Download Bio 101 Section 001

Bio 101 Section 001 – Handout 17
Reading:
Mendel and the Principles of Genetics
7.1-7.5
Gregor Mendel
1. Why was Mendel’s Work so Important?
(a) Principles of Heredity
(b) Quantitative Approach
2. Mendel’s Study Subject
Garden pea – good choice because:
(a)
(b)
(c)
(d)
(e)
3. Mendel’s Study Design
Crosses were made between pea plants in 3 steps:
(a) Ensured a True-Breeding Parental (P) Generation
Eg.
(b) Crossed 2 True-Breeding Pea Varieties with Alternate Traits ⇒ First Filial (F1)
Generation
Eg. P Generation
⇓
F1 Generation
(c) Self-Fertilized the F1 Generation ⇒ F2 Generation
Principles of Genetics
(These are the basic discoveries of Mendel, written up in terms of current biological
knowledge).
1. Genes
2. Homologous Chromosomes
(a)
(b) Terminology
(i) Homozygous
(ii) Heterozygous
3. Alleles
(a) Definition
(b) Dominant and Recessive Alleles
(i)
(ii)
Eg. Dominant –
Recessive –
Heterozygous –
4. Genotype and phenotype
(a) Genotype
(b) Phenotype
Mendel’s Experiments
Monohybrid Cross
Read about Mendel’s reasoning – remember that he did not know the mechanism
of heredity.
Used Plants true-breeding for flower color in the P generation:
P Generation (Cross)
Phenotypes used
Purple X White
Genotypes
PP
pp
Gametes
Punnett Square:
Gametes
P
P
p
F1 Generation
Genotype
Phenotype
F1 Generation (Cross)
Phenotypes
Purple X Purple
Genotype
Gametes
Punnett Square:
Gametes
p
F2 Generation
Genotypes
Ratio
Phenotypes
Ratio
Mendel’s Actual Results for the F2 Generation:
Mendel saw this ratio in all 7 traits he examined.
Testcross
1. Description
2. Mendel’s Example
(a) Question (try writing a prediction for the experiment below)
(b) Experiment
(c) Results
Phenotype
Generation
Purple X White
F2
P
(i) When F2 is HomozygousDominant:
Cross
Gametes
Progeny Genotype(s)
Ratio
(ii) When F2 is Heterozygous:
Gametes
Therefore,
Dihybrid Cross
The inheritance of pairs of genes.
Mendel’s Example
Examined 2 traits at once, in this example, the traits for seed shape and color.
Seed Shape
Phenotype:
Allele:
Seed Color
Round Vs Wrinkled
R
r
Yellow Vs Green
Y
y
P Generation (Cross)
True breeding individuals that were homozygous dominant for both traits with
individuals that were homozygous recessive for both traits.
Phenotype
Genotype
Homozygous dominant X Homozygous recessive
Round, yellow
Wrinkled green
RRYY
rryy
Gametes
Punnett Square:
Gametes
RY
F1 Generation:
Phenotype
ry
F1 Generation (Cross)
Phenotypes
Genotypes
Gametes
Punnett Square:
Gametes
Complete the above table on your own.
Figure 7.10
Results
Mendel got a __________ ratio:
Mendel’s Laws
(In “modern” biological Terms)
Mendel’s First Law – Segregation
In Terms of Meiosis:
Mendel’s Second Law – Independent Assortment
In Terms of Meiosis: