1. Heredity Review
Chapters 13-15

2. Genes Segments of DNA that code for a protein
Locus is the location of a gene on the chromosome
Autosomes: body chromosomes 1-22
Sex chromosomes: X and Y

4. Meiosis Reduces chromosome number in half (diploid to haploid)
Meiosis I homologous chromosomes separate
Meiosis II sister chromatids separate

6. Meiosis is Special
Crossing over: regions of homologous chromosomes overlap and exchange DNA
Makes 4 genetically different cells
Occurs only in sex organs
Gonads make gametes

8. Mendel’s Laws
Independent Assortment: each homologous chromosome is divided into gametes randomly
Segregation: each gamete gets one copy of each allele as they separate

10. Genetic Diversity
Independent assortment of chromosomes creates different gametes (223)
Crossing over changes chromosomes’ genes (2-3 times per chromosome)
Random fertilization

11. Mendelian genetics Dominant vs. recessive Homozygous vs. heterozygous
P vs. F generation
Genotype vs. phenotype
Codominance vs. incomplete dominance
Monohybrid vs. dihybrid cross

12. Testcross To find the genotype of a dominant phenotype:
Cross it with a homozygous recessive
If any offspring are recessive, unknown was heterozygous
If all were dominant, unknown was homozygous dominant

14. Interesting genetics…
Pleiotropy: one gene, many effects
Polygenic inheritance: many genes, one effect
Epistasis: one gene controls the expression of another

16. Pedigrees Aka family trees Guys = square; ladies = circles
Shaded = has the condition, ½ shaded means carrier, no shade means normal
It allows you to identify genotypes by tracing phenotypes

18. Common genetic disorders
Albinism, cystic fibrosis, Tay-Sachs, sickle cell anemia are all recessively inherited
Achondroplastic dwarfism, Huntington’s are dominant
Heart disease, diabetes, cancer are polygenic

19. Morgan Discovered gene linkage
Linked genes occur on the same chromosome and are inherited together
Genetic maps: determine order of genes based on crossing over frequencies

20. Sex-linked disorders Duchenne muscular dystrophy Hemophilia
Red-green colorblindness
All x-linked

21. Barr body
One of female’s X chromosomes super condenses and is rarely used

22. Nondisjunction
When chromosomes do not separate properly; they remain attached
Some gametes get more, some less
Trisomy 21 (Down syndrome)
Trisomy 18 (death)
Aneuploidy vs. polyploidy

24. Genomic imprinting
Paternal and maternal chromosomes have special marks (methyl groups)
Some disorders arise only from paternal or maternal chromosomes
Prader-Willi = dad (retardation, obesity, short)
Angelman = mom (uncontrollable laughter, jerky movements)