Genetics IIGenetics IIPedigrees and patterns of Pedigrees and patterns of

inheritanceinheritance

Mr. HunterMr. HunterKennedy High SchoolKennedy High School

BiologyBiology03/15/201103/15/2011

Mr. HunterBiology 03/06/2013

• Objective(s)Objective(s)• SWBATSWBAT• Explain the concept of linked genes.Explain the concept of linked genes.• Define chromosome map.Define chromosome map.• Explain the purpose and analysis of a pedigree.Explain the purpose and analysis of a pedigree.• Distinguish between autosomal and sex-linked traits.Distinguish between autosomal and sex-linked traits.

• Bell Ringer – Bell Ringer – What is the difference between a genotype and What is the difference between a genotype and a phenotype?a phenotype?

Fruit Flies and Chromosomes

• In the early 1900s, Thomas Hunt In the early 1900s, Thomas Hunt Morgan experimented with the small Morgan experimented with the small fruit fly fruit fly Drosophila melanogaster.Drosophila melanogaster.

• They live for approximately 7-10 days They live for approximately 7-10 days

and their and their entire genomeentire genome has been has been recently sequenced.recently sequenced.

• Based on his experiments with fruit Based on his experiments with fruit flies, Morgan determined that if flies, Morgan determined that if genes are inherited together they genes are inherited together they must be on the same chromosomemust be on the same chromosome. . They are They are linked geneslinked genes..

• QuestionQuestion: : What are linked genes?What are linked genes?

Fruit Flies and Chromosomes

• The farther apart genes are located The farther apart genes are located on a chromosome, the more likely on a chromosome, the more likely that that crossing-overcrossing-over will occur. will occur.

• A A chromosome map chromosome map is a diagram is a diagram that shows the linear order of genes that shows the linear order of genes on a chromosome.on a chromosome.

• The percentage of crossing-over for The percentage of crossing-over for two traits is two traits is proportional to the proportional to the distance between them on a distance between them on a chromosomechromosome.

• Question: What determines if crossing over of genes will occur?

• Question : What is the percentage of crossing over for two traits equal to?

Family Pedigrees can be Family Pedigrees can be used to study how traits used to study how traits are inheritedare inherited

• Pedigree: Pedigree: A family history that A family history that that shows how a trait is that shows how a trait is inherited over several inherited over several generations.generations.

• Very helpful if the trait is a Very helpful if the trait is a genetic disorder.genetic disorder.

• Family members want to know if Family members want to know if they are carriers or if their they are carriers or if their children will be infected.children will be infected.

Family Pedigrees can be Family Pedigrees can be used to study how traits used to study how traits are inheritedare inherited

• A A carriercarrier of the disorder will be of the disorder will be heterozygous. Ex : heterozygous. Ex : Aa, Bb or Pp. Aa, Bb or Pp. They will have the genotype - They will have the genotype - genes, but will not display the genes, but will not display the phenotype – physical conditionphenotype – physical condition

• Carriers can pass the allele for the Carriers can pass the allele for the disorder to their offspring.disorder to their offspring.

• If the genotype is homozygous If the genotype is homozygous recessive, then the offspring will recessive, then the offspring will be infected. be infected. aa, bb , cc etc.aa, bb , cc etc.

• Question: What is a pedigree?Question: What is a pedigree?

Autosomal or sex linked traits

• If a trait is If a trait is autosomalautosomal, it will appear , it will appear in both sexes equally.in both sexes equally.

• If a trait is If a trait is sex-linked,sex-linked, it it usually usually appears only in males.appears only in males.

• A sex-linked trait is a trait whose A sex-linked trait is a trait whose allele is located on the X allele is located on the X chromosome.chromosome.

• Most sex-linked traits areMost sex-linked traits are recessiverecessive. . Because males have only one X Because males have only one X chromosome, chromosome, a male who carries a a male who carries a recessive allele on the X recessive allele on the X chromosome will exhibit the sex-chromosome will exhibit the sex-linked condition.linked condition.

• Question: Question: What is the difference What is the difference between an autosomal and sex-between an autosomal and sex-linked trait?linked trait?

Autosomal or sex linked Autosomal or sex linked traitstraits

• A female who carries an allele on the A female who carries an allele on the X chromosome will not exhibit the X chromosome will not exhibit the condition if there is a dominant condition if there is a dominant allele on her other X chromosomeallele on her other X chromosome..

• She will express the condition only if She will express the condition only if she inherits two recessive alleles.she inherits two recessive alleles.

• Her chances of inheriting and Her chances of inheriting and exhibiting the condition are exhibiting the condition are significantly less than a male.significantly less than a male.

• Question : Question : When will a female When will a female display the phenotype of a sex-display the phenotype of a sex-linked trait?linked trait?

Autosomal dominant and Autosomal dominant and recessive recessive

• If the trait is If the trait is autosomal dominant, autosomal dominant, every individual with the trait will every individual with the trait will have a parent with the trait.have a parent with the trait.

• If the trait is If the trait is recessiverecessive, , an individual an individual with the trait can have one, two or with the trait can have one, two or neither parent exhibit the trait.neither parent exhibit the trait.

Review 03/06/2013

1. What is a pedigree and how is it What is a pedigree and how is it useful?useful?

2.2. What is the difference between a What is the difference between a carrier of a genetic disorder and an carrier of a genetic disorder and an individual who is actually affected by individual who is actually affected by a disease.a disease.

3.3. What is the difference between an What is the difference between an autosomal and sex-linked trait?autosomal and sex-linked trait?

4.4. When will women display the When will women display the phenotype of a sex-linked trait?phenotype of a sex-linked trait?

5.5. What is the difference between What is the difference between genotype and phenotype?genotype and phenotype?

6.6. If a genetic trait is autosomal If a genetic trait is autosomal dominant, will the parents and dominant, will the parents and children have the trait? – Explain.children have the trait? – Explain.

Complex Patterns of Complex Patterns of HeredityHeredity

• Traits can be influenced by several Traits can be influenced by several genes. These traits are called genes. These traits are called polygenic traits.polygenic traits.

• The genes may be scattered along The genes may be scattered along the same chromosome or located on the same chromosome or located on different chromosomes.different chromosomes.

• Many different combinations appear Many different combinations appear in the offspring. Examples include: in the offspring. Examples include: eye color, height, weight, hair and eye color, height, weight, hair and skin color.skin color.

Intermediate TraitsIntermediate Traits

• A trait that is intermediate between A trait that is intermediate between two parents results in a condition two parents results in a condition known as known as incomplete dominanceincomplete dominance.

• For the snapdragon flower neither For the snapdragon flower neither the red or white allele is completely the red or white allele is completely dominant over the other allele. The dominant over the other allele. The flowers are pink because they have flowers are pink because they have less red pigment.less red pigment.

1. What is a pedigree and how is it What is a pedigree and how is it useful?useful?

2.2. What is the difference between a What is the difference between a carrier of a genetic disorder and an carrier of a genetic disorder and an individual who is actually affected by individual who is actually affected by a disease.a disease.

3.3. What is the difference between an What is the difference between an autosomal and sex-linked trait?autosomal and sex-linked trait?

4.4. When will women display the When will women display the phenotype of a sex-linked trait?phenotype of a sex-linked trait?