Two or More Traits: Dihybrid Crosses Mendelian Genetics Two or More Traits: Dihybrid Crosses Copyright Pearson Prentice Hall
Summary of Mendel’s laws Mendelian Genetics 11/9/2018 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale
copyright cmassengale Mendelian Genetics 11/9/2018 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2n (n = # of heterozygotes) copyright cmassengale
All possible gamete combinations Mendelian Genetics 11/9/2018 Dihybrid Cross Traits: Seed shape & Seed color Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations copyright cmassengale
copyright cmassengale Mendelian Genetics 11/9/2018 Dihybrid Cross RY Ry rY ry RY Ry rY ry copyright cmassengale
copyright cmassengale Mendelian Genetics 11/9/2018 Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy copyright cmassengale
copyright cmassengale Mendelian Genetics 11/9/2018 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale
Non-Mendelian Genetics
OBJECTIVE SWL the genetic patterns of inheritance and how they can be displayed. They will also learn what disorders are dominant and recessive.
Chromosomal theory of heredity – genes are located on chromosomes Practical application – Mendel’s laws only sort of apply some of the time.
Gene Linkage Not all genes will go through independent assortment. Genes on the same chromosome are called linked genes
TH Morgan worked with fruit flies in early 1900’s Instead of 1:1:1:1 like he expected in one of his many crosses, most flies were grey with large wings OR black with small wings. Morgan concluded that wing size and body color were linked. Linkage groups – groups of genes that are always inherited together
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Crossing-Over HOWEVER – some genes aren’t always inherited together in fruit flies Morgan proposed “crossing-over” to explain why this happened
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Copyright Pearson Prentice Hall Using the frequency of crossing over allows you to construct a “linkage map” showing how far apart genes are More frequent crossing-over – genes are farther apart (dice and letters activity) Copyright Pearson Prentice Hall
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Other Non-Mendelian genetics
OBJECTIVE SWL the difference between various complex disorders and how they can be analyzed and adapted for.
Sex linkage In 1905, Nettie Stevens found that not all chromosomes have a corresponding homologous chromosome. Sex chromosomes – look like a mismatch Autosomes – same in both female and males
Sex determination XX is female (in humans) XY is a mismatch to be male (in humans)
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Sex-linked genes Exist on one of the sex chromosomes, either X or Y (usually X) i.e. eye color in fruit flies, color-blindness and hemophilia in humans Because males only have one x, they always display the trait
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Gene Interactions Genes produce proteins – dominant genes produced much more protein than recessive ones. This is NOT always the case.
Copyright Pearson Prentice Hall 1. Incomplete Dominance In incomplete dominance, the heterozygous genotype results in a phenotype between the two homozygous phenotypes. i.e. white paint + red paint = pink Copyright Pearson Prentice Hall 26
Copyright Pearson Prentice Hall A cross between red and white snapdragons produces pink-colored flowers. Some alleles are neither dominant nor recessive. In four o’clock plants, for example, the alleles for red and white flowers show incomplete dominance. Heterozygous (RW) plants have pink flowers—a mix of red and white coloring. Copyright Pearson Prentice Hall 27
Copyright Pearson Prentice Hall 2. Codominance In codominance, both alleles contribute to the phenotype. In cattle, red hair is codominant with white hair. Cattle who are roan have both the red and white allele – they do not blend, they appear separately. VERY SIMILAR to incomplete dominance!! Generally goes along with multiple allelic traits Copyright Pearson Prentice Hall 28
Copyright Pearson Prentice Hall 3. Multiple Allelic Traits Genes that are controlled by more than two alleles are said to have multiple alleles. An individual can’t have more than two alleles. However, more than two possible alleles can exist in a population. i.e. Blood types in humans and rabbits’ coat color Copyright Pearson Prentice Hall 29
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Copyright Pearson Prentice Hall Different combinations of alleles result in the colors shown here. KEY C = full color; dominant to all other alleles cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Coat color in rabbits is determined by a single gene that has at least four different alleles. Different combinations of alleles result in the four colors you see here. photo credits: 1. ©John Gerlach/Visuals Unlimited 2.Animals Animals/©Richard Kolar 3. ©Jane Burton/Bruce Coleman, Inc. 4. ©Hans Reinhard/Bruce Coleman, Inc. AIbino: cc Himalayan: chc, or chch Full color: CC, Ccch, Cch, or Cc Chinchilla: cchch, cchcch, or cchc Copyright Pearson Prentice Hall 31
Copyright Pearson Prentice Hall 4. Polygenic Traits Traits controlled by two or more genes are said to be polygenic traits. Skin color, diabetes, height, cleft palate, cancer, etc in humans are polygenic traits controlled by at least ____ different genes. ???? Copyright Pearson Prentice Hall 32
20/64 15/64 6/64 1/64 AaBbCc AaBbCc aabbcc Aabbcc AaBbcc AaBbCc AABbCc Fraction of progeny 6/64 1/64
Answer these in your notes! Page 303 data analysis graph questions 1-2. Define and put vocabulary words (pg. 302) in your notebooks.
Mutations – when something goes wrong Some good, some bad Copyright Pearson Prentice Hall
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Copyright Pearson Prentice Hall Kinds of Mutations Kinds of Mutations Mutations are changes in the genetic material. Mutations that produce changes in a single gene are known as gene mutations (We’ll get to these in a few weeks. They have the same names, but occur WITHIN a gene not a whole chromosome.) Mutations that produce changes in whole chromosomes are known as chromosomal mutations. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Kinds of Mutations Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes. Chromosomal mutations include deletions, duplications, inversions, and translocations. Copyright Pearson Prentice Hall
Cri du chat – chromosome 5 Kinds of Mutations Deletions involve the loss of all or part of a chromosome. Chromosomal mutations involve changes in whole chromosomes. Cri du chat – chromosome 5 Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Kinds of Mutations Duplications produce extra copies of parts of a chromosome. Chromosomal mutations involve changes in whole chromosomes. Angelman syndrome – Chromosome 15 Fragile X – X chromosome Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Kinds of Mutations Inversions reverse the direction of parts of chromosomes. Chromosomal mutations involve changes in whole chromosomes. 5% of Downs syndrome cases Copyright Pearson Prentice Hall
Translocations occurs when part of one chromosome breaks off and attaches to another. Happens frequently and with fewer lethal consequences in plants and bacteria Chromosomal mutations involve changes in whole chromosomes. Most commonly (1:1000) between chromosome 13 and 14 Copyright Pearson Prentice Hall
Significance of Mutations Many mutations have little or no effect on gene expression. Some mutations are the cause of genetic disorders. Copyright Pearson Prentice Hall
Nondisjunction – homologous chromosomes did NOT separate during meiosis, results in several human disorders i.e. Turner syndrome, trisomy 21, Klinefelter’s syndrome Polyploidy - an organism has extra sets of chromosomes. (Most plants are at least tetraploid) i.e. triploid has three sets, tetraploid has four Aneuploidy is a condition when there is one too few or too many chromosomes. i.e. Trisomy 21 (Downs syndrome) is 3 of chromosome 21; poly-X females have 3+ X chromosomes
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