1. Human Genetic Analysis
Chapter 11
Human Genetic Analysis

2. Complex inheritance of traits does not follow inheritance patterns described by Mendel.

3. Several genes can influence a trait- polygenic trait.
Determining the effect of these genes is difficult.
Example: A horse with red hair mates with a horse with white hair, and their offspring has both red and white hair. How can this be?

4. Codominance
When two dominant alleles are expressed at the same time, both forms of the trait are displayed.
Different from incomplete dominance because both traits are displayed.

5. Example: red flower x white flower = red and white flowered offspring equal number of red and white flowers

6. Example: Black horse x white horse = roan coat equal number of black and white hairs

7. Intermediate Traits
Incomplete dominance - an individual displays a trait that is intermediate between the two parents.
Example: red flower x white flower = pink flower
Neither the red nor the white allele is completely dominant

8. Multiple Alleles
Genes with three or more alleles are said to have multiple alleles.
When traits are controlled by genes with multiple alleles, an individual can have only two of the possible alleles for that gene.
Example: Blood types in humans
Three different alleles –IA, IB, and i result in four different blood phenotypes – A, AB, B, and O.

9. Males will have the disorder because they only have one X chromosome.
X-Linked Traits
The trait is carried by females on the X chromosome through a recessive allele.
Males will have the disorder because they only have one X chromosome.

10. Traits influenced by the Environment
An individual’s phenotype often depends on conditions in the environment.
Example: fur color in Siamese cats
Dark fur around cooler parts of the body- ears, nose, paws, and tails.
Example: skin tone in humans
Exposure to the sun alters the color of the skin.

11. Mutations Changes in genetic material.
The harmful effects produced by inherited mutations are called genetic disorders.
Many mutations are carried by recessive alleles in heterozygous individuals. “carriers”

12. Genetic Counseling
Genetic counseling is a form of medical guidance that informs people about genetic problems that could affect them or their offspring.

13. 1. Genetic Abnormality
Rare, uncommon version of a trait.
2. Genetic Disorder
An inherited condition that sooner or later will cause mild to severe medical problems.

14. A recognized set of symptoms that characterize a given disorder.
3. Syndrome
A recognized set of symptoms that characterize a given disorder.
4. Disease
Illness caused by infectious, dietary, or environmental factors, NOT by inheritance of mutant genes.

15. Disorder Color blindness Cystic fibrosis Down syndrome Hemophilia
Mutation
Chromosome
Color blindness P X
Cystic fibrosis 7q
Down syndrome C 21
Hemophilia
Klinefelter syndrome
Sickle-cell disease
11p
Tay–Sachs disease 15
P – Point mutation, or any insertion/deletion entirely inside one gene
D – Deletion of a gene or genes
C – Whole chromosome extra, missing, or both
T –Trinucleotide repeat
disorders: gene is extended in length

16. Karyotypes

17. Karyotypes
micrograph in which the pairs of homologous chromosomes are arranged in decreasing size
22 autosomes are matched together with one pair of nonmatching sex chromosomes
Used to study chromosomes in hopes of identifying genetic abnormalities or disorders.

18. PEDIGREE CHARTS
© 2007 Paul Billiet ODWS

19. What is a pedigree chart?
a chart of the genetic history of a family over several generations.
used to study the transmission of hereditary conditions
© 2007 Paul Billiet ODWS

20. Constructing a Pedigree
Female
Male

21. Connecting Pedigree Symbols
Married Couple
Children

22. Symbols used in pedigree charts
Affected
X-linked
Carrier
Deceased . .
© 2007 Paul Billiet ODWS

23. Symbols used in pedigree charts
Normal male
Affected male
Normal female
Affected female
© 2007 Paul Billiet ODWS

24. Organizing the pedigree chart
A pedigree chart of a family showing 20 individuals
© 2007 Paul Billiet ODWS

25. Organising the pedigree chart
Generations are identified by Roman numerals. I II
III IV
© 2007 Paul Billiet ODWS

26. Organising the pedigree chart
Individuals in each generation are identified by Arabic numerals numbered from the left
Therefore the affected individuals are II3, IV2 and IV3 I II
III IV
© 2007 Paul Billiet ODWS

27. Interpreting a Pedigree Chart
Determine if the pedigree chart shows an autosomal or X-linked disease.
If most of the males in the pedigree are affected, then the disorder is X-linked.
If it is a 50/50 ratio between men and women the disorder is autosomal.

28. Example of Pedigree Charts
Is it Autosomal or X-linked?
Take a minute and try to decide if this slide is autosomal or X-linked.

29. Answer
Autosomal
It is autosomal because it is 50/50 men to women with the disorder, if it was X-linked most of the men in the diagram would have the disorder.
Make sure you count the number of men with the disorder and the number of women with the disorder. In this pedigree, 3 men and 3 women have the disorder.

30. Determine whether the disorder is dominant or recessive.
If the disorder is dominant, one of the parents must have the disorder.
If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

31. Example of Pedigree Charts
Dominant or Recessive?
Is this pedigree dominant or recessive?

32. Answer
Dominant
It is dominant because a parent in every generation have the disorder. Remember if a parent in every generation has the disorder, the disorder has not skipped a generation. If the disorder has not skipped a generation the disorder is dominant.

33. Example of Pedigree Charts
Dominant or Recessive?
Is this pedigree dominant or recessive?

34. Answer
Recessive
It is recessive because a parent in every generation does not have the disorder. Remember the disorder can skipped a generation if the disorder is recessive. The parents can be heterozygous and be carriers of the disorder but not have the symptoms of the disorder.