Chapter 14: Part 1 Flashcards
Mendel used the scientific approach to identify
two laws of inheritance
Mendel discovered two basic principles of heredity by breeding garden peas in carefully planned experiments
- Law of Segregation
- Law of Independent Assortment
What Mendel called a “heritable factor”
is what we now call a gene
Character
A heritable feature that varies among individuals (such as flower color) is called a
Trait
Each variant for a character, such as purple or white color for flowers, is called a
advantages of using peas
- Short generation time
- large numbers of offspring
- Mating could be controlled; plants could be allowed to self-pollinate or could be cross pollinated.
true-breeding
plants that produce offspring of the same variety when they self- pollinate
hybridization
Mendel mated two contrasting, true- breeding varieties
P generation
true-breeding parents
F1
generation
The hybrid offspring of the P generation
F2 generation
When F1 individuals self-pollinate or cross- pollinate with other F1 hybrids, it produces F2
When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants,
all of the F1 hybrids were purple
When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers,
but some had white
Mendel discovered a ratio of 3:1
purple to white flowers, in the F2 generation
dominant trait
purple flower
recessive trait
white flower
The factor for white flowers was not diluted or destroyed
because it reappeared in the F2 generation
First *alternative versions of genes
account for variations in inherited characters
First* : Ex. the gene for flower color in pea plants exists in two versions,
one for purple flowers and the other for white flowers
allele
alternative versions of a gene
Alleles are simply variations in a
gene’s nucleotide sequence
gene resides at a specific locus
on a specific chromosome
- Second: for each character, an organism
inherits two alleles, one from each parent
The two alleles at a particular locus may be identical,
as in the true-breeding plants of Mendel’s P generation
he two alleles at a locus may differ
as in the F1 hybrids
*Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and
he other (the recessive allele) has no noticeable effect on appearance
Third:
Ex., F1 plants had purple flowers because the allele for that trait is dominant
*Fourth (the Law of Segregation): the two alleles for a heritable character separate (segregate) during
gamete formation and end up in different gametes
Thus, an egg or a sperm gets only
1 of the 2 alleles that are present in the organism
This segregation of alleles corresponds to the distribution of homologous chromosomes
to different gametes in meiosis
So the Law of Segregation says the 2 alleles for
each gene
separate during gamete formation
