Section 10.1. pg. 253. Mendel’s Laws of Heredity. WHY MENDEL SUCCEEDED. Gregor Mendel (1822-1884) Austrian Monk known as the “father of modern genetics” Found that inheritance follows certain laws later known as Mendel’s Laws of Inheritance
Mendel’s Laws of Heredity
Gregor Mendel (1822-1884)
Austrian Monk known as the “father of modern genetics”
Found that inheritance follows certain laws later known as Mendel’s Laws of Inheritance
Heredity is the passing on of characteristics from parent to offspring
Inherited characteristics are called traits(factors)
The branch of biology that studies heredity is called genetics – which was founded upon the rediscovery of his work.
Mendel’s pea plant collection contained around 28,000 plants
Pea plants reproduce sexually by producing male and female sex cells (gametes)
Male gamete forms in pollen
Female gamete formed in ovary
Fertilization occurs when the male gamete unites with the female gamete
Pollination is the transfer of pollen to ovary in a plant – normal reproduction.
Remove male parts
Snipping the stamen could prevent self-pollination
A similar figure is in the book on pg. 642
Cross-pollination is transferring pollen of one plant to the ovary of another plant
Mendel did this to get certain plants to breed with others to be sure of the parents
Mendel was very careful with all of his work
Short pea plant
Tall pea plant
Mendel was able to create tall plants and short plants (purebreds)
He referred to the offspring of a purebred tall and a purebred short as a hybrid
Crossing a 6’ tall plant with a 2’ tall (short) plant resulted in all 6’ tall plants
Crossing the hybrid offspring resulted in 75% tall and 25% short
P1 refers to the “Parental generation”
F1 (“Filial”) refers to the offspring
All tall pea plants
3 tall: 1 short
So what does MONOHYBRID refer to?
Referring to figure 10.3:
When Mendel crossed a purebred tall with a purebred short he got all tall plants
When he crossed a purebred purple flower with a purebred white flower he got all purple flowers
He referred to the trait that was observed in these cases as ___________.
The trait that seemed to “disappear” he called _____________.
Mendel concluded that these plants have “factors” that control each of the traits (color, shape, height)
We call these factors genes (parts of DNA)
Alternative forms of genes (tall vs. short or yellow vs. green) are known as alleles.
These two alleles for each trait can be expressed as a single letter
For plant height we can use the letters “T” & “t”
Dominant allele is ___.
Recessive is ___.
Mendel’s purebred tall plants were “TT”
His purebred recessive plants were “tt”
Fill in the blanks in the figure to the right which t goes where?
All tall plants
Mendel concluded that the allele (gene form) of tall plants was dominant to the allele for short plants
Confirming that the plants had two alleles for each trait (TT = Tall, Tt = Tall, or tt = short)
Knowing that traits are inherited from parents, he also concluded that these alleles are inherited
However a plant can only get one allele from each parent
The gametes (sex cells) contained either one or the other form of the gene (T or t)
The Law of _________________ states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles.
It’s vocab time…
Phenotype refers to the organism’s physical characteristic (what you can see) Ex: Tall
Genotype refers to the organism’s genetic makeup (what you can’t see) Ex: TT or Tt
Homozygous/purebred represents two alleles that are the same (TT or tt)
Heterozygous/hybrid organisms have different alleles (Tt)
How are we going to distinguish Homo and Hetero?
Law of Dominance states that hybrid organisms (Tt) will express the dominant allele (ex: tall).
1905 - Reginald Punnett devised an easy way to find expected genotype proportions of offspring from known parent genotypes based off Mendel’s laws
G= 50% Tt : 25% TT : 25% tt
P= 3 Tall : 1 short
Monohybrid crosses are easy to separate alleles according to Mendel’s Law of Segregation
If we have heterozygous parents (Tt X Tt) we can just separate the T from the t
For Dihybrid crosses, the gamete separation is a little tricky
If we have two parents that are heterozygous for seed shape (Rr) and seed color (Yy) their genotype is RrYy
To separate alleles into gametes we use the FOIL method from algebra
RrYy makes four different gametes
Using the FOIL method we get…
Mendel also crossed plants with two different traits
Round=R, wrinkled=r & Yellow=Y, green=y
What is the genotype of a purebred (homozygous) plant with Round Yellow seeds?
What is the genotype of a purebred (homozygous) plant with wrinkled green seeds?
Purebred (homozygous) RoundYellow seeds X Purebred (homozygous) wrinkledgreen seeds
Result of F1…All plants had Round Yellow seeds
However crossing the Dihybrid F1 gives a ratio of 9:3:3:1
Which leads us to Mendel’s second law…
The Law of __________________ states that genes for different traits are inherited independently of each other.
All Round Yellow
Starting here what are the gametes?
Gametes from RrYy parent
Given the parents genotype and number of offspring, you should be able to predict the number of each genotype and phenotype.
R=Round seeds & r=wrinkled seeds
1. P1 genotype: RR X rr
2. All of the F1 offspring will be ______.
3. Assume 140 F2 offspring are created from F1.
4. ________ will have their parents (F1) genotype.
5. ________ will have Round seeds.
6. ________ will have wrinkled seeds.
7. ________ will have the same genotype as the P1.