1. Genetics II Pedigrees and patterns of inheritance Mr. HunterKennedy High School Biology 03/15/2011
2. 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?
3. • 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?
4. • 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?
5. • 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.
6. • 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?
7. • 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?
8. • 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?
9. • 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.
10. 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.
11. • 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.
12. • 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.
13. 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?