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BIOLOGY Ch -8 notes
MENDEL AND HEREDITY
Heredity –
Genetics –
Mendel worked with the Pea plant –
Useful Features in Peas:
Several traits of the garden pea exist in two clearly different forms.
1. The flower color is either purple or white— there are no intermediate forms. Table 1
shows the seven traits that Mendel chose to study.
2. The male and female reproductive parts of garden peas are enclosed within the same
flower. You can control mating by allowing a flower to fertilize itself (self-fertilization),
or you can transfer the pollen to another flower on a different plant (crosspollination).
3. The garden pea is small, grows easily, matures quickly, and produces many offspring.
Thus, results can be obtained quickly, and there are plenty of subjects to count.
The Seven Traits Mendel Studied and Their Contrasting Forms:
1
MONOHYBRID CROSS –
True Breeding –
Three steps of Mendel’s experiments:
Draw figure ___
2
MENDEL’s HYPOTHESIS
1. For each inherited trait, an individual has two copies of the gene—one from each
parent.
2. There are alternative versions of genes. For example, the gene for flower color in peas
can exist in a “purple” version or a “white” version. Today the different versions of a
gene are called its ____________
3. When two different alleles occur together, one of them may be completely expressed,
while the other may have no observable effect on the organism’s appearance. Mendel
described the expressed form of the trait as __________________.
The trait that was not expressed when the dominant form of the trait was present was
described as _____________
4. When gametes are formed, the alleles for each gene in an individual separate
independently of one another. Thus, gametes carry only one allele for each inherited trait.
When gametes unite during fertilization, each gamete contributes one allele.
Homozygous –
Heterozygous –
Genotype –
Phenotype –
Dominant trait
Recessive trait
THE LAWS OF HEREDITY
The Law of segregation –
3
The Law of independent assortment –
Studying heredity:
PUNNETT SQUARES
One pair of contrasting traits:
Monohybrid Cross –homozygous plants
Monohybrid Cross –heterozygous plants
4
TEST CROSS -
Probability-
Pedigree-
Autosomal trait-
Sex linked trait -
Two pairs of contrasting traits:
DIHYBRID CROSS
5
COMPLEX PATTERNS OF HEREDITY
Polygenic trait
Incomplete dominance
Multiple alleles
Codominance
Traits influenced by the environment
6
GENETIC
DISORDER
DOMINANT OR
RECESSIVE
SYMPTOMS
Sickle cell anemia
Hypercholesterolemia
Tay Sachs disease
Cystic fibrosis
Hemophilia A
Huntington's disease
GENE THERAPY
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