Download The Source of Heredity “Chapter 21”

The Source of Heredity
Beyond Mendel
“Chapter 19”
Curriculum Outcomes
Key Terms
Questions
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Questions 1-5 page 626
The Importance of Chromosomal
Theory
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Believed heredity traits were found in the blood.
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The term “pure bloodline”
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During dark ages laws prohibited dissection of corpses.
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Physicians and scientists performed dissections secretly
in caves.
Genes are found in the nucleus of cells.
Cytology and Genetics
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Aristotle suggested that heredity could be
traced to the power of the males semen.
He believed heredity factors from the male
outweighed the female.
Mendel’s papers made new speculations
that egg and sperm unit to form a new
individual.
Development of Chromosomal
theory
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Observed that chromosomes come in pairs and
they segregate during meiosis. The
chromosomes then form new pairs when the
egg and sperm unit.
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Today these factors are known as genes.
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Discovered humans have 46 chromosomes.
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The development and refinement of the
microscope led to advances in cytology.
Chromosomal Theory:
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Chromosomes carry genes, the units of heredity
structure.
Paired chromosomes segregate during meiosis. Each sex
cell or gamete has half the number of chromosomes
found in a somate cell.
Chromosomes assort independently during meiosis. This
means that each gamete receives one of the pairs and
that one chromosome has no influence on the
movement of a member of another pair.
Each chromosome contains many different genes.
Morgan’s Experiments
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Morgan used the fruit fly to study Mendel’s principles of inheritance.
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The fruit fly reproduces quickly.
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Females lay over 100 eggs.
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Life cycle 10-15 days makes it easy to study many generations.
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They are small in size.
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Have many mutations.
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Noticed a white eyed male among red eyed offspring.
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Traits that govern eye colour was located on the X chromosome
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Sex-linked traits – are controlled by
genes located on the sex chromosomes.
Sex Determination
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Sex-linked genes are found in humans.
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Red-green colour blindness determined by a recessive gene located
on the X chromosome.
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Barr Body – are small dark spots of chromatin, located in the
nuclei of female mammalian cells.
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You have 46 Chromosomes.
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If female you have 23 pairs of homologous chromosomes: 22
autosomes and 2 X sex chromosomes
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If male you have only 22 pairs of homologous chromosomes and
one X and one Y chromosome.
Homework
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Review Questions (old text)
Page 500 Questions 1-3
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Questions 1-7 page 634
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Gender Verification at the
Olympics
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Use a buccal mucosa smear, scraping from
inside the mouth. Look for evidence of X
and Y chromatin.
Summary
Gene Linkage and Crossing Over
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Linked genes – are located on the same
chromosomes.
Crossing over means that a single gene
can change as it passes from one
generation to generation.
Mapping Chromosomes
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Gene marker – are often recessive traits that are
expressed in the recessive phenotype of an organism.
The Markers can be used to identify other genes found
on the same chromosome.
Map distance – refers to the distance between two
genes along the same chromosome.
A crossover frequency of 5% means that the genes are
5 map units apart.
Summary
Gene recombinations in Nature
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Genes can move to new positions. Barbara
McClintock “Jumping Gene Theory”
Transposons – are specific segments of
DNA that can move along the
Chromosome.
Homework
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Review Questions (old text)
Page 512 Questions 4-8
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Questions 105 page 851
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Review questions page 657-659
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