This document discusses Mendelian genetics and Gregor Mendel's experiments with pea plants. It covers key concepts such as genotype and phenotype, Mendel's experimental design using true-breeding pea traits, his findings on monohybrid and dihybrid crosses, and the principles of segregation and independent assortment. It also discusses how Mendelian genetics applies to inheritance patterns in humans through pedigree analysis and examples of genetic traits.

1. Mendelian Genetics
Chapter 2

2. Phenotype and Genotype

3. Genotype and Phenotype
• Genotype – genetic
constitution of an organism
• Phenotype – observable
characteristic
• Genotype and environment
• Contribution of environment
varies between genes
• Can be controlled by many
genes
• Random developmental
events

4. Mendel’s Experimental Design

5. Mendelian Genetics
• Modern genetics began with
Gregor Mendel’s quantitative
genetic experiments
• Austrian monk
• Mathematician
• Numerical and observational
data
• Several generations Stamen
Carpel

6. Mendelian Genetics
• Heritable, obvious traits
• Simple crosses at first
• Used peas because:
• Easy to grow and available
• Many distinguishable
characteristics
• Self-fertilization
• True breeding peas

7. Pea Traits

8. Monohybrid Crosses and Mendel’s
Principle of Segregation

9. Breeding Crosses
• Initial cross is the P generation
• Parents
• Progeny of parents is first filial generation
• F1 generation
• Inbreeding of first generation creates
second filial generation
• F2 generation

10. Monohybrid Crosses
• Cross between true-
breeding individuals with
one different trait
• Mendel’s first crosses
• Resembled only one of
the parents
• Planted progeny and
allowed self-fertilization
• Revealed both phenotypes

11. Monohybrid Cross
• Mendel determined that P PLANTS
GENETIC MAKEUP (ALLELES)
PP pp
• Particulate factors for Gametes All All
genes, each contains a set P p
of two F1 PLANTS
All Pp
(hybrids)
• Transmitted by both parents Gametes 1
/2 P 1
/2 p
• Alternate forms called
alleles Eggs
P
P
P
Sperm
F2 PLANTS p P p
• True breeding forms Phenotypic ratio
3 purple : 1
P
p
P
p
contains identical set white
Genotypic ratio
1 PP : 2 Pp : 1 pp
p
p

12. Monohybrid Cross
• F1 generation had both alleles
• Only one expresses
• One allele masks
• Dominant
• Recessive
• Identical alleles – homozygous
• Different alleles - heterozygous

14. Monohybrid Cross

15. Principle of Segregation
• Recessive
characteristics are
masked
• Reappear in F2
• Members of a gene
pair (alleles)
segregated during
gamete formation

16. How cells carry characteristics
• Genes on chromosomes
• At a specific loci
• Homologous pairs carry the
same genes at the same
locus
• Different versions
• Separation of homologous
chromosomes yields
separation of alleles

17. Branch Diagrams
• Punnett squares can
become messy with
more than one gene
• Use branch diagram
to figure out genotype
and phenotype
expected frequency

18. Test Cross
• Mendel did several TESTCROSS:
crosses
• Followed over several GENOTYPES B_ bb
generations
Two possibilities for the black dog:
• Selfing also very BB or Bb
important
• Allowed plants to GAMETES
B B b
reveal their genotype
and not just their b Bb b Bb bb
phenotye OFFSPRING
All black 1 black : 1 chocolate

19. Test
Cross

20. Recessive Alleles
• Wild-type allele – functional allele
• Predominates in population
• Dominant allele
• Loss-of-function mutations – causes
protein product to be absent, partially
functional, or nonfunctional
• Recessive
• Function of other in heterozygote is sufficient

21. Wrinkled Peas
• SS type contains more
starch and lower
sucrose
• Also more water
• SBEI - starch-
branching enzyme
• Extra 800 bp piece in
mutation

22. Dihybrid and Trihybrid Crosses and
Mendel’s Principle of Independent
Assortment

23. The Principle of Independent
Assortment
• Factors for different
traits assort
independently of one
another
• Genes are inherited
independently of each
other
• Segregate randomly in
gametes
• Dihybrid Cross

25. Branch Diagram of Dihybrid Cross
P
h
e
n
o
t
y
p
e

26. Genotype vs.
Phenotype

27. Test Cross With Dihybrid

28. Trihybrid Cross

29. Tribble Traits Activity

30. Statistical Analysis of Genetic
Data: The Chi-Square Test

31. Statistical Analysis
• Data from genetics is quantitative
• Use statistics to show deviation of
observed results from predicted results
• Chance factors cause deviations
• Null-hypothesis – no difference between
the predicted and observed
• If not accepted then have to come up with a
new hypothesis for deviation

32. Chi-Square Test
• Goodness of fit test
• How much observed number deviates from
the expected number

34. Mendelian Genetics in Humans

35. Pedigree Analysis
• Inheritance patterns
are studied using
family trees
• Pedigree analysis
• Phenotypic records
• Proband is where gene
was discovered

36. Examples of Human Genetic Traits
• Most genetic disorders
are recessive
• Due to lack of function
• Homozygous recessive
expression
• Dominant usually
selected out
• Albinism

37. Characteristics of Recessive
Inheritance Traits
• Most have normal
heterozygous parents
• Heterozygotes have 3:1 ratio
• When both parents have the
trait then all progeny have
the trait
• Cystic Fibrosis, Sickle Cell
Anemia, Tay Sachs

38. Characteristics of Dominant
Inheritance Traits
• Gain of function mutations
• New property of the mutant
gene
• No loss of function
• Must have one parent with
disease
• Does not skip generations
• Will transmit to half its
progeny
• Huntingtons disease, Marfan
syndrome, achondroplasia