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Chapter 14.  In the 1800s the popular inheritance theory was “blending”--offspring were a mixture of their parents ◦ this suggests that organisms will.

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Presentation on theme: "Chapter 14.  In the 1800s the popular inheritance theory was “blending”--offspring were a mixture of their parents ◦ this suggests that organisms will."— Presentation transcript:

1 Chapter 14

2  In the 1800s the popular inheritance theory was “blending”--offspring were a mixture of their parents ◦ this suggests that organisms will become uniform over time (we know this isn’t true)  Mendel had a “particulate” theory (genes) ◦ this was observed through his observations of pea plants

3  He carefully planned all his breeding experiments, taking careful notes on the results.  his experiments started with true-breeding varieties ◦ then followed the offspring for 2 generations.  (P, F 1, and F 2 )

4  Through thousands of crosses, Mendel’s observations led to 2 fundamental principles of heredity. ◦ Law of Segregation  two alleles separate during gamete formation (meiosis) and end up in different gametes  dominant and recessive alleles  two heterozygous parents crossed always have a phenotypic ratio of 3:1 (Punnett Squares) ◦ Law of Independent Assortment  each pair of alleles segregates independently of each other pair of alleles during meiosis  the chance of inheriting one trait from either parent is separate from all other traits  for typical Medelian inheritance only


6  Certain patterns of inheritance are more complex than those discovered by Mendel (either controlled by one gene or 2+ genes)  When trait is controlled by a single gene... ◦ Complete Dominance--classic Mendelian patterns (strictly dominant or recessive) ◦ Incomplete dominance--neither allele is completely dominant (blending in heterozygous phenotype)  flower color ◦ Codominance--two alleles shown independently in heterozygous phenotype  animal coloration

7 Incomplete Dominance Codominance

8  multiple alleles-when a gene for a specific trait has more than two alleles. Results in multiple phenotypes. ◦ This usually works in combination with incomplete or codominance  Human ABO blood groups  Rabbit Fur Color

9  pleiotropy--when a gene has multiple phenotypic effects. ◦ Single gene affects multiple things in an organism. ◦ Most genetic diseases present this way  Cystic fibrosis and Sickle Cell anemia

10  Lethal Genes: a gene that leads to the death of the organism when inherited in homozygous genotype (either dominant or recessive) ◦ Dwarfism in humans (dominant allele) ◦ Manx cats (recessive) ◦ Yellow coat color in mice (dominant)

11  When a trait is determined by two or more genes... ◦ epistasis-the phenotype at one locus alters the gene at a second locus  Interaction of two genes to control a single phenotype, does not have an additive effect  Might mask another gene, or cause a completely new phenotype  Labrador Retrievers and coat color  2 genes: E (pigment) e (no pigment) ; B (black), b (brown)

12 ◦ polygenic inheritance--an additive effect of two or more genes on a single phenotypic character  Many genes working together to determine a particular trait  skin color, height, weight, hair color, eye color in humans

13  When inheritance depends on chromosomes... ◦ sex-linked traits--specific traits are carried on the X or Y chromosome.  results in some traits affecting boys more often than girls  X-linked traits: carried on X chromosome  females carriers; males have trait or not

14  Colorblindness, baldness, sickle-cell anemia, hemophilia, Duchenne muscular dystrophy all are examples of sex-linked traits. If a normal-sighted woman whose father was colorblind marries a colorblind man, what percentage of their sons will be colorblind? Daughters?

15  Chromosome Number ◦ During meiosis chromosomes can fail to split evenly (nondisjunction)  Aneuploidy ◦ Results in severe phenotypic changes in an individual ◦ Diagnosed via karyotype ◦ Down Syndrome (trisomy 21) ◦ Klinefelters Sydrome (XXY) ◦ Turner Syndrome (X)

16  Chromosome Structure ◦ Sometimes parts of chromosomes are altered during cell division or altered due to environment  Deletion: missing piece  Duplication: extra piece  Inversion: attach upside down in homologous pair, or within chromosme  Translocation: piece joins non-homologous chromosome  Cri du chat: deletion chromosome 5  Leukemia: translocation (chromosome 9 attaches to 22) “Philadelphia Chromosome”  Fragile X: duplication (repeat at end of X)

17 Good Morning AP Bio!  Today we are going to discuss our last type of inheritance pattern (linked genes)…then practice solving some of those problems.  Reminder: Test corrections are due tomorrow!  You will have time tomorrow to work through and finish your genetics practice problems packet (due Monday)

18  Remember: crossing over occurs during meiosis, when chromosomes trade alleles ◦ Produces “recombinant chromosomes” Some genes are located very closely on a chromosome, and are usually inherited together. They are called “linked genes”

19  linked genes: genes located near each other on the same chromosome are often inherited together ◦ genes do not assort independently, so ratio of offspring varies depending on location of genes  result in genetic recombination (offspring with traits different from parents)  This lack of independent assortment indicates the genes are on the same chromosome.

20  Thomas Morgan and his grad student first discovered linked genes in drosophila (fruit flies).  When crossing a heterozygous wild-type fly (b + b vg + vg) to a black body, vestigial wings (b vg) he discovered allele frequencies that didn’t match the prediction ◦ 83% parental types, 17% recombinant types ◦ Identified that crossing over had occurred. recombination-gene-mapping/

21  The recombination frequency (%) is the same as the map units (distance) between genes on a chromosome ◦ Less than 50% recombination = same chromosome  We can use this information to map genes  Smaller number = closer together ◦ Greater than 50% recombination = different chromosome  Not able to map

22  The crossover frequency (recombination) between genes E and F is 6%, between E and G is 10% and between F and G is 4%. Determine the sequence of genes on the chromosome.

23  Environmental Influence ◦ Nature vs. nurture ◦ Expression of traits determined by environmental influences

24  Nonnuclear Inheritance (mitochondria and chloroplasts) ◦ These organelles have their own DNA that replicates separately from nuclear DNA ◦ Follows non-mendelian inheritance ◦ All your mitochondrial DNA (mDNA) is from your mom!  “mitochondrial diseases”—result from mutations in mDNA

25  Genomic Imprinting ◦ Phenotype depends on if allele is inherited from mom or dad (autosomal)  Allele from either parent is “silenced” by the presence of other allele  Example of epigenetics ◦ Affects very few genes, not common

26  Chimera ◦ Single organism composed of genetically distinct traits  Two genomes, one organism!  Results from multiple fertilized eggs fusing during development

27  Used to visually trace traits within human families (helps identify inheritance patterns) ◦ Circle= female ◦ Square = male

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