homozygous dominant = p*p Probability of being heterozygous = p*q and q*p Probability of being homozygous recessive = q*q Probability of having one of these genotypes = 1 p2 + 2pq + q2 = 1 This is the Hardy-Weinberg Equation 43 Genotypic Frequency in Hardy Weinberg Equilibrium Probability of being homozygous dominant = p*p Probability of being heterozygous = p*q and q*p Probability of being homozygous recessive = q*q Probability of having one of these genotypes = 1 bb Bb p2 + 2pq + q2 = 1 BB BB Bb 44 Phenotypic Frequency in Hardy Weinberg Equilibrium p2 + 2pq + q2 = 1 Probability of having the dominant phenotype = p2 + 2pq Probability of having the recessive phenotype = q2 bb Bb BB BB Bb 45