1. Patterns of Inheritance
Chapter 10

2. Genetics developed from curiosity about inheritance
Gregor Mendel
Late 1800s
Pea plants

4. Genetics developed from curiosity about inheritance
Trait= a variation of a particular character
Genetics= study of heredity
Self-fertilization= fertilization of an ovum of a plant by a male gamete from the same flower
True breeding
Cross-fertilization= sperm from the pollen of one flower fertilizes the eggs in the flower of a different plant

5. Mendel discovered that inheritance follows rules of chance
Hybrids= the offspring of two different true-breeding varieties
P generation= P for parent
F1 generation= F for filial (Latin for son)
F2 generation= offspring of the F1 generation…“grandchildren”
Monohybrid cross= a pairing in which the parent plants differ in only one (mono) character
Mendel crossed purple-flowered pea plants with white-flowered pea plants

6. Mendel discovered that inheritance follows rules of chance

7. Mendel discovered that inheritance follows rules of chance
Mendel not only used flower color, he also used flower position, seed color, seed shape, pod shape, pod color, and stem length
He used monohybrid crosses to study the heredity of these traits

8. Mendel discovered that inheritance follows rules of chance
Mendel’s 4 hypotheses:
There are other forms of genes.
Such as the gene for flower color
One form for purple flowers
Another for white flowers
Alternative forms of genes are called alleles
For each inherited trait, an organism has two alleles for the gene controlling that trait…one from mom and one from dad.
Heterozygous= two alleles for a trait are different
Homozygous= two alleles for a trait are the same

9. Mendel discovered that inheritance follows rules of chance
3. When only one of the two different alleles appears to affect the trait, that allele is called the dominant allele. The other allele that does not appear is called the recessive allele.
Flower color- Purple
P = dominant
p= recessive
4. The two alleles for a trait separate during the formation of gametes (remember…meiosis!). Each gamete has only one allele for each trait. The union of sex cells, during fertilization, reunites the alleles to form pairs again.

10. Mendel discovered that inheritance follows rules of chance
You can calculate the probabilities for different combinations of alleles resulting from a genetic cross
Punnett square= a diagram that shows all possible outcomes of a genetic cross

11. Mrs. B’s QUICK QUIZ The father of genetics is Friar Tuck Gregor Mendel
Anton van Leeuwenhoek
Bill Nye

12. 2. _____________ is the fertilization of an ovum of a plant by a male gamete from the same flower.
True breeding
Cross fertilization
Self fertilization
Genetics

13. Hybrids= the offspring of two different true-breeding varieties
3. A hybrids is the offspring of one true breeding plant.
True
False
Hybrids= the offspring of two different true-breeding varieties

14. Mendel discovered that inheritance follows rules of chance
The genetic makeup , or combination of alleles is called the genotype
The genotypic ratio is 1PP:2Pp:1pp
The observable trait is called the phenotype (purple flowers)
The 3:1 ratio is called a phenotypic ratio

15. Mendel discovered that inheritance follows rules of chance
Testcross= breeds an individual of unknown genotype, but dominant phenotype with a homozygous recessive individual
The appearance of the phenotype of the offspring will reveal the mystery plant

16. Mendel discovered that inheritance follows rules of chance
Dihybrid cross= crossing individuals that differ in two characters
Mendel used this when studying peas with
different colors (yellow =dominant)
different shapes (round= dominant)
RRYY
RrYy
Rryy
A punnett square can be used in the same way

17. Mendel discovered that inheritance follows rules of chance
Mendel used dihydrid crosses to study all seven characteristics of pea plants
Proposed his principle of independent assortment, which states that during gamete formation in an F2 cross, a particular allele for one character can pair up with a particular allele of another character
R can end up with Y or y
r can end up with Y or y
The alleles are sorted into gametes independently of one another

18. There are many variations of inheritance patterns
For some characters of organisms, neither allele is dominant
The heterozygotes have a phenotype that is intermediate between the phenotypes to the two parents
This is called incomplete dominance
Ex: Andalusian chickens
A heterozygote chicken=CBCW
This is NOT blending, because the parent phenotypes can reappear in the F2 generation

20. There are many variations of inheritance patterns
Many genes have multiple alleles, instead of just two
Ex: human blood type
A, B, AB, O
IA and IB display codominance, meaning that a heterozygote expresses both traits
This is NOT intermediate, due to the fact that the phenotype shows the separate traits of both alleles

22. There are many variations of inheritance patterns
When multiple genes affect a character, the variation in phenotypes can increase
When two or more genes affect a single character, it is called polygenic inheritance
ex: height in humans
3 tall alleles: A, B, C
3 short alleles: X, Y, Z
Intermediate inheritance
AABBCC= very tall
AZBBCC= slightly shorter, etc.
Some characters are affected by dozens of genes, which lead to numerous combinations of alleles

23. There are many variations of inheritance patterns
An individual’s phenotype depends on environment as well as on genes
Ex: tree
Temperature
The product of a genotype is generally a range of possibilities influenced by the environment

24. Meiosis explains Mendel’s principles
Chromosome theory of inheritance: genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization accounts for inheritance

25. Meiosis explains Mendel’s principles
Gene locus
When genes are located on separate chromosomes, they sort independently of each other during meiosis
Crossing over allows genes on the same chromosome to sort independently
The tendency for alleles on one chromosome to be inherited together is called genetic linkage…the closer the 2 genes are on a chromosome, the greater the genetic linkage…the farther apart they are, the more likely a cross over will occur

27. Sex-linked traits have unique inheritance patterns
Eggs contain what kind of chromosome? X
Sperm contain what kind of chromosome?
Half have X and half have Y
An offspring’s sex is determined by whether or not the sperm cell carries an X or a Y
Any gene that is located on a sex chromosome is called a sex-linked gene
In humans, most are on the X chromosome

28. Sex-linked traits have unique inheritance patterns
Thomas Morgan
Fruit flies
Sex-linked disorders
Red-green colorblindness
X-linked recessive
Recessive sex-linked traits are
much more common in men than
in women

31. Pedigrees
Family tree that records and traces the occurrence of a trait in a family
Circles = females
Squares = males
Horizontal lines connecting a square to a circle means the couple had children

32. Pedigrees
If shape has two colors the person in a carrier