1. Chapter 10

2. Mendel’s Pea Plant Experiments

3. Gregor Johann Mendel Austrian monk
Studied the inheritance of traits in pea plants
Developed the laws of inheritance
He found that the plants' offspring retained traits of the parents
He did not know at the time he was observing allele/gene inheritance

4. Site of Gregor Mendel’s experimental garden in the Czech Republic
Mendelian Genetics
5/19/2019
Site of Gregor Mendel’s experimental garden in the Czech Republic
Fig. 5.co

5. Particulate Inheritance
Mendel stated that physical traits are inherited as “particles”
Mendel did not know that the “particles” were actually chromosomes & DNA

6. How Mendel Began
Mendel produced pure strains by allowing the plants to self-pollinate for several generations

9. Mendel’s Experimental Results

10. Did the observed ratio match the theoretical ratio?
The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled
Yes, as Mendel’s observed ratio was 2.96:1
The discrepancy is due to statistical error
The larger the sample, the more the results approximate to the theoretical ratio

11. Summary of Mendel’s laws
PARENT CROSS
OFFSPRING
DOMINANCE
TT x tt tall x short
100% Tt tall
SEGREGATION
Tt x Tt tall x tall
75% tall 25% short
INDEPENDENT ASSORTMENT
RrGg x RrGg round & green x round & green
9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods

12. Law of Dominance
This law of Mendel’s states that traits are either dominant or recessive
The law does NOT apply to codominant inheritance!!

13. Law of Segregation
During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other and only 1 allele is inherited per gamete.
Alleles can be equally passed onto male or female offspring

14. Applying the Law of Segregation

15. This law does not consider nondisjunction or sex-linked genes

16. Law of Independent Assortment
Alleles for different traits are distributed to sex cells (& offspring) independently of one another.
This law does NOT apply to linked genes and does not consider random reassortment in meiosis.

17. Traits are controlled by 2 “factors”
Since he only examined dominant and recessive traits, he concluded only 2 factors (alleles) control each trait
This law does not apply to multiple alleles or polygenic traits (traits coded for by more than one gene…e.g. skin colour)

18. Other exceptions from Mendels Laws
Mutations (the traits he examined remained the same and stable throughout generations)

19. DNA – Discovered after Mendel
Structure
Double helix
Made of nucleotides
Nucleotides joined
via bonds between
the phosphates
and sugars
(phosphodiester bond)

21. DNA has direction DNA has a 5’ and a 3’ end
The strands run ANTIPARALLEL (they run in opposite directions to eachother)

22. Weak hydrogen bonds are between complementary base pairs

23. Chargaff’s Rule The proportions of the bases A and T are equal
The proportions of the bases G and C are equal
Indicated that A binds to T, and G binds with C (or vice versa)

24. Some terms…..
Dissociation – the separation of both DNA strands, using heat, to break hydrogen bonds between complementary base pairs
Re-association – the binding of both DNA strands to each other again when DNA is cooled
Hybridisation – pairing of complementary base pairs from different sources

26. Mitochondrial DNA Chloroplasts and mitochondria have DNA too.
Their DNA is circular and codes for proteins and RNA required for photosynthesis or cellular
respiration

27. Mitochondrial DNA (mtDNA)
D – loop: non-coding region of mtDNA.
The part where mtDNA replication begins from
The part where most mutations occur

28. mtDNA is passed from the mother to sons and daughters (no paternal mt DNA is in any children)

29. Gene Sequencing
Identifying the order (sequence) of nucleotides in a gene
Done using computers
Can identify genetic disorders, identify products of genes, compare sequences of different species to determine how closely related they are or which species proteins might be used in humans (e.g. insulin)
Human Genome Project – aims to sequence all the human genome

30. Single Nucleotide Polymorphisms (SNP’s)
Not everyone’s genome is identical
Many of the differences are due to single base changes (called SNP’s) in non-coding regions of DNA (regions between genes or in non-coding regions within a gene – called introns)
Base changes in coding regions could alter protein function

31. SNP’s

32. Introns and Exons
Introns are NON-CODING regions in a gene. They do not contribute to the code for the protein that the gene codes for.

33. There are also non-coding regions between genes
Regulatory sequence – controls switching genes on or off, and how fast the gene is decoded
Coding region – codes for protein

34. Gene structure
Flanking region – regions either side of the coding region. Includes:
Upstream region – the region before the coding region
- contains the START codon (3 nucleotide sequence signalling the start of the coding region)
contains regulatory sequences (control the gene being switched on or off, and how fast it is transcribed)
Downstream region – the region after the coding region
- contains the STOP codon (3 nucleotide sequence to signal the end of the coding region)

35. Gene structure Flanking regions (non-coding) Upstream region
Downstream region

36. Comparative Genomics
Comparing gene sequences, and chromosome number and structure (karyotypes) between species
Can show how closely related, according to evolution, species are to each other
Can also show conserved genes – genes present in multiple species and therefore carry out important functions for survival.

37. More terms…. Also discovered in comparative genomics:
Gene duplication – when multiple copies of a gene are present in a species
Horizontal gene transfer – a gene from one species transfers to another species

38. Horizontal gene transfer example