Genotype DETERMINES Phenotype
Genetics: The study of the inheritance of observable traits from one generation to the
next, and their affect on populations and species.
Molecular Biology: The study of molecular processes involved in the transfer of genetic
information from GENOTYPE to PHENOTYPE of an organism.
Why study Genetics and Molecular Biology?
Human & Vet Medicine
Lawyer, Police, Forensics
Genotype determines Phenotype
Phenotype: An organism’s physical and biochemical traits. (e.g. flower colour, ear shape
genetic disease, etc.)
Genotype: An organism’s genetic makeup, the genetic information, contained in genes.
Mitosis and Meiosis
Relationship between gene, DNA and chromosome.
Stage of mitosis/meiosis
Structure of the DNA molecule
DNA molecule is made up of subunit with chemical units that have been
abbreviated A, C, T and G (organized in a certain way)
Inside the nucleus
Chromosomes contain DNA, DNA has the genetic language
During cell division, we can see the chromosomes under a light microscope
Structure of a Eukaryotic Chromosome
Centromere (constricted region of chromosome)
Telomere (end of chromosome)
Replicate DNA during cell division
Two Sister Chromatids are held together in the center by a centromere
▯one centromere, one chromosome
Pair them according to their shape and size
▯Karyotype of that organism Pairs of chromosome with the same size and shape (i.e. morphology) are called
Chromosomes Number in Eukaryotes
Number of chromosomes differs form species to species, but are always a multiple of two
While the human sex chromosomes, X and Y, have different morphology, they are still
referred to as homologous chromosomes.
Chromosomes consist of DNA and Protein
DNA is complexed with proteins called histones.
DNA + Protein = chromatin
Several conformations (types) of chromatin exist in the nucleus of living cells.
Average chromosome = 5cm of DNA
46 chromosomes = 230 cm
Human nucleus diameter =10mm
Tennis ball = 7 cm
16 Km of DNA in a tennis ball
Organization of DNA in Chromatin (Hierarchial Structure of a Chromosome)
• First Level
DNA’s are wrapped twice around balls of protein.
▯Beadsonastring or 10nm Fibre
Each bead is called Nucleosome
• Second Level
▯ 0 nm Fibre AKA Solenoid Structure
• Third Level
▯Organized in Chromosome Looped Domains
• Fourth Level
This is what we see under the light microscope during cell division
▯ he Metaphase Chromosome
Cell Cycle Interphase
G1 (Growth), S (Growth and DNA Replication), and G2 (Growth and final
preparation for division)
Mitosis ▯essential process
chromosomal DNA becomes more condense/more packaged
Centrioles start to appear
Chromosomes line up in the equator (metaphase plate) of the cell
Microtubules fibres are attached to the centromeres of the sister chromatids
Centromeres splits sister chromatids at the opposite poles of the cell
Double the amount of DNA
Sister chromatids at mitotic metaphase
Nuclear envelope start to appear around the chromosomes
Chromosomes starts to recondense
Cytokenesis (happens outside mitosis)
Most of the cells in your body have exactly the same chromosomes.
Asexual Reproduction (mitosis, cell division)
Gametes (eggs & sperm) of an organism contain a single basic complement (haploid) of
The zygote produced by fusion of egg and sperm (and the adult from the zygote) contains
in each cell two copies of each chromosome (diploid).
Fusion of haploid gametes to form a new diploid cell is FERTILIZATION or
Meiosis The cellular process of reducing the diploid complement of chromosomes to a haploid
complement of chromosomes to produce sex cells (gametes), an essential process for
2 cell divisions
Diploid (2N) > Haploid (1N)
Meiotic Division 1
chromatin condenses into chromosomes
homologous chromosomes pair up together
homologous chromosomes separates NOT sister chromatids
Telophase 1 and Cytokinesis
gives us two cells
Homologous Chromosomes pair at Metaphase of Meiotic Division 1
homologous chromosome goes one way, and the other homologous chromosome
goes the other way.
