1. Inheritance
3.4

2. Essential Idea: The inheritance of genes follows patterns.
3.4
Inheritance
Understandings:
Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed
Gametes are haploid so contain only one allele of each gene
The two alleles of each gene separate into different haploid daughter nuclei during meiosis
Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles
Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects
Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles
Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes
Many genetic diseases have been identified in humans but most are very rare
Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer
Applications:
Inheritance of ABO blood groups
Red-green color blindness and hemophilia as examples of sex-linked inheritance
Inheritance of cystic fibrosis and Huntington’s disease
Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl
Skills:
Construct Punnett grids for predicting the outcomes of monohybrid genetic crosses
Compare predicted and actual outcomes of genetic crosses using real data
Analyze of pedigree charts to deduce the pattern of inheritance of genetic diseases

3. Gregor Mendel (1822 – 1884)
Austrian monk, experimented with pea plants

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

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

7. 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

8. 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

9. 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

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

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

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

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

14. 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

15. 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.

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