1. Warm-Up
The Q gene encodes a protein responsible for arm length: people with one or more of the Q allele have super-long arms (like, 6 feet long), and people with two q alleles have super-short arms (like a T Rex). The H gene encodes a protein responsible for making hair: people with one or more of the H allele have hair, and people with two h alleles have no hair whatsoever. The two genes are on different chromosomes. Draw a somatic cell with the genotype QqHh (actually draw the chromosomes), and then draw the four possible gametes it can produce. Then draw a somatic cell with the genotype Qqhh, as well as the four possible gametes it can produce. Then draw all of the possible progeny (fertilized eggs) that can result in a dihybrid cross, and write the phenotype ratio. (LO 3.12)

2. UNIT 3D
Yesterday’s Picture

3. Non-Mendelian Genetics, Part I
UNIT 3D
Non-Mendelian Genetics, Part I

4. 3D XX XY Non-Mendelian Genetics, Part I UNIT
Gender is a phenotype, not encoded by one gene but by an entire chromosome. XX XY
Chromosomes, not alleles!

5. 3D Non-Mendelian Genetics, Part I UNIT
Gender is a phenotype, not encoded by one gene but by an entire chromosome.
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome.

6. 3D Non-Mendelian Genetics, Part I UNIT
Gender is a phenotype, not encoded by one gene but by an entire chromosome.
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome.
Males have an X and a Y chromosome (XY) and females have two X chromosomes (XX).

7. 3D Non-Mendelian Genetics, Part I UNIT
Gender is a phenotype, not encoded by one gene but by an entire chromosome.
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome.
Males have an X and a Y chromosome (XY) and females have two X chromosomes (XX).

8. Male testes somatic cell
UNIT 3D
Non-Mendelian Genetics, Part I
Male testes somatic cell
Gender is a phenotype, not encoded by one gene but by an entire chromosome. 1m 1p
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome. 2p 2m
Males have an X and a Y chromosome (XY) and females have two X chromosomes (XX). 3p 3m X Y
All non-gender genes on the X chromosome are sex-linked or x-linked genes. 1p 1m 2p 2m r 3p 3m X Y S t

9. 3D Non-Mendelian Genetics, Part I X Y UNIT
Gender is a phenotype, not encoded by one gene but by an entire chromosome.
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome. X t
Males have an X and a Y chromosome (XY) and females have two X chromosomes (XX). Y
All non-gender genes on the X chromosome are sex-linked or x-linked genes.
Males can be “hemi-zygous” and express the recessive trait with only one recessive allele!

10. Phenotype: recessive t
UNIT 3D
Non-Mendelian Genetics, Part I
Gender is a phenotype, not encoded by one gene but by an entire chromosome.
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome.
Males have an X and a Y chromosome (XY) and females have two X chromosomes (XX). X t
All non-gender genes on the X chromosome are sex-linked or x-linked genes. Y
Males can be “hemi-zygous” and express the recessive trait with only one recessive allele!
Genotype: XtY
Phenotype: recessive t

11. 3D Non-Mendelian Genetics, Part I UNIT
Gender is a phenotype, not encoded by one gene but by an entire chromosome.
The “sex chromosome” and its homologue is either an X chromosome or a Y chromosome.
Males have an X and a Y chromosome (XY) and females have two X chromosomes (XX).
All non-gender genes on the X chromosome are sex-linked or x-linked genes.
Males can be “hemi-zygous” and express the recessive trait with only one recessive allele!
Non-sex chromosomes are called “autosomes.”

12. UNIT 3D
CTQ #1
Eye pigment in a particular strain of fly is determined by two genes. An autosomal gene that controls the color of the pigments in the eye has two alleles: a dominant allele (R) that results in red eyes and a recessive allele (r) that results in sepia eyes. A sex-linked gene that controls the expression of the colored pigments also has two alleles: a dominant allele (T) that allows for expression of the colored pigments and a recessive allele (t) that does not allow for expression of the colored pigments. Individuals without a T allele have white eyes regardless of the alleles of other eye-color genes.
Which of the following represents a cross between a white-eyed female and a red-eyed male?
TtXRXR x ttXrY
TtXrXr x ttXRY
RRXTXT x RrXTY
RrXtXt x RrXTY

13. - OR - 3D Non-Mendelian Genetics, Part I m p m p UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other. 1m 1p m p 2m 2p
allele a
allele A m p
- OR -
allele F
allele f

14. 3D Non-Mendelian Genetics, Part I m p p m UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other. 1m 1p m p 2p 2m
allele a
allele A p m
allele f
allele F

15. 3D Non-Mendelian Genetics, Part I a F A f a f A F UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
one possibility
a F
A f
another possibility
a f
A F

16. 3D Non-Mendelian Genetics, Part I m p p m UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
But the Law of IA only works if the two genes are on different chromosomes. 1m 1p m p 2p 2m
allele a
allele A p m
allele f
allele F

17. 3D Non-Mendelian Genetics, Part I m p UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
But the Law of IA only works if the two genes are on different chromosomes. 1m 1p
If two genes are on the same chromosome, they are linked. m p
allele a
allele A
allele B
allele b
a and B are always going to go together;
A and b are always going to go together.

18. 3D Non-Mendelian Genetics, Part I a B A b UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
But the Law of IA only works if the two genes are on different chromosomes.
If two genes are on the same chromosome, they are linked.
the only possibility
a B
A b

19. 3D Non-Mendelian Genetics, Part I 4m 4p UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
But the Law of IA only works if the two genes are on different chromosomes.
If two genes are on the same chromosome, they are linked. Q q
Crossing over unlinks the genes, but it is less likely to happen the closer the two genes are to each other. 4m 4p h H
Not linked anymore!

20. 3D Non-Mendelian Genetics, Part I 4m 4p UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
But the Law of IA only works if the two genes are on different chromosomes.
If two genes are on the same chromosome, they are linked. Q q h H
Crossing over unlinks the genes, but it is less likely to happen the closer the two genes are to each other. 4m 4p
Still linked!

21. 3D Non-Mendelian Genetics, Part I UNIT
Another way to put the Law of IA: two alleles from two different genes don’t have a preference for each other.
But the Law of IA only works if the two genes are on different chromosomes.
Predicted Phenotype Distribution:
purple, smooth: ¼ =
purple, wrinkled: =
white, smooth: =
white, round:
If two genes are on the same chromosome, they are linked.
Crossing over unlinks the genes, but it is less likely to happen the closer the two genes are to each other.
Actual Phenotype Distribution:
purple, smooth: 14
purple, wrinkled: 456
white, smooth: 502
white, wrinkled: 0
Linked genes have non-Mendelian genotype distributions.

22. UNIT 3D
CTQ #2
In Drosophila melanogaster the allele for wild-type tan body color (B) is dominant to the recessive allele for black body color (b). Similarly, the allele for wild-type wing shape (V) is dominant to the recessive allele for vestigial wing phenotype (v). In the cross diagrammed above, the expected and observed results are shown. Which of the following best explains the observed results of the cross? (LO 3.15)
The alleles for body color and wing shape assort independently, as predicted by Mendel’s laws.
The genes for body color and wing shape are located close to each other on the same chromosome.
The traits of body color show complete dominance over the traits of wing shape.
The observed variations in body color and wing shape are detectable in males but not in females.

23. Closure
Explain why a male with only one X-linked recessive allele expresses the recessive phenotype.