Genetics Flashcards
(813 cards)
1
Q
What is a mutation?
A
A change in the DNA sequence that may or may not affect an organism’s phenotype.
Mutations can occur in various regions of DNA, influencing gene function and expression.
2
Q
Why are mutations important?
A
They can lead to genetic diversity and evolution, and they may cause diseases or affect traits.
Understanding mutations is crucial for fields like genetics, medicine, and evolutionary biology.
3
Q
What are the different types of mutations?
A
- Point
- Transition
- Transversion
- Silent
- Missense
- Neutral
- Frameshift
- Inframe
Each type of mutation has distinct characteristics and effects on protein function.
4
Q
What is a trinucleotide repeat expansion mutation?
A
A mutation where a sequence of three nucleotides is repeated more times than normal, potentially leading to disease.
This type of mutation is associated with conditions like Huntington’s disease.
5
Q
How might mutations in the promoter influence protein products?
A
They can affect the transcription of the gene, leading to changes in the amount or functionality of the protein produced.
Promoter mutations can enhance or reduce gene expression.
6
Q
What causes cystic fibrosis (CF)?
A
Mutations in the CFTR gene, which encodes a protein responsible for regulating chloride and sodium ions across epithelial cell membranes.
CF is a genetic disorder that affects the lungs and digestive system.
7
Q
What protein is responsible for cystic fibrosis?
A
Cystic Fibrosis Transmembrane Conductance Regulator (CFTR).
The CFTR protein plays a crucial role in maintaining the balance of salt and water on epithelial surfaces.
8
Q
What mutations are commonly involved in the development of cystic fibrosis?
A
- F508del
- G551D
- N1303K
F508del is the most common mutation associated with CF.
9
Q
How are mutations named, such as PHE508DEL?
A
They are named based on the amino acid change and the specific deletion or alteration in the DNA sequence.
PHE508DEL indicates a deletion of phenylalanine at position 508.
10
Q
Why might genetic testing for cystic fibrosis not provide an accurate diagnosis?
A
Not all mutations in the CFTR gene are tested, and some mutations may not be well understood or detectable.
Genetic variability and the presence of atypical mutations can complicate diagnosis.
11
Q
In what types of cells can mutations occur?
A
- Germ-line cells
- Somatic cells
Germ-line mutations can be inherited, while somatic mutations affect only the individual.
12
Q
INHERITANCE PATTERNS OF SINGLE GENES
A
13
Q
There are many ways in which two alleles of a single gene may govern
A
14
Q
the outcome of a trait
A
15
Q
• Simple Mendelian
A
16
Q
• Incomplete penetrance
A
17
Q
Incomplete dominance
A
18
Q
Overdominance
A
19
Q
Codominance
A
20
Q
…
A
21
Q
X-linked
A
22
Q
Sex-influenced inheritance
A
23
Q
Sex-limited inheritance
A
24
Q
Lethal alleles
A
25
Exercise
26
The pattern of inheritance in this allele is
27
presumably dominant. Is the pedigree analysis
28
consistent with a dominant disorder?
29
Why?
30
Polydactyly:
31
Additional fingers
32
and/or toes. Might be
33
caused by mutant
34
alleles.
35
1-2
36
II-1
37
II-2
38
II-3
39
II-4
40
II-5
41
III-1
42
III-2
43
III-3
44
IV-
45
1
46
IV-
47
2
48
3
49
III-4
50
III-5
51
Inherited the polydactyly allele from his
52
mother and passed it on to a daughter and son
53
Does not exhibit the trait himself even
54
though he is a heterozygote
55
Incomplete Penetrance
56
• In some instances
a dominant allele does not influence the outcome of a trait in
57
a heterozygote individual
58
Example = Polydactyly
59
-
60
-
61
Autosomal dominant trait
62
A single copy of the polydactyly allele is usually sufficient to cause this
63
condition
64
But
In some cases
65
the trait
66
The term Incomplete Penetrance indicates
67
that a dominant allele does not always
68
"penetrate" into the phenotype of the
69
individual
70
Incomplete Penetrance
71
• The measure of penetrance is described at the population level
72
If 60% of heterozygotes carrying a dominant allele exhibit the trait allele
the
73
trait is 60% penetrant
74
• Note:
75
-
76
In any particular individual
the trait is either penetrant or not
77
Expressivity
78
Expressivity is the degree to which a trait is expressed
79
What is expressivity?
