Transcript 6.3 Mendel and Heredity

6.3 Mendel and Heredity
6.3 Mendel and Heredity
How do physical traits we exhibit correspond to the
DNA we inherit?
6.3 Mendel and Heredity
Recall:
• Meiosis produces haploid cells.
• How do these haploid cells become eggs and sprem?
6.3 Mendel and Heredity
• Gametogenesis is the production of
gametes.
• Gametogenesis differs between
females and males.
– Sperm become streamlined and
motile.
– Sperm primarily contribute DNA to an
embryo.
– Eggs contribute DNA, cytoplasm, and
organelles to an embryo.
– During meiosis, the egg gets most of
the contents; the other cells form polar
bodies (which get broken down and
recycled).
6.3 Mendel and Heredity
Fertilization is the combining of gametes.
• Fertilization
– Results in diploid cells.
– Is a part of sexual reproduction.
– Produces offspring that are genetically different from
their parents.
What determines how an offspring looks?
• Genetics is the study of biological patterns of trait
inheritance and genetic variation.
6.3 Mendel and Heredity
Mendel laid the groundwork for genetics.
• Traits are distinguishing
characteristics that are
inherited.
• Gregor Mendel, an Austrian
monk, showed that traits are
inherited as discrete units.
• Many in Mendel’s day thought
traits were blended.
• He bred pea plants to
research heredity.
6.3 Mendel and Heredity
Which of the following is an example of a biological trait?
A.
B.
C.
D.
personality
hair style
eye color
regional accent
6.3 Mendel and Heredity
Why peas?
• They reproduce quickly.
• He had control over mating.
– Mendel used purebred pea plants. This meant that a
line of pea plants had self-pollinated for so long that
they were genetically uniform.
– He was able to breed selectively by interrupting and
controlling the pollination process.
– Because he used purebred pea plants, he knew that
any genetic variation resulted from his experiments.
6.3 Mendel and Heredity
Mendel began his experiments with purebred pea plants.
This approach enabled him to determine that variations
among offspring were the result of
A.
B.
C.
D.
genetic uniformity.
self-pollination.
his crossings.
random mutations.
6.3 Mendel and Heredity
• Mendel used pollen to fertilize selected pea plants.
– interrupted the self-pollination process by removing male
flower parts
– the mating of two organisms is called a cross.
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
6.3 Mendel and Heredity
• The P generation (parent) crossed to produce the F1
generation (first filial, meaning 1st generation)
• Mendel crossed a purebred purple flower with a purebred
white
• All F1 generation plants had purple flowers
6.3 Mendel and Heredity
• Mendel allowed the resulting plants (F1) to self-pollinate,
producing the F2 generation.
- White flowers appeared in some of the offspring.
- The trait for white flowers had not disappeared in the F1
generation, it had only been hidden, or masked.
6.3 Mendel and Heredity
• Mendel did similar crosses focusing on other traits.
• He determined which traits were dominant and which were
recessive.
6.3 Mendel and Heredity
– Mendel Learned:
– Traits are inherited as discrete units.
– This explains why individual
traits persist without being
blended or diluted over
successive generations
– Mendel discovered the law of
segregation
– Organisms inherit two copies of
each gene, one from each parent.
– The two copies segregate
(separate)
during gamete formation (meiosis).
purple
white
6.3 Mendel and Heredity
When Mendel crossed plants that were purebred purpleflowered with plants that were purebred white-flowered, the
resulting offspring all had purple flowers. When allowed to
self-pollinate, this F generation gave rise to white-flowered
plants as well as purple. As a result, Mendel determined that
individual traits are
A. inherited as discrete units.
B. diluted in offspring.
C. merged with successive generations.
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D. lost in the pollination process.
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