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
Objectives
Students will be able to describe the patterns of
inheritance that Mendel’s data revealed.
Students will be able to summarize Mendel’s Law of
Segregation.
6.3 Mendel and Heredity
Mendel laid the groundwork for genetics.
• Traits are distinguishing
characteristics that are
inherited.
• Genetics is the study of
biological inheritance patterns
and variation.
• Gregor Mendel showed that
traits are inherited as discrete
units.
• Many in Mendel’s day thought
traits were blended.
– Mixing red and white gets
pink all the time
6.3 Mendel and Heredity
Mendel’s data revealed patterns of inheritance.
• Mendel made three key decisions in his experiments.
– use of purebred plants
– control over breeding
– observation of seven
“either-or” traits
6.3 Mendel and Heredity
• Mendel used pollen to fertilize selected pea plants.
– P generation crossed to produce F1 generation
– interrupted the self-pollination process by removing male
flower parts
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
• Mendel allowed the resulting plants to self-pollinate.
– Among the F1 generation, all plants had purple flowers
– F1 plants are all heterozygous
– Among the F2 generation, some plants had purple
flowers and some had white
6.3 Mendel and Heredity
• Mendel observed patterns in the first and second
generations of his crosses.
6.3 Mendel and Heredity
• Mendel drew three important conclusions.
– Traits are inherited as discrete units.
– Organisms inherit two copies of each gene, one from
each parent.
– The two copies segregate
during gamete formation.
– The last two conclusions are
called the law of segregation.
purple
white
6.3 Mendel and Heredity
Review
• Give two examples of traits that haven’t already been
discussed.
• Explain why Mendel’s choice of either-or characteristics
aided his research.
• Why is it important that Mendel began with purebred
plants?
• Mendel saw purple flowers in the F1 generation, but both
purple and white flowers in the F2. How did this help him
see that traits are inherited as discrete units?
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6.3
KEY CONCEPT
Genes encode proteins that produce a diverse range
of traits.
4 Mendel and Heredity
6.3
• Objectives:
– Students will be able to explain how there can be many
versions of one gene.
– Students will be able to describe how genes influence the
development of traits.
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6.3
The same gene can have many versions.
• A gene is a piece of DNA that directs a cell to make a
certain protein.
• Each gene has a locus, a
specific position on a pair of
homologous chromosomes.
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6.3
• An allele is any alternative form of a gene occurring at a
specific locus on a chromosome.
– Each parent donates
one allele for every
gene.
– Homozygous
describes two alleles
that are the same at a
specific locus.
– Heterozygous
describes two alleles
that are different at a
specific locus.
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6.3
Genes influence the development of traits.
• All of an organism’s genetic material is called the genome.
AA, Aa, aa
Green Eyes, Blue Body etc.
• A genotype refers to the makeup of a specific set of genes.
• A phenotype is the physical expression of a trait.
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6.3
• Alleles can be represented using letters.
– A dominant allele is
expressed as a phenotype
when at least one allele is
dominant.
– A recessive allele is
expressed as a phenotype
only when two copies are
present.
– Dominant alleles are
represented by uppercase
letters; recessive alleles by
lowercase letters.
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6.3
• Both homozygous dominant and heterozygous genotypes
yield a dominant phenotype.
• Most traits occur in a range
and do not follow simple
dominant-recessive patterns.
4 Mendel and Heredity
6.3
• Review
– Distinguish between the terms locus and allele.
– Explain the difference between genotype and phenotype.
– How are the terms gene, locus, and allele related?
– Explain why an organism’s genotype may be homozygous
dominant, homozygous recessive or heterozygous but never
heterozygous recessive.
– Suppose you are studying a fruit fly’s DNA and you discover a
gene for antenna length on chromosome 2. What word describes
it’s location, and where would it be found in other fruit flies’ DNA?
– If a recessive allele helps an organism reproduce, nut the
dominant allele hinders reproduction, which will be more common
in a population?
– Cystic Fibrosis is a recessive disease that causes the production
of abnormally thick, life-threatening mucus secretions. What is the
genotype of a person with cystic fibrosis: CC, Cc, or cc? Explain