Meiotic Division II
Telophase II and Cytokinesis
4 daughter cells
Genetic variation that benefits the survival of a sexually reproducing species.
Patterns of Inheritance Mendel’s Law of:
Segregation of traits
Independent assortment of traits
Deviations from Mendel’s Laws:
Traits not on nuclear chromosomes
Traits on the same chromosome
Traits on sex chromosomes
Incomplete dominance; multiple alleles; codominance; lethal alleles
Charles Darwin in 1859, the year he published The Origin of Species.
Inherited variation has to be evident in a population for evolution to happen in a natural
selection. Darwin didn’t like the “blending” hypothesis.
Gregor Mendel used garden peas in his experiment.
The Garden Pea: A Genetic Model
1. Easy to grow
2. Varieties with easily distinguishable traits
3. True breeding varieties, i.e. a particular trait was consistently inherited from
generation to the next.
4. Crossfertilize (Crossmate) and selffertilize (Selfmate) different varieties of
Purple x White (Parentals or P Generation)
All 100% Purple (Filial, F1 Generation)
[then he selffertilized them]
Purple : White (F2 Generation)
3 : 1 Ratio
2 units of heredity
separated in the production of sex gametes
1 variance appeared in the F1 generation, and the other one didn’t
▯Purple trait (Dominant, P) is dominant to the White trait (Recessive, p)
Each Plant has 2 units of heredity
To get the true breeding Purple ▯PP
To get the true breeding White ▯pp
p p Pp Pp
PP or pp = Homozygous (same)
Pp = Heterozygous (different)
Allele – variant of a trait
Punnett Squares are used to determine genotypes
The Testcross – determine genotypes
Mendel’s Law of Heredity
1. The segregation of traits
Allelic Variants on Homologous Chromosomes
Locus – point on the chromosome
Important Genetics Terminology
Alleles: alternative versions of a gene, e.g., purple and white flowers.
Dominant and Recessive Alleles: If two alleles differ, the one, the dominant allele, is
fully expressed in the organism’s appearance, the other, the recessive allele, has no
noticeable effect on the organism’s phenotype.
Homozygous: an organism with a pair of identical alleles.
Heterozygous: an organism with two different alleles for a character.
Dihybrid Cross Showing Independent Assortment of Traits
Two peas with two traits each with two variance and crossed them.
P generation ▯Round yellow seeds (WWGG) x Wrinkled green seeds (wwgg)
F1 generation ▯all round yellow seeds
F2 generation ▯9/16 round yellow, 3/16 round green, 3/16 wrinkled green, 1/16 wrinkled
green [Ratio was 9:3:3:1 ] ▯called this experiment Dihybrid Cross
Monohybrid Cross ▯Ratio 3:1
Mendel’s Second Law of Heredity
2. Independent assortment of traits
Traits have to be on different chromosomes in order for this to happen.
Deviations from Mendel’s Law
a. Some traits not on nuclear chromosomes, e.g., mitochondrial or chloroplast
In Eukaryotic cells, they are organelles that have pieces of genes.
▯ itochondria and chloroplast
Sperms and pollen don’t have mitochondrial DNA. Eggs have mitochondria.
▯ raits that determined by the mitochondria are from the mother.
b. Traits on the same chromosome
If there is no Dihybrid cross (9:3:3:1 ratio), then the traits are on the same
c. Traits carried on sexchromosomes e.g., mammals XX female, XY male
[Recessive traits that are carried on the X chromosome are evident in males, and
not in females]; birds ZW females, ZZ males.
Other Deviations from Mendel’s Laws:
1. Incomplete dominance
Red ( R1R1) x White (R2R2)
Pink (R1R2) [selfreplicate]
R1 R1R1 R1R2
R2 R2R1 R2R2
F2 Generation has the ration of 1:2:1.
2. Multiple alleles
3. Codominance – 1 allele doesn’t mask the other allele
4. Lethal alleles – genes that kill
Huntington’s Disease (only need 1 copy) (50’s60’s years old)
Sickle Cell Anemia (10 years old)
Miscarriages FF <<