Chapter 11: Introduction to Genetics
Section 11-1: The Work of Gregor Mendel
Gregor Mendel
• Genetics –
• Gregor Mendel –
Mendel bred (“crossed”) plants with 7 different traits, each trait could turn out 2 different ways.
P generation – original pair of plants
F1 generation – “first generation,” P generation’s offspring
F2 generation – “second generation, F1 generation’s offspring
Genotype & Phenotype
·
o Examples:
· Mendel knew families tended to have similar phenotypes… and he wanted to know why.
Mendel’s Experiments
He crossed peas with the same phenotypes, and peas with different phenotypes, then counted how many of their offspring shared their parents’ traits.
Mendel made four conclusions:
1. Inheritance
After his death, other scientists discovered:
· Genes -
· Alleles -
o
Example: All peas inherit a gene for the “seed color” trait. There are two versions (alleles) of the gene: green and yellow.
Practice: All humans inherit a gene for blood type. What are the different alleles for that gene?
2. Mendel’s Law of Dominance:
· Dominant allele –
o
· Recessive allele –
o
Genotype =
Rules for writing:
· Gene & allele examples:
· Genotype examples:
· Mendel learned that
Practice
If G is the allele for pointy ears and g is the allele for floppy ears, what will be the ear shape phenotypes of puppies with these genotypes?
The dominant allele is ___ for the trait ______
The recessive allele is ___ for the trait ______
Genotype GG = Phenotype ______
Genotype Gg = Phenotype ______
Genotype gg = Phenotype ______
Also, H is for a pink nose and h is for a black nose.
Genotype GGHH = Phenotype ______
Genotype GgHh = Phenotype ______
Genotype gghh = Phenotype ______
Genotype GGhh = Phenotype ______
Genotype Gghh = Phenotype ______
Genotype ggHH = Phenotype ______
Which of these are traits and which are phenotypes?
1. Finger length ______
2. Blue eyes ______
3. Long hair ______
4. Number of leaves ______
5. Shape of tentacles ______
6. Warbling song ______
Which of these are alleles and which are traits?
1. Eye color ______
2. Bone integrity ______
3. i ______
4. Insulin shape ______
5. B ______
6. Na ______
Which of these are phenotypes and which are genotypes?
1. Curly hair ______
2. Jj ______
3. PP ______
4. Arthritic knees ______
5. Type B blood ______
6. Spotted fur and a pink nose ______
7. HHGg ______
8. Purple leaves and spiny stem ______
Summary Example
In an alien species, there is a gene for the ______trait. This trait can express as one of two phenotypes: an individual has ______or ______.
The allele for ______is A, the allele for ______is a.
If your genotype is Aa, your phenotype will be ______.
Mendel found that if he crossed peas with different phenotypes for a trait, all the F1 plants would have the same dominant phenotype. He wondered if the recessive allele had disappeared… so he let the F1 plants self-pollinate, creating the F2 generation. The recessive phenotype reappeared in 1/4th of the F2 generation!
3. Mendel’s Law of Segregation:
·
Practicing the Law of Segregation
If an individual’s genotype is YY, all of that individual’s gametes will have just ONE Y allele.
If an individual’s genotype is Tt, that individual’s gametes will have EITHER the T allele OR the t allele, not both.
(Some gametes are written with more than one letter. If Dad’s genotype is LTLt, he will make a sperm that has the LT allele or a sperm that has the Lt allele.)
1. Genotype YY makes gamete Y or gamete Y.
2. Genotype Tt makes gamete T or gamete t.
3. Genotype bb makes gamete _ or gamete _
4. Genotype Ii makes gamete _ or gamete _
5. Genotype K1K2 makes gamete _ or gamete _
(4. Final conclusion appears later in the notes.)
Overview
¢ Suppose there’s a gene for eye color, with the alleles B for brown eyes or b for blue eyes.
¢ A woman has the genotype Bb, which gives her the phenotype brown eyes.
¢ Meiosis produces her gametes…
She can make gametes that are EITHER B or b. Half of her gametes will be one, half will be the other.