Expressivity is the degree to which a trait is expressed.
80
How does expressivity vary in polydactyly?
In polydactyly, the number of digits can vary. A person with several extra digits has high expressivity of this trait, while a person with a single extra digit has low expressivity.
81
What are essential genes?
Essential genes are those that are absolutely required for survival.
82
What happens in the absence of essential genes?
The absence of their protein product leads to a lethal phenotype.
83
What proportion of genes are estimated to be essential for survival?
It is estimated that about 1/3 of all genes are essential for survival.
84
What are nonessential genes?
Nonessential genes are those not absolutely required for survival.
85
What is a lethal allele?
A lethal allele is one that has the potential to cause the death of an organism, usually inherited in a recessive manner.
86
What effect do many lethal alleles have?
Many lethal alleles prevent cell division, which can kill an organism at an early age.
87
What do many lethal alleles prevent?
Many lethal alleles prevent cell division.
88
When do some lethal alleles exert their effect?
Some lethal alleles exert their effect later in life.
89
What are examples of diseases caused by lethal alleles?
Huntington disease and Early Onset Alzheimer's Disease.
90
What are the characteristics of Huntington disease and Early Onset Alzheimer's Disease?
They are characterized by progressive degeneration of the nervous system, dementia, and early death.
91
What is the typical age of onset for Huntington disease and Early Onset Alzheimer's Disease?
The age of onset of the disease is usually between 30 and 50.
92
How can a lethal allele affect phenotypic ratios?
A lethal allele may produce ratios that seemingly deviate from Mendelian ratios.
93
What is an example of a lethal allele in cats?
The Manx cat carries a dominant mutation that affects the spine.
94
What effect does the Manx cat mutation have?
This mutation shortens the tail.
95
Why is the Manx allele considered lethal?
This allele is lethal as a homozygote dominant.
96
What is the expected phenotypic ratio of live offspring when crossing two heterozygous Manx cats?
The expected phenotypic ratio of the live offspring is 2:1.
97
What is the P generation?
P generation refers to the parental generation in a genetic cross.
98
What is the F1 generation?
F1 generation is the first filial generation resulting from a cross between the P generation.
99
What is incomplete dominance?
In incomplete dominance, the heterozygote exhibits a phenotype that is intermediate between the corresponding homozygotes.
100
What are the alleles for flower color in the four o'clock plant?
CR = wild-type allele for red flower color, CW = allele for white flower color.
101
What phenotype results from the F1 generation in the four o'clock plant?
The F1 generation exhibits a pink phenotype.
102
What is the significance of the CR protein in the F1 generation?
In this case, 50% of the CR protein is not sufficient to produce the red phenotype.
103
What is the phenotypic ratio observed in codominance?
1:2:1 phenotypic ratio
## Footnote
This is different from the 3:1 ratio observed in simple Mendelian inheritance.
104
What is codominance?
Codominance occurs when two alleles are both expressed in heterozygous individuals.
105
How many different alleles can influence the same trait?
Three or more different alleles can influence the same trait.
## Footnote
Example: ABO blood group.
106
What determines the ABO blood group?
The ABO blood group is determined by the type of antigen present on the surface of red blood cells.
107
What are the alleles that determine the ABO blood group?
The three alleles are:
1. Allele IA, produces antigen A
2. Allele IB, produces antigen B
3. Allele i, no surface antigen is produced.
108
What is the relationship between allele i and alleles IA and IB?
Allele i is recessive to both IA and IB.
109
What is the relationship between alleles IA and IB?
Alleles IA and IB are codominant.
110
What type of allele is recessive to both IA and IB?
The allele is recessive to both IA and IB.
111
How are alleles IA and IB related?
Alleles IA and IB are codominant.
112
What happens in a heterozygous individual with alleles IA and IB?
Both IA and IB are expressed in a heterozygous individual.
113
What is the genotype for blood type A?
The genotype can be pApa or lAi.
114
What surface antigen is present in blood type A?
Antigen A.
115
What serum antibodies are present in blood type A?
Against B.
116
What is the genotype for blood type B?
