1. Extending Mendelian Genetics
Chapter 7
Extending Mendelian Genetics

2. Basic Patterns of Human Inheritance
Autosomal Recessive Genetic Disorders
A recessive trait is expressed when the individual is homozygous recessive for the trait.
Basic Patterns of Human Inheritance

3. Affects the mucus-producing glands, digestive enzymes, and sweat glands
Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat.
Without sufficient chloride ions in the cells, a thick mucus is secreted.
Video
Cystic Fibrosis

4. Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
Albinism

5. Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides
Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.
Tay-Sachs Disease

6. Cystic Fibrosis Punnett Square

7. Basic Patterns of Human Inheritance
Autosomal Dominant Genetic Disorders
Huntington’s disease affects the nervous system.
Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively short.
Basic Patterns of Human Inheritance

8. Huntington’s Disease Punnett Square

9. A diagram that traces the inheritance of a particular trait through several generations
Pedigrees

10. Inferring Genotypes
Knowing physical traits can determine what genes an individual is most likely to have.
Predicting Disorders
Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes.

11. Sex chromosomes determine an individual’s gender
Sex Determination

12. Sex-Linked Traits Genes located on the X chromosome
Red-green color blindness
Hemophilia
Punnett Square
Sex-Linked Traits

13. Dosage Compensation
The X chromosome carries a variety of genes that are necessary for the development of both females and males.
The Y chromosome mainly has genes that relate to the development of male characteristics.
In females, one X chromosome is inactivated in each cell. The inactivated X chromosome is visible in stained cells as a Barr body.

14. X Chromosome Inactivation
Tutorial
X Chromosome Inactivation

15. Variety is the result of one allele hiding the effects of another allele.
An epistatic gene can interfere with the expression of other genes.
Albinism in mammals is caused by an epistatic gene that blocks the production of pigments.
Epistasis

16. Complex Patterns of Inheritance
Phenotype can depend on interactions of alleles.
Complex Patterns of Inheritance

17. The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.
Incomplete Dominance

18. Codominance Both alleles are expressed in the heterozygous condition.
Sickle-cell disease is one example.
People who are heterozygous for the trait have both normal and sickle-shaped cells.
Codominance

19. Multiple Alleles Blood groups in humans
ABO blood groups have three forms of alleles.
Sometimes said to be codominant.
Multiple alleles can demonstrate a hierarchy of dominance.
Multiple Alleles

20. Polygenic traits arise from the interaction of multiple pairs of genes.
Read pg. 206 in textbook.
Polygenic Traits

21. Environmental Influences
Environmental factors influence an organism’s phenotype
Diet and exercise
Sunlight and water
Temperature
Environmental Influences

22. Read pgs
Gene Linkage

23. Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size
Images of chromosomes stained during metaphase
Chromosomes are arranged in decreasing size to produce a micrograph.
Karyotype Studies

24. Is this a normal karyotype?
Male or female?

25. Is this a normal karyotype? Male or Female?

26. Is this a normal karyotype? Male or Female?

27. Cell division during which sister chromatids fail to separate properly
Down syndrome, also called trisomy 21
Nondisjunction