Pedigree Analysis Genetics Inheritance ppt

Genetics

1. Pedigree Analysis

2. Objectives 1. Identify the mode of inheritance o a particular trait given the pedigree. 2. Predict the genotypes of parents. 3. Predict the probability of having an affected offspring.

3. Autosomal Dominant - If the phenotype associated with a given version of a gene is observed when an individual has only one copy, the allele is said to be autosomal dominant. The phenotype will be observed whether the individual has one copy of the allele (is heterozygous) or has two copies of the allele (is homozygous).

4. Autosomal Recessive - If the phenotype associated with a given version of a gene is observed only when an individual has two copies, the allele is said to be autosomal recessive. The phenotype will be observed only when the individual is homozygous for the allele concerned. An individual with only one copy of the allele will not show the phenotype, but will be able to pass the allele on to subsequent generations. As a result, an individual heterozygous for an autosomal recessive allele is known as a carrier.

5. Sex-Linked or X-Linked Inheritance - The X chromosome carries hundreds of genes, and many of these are not connected with the determination of sex. The smaller Y chromosome contains a number of genes responsible for the initiation and maintenance of maleness, but it lacks copies of most of the genes that are found on the X chromosome. As a result, the genes located on the X chromosome display a characteristic pattern of inheritance referred to assex-linkage or X-linkage.

6. Sex-Linked or X-Linked Inheritance - Females (XX) have two copies of each gene on the X chromosome, so they can be heterozygous or homozygous for a given allele. However, males (XY) will express all the alleles present on the single X chromosome that they receive from their mother, and concepts such as 'dominant' or 'recessive' are irrelevant. A number of medical conditions in humans are associated with genes on the X chromosome, including haemophilia, muscular dystrophy and some forms of colour blindness.

7. Pedigree Chart - Pedigree analysis is also useful when studying any population when progeny data from several generations is limited. Pedigree analysis is also useful when studying species with a long generation time. - A series of symbols are used to represent different aspects of a pedigree. To the right are the principal symbols used when drawing a pedigree.

8. Pedigree Chart - For those traits exhibiting dominant gene action: affected individuals have at least one affected parent. the phenotype generally appears every generation. two unaffected parents only have unaffected offspring.

9. Pedigree Chart - And for those traits exhibiting recessive gene action: unaffected parents can have affected offspring. affected progeny are both male and female.

10. Pedigree Chart - This chart shows four generations of a family with four individuals who are affected by a form of colorblindness.

11. Pedigree Chart - In this pedigree, the unaffected founding mother, I-1, and affected founding father, I-2, are parents to two affected daughters, II-1 and II-2. The affected founding daughter II-2 and the unaffected male II-3 who “marries into the family” have two offspring, an unaffected daughter III-1 and affected son, III-2. Finally, this affected male III-2 and the unaffected female III-3 who “marries in” have an unaffected son, IV-1.

12. Pedigree Chart In pedigree analysis, we use certain rules to determine whether a trait or disorder is autosomal dominant or autosomal recessive. Here are some key guidelines: 1. Autosomal Dominant Inheritance: - Affected individuals have at least one affected parent. - The trait appears in every generation of the pedigree. - Two unaffected individuals can have an affected child. - If an affected individual mates with an unaffected individual, approximately half of their children will be affected.

13. Pedigree Chart 2. Autosomal Recessive Inheritance: - Affected individuals may have unaffected parents. - The trait can skip generations. - Two unaffected individuals can have an affected child if they both carry a recessive allele. - If both parents are carriers (heterozygous), approximately 25% of their children will be affected. 3. Sex-Linked Dominant Inheritance: - Affected males will have affected daughters but not affected sons. - Affected females can have both affected sons and daughters. - If an affected male mates with an unaffected female, none of their sons will be affected, but all of their daughters will be affected. - If an affected female mates with an unaffected male, approximately half of their sons and half of their daughters will be affected.

14. Pedigree Chart 4. Sex-Linked Recessive Inheritance: - Affected males will pass the trait to all of their daughters, who will be carriers, but none of their sons. - Affected females will pass the trait to approximately half of their sons and half of their daughters. - If an affected male mates with an unaffected female, none of their children will be affected, but all of their daughters will be carriers. - If an affected female mates with an unaffected male, approximately half of their sons will be affected, and half of their daughters will be carriers.

15. Pedigree Chart 5. Y-Linked Inheritance: - Only males are affected by Y-linked traits or disorders. - Affected males will pass the trait to all of their sons. - There is no transmission of Y-linked traits from fathers to daughters or from affected males to their unaffected offspring. - If a male is unaffected, none of his sons will be affected.

16. Key Patterns in Pedigree Analysis

17. Key Patterns in Pedigree Analysis

18. Key Patterns in Pedigree Analysis