1. Mendel & the gene idea
Chapter 14

2. YOU MUST KNOW
Terms associated with genetics problems: P, F1, F2, dominant, recessive, homozygous, heterozygous, phenotype, genotype
How to derive the proper gametes when working a genetics problem
The difference between an allele and a gene
How to read a pedigree
How to use data sets to determine Mendelian patterns of inheritance

4. Alternative versions of genes (alleles) account for variations in inherited characteristics among offspring
Ex. 2 alleles for flower color – both are the flower color gene, found at the same locus, but one version codes for purple flowers while the other codes for white

5. For each characteristic, every organism inherits one allele from each parent

6. If the two alleles are different, then the dominant allele (shown as a capital letter) will be expressed in offspring, and the recessive allele (shown as a lower case letter) will have no noticeable effect on the offspring

7. Law of Segregation
The two alleles for each trait separate during gamete production
-If a parent is homozygous (has two of the same allele- PP or pp), all offspring will get that allele, but if the parent is heterozygous (has two different alleles-Pp), each offspring has a 50% chance of getting either allele

8. Law of Independent Assortment
Alleles on different chromosomes separate independently of each other during anaphase I of meiosis

9. Phenotype – an organism’s physical expression of a trait
Genotype – an organism’s genetic combination of alleles

10. Test Cross – done to determine if a phenotypically dominant organism is homozygous or heterozygous
Note: Really only practical in species that produce large numbers of offspring

11. Monohybrid cross – examine one trait at a time
Dihybrid cross – examine two traits together

12. Laws of Probability
Rule of multiplication – used when calculating the probability that two or more independent events will occur together in a specific combination
If you cross two individuals that both have genotypes of AaBbCc, what is the probability of an offspring being AaBBcc?
½ x ¼ x ¼ = 1/32

13. The Rule of Addition – used when calculating the probability that any of two or more mutually exclusive events occur
If two parents are crossed that are AaBb, what are the chances of an offspring being either AABB or aabb?
1/16 + 1/16 = 1/8

14. Codominance
Two alleles are both dominant and are both full expressed in the phenotype
Note: Use superscripts to denote different alleles

15. Incomplete Dominance
Hybrids are a blend of the two traits

16. A gene has more than 2 alleles
Multiple alleles
A gene has more than 2 alleles
*Blood types are also an example of codominance

17. Pleiotropy – one gene has multiple phenotypic effects

18. Epistasis – a gene at one locus alters the effects of a gene at another locus

19. Polygenic Inheritance
Two or more genes have an additive effect in a single characteristic

20. Pedigrees
Diagram that shows the relationship between parents and offspring across generations

21. Recessively inherited disorders
Cystic fibrosis – defective cell membrane protein for movement of chloride ions leading to high levels of extracellular chloride which causes thickening of mucus which causes organ malfunction and chronic infections

22. Tay-Sachs – codes for a dysfunctional enzyme that doesn’t properly breakdown lipids in the brain. Lipids accumulate causing blindness, seizures, loss of brain function, death by 5.

23. Sickle-cell disease – hemoglobin gene is mutated, resulting in sickle shaped red blood cells

24. Lethal Dominant Alleles – require only one copy of the gene to be expressed
Usually symptoms are not present until later in life (after genes have already been passed on)
Huntington’s disease – degenerative disease of the nervous system, onset usually in 40s

25. Prenatal Genetic Testing
Amniocentesis – removal of amniotic fluid an generation of a karyotype
Chorionic villus sampling – suction of a small sample of portion placenta that contains fetal cells and generation of a karyotype