2 Points to PonderWhat is the genotype and the phenotype of an individual?What are the genotypes for homozygous recessive and dominant individuals and a heterozygote individual?Be able to draw a punnett square for any cross (1-trait cross, 2-trait cross, and a sex-linked cross).What are Tay-Sachs disease, Huntington disease, sickle-cell disease, and PKU?How are each of the above inherited?What is polygenic inheritance?What is a multifactorial trait?What is sex-linked inheritance?Name 3 X-linked recessive disorders.What is codominance?What is incomplete dominance?What do you think about genetic profiling?
3 These traits are genetically inherited 20.1 Genotype and phenotypeThese traits are genetically inheritedAnswer these questions about your inheritance:Do you have a widow’s peak?Are your earlobes attached or unattached?Do you have short or long fingers?Do you have freckles?Can you roll your tongue?Do you have Hitchhiker’s thumb?
4 20.1 Genotype and phenotype Genotype – specific genes for a particular trait written with symbolsAlleles: alternate forms of a specific gene at the same position (locus) on a gene (e.g., allele for unattached earlobes and attached lobes); alleles occur in pairsDominant gene: will be expressed and will mask a recessive gene (Tt or TT)Recessive allele: allele that is only expressed when a gene has two of this type of alleleHomozygous dominant genotype: 2 dominant alleles (TT or AA)Homozygous recessive genotype: 2 recessive alleles (tt or aa)Heterozygous genotype: one dominant allele and one recessive allele (Tt or Aa)
5 20.1 Genotype and phenotype Phenotype – the physical or outward expression of the genotypeGenotype PhenotypeEE unattached earlobeEe unattached earlobeee attached earlobeWhat are your genotype and phenotype?
10 Practicing punnett squares 20.2 One-and Two-trait inheritancePracticing punnett squareseggsWhat would a punnett square involving a man (M) with a genotype Ff and a woman (F) with a genotype Ff look like?F – frecklesf – no frecklesM/FFfFFFfffsperm
11 Practicing ratios F f FF Ff ff M/F 20.2 One-and Two-trait inheritancePracticing ratiosGenotypic ratio: the number of offspring with the same genotypePhenotypic ratio: the number of offspring with the same outward appearanceWhat is the genotypic ratio?1: 2: 1 (1 FF: 2 Ff: 1 ff)What is the phenotypic ratio?3: 1 (3 with freckles and 1 with no freckles)eggsM/FFfFFFfffsperm
18 Genetic disorders of interest 20.3 Inheritance of genetic disordersGenetic disorders of interestTay-Sachs disease: lack of the enzyme that breaks down lipids in lysosomes resulting in excess and eventually death of a babyCystic fibrosis: Cl- do not pass normally through a cell membrane resulting in thick mucus in lungs and other places often causing infectionsPhenylketonuria (PKU): lack of an enzyme needed to make a certain amino acid and affects nervous system developmentSickle-Cell disease: red-blood cells are sickle shaped rather than biconcave that clog blood vesselsHuntington disease: huntington protein has too many glutamine amino acids leading to the progressive degeneration of brain cells
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21 Polygenic inheritance 20.4 Beyond simple inheritance patternsPolygenic inheritancePolygenic traits - two or more sets of alleles govern one traitEach dominant allele codes for a product so these effects are additiveResults in a continuous variation of phenotypesEnvironmental effects cause intervening phenotypese.g., skin color ranges from very dark to very lighte.g., height varies amongMultifactorial trait – a polygenic trait that is particularly influenced by the environmente.g., skin color is influenced by sun exposuree.g., height can be affected by nutrition
23 Demonstrating environmental influences on phenotype 20.4 Beyond simple inheritance patternsDemonstrating environmental influences on phenotypeHimalayan rabbit’s coat color influenced by temperatureThere is an allele responsible for melanin production that appears to be active only at lower temperaturesThe extremities have a lower temperature and thus the ears, nose, paws, and tail are dark in color
24 20.4 Beyond simple inheritance patterns Incomplete dominanceOccurs when the heterozygote is intermediate between the 2 homozygotesExample:(curly hair) CC x SS (straight hair)CS (wavy hair)
25 20.4 Beyond simple inheritance patterns CodominanceOccurs when the alleles are equally expressed in a heterozygoteExample:(Type A blood) AA x BB (Type B blood)AB (Type AB blood that has characteristicsof both blood types)
26 Multiple allele inheritance 20.4 Beyond simple inheritance patternsMultiple allele inheritanceThe gene exists in several allelic formsA person only has 2 of the possible allelesA good example is the ABO blood systemA and B are codominant allelesThe O alleles is recessive to both A and B therefore to have this blood type you must have 2 recessive alleles
27 Multiple allele inheritance 20.4 Beyond simple inheritance patternsMultiple allele inheritanceBased on what you know what type of blood would each of the following individuals have in a cross between Ao and Bo?possible genotypes: phenotypes:AB Type AB bloodBo Type B bloodAo Type A bloodoo Type O blood
29 Sex-linked inheritance Traits are controlled by genes on the sex chromosomesX-linked inheritance: the allele is carried on the X chromosomeY-linked inheritance: the allele is carried on the Y chromosomeMost sex-linked traits are X-linked
31 20.5 Sex-linked inheritance X-linked disordersMore often found in males than females because recessive alleles are always expressedMost X-linked disorders are recessive:Color blindness: most often characterized by red-green color blindnessMuscular dystrophy: characterized by wasting of muscles and death by age 20Fragile X syndrome: most common cause of inherited mental impairmentHemophilia: characterized by the absence of particular clotting factors that causes blood to clot very slowly or not at all