Chapter 12-More complications! Sex chromosomes/ sex ...Which are sex chromosomes below? Fly notation is different We draw the chromosome itself! We use a lower case letter that is

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UNIT 2 A.  Mendel and the Gene Idea (Ch11) B.  Chromosomal Basis of Inheritance (Ch12) C.  Molecular Basis of Inheritance (Ch13) D.  Gene Expression from Gene to Protein (Ch 14)

Chapter 12-More complications! •  Sex chromosomes/ sex linkage •  Recombination •  Y Chromosome reading for Friday


Who was Morgan and what did he do??

http://www.columbia.edu/cu/alumni/Magazine/Legacies/Morgan/


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation

All offspring had red eyes.

Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation

Given red eyed offspring…What would you predict genotypes of parental generation to be?

Would this work…. Rr x rr Why/Why not?How about…..RR x rr

If that is the case then all those red-eyed offspring must be Rr, right?

Imagine you crossed the F1…what would you get?

Rr x Rr cross…¼ RR ½ Rr and ¼ rr


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation


Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation

What caught his attention in the F2?

Males and Females had different ratios!

This is a hint that this eye color locus is on the sex chromosome.


How many chromosomes total in flies? 2N=?8 (3 pairs autosomes and a set of sex chromosomes..)Which are sex chromosomes below?

Fly notation is different

We draw the chromosome itself! We use a lower case letter that is the first letter of mutant! Mutant is recessive (unless noted otherwise) We use a + to indicate “wildtype”! No + if it is the mutant! Which are the sex chromosomes here…. Fly males are heterogametic What are we?


There are essentially NO TRAITS on the Y Why is this the case?

How would we write a red eyed female and a white eyed male? So…w=white eyed, w+=red eyed


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation


Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation

Make a Punnet square! And yes put the little images of the chromosomes on the Punnet square!


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation


Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation


Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation


Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation


Figure 12.4

Experiment P

Generation

Results

F1 Generation

F2 Generation


Eggs

Eggs

w+ w+

w

w

w+

w+

w+

w+ w

Sperm

Sperm

X Y

X X

w+ w+ w+

w+

w+

w w w

Conclusion

F1 Generation

F2 Generation

P Generation


Set aside sex chromosomes lets go back to flies with two genes on same chromosome… In our last example we assumed no recombination! This will be true as long as loci are close to one another on the chromosome.


Figure 12.10a

P generation (homozygous)

Wild type (gray body, normal wings)

Wild-type F1 dihybrid (gray body, normal wings)

Double mutant (black body, vestigial wings)

b+ vg+

b vg


Figure 12.10a




b+ vg+


b+ vg+

b+ vg+

b vg

b vg

b vg


Figure 12.10a




b+ vg+


b+ vg+

b+ vg+

b vg

b vg

b vg

Why not worry about crossing over here?


Figure 12.10b

b+ vg+

b vg

b+ vg+

b+ vg+ b vg

b vg

b+ vg+

b+ vg b vg+

b vg

b vg

b vg b vg

b vg

b vg

b vg

Meiosis I

Meiosis I and II

Meiosis II

Eggsb vg b vg b vg+ b+ vg b+ vg+

Sperm


F1 dihybrid testcross

Recombinant chromosomes

Homozygous Recessive= TEST CROSS (black body, vestigial wings)

Gametes?? How many different kinds of gametes from male? How many different gametes from female? If no recombination? With recombination?


Figure 12.10c

b+ vg+ b vg b vg+ b+ vg


Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg

Parental-type offspring Recombinant offspring

Recombination frequency = × 100 = 17%

2,300 total offspring391 recombinants

Female gametes


Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg




Female gametes


Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg




Female gametes


Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg





Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg



2,300 total offspring391 recombinantsWhich do you get more of and why?


Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg



2,300 total offspring391 recombinantsWhich do you get more of and why?

What are the phenotypes???


Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg



2,300 total offspring391 recombinantsHow would you calculate recombination rate or

frequency?


