1. Patterns of Inheritance
Chapter 10
Patterns of Inheritance

2. 10.1 Genetics trait: a variation of a particular character
Ex yellow or red flowers
gene: a unit of inherited information

3. Blending Hypothesis
1800
Explains how offspring inherit traits from both parents
Ex. yellow flower + red flower = orange flower
Discarded because it could not explain traits disappearing and reappearing in another generation

4. Gregor Mendel 19th century Austrian Monk
First to apply an experimental approach to the question of inheritance
genetics: the study of heredity
Used pea plant breeding

5. Particulate Hypothesis
Parents pass on to their offspring separate and distinct factors (genes) that are responsible for inherited traits
Heritable factors retain their identity through generations

6. Mendel’s Pea Plants

7. Mendel’s Experiment Identify pea plants that were true-breeding
When self-fertilized, only produces identical offspring
To insure self-fertilization, Mendel tied cloth bags around each plant’s flowers to prevent cross pollination
Mendel crossed true-breeding plants with two distinct traits (color and roundness)
cross-fertilization: sperm from the pollen of one flower fertilizes the eggs in the flower of a different plant
The fertilized eggs developed into embryos within seeds (peas) that were planted
These then grew to produce flowers
Purple crossed with white flowers

8. 10.2 Mendel’s Principle of Segregation
hybrids: the offspring of two different true-breeding varieties
P generation= parental
F1 generation = the hybrid offspring
F2 generation = offspring when F1 self-fertilize each other

9. Monohybrid Cross
monohybrid cross: a pairing in which parent plants differ in only one character
Mendel found that F1 produced all purple flowers but F2 3/4 purple and 1/4 white
He repeated this for other traits (seed color, shape, pod shape & color, flower position, and stem length)
Same result

10. Mendel’s 4 Hypotheses There are alternate forms of genes
alleles: the alternate forms of genes
Ex. Purple and white
For each inherited character, an organism has 2 alleles for the gene controlling that character, one from each parent
homozygous: 2 alleles are the same for that character
heterozygous: the 2 alleles are different

11. 3. dominant: only one allele appears to affect the trait
recessive: the allele that does not appear to affect the trait
Pp; P = dominant, p = recessive
4. Principle of Segregation
Two alleles for a character separate during formation of gametes (meiosis) so that each gamete carries only one allele for each character

12. Punnett Square
Diagram that shows all possible outcomes of a genetic cross

13. Phenotype and Genotype
phenotype: an observable trait
Hair color, height, tongue rolling
The dominant trait shows up
Bb and BB = dominant; brown
bb = recessive; blond
genotype: the genetic makeup (combination of alleles)
1/2 Bb; 1/2 bb = 2:2

14. Test Cross
test cross: breeds an individual of unknown genotype but dominant phenotype with a homozygous recessive individual

15. Principle of Independent Assortment
During gamete formation in an F2 cross, a particular allele for one character can be paired with either allele of another

16. Dihybrid Cross
dihybrid cross: crossing organisms differing in 2 characters

17. 10.3 Variations of Inheritance Patterns

18. Intermediate Inheritance (Incomplete Dominance)
intermediate inheritance: the heterozygotes have a phenotype that is intermediate between the two homozygotes
Ex. Red + white flowers = pink, red & white

19. Codominance codominance: a heterozygote expresses both traits
Ex. Blood Type
A, B, AB, O
A & B refer to 2 carbohydrates that are found on the surface of red blood cells
O = ii = neither carbohydrates
Universal donor
A= IAIA or IAi = A carb (A)
B= IBIB or IBi = B carb
AB= IAIA or IAi = both A & B
Universal receiver

20. Polygenic Inheritance
polygenic inheritance: two or more genes affect a single character
Ex. Eye color, skin, height
Eye color = tone of pigment , amount, and position
pleiotropy: a single gene affects more than one trait
Ex sickle cell anemia

21. Importance in the Environment
Temperature can have an effect on animal coloring
Ex siamese cats, rabbits
Height can be affected by nutrition and exercise
Ex. Dancers
Nature vs Nurture

22. 10.4 Meiosis Explains Mendel’s Principles
Chromosome Theory of Inheritance
States that genes are located on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns

23. Genes
gene locus: the alleles of a gene reside at the same location on homologous chromosomes
The homologous chromosomes may bear the same or different alleles

24. Genetic Linkage
genetic linkage: the tendency for the alleles on one chromosome to be inherited together
The closer the genes are on a chromosome, the greater the genetic linkage and crossing over will not separate them
The probability of genetic linkage is measured in centiMorgans (cM)
Represents 1% of the probability of crossing over
1 cM apart = 1% chance of separation
20 cM = 20% chance

25. 10.5 Sex-Linked Genes
sex-linked gene: any gene located on a sex chromosome
Most are found on the X chromosome
Thomas Hunt Morgan
Discovered sex-linked genes while studying fruit flies
Normal fruit flies have red eyes which is carried on the X, but sometimes males have white (recessive)

26. Sex-linked Traits in Humans
Colorblindness
X-linked recessive
Lack of red receptors in the retina
8% males
0.4% females