1. Chapter 12 Mendel’s Genetics

2. 12.1 Mendel’s Experiments Gregor Mendel started breeding pea plants
Cross fertilized traits and recorded offspring
Monohybrid cross: Breeding experiment in which individuals True breeding for one gene are crossed
Dihybrid cross: Breeding experiment where individuals true breeding for two traits
Frequency of traits among offspring offers information about relationship between the alleles
Began to formulate how inheritance works

4. An individual carrying identical alleles for a gene are homozygous
An individual carrying two different alleles of a gene is heterozygous
Hybrids are heterozygous offspring of a cross between individuals that breed true for different forms of a trait
The particular set of alleles that an individual carries is their genotype
The observable traits, such as flower color, make up an individual’s phenotype

5. 12.2 Characteristics of Traits
Testcross are breeding experiments used to describe Genotype and phenotype
An allele is dominant when its effect masks that of a recessive allele paired with it.
An individual that has a dominant trait (but an unknown genotype) is crossed with one that is homozygous recessive
Incomplete dominance
One allele is not fully dominant over another
The heterozygous phenotype is between the two homozygous phenotypes

7. P Generation Red White RR rr Gametes R r F1 Generation Pink Rr 1 2 1 2
Figure 9.18 Incomplete dominance in snapdragons. (Step 3)
F2 Generation
Sperm 1 2 1 2 R r 1 2 R RR Rr
Eggs 1 2 r Rr rr
Figure

8. Mendel’s Laws of Inheritance
Law of segregation: The pairs of genes are separated during meiosis and end up on different gametes
The 3:1 phenotype ratios in F2 became the basis of Mendel’s law of segregation
Law of independent assortment: a pair of genes distributed into gametes independently of other gene pairs
Mendel discovered the 9:3:3:1 ratio in his dihybrid experiments
Each trait still kept its individual 3:1 ratio

10. Codominance
Two alleles are fully expressed in heterozygous
Multiple allele systems – gene have more than two alleles in a population

11. Epistasis: the effect in which a trait is influenced by the products of multiple genes
Example: Fur color in mice

13. Chapter 13

14. Chromosomal Theory of Inheritance
Each gene has specific location on a particular chromosome is called a locus
Because there are more genes than there are chromosomes
Genes on the same chromosome (linked) will not obey Law of Independent Assortment

15. Recombinant phenotypes 17%
Dihybrid testcross
Gray body,
long wings
(wild-type)
Black body,
short wings
(mutant)
GgLl
ggll
Female
Male
Results
Offspring
Gray-long
GgLl
Black-short
ggll
Gray-short
Ggll
Black-long
ggLl
Figure 9.25 Thomas Morgan's experiment and results.
965
944
206
185
Parental phenotypes 83%
Recombinant phenotypes 17%
Figure

16. Recombinant phenotypes 17%
Dihybrid testcross
Gray body,
long wings
(wild-type)
Black body,
short wings
(mutant)
GgLl
ggll
Female
Male
Results
Offspring
Gray-long
GgLl
Black-short
ggll
Gray-short
Ggll
Black-long
ggLl
Figure 9.25 Thomas Morgan's experiment and results.
944
185
206
965 re
Parental phenotypes 83%
Recombinant phenotypes 17%

17. Linkage Map Linkage group – all genes on a chromosome
Genes far apart on a chromosome sort independently by crossing over
Close genes are normally not separated
Determines relative position on a chromosome

19. Chromosomal genetic disorders
Aneuploidy - individual’s cells have too many or too few copies of a chromosome
Most cases of autosomal aneuploidy are lethal in embryos
Trisomy 21 (Down syndrome) - 1/700 births
Risk increases with maternal age
In individuals with trisomy (XXY, XXX, and XYY), effects can be subtle and may never be diagnosed
Turner syndrome have an X chromosome and no X or Y

22. X-linked Traits X-linked recessive pattern
Men can transmit an X-linked allele to daughters
Only a woman can pass an X-linked allele to a son
Color Blindness
Hemophilia