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MENDEL GENECTICS:The study of passing on simple traits to the next generation.
WHO IS GREGOR MENDEL? Mendel was born in Austria and after
completing college, he entered a monastery.
The monastery had a garden, and Mendel was able to use plants for his studies.
Mendel examined the patterns of inheritance.
Mendel published his work on the behavior of genes in 1865.
WHY PEAS? Mendel used peas for his studies because:
They grow into mature plants quickly (60-80 days).
They produce numerous seeds quickly. They have many observable characteristics
that come in just two choices (such as purple and white flowers).
They can self-pollinate (fertilize themselves).
MENDEL’S PEA PLANTS Mendel bred large numbers of pea plants and searched for simple patterns in seven traits of their offspring.
He studied one trait at a time (plant height, flower color, seed color, seed shape, pod shape, pod color flower position)
MENDEL’S BIG DISCOVERY!
When Mendel bred pea plants with the two traits (ex: a white flowered with a purple flowered plant) he found that one characteristic always seemed to disappear in the first generation offspring (ex: all white flowers).
Mendel called the trait that appeared the dominant trait.
The other trait that seemed to recede (go away) he called the recessive trait.
MENDEL’S BIG DISCOVERY!
Mendel allowed the first generation pea plants that showed the dominant trait to self-pollinate to produce a second generation.
When he did this, the recessive trait showed up again!
MENDEL’S BIG DISCOVERY!
Mendel then counted the number of plants with each trait that showed up in the second generation.
Mendel noticed that for each one of the seven traits the ratio of dominant trait to recessive trait in second generation was about 3:1.
The probability that the second generation has the recessive trait is ¼.
MENDEL’S APPLICATION OF THE RATIO
Mendel realized that his results could only be explained if each plant has two copies of the gene for each characteristic.
These two copies are called alleles. Each pea plant receives only one allele for
each characteristic from each parent and ends up with two alleles of its own.
PUNNETT SQUARE A Punnett square is a diagram used to show all
the possible combinations of alleles from parents. You can use Punnett squares to predict the
chances that each kind of offspring will occur. Dominant alleles are symbolized with capital
letters (TT). Recessive alleles are symbolized
by lowercase letters. (tt).
PUNNETT SQUARE An organism that has only one kind of allele for a characteristic is called homozygous (ex: PP or pp).
An organism that has alleles for two different traits is called heterozygous (ex: Pp).
PUNNETT SQUARE – GENOTYPE VS. PHENOTYPE Genotype – an organisms
combination of alleles. (PP) – what the genes are.
Phenotype – an organisms physical appearance. (PP = purple flower)
PUNNETT SQUARE PRACTICE
W w
W
w
PUNNETT SQUARE PRACTICE
V V
V
v
