Genetics II Pedigrees and patterns of inheritance Mr. HunterKennedy High School Biology 03/15/2011
Mr. Hunter Biology 03/06/2013• Objective(s)• SWBAT• Explain the concept of linked genes.• Define chromosome map.• Explain the purpose and analysis of a pedigree.• Distinguish between autosomal and sex-linked traits.• Bell Ringer – What is the difference between a genotype and a phenotype?
• In the early 1900s, Thomas HuntFruit Flies and Morgan experimented with theChromosomes small fruit fly Drosophila melanogaster. • They live for approximately 7-10 days and their entire genome has been recently sequenced. • Based on his experiments with fruit flies, Morgan determined that if genes are inherited together they must be on the same chromosome. They are linked genes. • Question: What are linked genes?
• The farther apart genes are locatedFruit Flies and on a chromosome, the more likelyChromosomes that crossing-over will occur. • A chromosome map is a diagram that shows the linear order of genes on a chromosome. • The percentage of crossing-over for two traits is proportional to the distance between them on a chromosome. chromosome • Question: What determines if crossing over of genes will occur? • Question : What is the percentage of crossing over for two traits equal to?
• Pedigree: A family history thatFamily Pedigrees can beused to study how traits that shows how a trait isare inherited inherited over several generations. • Very helpful if the trait is a genetic disorder. • Family members want to know if they are carriers or if their children will be infected.
• A carrier of the disorder will beFamily Pedigrees can beused to study how traits heterozygous. Ex : Aa, Bb or Pp.are inherited They will have the genotype - genes, but will not display the phenotype – physical condition • Carriers can pass the allele for the disorder to their offspring. • If the genotype is homozygous recessive, then the offspring will be infected. aa, bb , cc etc. • Question: What is a pedigree?
• If a trait is autosomal, it will appearAutosomal or sex linked in both sexes equally.traits • If a trait is sex-linked, it usually appears only in males. • A sex-linked trait is a trait whose allele is located on the X chromosome. • Most sex-linked traits are recessive. Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will exhibit the sex- linked condition. • Question: What is the difference between an autosomal and sex- linked trait?
• A female who carries an allele on theAutosomal or sex linked X chromosome will not exhibit thetraits condition if there is a dominant allele on her other X chromosome. • She will express the condition only if she inherits two recessive alleles. • Her chances of inheriting and exhibiting the condition are significantly less than a male. • Question : When will a female display the phenotype of a sex- linked trait?
• If the trait is autosomal dominant,Autosomal dominant and every individual with the trait willrecessive have a parent with the trait. • If the trait is recessive, an individual with the trait can have one, two or neither parent exhibit the trait.
1. What is a pedigree and how is itReview 03/06/2013 useful? 2. What is the difference between a carrier of a genetic disorder and an individual who is actually affected by a disease. 3. What is the difference between an autosomal and sex-linked trait? 4. When will women display the phenotype of a sex-linked trait? 5. What is the difference between genotype and phenotype? 6. If a genetic trait is autosomal dominant, will the parents and children have the trait? – Explain.
• Traits can be influenced by severalComplex Patterns of genes. These traits are calledHeredity polygenic traits. • The genes may be scattered along the same chromosome or located on different chromosomes. • Many different combinations appear in the offspring. Examples include: eye color, height, weight, hair and skin color.
• A trait that is intermediate betweenIntermediate Traits two parents results in a condition known as incomplete dominance. dominance • For the snapdragon flower neither the red or white allele is completely dominant over the other allele. The flowers are pink because they have less red pigment.
1. What is a pedigree and how is it useful?2. What is the difference between a carrier of a genetic disorder and an individual who is actually affected by a disease.3. What is the difference between an autosomal and sex-linked trait?4. When will women display the phenotype of a sex-linked trait?