The genotype can be B/B or Bi.
117
What surface antigen is present in blood type B?
Antigen B.
118
What serum antibodies are present in blood type B?
Against A.
119
What is the genotype for blood type AB?
The genotype is JAB.
120
What surface antigens are present in blood type AB?
Antigen A and Antigen B.
121
What serum antibodies are present in blood type AB?
None.
122
What is the role of glycosyl transferase in blood type A?
It is encoded by the A allele and produces Antigen A.
123
What is the role of glycosyl transferase in blood type B?
It is encoded by the B allele and produces Antigen B.
124
What is the carbohydrate tree on the surface of RBCs composed of?
It is composed of three components.
125
What is the carbohydrate tree on the surface of RBCs composed of?
The carbohydrate tree is composed of three sugars.
126
What can be added to the carbohydrate tree by the enzyme glycosyl transferase?
A fourth sugar can be added.
127
What does the i allele encode?
The i allele encodes a defective enzyme.
128
What is the effect of the i allele on the carbohydrate tree?
The carbohydrate tree is unchanged.
129
What does the IA allele encode?
IA encodes a form of the enzyme that can add N-acetylgalactosamine to the carbohydrate tree.
130
What does the IB allele encode?
IB encodes a form of the enzyme that can add galactose to the carbohydrate tree.
131
How are the A and B antigens recognized?
The A and B antigens are different enough to be recognized by different antibodies.
132
What must occur for safe blood transfusions?
The donor's blood must be a 'match' with the recipient's blood.
133
What happens if a type O individual receives blood from a type A, B, or AB?
Antibodies in the recipient's blood will react with antigens in the donated blood cells.
134
What is the result of the reaction between antibodies and antigens during a transfusion?
This causes the donated blood to agglutinate.
135
What may result from the agglutination of donated blood?
A life-threatening situation may result because of clogging of blood vessels.
136
What is the composition of the carbohydrate tree on the surface of RBCs?
The carbohydrate tree is composed of three sugars.
137
What role does the enzyme glycosyl transferase play in the carbohydrate tree?
It can add a fourth sugar to the carbohydrate tree.
138
What does the i allele encode?
The i allele encodes a defective enzyme.
139
What is the effect of the i allele on the carbohydrate tree?
The carbohydrate tree is unchanged.
140
What does the IA allele encode?
IA encodes a form of the enzyme that can add the sugar N-acetylgalactosamine to the carbohydrate tree.
141
What does the IB allele encode?
IB encodes a form of the enzyme that can add the sugar galactose to the carbohydrate tree.
142
How do the A and B antigens differ?
The A and B antigens are different enough to be recognized by different antibodies.
143
What must occur for safe blood transfusions?
The donor's blood must be a 'match' with the recipient's blood.
144
What happens if a type O individual receives blood from a type A, B, or AB?
Antibodies in the recipient blood will react with antigens in the donated blood cells, causing agglutination.
145
What may result from the agglutination of donated blood?
A life-threatening situation may result because of clogging of blood vessels.
146
What are the ABO blood types?
A, B, AB, O
147
What is the genotype for blood type A?
JAJA or lAi
148
What are the serum antibodies for blood type A?
against B
149
What is the genotype for blood type B?
B/B or /Bi
150
What are the serum antibodies for blood type B?
against A
151
What is the genotype for blood type AB?
JAB
152
What are the serum antibodies for blood type AB?
none
153
Who is a universal recipient?
Blood type AB
154
Who is a universal donor?
Blood type O
155
What is overdominance?
The phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes.
156
What is another name for overdominance?
Heterozygote advantage
157
What is an example of overdominance?
Sickle-cell anemia
158
What type of disorder is sickle-cell anemia?
Autosomal recessive disorder
159
What alleles are involved in sickle-cell anemia?
HbA and HbS
160
What does HbA encode?
Normal hemoglobin, hemoglobin A
161
What does HbS encode?
Abnormal hemoglobin, hemoglobin S
162
What happens to HbSHbS individuals under low oxygen tension?
Their red blood cells deform into a sickle shape.
163
What is expressivity?
Expressivity is the degree to which a trait is expressed.
164
What does high expressivity indicate in polydactyly?
