1. Chapter 8 Mendel, Peas, and Heredity

2. 8-1 Origins of Genetics
Heredity – the passing of traits from parents to offspring
Genetics – science that focuses of heredity
Gregor Mendel – considered the father of genetics
Why?

3. Mendel
Austrian monk who used his math and science background to study heredity
Used the experiments of T.A. Knight (studied pea plants)
Used math to analyze his results (1st to do so)
Published his work in 1866

4. Why Peas? They taste good with butter
You can smash them with mashed potatoes
Just kidding

5. Has many traits that come in only two forms
Can easily control the mating of plants
Small, grows fast, produces many offspring

6. Mendel’s Classic Experiment
His experiment was called a monohybrid cross (cross that involves one pair of contrasting traits)
Used plants that were true-breeding in the beginning
True-breeding – all offspring would display one form of a specific trait

7. Step 1
Allowed a group of plants to self-pollinate for several generations
Why?
To ensure they were true-breeding
These plants would serve as the P Generation (Parent)
White Flowered TB Plant x Purple Flowered TB Plant

8. Step 2
Results of P generation cross were all Purple Flowered Offspring
Called the F1 Generation
Recorded the number of plants expressing the trait

9. Step 3 Allowed the F1 plants to self-pollinate
Resulting offspring called the F2 Generation
Most were purple flower plants, some were white flowered plants
Why?

10. 8-2 Mendel’s Hypotheses
For each inherited trait, an individual has a copy of a gene from each parent
There are alternative versions of genes (allele)
When two different alleles occur together, one may be completely expressed, while the other is not observable (dominant vs. recessive)

11. When gametes form, alleles for each gene separate independently of one another (haploid cells)

12. Homozygous – two of the same alleles (TT or tt)
Heterozygous – two different alleles (Tt)
Genotype – set of alleles an organism has (TT or Tt or tt)
Phenotype – physical expression of a trait (tall or short)

13. Laws of Heredity
Law of Segregation – the alleles of a gene are separated during meiosis

14. Law of Independent Assortment – States that a random assortment of maternally and fraternally derived chromosomes during meiosis results in gametes that have different combinations of genes
Allele for plant height separates from allele for flower color during meiosis

15. 8-3 Studying Heredity
Punnett Squares show the probability of a certain cross
Remember, not actual results, only possible results

16. Pedigree
Pedigree – a family history that shows how a trait is inherited over several generations
Helpful for tracking genetic disorders

17. Autosomal or Sex-Linked?
If a trait is autosomal, it will affect both males and females equally
Sex-Linked traits have their allele on the X chromosome
Most are recessive
Males usually exhibit the trait because they only have one X chromosome. Why?

18. Females get two chances to get a dominant allele while males only get one allele
Females can be carriers of a sex-linked trait (if they are heterozygous)

19. Rules of Pedigrees Squares = Male Circle = Female
Line between male and female means they are married
Different generations happen on different levels of the pedigree

22. Example of a Pedigree This pedigree tracks albinism
Albinism is a recessive trait that is autosomal
All genotypes are known

24. Example of a Pedigree This pedigree tracks albinism
Only genotype known are those showing the recessive condition

26. Modes of Inheritance
Autosomal Dominant – males and females can be affected, and trait does not skip generations
Autosomal Recessive – can affect males and females, and may skip generations

27. 8-4 Patterns of Heredity
Most traits are not controlled by dominant vs. recessive alleles
When several genes control a trait, they are called polygenic traits
Eye color, skin color, height, and weight are all polygenic traits

28. Incomplete Dominance
When an individual is heterozygous for a trait, the individual displays an intermediate form between the two alleles
Red Snap Dragon crossed with a White Snap Dragon, and the offspring are pink

29. Codominance
When an individual is heterozygous for a trait, both alleles are expressed at the same time
When a homozygous white horsed is crossed with a homozygous red horse, the offspring is roan (red and white hairs)

30. Multiple Alleles Traits with three or more alleles
Human Blood Type has three alleles,
IA, IB, and i

31. Sex Linked Traits
Traits whose genes are located on the X or Y chromosome
Usually men are more likely to be affected with diseases that are sex linked traits

32. Environmental Influence
Phenotypes often are influenced by the environment
Examples of influences include nutrition, social exposure, and temperature

33. Genetic Disorders
Sickle Cell Anemia – autosomal recessive condition caused by abnormal hemoglobin molecules
Tay-Sachs – autosomal recessive condition that causes a defective form of a brain protein

34. Cystic Fibrosis – autosomal recessive condition that causes a defective chloride-ion transport protein
Hemophilia A – sex-linked recessive condition that causes a defective blood clotting factor
Huntington’s Disease – autosomal dominant condition that causes an inhibitor of brain-cell metabolism