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1 Review What did Mendel conclude determines inheritance Explain What are dominant and recessive alleles Apply Concepts Why were true breeding pea plants important for Mendel’s experiments 2 Review What is segregation Explain What happens to alleles between the P generation and the F2 generation
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Ch 11 Introduction to Genetics
11.1 The Work of Gregor Mendel
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Heredity Genetics Delivery of characteristics from parent to offspring
Scientific study of heredity.
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The Experiments of Gregor Mendel
Founded modern science of genetics Austrian monk Charge of the monastery garden.
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The Experiments of Gregor Mendel
Worked with pea plants Multiple generations each growing season Many traits Traits in one of two forms Easy to grow Lots of offspring.
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The Role of Fertilization
Stamen Male part of each flower makes pollen (contains sperm) Carpel Female portion of each flower produces reproductive cells called eggs.
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Fertilization Male and female reproductive cells join
For peas tiny embryo encased within a seed Peas normally are self pollinating Sperm and egg are from same parent.
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True-breeding or Pure Breeding
Trait Specific characteristic of an individual, such as seed color or plant height May vary from one individual to another True-breeding or Pure Breeding Produce offspring with identical traits to themselves.
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He cut away the pollen-bearing male parts and then dusted on the pollen from a different flower.
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Hybrid Offspring of crosses between parents with different traits.
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Generations P1- original parents F1- first offspring, F is for filial
F2- second generation of offspring; F1’s kids.
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Mendel’s Two Conclusions
Individual’s characteristics are determined by factors that are passed from one parental generation to the next These factors come in two varieties Principle of dominance Some alleles are dominant and will cover up the recessive version of the allele.
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Genes Alleles Factors that are passed from parent to offspring
Different forms of the gene.
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Dominant Version of trait that shows up in each generation of Mendel’s experiments Can hide the other form of that trait Capital letter Recessive Version that was covered up in the F1 generation Lower case letter.
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Tall plant is dominant over short.
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Where Did the Recessive Gene Go
Mendel allowed all seven kinds of F1 hybrids to self-pollinate He found recessive trait in about ¼ of the F2 generation.
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Segregation Gamete Alleles split and each gamete only carries one
Sex cells (egg or sperm).
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Dominant allele had masked the corresponding recessive allele in the F1 generation.
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F1 plants were tall with a tall allele from one parent and a short allele from the other parent.
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F1 adults produces gametes, the alleles for each gene segregate from one another.
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Whenever two t’s combine, a short plant results
Whenever there is even one T, a tall plant results.
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Ch 11 Introduction to Genetics
11.2 Applying Mendel’s Principles
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Probability Math prediction as to chances of something happening
Chance of passing on a particular gene Coin has two sides, a head and a tail, if you flip it, the chance of getting a head is ½.
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If you flip a coin three times in a row, what is the probability that it will land heads up every time Each flip is and independent event with a chance of ½ 1/2 × 1/2 × 1/2 = 1/8.
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F1 plant had one tall allele and one short allele (Tt)
1/2 of the gametes would carry the short allele (t).
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The only way to produce a short (tt) plant is for two gametes carrying the t allele.
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½ x ½ = ¼. Chance of getting t allele is ½
Probability of being short (tt) is ½ x ½ = ¼.
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For each of Mendel’s seven crosses, about ¾ of the plants showed the trait controlled by the dominant allele ¼ showed the recessive trait.
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Probabilities predict the average outcome
The larger the sample the closer to the predicted.
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Homozygous Heterozygous Two of the same alleles TT or tt
One of each version of the alleles, Hybrid Tt.
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Genotype Phenotype What the actual genes are, you can’t physically see
TT, Tt, or tt Phenotype What the trait looks like, what you can physically see Tall or short.
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Punnett Squares Genetic cross to predict the genotype and phenotype using mathematical probability Monohybrid One trait cross Dihybrid Two trait cross.
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How To Make a Punnett Square
Start with the Parents Figure out the Gametes Line them up Fill in the Punnett Square Figure out the Results.
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Start with the Parents Bb and Bb.
Write the genotypes of the two parents Bb and Bb.
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Figure out the Gametes Determine what alleles would be found in all of the possible gametes that each parent could produce.
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Line them up Draw a table with enough spaces for each pair of gametes from each parent Enter the genotypes of the gametes produced by both parents on the top and left sides of the table.
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Fill in the Punnett Square
Fill in the table by combining the gametes’ genotypes.
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Figure out the Results Determine the genotypes and phenotypes of each offspring Calculate the percentage for each.
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Homozygous round x Homozygous wrinkled
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Homozygous round x Homozygous wrinkled
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Homozygous round x Homozygous wrinkled
Rr
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Homozygous round x Homozygous wrinkled
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Independent Assortment
Genes for different traits can segregate independently during gamete formation A past coin flip won’t influence a future coin flip.
