All of the plants in the next generation were tall.
These are the results Mendel obtained when he crossed two heterozygotes.
‘Paint-pot’ theory of inheritance
Mendel’s finding was contrary to the prediction of the ‘Paint-pot’ theory of
inheritance
Mendel’s 1st law-law of segregation
Mendel’s law of segregation -explanation of monohybrid ratio
Mendel described patterns of inheritance in the 1860s, but it wasn’t until the early 1900s that inherited traits,
genes, were linked to cellular structures called chromosomes. The number of chromosomes varies among species, but all chromosomes contain genes
arranged linearly at specific locations, called loci.
This is how geneticists today represent the cross from the previous screen. The original plants are the P generation and their offspring are the F1 generation. The
T and t symbols represent dominant and recessive alleles of a single gene.
we breed the offspring to one another in the
cross Tt x Tt, and wish to predict the results
we need to follow the production of gametes
during meiosis.
These individuals make gametes with either T or t in equal
numbers.
The chance of gametes of different types encountering one another is represented on a Punnett square.
The genotypic ratio of homozygous dominant: heterozygous: homozygous recessive individuals is 1:2:1.
Many genetics problems will fall in the category of a monohybrid cross. They all can be approached using
the model above
Testcross. a heterozygote was crossed with a homozygous recessive individual.
A situation in which an individual of dominant phenotype, but of unknown genotype, is crossed with one or more recessive individuals. This can provide information on the unknown genotype.
Dihybrid cross
Dihybrid cross
Dihybrid cross
The inheritance of two contrasting characters were considered at the same time
Law of independent assortment
Mendel’s 2nd law
Mendel’s 2nd law
explained byobserving
movement of chromosomes at
meiosis
Cell division
The cell cycle
Interphase
Interphase
Mitosis – division of the nucleus
Prophase
metaphase
anaphase
telophase
Division of the nucleus
Division of the cytoplasm
Produce identical daughter cells
Mitosis and cell cycle
Meiosis
• Reduction division
• Generate variability in gametes
Meiosis-Interphase
Meiosis-prophase I
Meiosis-metaphase I
Meiosis-anaphase I
Meiosis-telophase I
Meiosis I -animated
Meiosis II
anaphase II
metaphase II
prophase II
telophase II
Meiosis II -animated
Meiosis-overall
Independent assortment
Crossing over
Anaphase I and II
note new gene combinations as a result of crossing
over
Comparing Mitosis
and Meiosis
Comparing Mitosis
and Meiosis
Incomplete dominance
In some cases, alleles may not interact in a dominant/recessive pattern. Heterozygotes have an intermediate phenotype or express both alleles. The genotypic ratio will match the phenotypic ratio. Snapdragons demonstrate incomplete dominance.
Incomplete dominance II
Multiple allele
Linkage and crossing-over
Recombinant frequency
Skin colour_a pair of twin sisters
Continuous or discontinuous
Polygenic effects on genetic variation
Polygenic inheritance_skin colour
Skin colour is a
continuous variation
because…
How would U explain the very different skin colour of the twin sisters?