A person with several extra digits has high expressivity of this trait.
165
What does low expressivity indicate in polydactyly?
A person with a single extra digit has low expressivity.
166
What are essential genes?
Essential genes are those that are absolutely required for survival.
167
What happens if essential genes are absent?
The absence of their protein product leads to a lethal phenotype.
168
What proportion of all genes are estimated to be essential for survival?
It is estimated that about 1/3 of all genes are essential for survival.
169
What are nonessential genes?
Nonessential genes are those not absolutely required for survival.
170
What is a lethal allele?
A lethal allele is one that has the potential to cause the death of an organism.
171
How are lethal alleles usually inherited?
Lethal alleles are usually inherited in a recessive manner.
172
What effect do many lethal alleles have on cell division?
Many lethal alleles prevent cell division, which can kill an organism at an early age.
173
What do many lethal alleles prevent?
Many lethal alleles prevent cell division.
174
What is the effect of some lethal alleles?
Some lethal alleles exert their effect later in life.
175
What diseases are associated with lethal alleles that exert effects later in life?
Huntington disease and Early Onset Alzheimer's Disease.
176
What are the characteristics of Huntington disease and Early Onset Alzheimer's Disease?
They are characterized by progressive degeneration of the nervous system, dementia, and early death.
177
What is the usual age of onset for Huntington disease and Early Onset Alzheimer's Disease?
The age of onset is usually between 30 and 50.
178
How may a lethal allele affect phenotypic ratios?
A lethal allele may produce ratios that seemingly deviate from Mendelian ratios.
179
What is an example of a lethal allele in cats?
The Manx cat carries a dominant mutation that affects the spine.
180
What does the Manx mutation do?
This mutation shortens the tail.
181
Why is the Manx allele considered lethal?
This allele is lethal as a homozygote dominant.
182
What is the expected phenotypic ratio of live offspring when crossing two heterozygous Manx cats?
The expected phenotypic ratio of the live offspring is 2:1.
183
Tt
184
What is the difference?
185
White
186
Re
187
d
188
P generation
189
P (parental)
190
generation
191
Cross-
192
fertilize
193
Purple
194
White
195
Pin
196
F1 generation
197
Self-fertilize
198
F1
199
generation
200
Purple
201
Incomplete Dominance
202
In incomplete dominance the heterozygote exhibits a
203
phenotype that is intermediate between the corresponding
204
homozygotes
205
Red
206
White
207
• Example:
208
Flower color in the four o'clock plant
209
Two alleles
210
•
211
CR = wild-type allele for red flower color
212
CW = allele for white flower color
213
P generation
214
Pink
215
F
generation
216
Re
217
Whit
218
generation
219
CWC
220
W
221
In this case
50% of
222
the CR protein is not
223
cufficiant to produca
224
Human Pedigree for Duchenne muscular dvstronhv-Affected individuals are shown
225
with filled symbol $ @ • OTt ? dO>bols.
226
X-linked Genes
227
Many species have males and females that
228
differ in their sex chromosome composition
229
Certain traits are governed by genes on the sex
230
chromosomes
231
Question 1: A X-linked recessive trait that leads to disease will
232
affect males or females the most? Complete a Punnett Square to
233
answer this question.
234
• Question 3: Complete a Punnett Square
235
Consider a cross between an affected female
236
golden retriever (XdXd) and unaffected male
237
(XDY). What offspring would you expect?
238
Affected offspring?
239
Carriers?
240
Reverse the genotype of the aft
241
does the outcome differ from the scenario
242
above?