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Mendel crossed true-breeding round yellow peas with wrinkled green peas.
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Round yellow peas had the genotype RRYY, which is homozygous dominant.
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Wrinkled green peas had the genotype rryy, which is homozygous recessive.
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All of the F1 offspring produced round yellow peas
F1 offspring was RrYy, heterozygous for both seed shape and seed color.
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Mendel then crossed the F1 plants to produce F2 offspring.
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Alleles for seed shape segregated independently of those for seed color
Mendel’s experimental results were very close to the 9:3:3:1 ratio that the Punnett square shown predicts.
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Start with Parents
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Figure out the Gametes
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Line them Up
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Fill in the Punnett Square
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Figure out the Results
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Thomas Hunt Morgan Repeated Mendel’s work using fruit flies.
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Ch 11 Introduction to Genetics
11.3 Other Patterns of Inheritance
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In most organisms, genetics is more complicated, because the majority of genes have more than two alleles Many important traits are controlled by more than one gene.
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Incomplete Dominance Heterozygous phenotype is a blending or mixing of the homozygous phenotypes.
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Codominance Both alleles are visible Speckled fur/feathers.
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Multiple Alleles Gene with more than two alleles.
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Polygenic Traits Traits controlled by two or more genes
Wide range of phenotypes Skin color.
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Genes and the Environment
Genes provide a plan for development Environment plays a role in how the plan unfolds.
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Western White Butterfly
Spring hatches have more wing pigments than summer hatches To fly the body temperature needs to be 28–40°C.
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Ch 11 Introduction to Genetics
11.4 Meiosis
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Diploid Cells Two sets of homologous chromosomes Somatic cells
One chromosome 2 from mom and one chromosome 2 from dad Somatic cells All cells other than sex cells “2n”.
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Haploid Cells Only one set of chromosomes Gametes “n”.
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Meiosis Similar in process to Mitosis Forms gametes Goes from 2n to n
Fertilization goes from n to 2n Meiosis I Meiosis II Create FOUR haploid cells from ONE diploid cell.
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Meiosis Phases Interphase Prophase 1 Metaphase 1 Anaphase 1
Telophase 1 Cytokinesis Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis.
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Chromosomes Each chromosome consists of two copies ensuring that each new cell will have the same genetic information The identical strands of DNA are each called chromatids and are held together by a centromere.
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Interphase 1 Chromosome replicate.
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Prophase 1 DNA coils up into Chromosomes Nuclear membrane breaks down
Chromosomes pair up into Tetrads Tetrad Homologous pair.
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Prophase 1 Crossing over may occur
Chromatids of the homologous chromosomes cross over one another Crossed sections of the chromatids are exchanged.
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Metaphase 1 Homologous Pairs Line up down center of cell.
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Anaphase 1 Chromosome Pairs separate Pulled to opposite poles of cell.
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Telophase 1 and Cytokinesis
Nuclear membrane forms around each cluster of chromosomes Cytokinesis occurs forming two cells.
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Now have two daughter cells that are genetically different
Now are Haploid.
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Prophase 2 Chromosomes become visible Nuclear membrane breaks down
No additional crossing over.
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Metaphse 2 Chromosomes line up in the center of each cell.
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Anaphase 2 The paired chromatids separate.
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Telophase 2 and Cytokinesis
Chromosomes arrive at poles Nuclear envelope reforms Cytokinesis occurs forming four cells.
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Sperm Ova or Ovum (egg) Fertilization Zygote Male Gamete Female Gamete
When the two gametes combine Zygote Fertilized egg.
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Mitosis vs. Meiosis Creates 4 daughter cells Creates 2 daughter cells
Genetically different from parent cell Haploid (n) 2 divisions Produces gametes Crossing over Genetic Variations. Creates 2 daughter cells Cell is identical to parent Diploid (2n) 1 division Produces ‘body cells’ (somatic cells)
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You are “One in a Million”
Over 8 million possible gamete combinations from dad Over 8 million possible gamete combinations from mom.
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You are actually “One in 64 TRILLION”
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Gene Linkage The closer two genes are located on a chromosome the more likely those alleles will occur together Less of a chance for crossing over to occur in between Used to map out location of genes.
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Gene Map
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Haploid and diploid numbers are designated N and 2N
Haploid and diploid numbers are designated N and 2N. The table shows haploid or diploid numbers of a variety of organisms. Copy the table and complete it and then use it to answer the questions on the next slide.
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Calculate What are the haploid numbers for the fern and onion plants
Interpret Data In the table, which organisms diploid number is closest to a human Apply Concepts Why is a diploid number always even Evaluate Which organism’s haploid and diploid numbers do you find most surprising- why
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