Presentation on theme: "Mendelian Genetics CH 6 Section 6.3 – 6.5. Slide 2 of 26."— Presentation transcript:
Mendelian Genetics CH 6 Section 6.3 – 6.5
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Slide 3 of 26 ?? Sometimes, certain traits seem to disappear for a generation but then return in the next generation. How does this happen? Is this a “law” or “theory”? Law since we are describing something, not trying to explain it.
Slide 4 of 26 Vocabulary Character – heritable feature Hair Color Height of plant Eye color Pea color Pea shape Trait – variant of a character (heritable feature) Brown hair color Tall plant height Blue eye color Yellow pea color
Slide 5 of 26 More Vocab Dominant trait One that will mask the recessive trait if found together Recessive trait Trait that will be masked if found with the dominant trait
Slide 6 of 26 Breeding True Breed (purebred)– Whatever traits the parent has are expressed in ALL subsequent populations For example, self-pollinating a purple flowered plant produces a generation of only purple flowered plants. Typically, need to do this for at least two (2) generations to ensure that the parent is a true-breed (purebred) Hybrid – Mating (crossing) of two (2) true-breeding varieties of true-breeds
Slide 7 of 26 Vocabulary (Page 2) P Generation – Parent generation Two (2) true-breeding parents being crossed F1 – First filial (child or son) generation Hybrids F2 – Second filial generation Each member of F1 self-pollinates Hybrids again 3:1 Dominant to Recessive ratio
Slide 8 of 26 What Mendel found (stretched the truth about) Only looked at “all-or-nothing” traits Sometimes called binary traits – “yes” vs. “no” Mendel took purebreds for 1 trait, and pollinated it with a purebred for another trait What is the difference between trait & character? Purple flowered + White flowered F1 = All colored purple (all expressed only one trait) F2 = 3:1 ratio of Dominant to Recessive trait
Slide 9 of 26 ___ Generation What type of plants? ____________ ___ Generation What type of plants? ____________ ___ Generation What type of plants? ____________
Slide 10 of 26 Genes Gene Portion of DNA that provides the instructions for making a particular protein Each gene has a particular location on a chromosome called its locus Like a house’s address Allele One of the different forms of the gene Mendel looked at genes that had ONLY 2 alleles
Slide 11 of 26 Mendel’s Model 1. Alternate versions of genes account for variations in inherited characteristics The alternative versions are called alleles One plant had the allele for purple flower color while the other had the allele for white flower color 2. For each character, an organism inherits two (2) alleles, one from each parent The two alleles may be the same or different If the 2 alleles are the same = Homozygous Different = Heterozygous
Slide 12 of 26 Allele Dominance Just as there are dominant and recessive traits, there are dominant and recessive alleles Dominant allele If present, always expressed Represented by a capitalized letter: A Recessive allele Only expressed when BOTH alleles are recessive is represented by a lowercase letter: a
Slide 13 of 26 Mendel’s Model (Page 2) 3. If the alleles differ (heterozygous), then the dominant allele determines the organism’s appearance Heterozygous individuals display dominant trait Homozygous Dominant display _________ trait Homozygous Recessive display _________ trait
Slide 14 of 26 Mondel’s Model (Page 3) 4. Law of Segregation 2 alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes We already know that homologous chromosomes assort independently during meiosis into gametes But Mendel did not know about chromosomes
Slide 15 of 26 Questions What is the difference between a gene and a character? What is the difference between a gene and an allele? What is the difference between a character and a trait?
Slide 16 of 26 Important Vocab. Phenotype - appearance Characters Traits are different types of the character IF character is eye color, trait is brown, blue, etc Genotype - genetic makeup Genes Alleles are different types of genes Gene for eye color, alleles = brown (dominant), blue (recessive), etc.
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Slide 18 of 26 Punnett Squares One parent at top, other on the left Here we are crossing homozygous dominant (HD) in the form of [AA] with Heterozygote (Ht) as [Aa] AA AAA aAa
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Slide 20 of 26 Cross all 6 combinations CrossGenotypic Ratio Phenotypic Ratio HomoD x HomoD HomoR x HomoR Heter x Heter HomoD x HomoR HomoD x Heter HomoR x Heter
Slide 21 of 26 Monohybrid vs. Dihybrid Monohybrid Cross – Take pure breeds for 1 character and cross (AA x aa) You should already understand these. Dihybrid Cross – Take pure breeds for 2 characters and cross (AABB x aabb) 2 Characters like seed color + seed shape
Slide 22 of 26 Law of Independent Assortment States that each pair of alleles segregates independently of other pairs of alleles during gamete formation This rule really only pertains to genes (allele pairs) on different chromosomes If on the same chromosome = linked genes
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Slide 24 of 26 Repeat but use Probability Compute P(green & wrinkled) from the table Now do so from Punnett Squares for each character Compute P(Yellow & Round) from table Now do so from Punnett Squares for each character
Slide 25 of 26 Problems In a dihybrid cross, what is the possibility of heterozygous in one trait and homozygous recessive in the other, given both heterozygous parents? In a trihybrid cross, what is the probability of getting exactly 2 recessive phenotypes, if one parent is heterozygous for all 3 genes and the other is homozygous recessive for 2 genes, and hetero for the 3rd?
Slide 26 of 26 Mendel’s Big Ideas The Law of Segregation The 2 alleles of a gene separate (segregate) during gamete formation, so that a sperm or egg only carries 1 allele of each pair Explains 3:1 ratio found in hybrid crosses The Law of Independent Assortment Each pair of alleles separates independently (of other allele pairs) into gametes Genes assort independently of one another