Download 6.3 Mendel and Heredity

6.3 Mendel and Heredity
KEY CONCEPT
Mendel’s research showed that traits are inherited as
discrete units.
6.3 Mendel and Heredity
Mendel laid the groundwork for genetics.
* Gregor Mendel
- showed that traits are
inherited as “discrete units” (are
inherited separately)
Many people in Mendel’s day thought
traits were blended
6.3 Mendel and Heredity
~ genetics = the study of biological inheritance
patterns and variation
~ traits are characteristics that are inherited
Ex: color, shape, height
6.3 Mendel and Heredity
~ genes = are what determine traits (there is a different
gene for hair color, a different gene for eye color, and a
different gene for height)
- alleles = the different forms of a gene
Ex:
A
(dominant)
or
a
(recessive)
6.3 Mendel and Heredity
~ true breeding = organism will produce offspring
identical to itself; also called pure bred
6.3 Mendel and Heredity
~ hybrid = is the offspring produced
from a cross between parents with
different traits
Ex:
x
horse
=
donkey
mule
6.3 Mendel and Heredity
* Inheritance
- Mendel experimented using pea
plants
~ his data revealed certain
patterns of inheritance
6.3 Mendel and Heredity
Mendel’s experiments:
1. he used purebred (true breeding) plants
2. he maintained control over breeding (controlled
which plants would breed together)
3. he observed seven “either-or” traits
6.3 Mendel and Heredity
- from his experimental data, Mendel formed 3 laws:
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
6.3 Mendel and Heredity
• Mendel’s Law of Dominance
– Mendel chose certain pea plants
- he controlled the fertilization of his pea plants by
removing the male parts (stamens)
6.3 Mendel and Heredity
- he fertilized the female part (pistil) with pollen from
a different pea plant
6.3 Mendel and Heredity
- experiment:
- crossed purebred purple plants with purebred white
plants (P generation)
- got all purple plants (F1 generation = first filial)
- white trait disappeared
6.3 Mendel and Heredity
- concluded that the allele for the observed trait (purple)
was dominant over the allele for the hidden trait (white)
 white allele is recessive
 purple allele is dominant
6.3 Mendel and Heredity
• Mendel’s Law of Segregation
experiment:
– crossed purebred purple with purebred white
– then F1 generation was crossed (F1 x F1)
6.3 Mendel and Heredity
– resulted in ¾ purple flowers and ¼ white flower in
F2 generation (the white flower trait reappeared)
6.3 Mendel and Heredity
– based on results, concluded that:
1. traits are inherited as discrete units
2. organisms inherit two copies of each gene, one from
each parent
3. the two copies segregate during gamete formation
(gametogenesis)
- the last two conclusions are called the Law of Segregation
6.3 Mendel and Heredity
• Mendel observed patterns in the first and second
generations of his crosses.
6.3 Mendel and Heredity
• Mendel’s Law of Independent Assortment
– experiment:
– conducted a dihybrid cross involving 2 different
traits (seed shape x seed color)
– he then crossed the F1 generation
– F2 generation had a variety of traits, some different
from both parents
6.3 Mendel and Heredity
– concluded that genes for different traits are
separated during meiosis
~ therefore, are inherited independently of
each other (if on different chromosomes)
6.3 Mendel and Heredity
Ex: you may not inherit
your mother’s eye color
and hair color if the
gene for hair color and
the gene for eye color
are on different
chromosomes
6.3 Mendel and Heredity
genes
gene
centromere
sister chromatid