Figure 12.10c



Eggs

185 Black- normal

206 Gray-

vestigial

944 Black-

vestigial

965 Wild type

(gray-normal)

Testcross offspring

Sperm

b vg

b vg

b vg+ b+ vg

b vg b vg b vg

b+ vg+ b vg




How do we use this info?


Figure 12.12

Short aristae

Black body

Cinnabar eyes

Vestigial wings

Brown eyes

Red eyes

Normal wings

Red eyes

Gray body

Long aristae (appendages on head)

Wild-type phenotypes

0 48.5 57.5 67.0 104.5

Mutant phenotypes

How do we use this information? What does it show us?


Being diploid evolved in Eukaryotes

Advantages?Disadvantages?

“Dose” issues are important in animals with sex chromosomes!

Are 800-900 genes on the x chromosome..

X Inactivation-WHY????

At 32 cell stage (D)


EX. Calico cats (One of the genes for hair/fur color is on X chromosome)

Two alleles (orange and black)

Why are females patchy??Each patch has a different X randomly turned on (orange or black)

Orange patch=bunch of cells with the orange X turned on. Black patch=bunch of cells with the black X on.

Why are males not patchy like females?

Single X and so either the orange or the black hair color gene on in entire body.


Possible genotypes and phenotypes of males and females

X = orangeX = black

MALES:XY = orangeXY = black

FEMALES:XX = orangeXX = blackXX = orange or black patches


Figure 12.8

Early embryo:

Two cell populations in adult cat:

X chromosomes

Cell division and X chromosome inactivation

Allele for orange fur

Allele for black fur

Active X

Orange fur Black fur

Inactive X Active X


Anhydrotic dysplasia X-linked sweat gland problem

X = normal sweat glands X' = absence of sweat glands.

XY….would be?Normal maleX’Y…?No sweat glands male

XX…..Normal femaleX'X' female do not have sweat glandsXX' …..have patches of skin with sweat glands and patches of skin without sweat glands (populations of cells that have one X turned on and other patches with a different X on).


What do you know about colorblindness?

X linkedSuppose: X = color vision X’ = color blind

Females might be XX XX’ X’X’Males might be XY X’Y

Given X inactivation …….should heterozygous females for colorblindness be able to see color?


Retina of a heterozygous (XX’) female have some cells with the X inactivated and other cells with the X’ inactivated.

A heterozygous female has some color blind cells in her retina.

The non-color blind cells enable her to see color.


Sex Determination patterns

Chromosomal determination

Remember…..we have autosomes as well as sex chromosomes

1.  XX/XY Who has this??? Humans and Drosophila


2. ZW/ZZ Who has this?Birds

reversed compared to the XY system

females are heterogametic- what does that mean? (ZW)

males have two of the same kind of chromosomes (ZZ) So they are…….


3. HaplodiploidyWho has this?Insect such as ants and bees

Unfertilized eggs develop into haploid individuals, which are males.

Diploid individuals are female

Males cannot have sons or fathers.

Females can decide the sex of their offspring by storing received sperm and either releasing it for fertilization or not.


Environmental Sex Determination

Temperature at which egg is incubatedWho does this? alligators, turtles

Sometimes one sex hatches out when it is hot and the other when it is cool. Males are cool in turtles.

For others, the extreme temperatures are one sex and the middle temperature is the other. Males hatch out of middle temps in alligators.


1. What kind of sex determination did our ancestors have and when did the y chromosome evolve? 2. Did you want to guess (given the timing) what kind of terrestrial animal the y chromosome evolved in? What lineage dominated terrestrial realms at this time? 3. What do they mean SRY evolved from a related gene?? (and what does SRY, what does it stand for?) 4. Why do you think the Y lost its ability to recombine (other than at the tips)?? 5. Why would the Y lose genes? What kinds of genes would it be unlikely to lose and why?


6. Chimps have lost some genes as well but there seems to be many duplicated genes on the chimp Y, what might these genes be doing? 7. To review…What is the debate about in the article? 8. What are the “dying gasps of the Y chromosome”?

Chapter 12-More complications! Sex chromosomes/ sex ...Which are sex chromosomes below? Fly notation is different We draw the chromosome itself! We use a lower case letter that is

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