SBI3U Mendel Demonstrated Law of Segregation Law of Independent Assortment The alleles for a gene segregate independently during meiosis This applies to alleles located on homologous chromosomes ID: 622851
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Slide1
6.2-Inheritance of Linked Genes
SBI3USlide2
Mendel Demonstrated:
Law of Segregation
Law of Independent AssortmentThe alleles for a gene segregate independently during meiosis. This applies to alleles located on homologous chromosomesThis theory was proven to be incorrect.
Recall: Mendel’s ObservationsSlide3Slide4
Theory of Linked Genes
See pg.
251- Does not show the 9:3:3:1 ratioSlide5
Alleles on the same chromosome
do not
assort independently. Some genes that are on the same chromosome are inherited together and are called linked genes
.
An
example of this additional complex pattern is found in sweet pea plants.
Theory of Linked GenesSlide6
Linked genes:
on the same chromosome and tend to be inherited together.
Linkage Group:Genes on a chromosome that are always inherited together (unless crossing over occurs)Slide7
Crossing Over & Linked Genes
All genes
on any one chromosome are called a
linkage group
b/c they
tend to be inherited
together
Crossing
over can prevent linked genes from staying together.
Ex. 2 genes are on the same chromosome
The alleles for the linked genes switch
Now they are unlinked and will migrate to different gametes
Slide8
Linked Genes
UNIT 2
Chapter 6: Complex Patterns of Inheritance
Section 6.2
In most of the gametes formed, there is no crossing over—they maintain the linkage of the alleles. In a small minority of gametes, crossing over occurs and alleles of previously linked genes become unlinked.
Recombinant alleles:
linked genes that have been separated during crossing overSlide9
Used to determine location of genes on a chromosome
Useful for organisms that reproduce rapidly (e.g. fruit flies)
Frequency of crossing over is connected to how close the pairs of linked genes areCloser together = low frequencyFurther apart = high frequencyChromosome MappingSlide10
Thomas Hunt Morgan studied the fruit fly (
Drosphila
melanogaster)He crossed a pure red eyed female with a white eyed male and this is what he found…Sex-Linked InheritanceSlide11
Genotype
Phenotype
XR XR
Female
with red eyes (homozygous dominant)
X
R
X
r
Female with red eyes (heterozygous)
X
r
X
r
Female with white eyes (homozygous recessive)
X
R
Y
Male with red eyes Xr YMale with white eyesSlide12
Sex-Linked Inheritance cont’d
In the F1 generation:
100% of offspring had red eyes.
X
R
X
R
X
r
Y
X
R
X
r
X
R
X
r
X
R
YXR YSlide13
Sex-Linked Inheritance cont’d
In the F2 generation:
100% of the females have red eyes.
50% of the males have white eyes
50% of the males have red eyes
.
X
R
X
r
X
R
Y
X
R
Y
X
R
X
R
XRXrXrYSlide14
Conclusion:
The gene for eye colour is
connected to gender and located on the X chromosome.Traits that are controlled by genes on either the X or Y chromosome are called sex-linked
traits
.
Experimental ConclusionsSlide15
The X chromosome contains
2000
genesThe Y chromosome only contains 100 genesSex chromosomes contain some genes that are unrelated to sex determination
.
Each sex-linked gene can contain dominant or recessive alleles,
Sex ChromosomesSlide16
Sex-Linked Traits in HumansSlide17
X-Linked Dominant
Vs
. X-Linked Recessive X-Linked Dominant:X-Linked Recessive
Affected
males pass on only to daughters (100% chance)
Females pass to both sons and daughters (100% chance)
Very rare
Ex. Fragile X Syndrome
:
Affect
more males than females because males only need one
allele to be affected, while females need 2 recessive alleles to be affected
Ex. hemophilia, red-green colour vision deficiencySlide18
X – linked recessiveSlide19
X – linked dominantSlide20
X-Link Recessive:
Colour Vision Deficiency (CVD)
An X-linked recessive trait like CVD will affect more males than females in a family
. These males will have
difficuty
distinguishing between shades of red and greenSlide21
Determine the probability that a woman who is a carrier for hemophilia and a man without hemophilia will have a child with hemophilia.
What proportion of the female children with have hemophilia?
What proportion of male children will have hemophilia?Is it possible for these parents to have a female with hemophilia?Test Your Understanding…Slide22
A human female with red-green color deficiency (CVD) marries a normal male.
What proportion of their children will have CVD?
Is it possible for the parents to have a female with CVD? Why or why not?Test Your Understanding…Slide23
Read and make notes 6.2Complete pg.
258 Q# 11-13, 16, 17
Homework: