BIO 143 Lecture Notes - Lecture 10: Homologous Chromosome, Chromosome, Heredity

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Chapter 10
Patterns of Inheritance
What is the Physical Basis of Inheritance
Inheritance is the process by which the characteristics of individuals are passed to their
offspring
Genes are the unit of heredity that encodes information needed to produce proteins, cells,
and entire organisms
Loci are the location of a gene on a chromosome
Homologous chromosomes carry the same kinds of genes for the same characteristics and
are found at the same loci on both homologous chromosomes
Alleles are alternative versions of the genes found at the same gene locus
Mutations are the sources of alleles
-arise as mutations in the nucleotide sequence in genes
-if a mutation occurs in the cells that become sperm or eggs, it can be passed on from
parent to offspring
An organisms’ two alleles may be the same or different
-each cell carries two alleles per characteristics, one on each of the two homologous
chromosomes
How Were the Principles of Inheritance Discovered
Mendel was the first to perform experiments by correctly applying three key scientific steps
to his research
1. Choosing the right organism
2. Designing and performing the experiment correctly
3. Analyzing the data properly
-unlike previous researchers, Mendel chose a simple experimental design
-he chose to study individual characteristics that had different forms, such as white versus
purple flowers
-he started out by studying only one trait at a time
-he followed the inheritance of these traits for several generations, counting the numbers of
offspring with each type of trait
-by analyzing these numbers, he saw the basic patterns of inheritance emerge
Research into inheritance begins with parental organisms that have easily identified traits
that are inherited consistently from generation to generation
Pea plants that are homozygous for a particular characteristic always produce the same
physical forms
-if a plant is homozygous for purple flowers, it will always produce offspring with purple
flowers
-plants homozygous for a characteristic are true breeding
How Are Single Traits Inherited
The inheritance of dominant and recessive alleles on homologous chromosomes can explain
the result of Mendel’s crosses
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