1. Chapter 14 Mendel and Gene Idea

2. Particulate Hypothesis Idea that parents pass on discrete heritable units or genes that retain their separate identities in offspring Genes can be passed on, generation after generation, in undiluted form Comparison to deck of cards or a bucket of marbles

3. Mendel’s Approach Character- a heritable feature such as flower color Trait – choice of color such as purple or white Mendel’s pea plants were true breeding plants which meant that if the parent had purple flowers the offspring would be the same Hybridization – Crossing of two true breeding plants parents – P 1 generation offspring – F 1 generation F 1 offspring – F 2 generation Analysis of F 2 generation that gave rise to fundamental principles of heredity.

4. Law of Segregation Four principles of Law of Segregation: 1. Alternative versions of genes account for variations in inherited characters. Now known as alleles. 2. For each character, an organism inherits two alleles, one from each parent. 3. If the two alleles at a locus differ, the dominant allele determines the appearance, the recessive has no noticeable effect. 4. Two alleles for a heritable character separate during gamete formation and end up in different gametes. (corresponds to homologous chromosomes distributed to different gametes in meiosis)

5. Alleles in DNA

6. Terminology Homozygous alleles – 2 of the same for a character Heterozygous alleles – 2 different alleles for the same character Phenotype – physical traits or outward characteristics Genotype – genetic makeup or the alleles themselves

7. Law of Independent Assortment States that each pair of alleles segregates independently of other pairs of alleles during gamete formation *monohybrid cross – tests one character *dihybrid cross – tests 2 characters and gives rise to 4 possible phenotypes based on how genes separate into each gamete

8. Dihybrid Cross

9. Laws of Probability Coin tosses, rolling dice, or drawing cards from a deck Probability that an event will happen is 1 Multiplication rule: states that to determine the probability of an event with 2 variables we must multiply probability of one event by the probability of another event ex: 2 coins landing on heads ½ X ½ = ¼ Addition rule: Probability of any one of 2 or more mutually exclusive events occurring is calculated by adding together their individual probabilities ex: 2 coins each heads ¼ + ¼ = ½

10. Inheritable Patterns Spectrum of dominance – different degrees of dominance and recessiveness in relation to each other. *Complete dominance – one allele is displayed over the other *Incomplete dominance – creates a third trait somewhere between true breeds Ex: red X white = pink *Codominance – two alleles affect the phenotype in separate ways Ex: blood typing – A, B, AB, O

11. Relationship between Dominance and Phenotype Dominance isn’t established from one trait subduing the other Dominance can be an allele coding for an enzyme that allows proper functioning processes to occur, whereas the recessive allele codes for the defective form of the enzyme and can lead to inherited disorders Ex: Tay-Sachs disease – inability to metabolize certain lipids leads to seizures, blindness, and motor or mental degeneration

12. Multiple Alleles ABO blood system in humans has 4 possible phenotypes

13. Allele Effects Pleiotropy – a single gene can phenotypically affect multiple characteristics in an organism Ex: cystic fibrosis & sickle cell Epistasis – a gene at one locus alters the phenotypic expression of a gene at a second locus. Ex: black vs. brown coat color in mice -epistatic gene is pigment deposited in the coat; recessive locus could produce white coat

14. Epistasis Example

15. Polygenic Inheritance Polygenic inheritance - Indicates that multiple genes could affect a single phenotypic character - Ex: skin pigment in humans - opposite of pleiotropy

16. Pedigree Analysis Pedigree – collects information about a family’s history for a particular trait and assembles it into a tree describing interrelationships of parents and children across generations *can be used to predict future occurrences of a character

17. Pedigrees

18. Recessive Inherited Disorders Individuals that inherit recessive alleles from both parents are targets Typically recessive allele codes for a malfunctional protein or no protein at all that leads to disorder Heterozygotes are labeled as carriers, even though they function normally

19. Recessive Inherited Disorders Cystic Fibrosis – allele codes for defective chloride transport channels or no channels which leads to build up of thick, sticky mucus in the pancreas, lungs, and digestive tract. -Ultimately leading to increase chronic bronchitis, bacterial infections, and poor absorption of nutrients Sickle-Cell disease – substitution of a single amino acid in hemoglobin of red blood cells leads to clumping or clogging of blood vessels from deformed hemoglobin molecule

20. Dominantly Inherited Disorders Achondroplasia – form of dwarfism *affects 1 in 25,000 *recessive allele is more prevalent than dominant allele Huntington’s disease – degenerative disease of the nervous system *affects 1 in 10,000 *high incidence lead to discovery of locus in tip of chromosome 4 *a test has been developed to detect presence of Huntington’s allele

21. Identifying Carriers Fetal Testing: 1. Amniocentesis – between 14 th and 16 th week of pregnancy can determine presence of disorder by examining extracts from amniotic fluid in uterus 2. Chorionic villus sampling – during 8 th to 10 th week of pregnancy, uses a small suctioned sample of placenta to detect presence of disorder New born screening: phenylketonuria – impaired ability to break down phenylalanine which can lead to mental retardation -1 in 10,000 to 15,000 affected -detection can lead to altered diet to promote normal development