Transcript File - Pearson`s Place

Biology Unit Four D–
Human Genetics and Pedigrees
Mrs. Pearson’s First Semester Biology
*For those watching by recording, watch for questions on the slides throughout
the presentation. Email me the answers to the questions within two days of the
lesson being presented in order to receive credit for watching the recording.
AND THE WINNER IS…
• Food Spoilage!!
– Because I won’t know what foods I can use until I
get there, I will do it in reverse and run the Costa
Rica piece first and the Wisconsin piece second.
– Because the amount of “critters” in Costa Rica, I
will use a container with a thin fabric screen and
will not leave it outside.
Let’s have a hand for…
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Caitlyn Abbott
Kristen Barstow
Sabrina Haug
Leeanna Heinrichs
Melissa Hunt
Christopher King
Kayla Morris
Chyenne Nechkash
Emily Patik
Courtney Pigeon
Dana Radtke
Stephanie Spatz
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• 50 extra credit points
OR
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to tell me which one)
• Email Mrs. P today with your choice!
7.3 Gene Linkage and Mapping
KEY CONCEPT
Genes can be mapped to specific locations on
chromosomes.
7.3 Gene Linkage and Mapping
Lesson Objectives
• Discuss gene linkage and mapping
• Discuss expression of sex-linked traits
• Understand pedigrees and karyotypes
7.3 Gene Linkage and Mapping
Gene linkage was explained through fruit flies.
• Morgan found that linked traits are on the same
chromosome
Wild type
Mutant
7.3 Gene Linkage and Mapping
Chromosomes, not genes, assort independently during
meiosis
• Remember that meiosis is the making of sperm and egg
cells
• Remember that during meiosis the cell divides in such a
way that only half of the genetic material will be passed
on
• So what does it mean when we say that the
chromosomes assort independently?
7.3 Gene Linkage and Mapping
Chromosomes, not genes, assort independently during
meiosis
• Maybe they will separate like this…
4
4
4
4
7
7
7
7
7.3 Gene Linkage and Mapping
Chromosomes, not genes, assort independently during
meiosis
• BUT maybe they will separate like this…
4
4
4
4
7
7
7
7
7.3 Gene Linkage and Mapping
Chromosomes, not genes, assort independently during
meiosis
• They are independent – don’t have to separate the same
4
4
4
4
7
7
7
7
7.3 Gene Linkage and Mapping
• Linked genes are not inherited together every time.
• Chromosomes exchange homologous genes during
meiosis – what do we call this process?
7.3 Gene Linkage and Mapping
Linkage maps estimate distances between genes.
• The closer together two genes are, the more likely
they will be inherited together.
• Cross-over frequencies are related to distances
between genes.
• Linkage maps show the relative locations of genes.
7.3 Gene Linkage and Mapping
• When crossing over happens here, genes A and B stay
together.
A
B
A
B
A
B
A
B
7.3 Gene Linkage and Mapping
• But, when crossing over happens here, genes A and B
get separated.
• When genes are close to each other on the
chromosome, it’s more likely that they will be inherited
together.
A
B
A
B
A
B
A
B
7.3 Gene Linkage and Mapping
• Cross-over frequencies can be converted into map units.
– gene A and gene B cross over 6.0
percent of the time
– gene B and gene C
cross over 12.5 percent
of the time
– gene A and gene C cross over 18.5 percent of the
time
**Those watching by
recording, include in
your email why genes A
and B would be more
likely to be linked than A
and C.
7.4 Human Genetics and Pedigrees
KEY CONCEPT
A combination of methods is used to study human
genetics.
7.4 Human Genetics and Pedigrees
Human genetics follows the patterns seen in other
organisms.
• The basic principles of genetics are the same in all sexually
reproducing organisms.
– Inheritance of many human
traits is complex.
– Single-gene traits are
important in understanding
human genetics – why?
**Those watching by recording, include in your
email why single-gene traits are important in
understanding human genetics.
7.4 Human Genetics and Pedigrees
Females can carry sex-linked genetic disorders.
• Males (XY) express all of their sex linked genes – why?
• Expression of the disorder depends on which parent carries
the allele and the sex of the child – why?
Y
X
7.4 Human Genetics and Pedigrees
What chromosome will the mom give to the baby? The X
or the Y chromosome? Why?
• She will always give the baby an X chromosome because
that is all she has.
• So… if mom is a carrier of a sex-linked disease, will her
daughters have the disease?
• Her daughters will only have the disease if they receive
mom’s X chromosome that has the disease gene
Y on it AND
X
they receive an X chromosome from dad with the disease
gene on it.
• They might be a carrier.
• They might not be a carrier
• Will her sons have the disease?
7.4 Human Genetics and Pedigrees
What chromosome will the mom give to the baby? The X
or the Y chromosome? Why?
• Will her sons have the disease?
• Her sons will only have the disease if they receive mom’s X
chromosome that has the disease gene on it.
Y
X
7.4 Human Genetics and Pedigrees
What chromosome will the dad give to the baby? The X
or the Y chromosome?
• The dad’s sons will receive the Y chromosome from their
dad.
• The dad’s daughters will receive the X chromosome from
their dad.
• If the dad has a sex-linked disease gene on his X
chromosome, will his daughters have the disease?
Y
X
• They will ONLY have the disease if they also receive an X
chromosome from their mom that ALSO has the disease
gene on it.
• If they do not have the disease, will the daughters be
carriers?
• Yes – they will for certain have the disease gene from the X
chromosome from their dad.
7.4 Human Genetics and Pedigrees
What chromosome will the dad give to the baby? The X
or the Y chromosome?
• If the dad has a sex-linked disease on the Y chromosome,
will his sons have the disease?
• Yes – they can only receive the Y chromosome from their
dad so they will have the disease.
Y
X
7.4 Human Genetics and Pedigrees
A pedigree is a chart for tracing genes in a family.
• Phenotypes are used to infer genotypes on a pedigree –
which phenotype would help the most in determining
unknown genotypes?
• Autosomal genes show different patterns on a pedigree
than sex-linked genes.
7.4 Human Genetics and Pedigrees
• If the phenotype is more common in males, the gene is
likely sex-linked – why?
7.4 Human Genetics and Pedigrees
Several methods help map human chromosomes.
• A karyotype is a picture of all chromosomes in a cell.
** Those watching by recording,
include in your email whether the
person this karyotype came from was
male or female.
XY
7.4 Human Genetics and Pedigrees
• Karyotypes can show changes in chromosomes.
– deletion of part of a chromosome or loss of a
chromosome
– large changes in chromosomes
– extra chromosomes or duplication of part of a
chromosome
7.4 Human Genetics and Pedigrees
Review
• Linkage maps estimate distances between genes
• Human genetics follows the patterns seen in other
organisms
• Females can carry sex-linked genetic disorders
• A pedigree is a chart for tracing genes in a family
• If the phenotype is more common in males, the gene is
likely sex-linked
• A karyotype is a picture of all chromosomes in a cell
7.4 Human Genetics and Pedigrees
Questions?