243
Reciprocal Cross
244
• Allele / is recessive to both IA and IB
245
•Alleles IA and IB are codominant
246
• They are both expressed in a heterozygous individual
247
Blood type:
248
Genotype:
249
Surface antigen:
250
Serum antibodies:
251
(a) ABO blood type
252
RBC
253
N-acetyl-
254
galactosamine
255
ii
256
neither A or B
257
against A and B
258
Antigen A
259
RBC
260
pApa orlAi
261
against B
262
Antigen B
263
Antigen A
264
Antigen B
265
RBC
266
B
267
B/B or Bi
268
B
269
against A
270
Galactose
271
RBC
272
AB
273
JAB
274
A and B
275
none
276
Glycosyl transferase
277
encoded by A allele
278
Antigen A
279
Active
280
site
281
RBC
282
N-acetyl-
283
galactosamine
284
Glycosyl transferase
285
encoded by B allele
286
RBC
287
Antigen B
288
• Active
289
site
290
RBC
291
Galactose
292
(c) Formation of A and B antigen by glycosyl transferase
293
RBC
294
The carbohydrate tree on the surface of RBCs is composed of three
295
• Allele / is recessive to both IA and IB
296
•Alleles IA and IB are codominant
297
• They are both expressed in a heterozygous individual
298
Blood type:
299
Genotype:
300
Surface antigen:
301
Serum antibodies:
302
(a) ABO blood type
303
RBC
304
N-acetyl-
305
galactosamine
306
ii
307
neither A or B
308
against A and B
309
Antigen A
310
RBC
311
pApa orlAi
312
against B
313
Antigen B
314
Antigen A
315
Antigen B
316
RBC
317
B
318
B/B or Bi
319
B
320
against A
321
Galactose
322
RBC
323
AB
324
JAB
325
A and B
326
none
327
Glycosyl transferase
328
encoded by A allele
329
Antigen A
330
Active
331
site
332
RBC
333
N-acetyl-
334
galactosamine
335
Glycosyl transferase
336
encoded by B allele
337
RBC
338
Antigen B
339
• Active
340
site
341
RBC
342
Galactose
343
(c) Formation of A and B antigen by glycosyl transferase
344
RBC
345
The carbohydrate tree on the surface of RBCs is composed of three
346
• Tt (
347
10 >
348
L
349
• The carbohydrate tree on the surface of RBCs is composed of three
350
sugars
351
• A fourth can be added by the enzyme glycosyl transferase
352
The i allele encodes a defective enzyme
353
The carbohydrate tree is unchanged
354
IA encodes a form of the enzyme that can add the sugar N-
355
acetylgalactosamine to the carbohydrate tree
356
IB encodes a form of the enzyme that can add the sugar galactose to the
357
carbohydrate tree
358
• The A and B antigens are different enough to be recognized by
359
different antibodies
360
Copyright ©The McGraw-Hill Companies
Inc. Permission required for reproduction or display
361
For safe blood transfusions to occur
the donor's blood must be
362
a
363
match
364
(answer: always the same
always different or a
365
"match") with the recipient's blood.
366
What it might occur if a type O individual receives blood from a type
367
A
B or AB?
368
Antibodies in the recipient blood will react with antigens in the donated blood
369
cells
370
This causes the donated blood to agglutinate
371
A life-threatening situation may result because of clogging of blood vessels
372
Antigen A
373
Antigen B
374
Antigen A
375
Antigen B
376
Antigen A
377
Antigen B
378
Antigen A
379
Antigen B
380
RBC
381
N-acetyl-
382
galactosamine
383
RBC
384
Blood type:
385
Genotype:
386
Surface antigen:
387
Serum antibodies:
388
(a) ABO blood type
389
ii
390
neither A or B
391
against A and B
392
JAJA or lAi
393
against B
394
RBC
395
B
396
B/B or /Bi
397
against A
398
Galactose
399
RBC
400
AB
401
JAB
402
A and B
403
none
404
Who is an universal recipient?
405
Who is an universal donor?
406
Overdominance
407
•
408
-
409
Overdominance is the phenomenon in which a heterozygote is
410
more vigorous than both of the corresponding homozygotes
411
It is also called heterozygote advantage
412
• Example = Sickle-cell anemia
413
-
414
-
415
-
416
Autosomal recessive disorder
417
Affected individuals produce abnormal form of hemoglobin
418
Two alleles
419
HbA • Encodes the normal hemoglobin
hemoglobin A
420
•
421
HoS • Encodes the abnormal hemoglobin
hemoglobin S
422
• HbSHbS individuals have red blood cells that deform into a sickle
423
shape under conditions of low oxygen tension
424
Tt
425
• HbSHbS individuals have red blood cells that deform into a sickle
426
shape under conditions of low oxygen tension
427
Two major effects
428
1. Sickling phenomenon greatly shortens
429
the life span of the red blood cells
430
Anemia results
431
2. Odd-shaped cells clump
432
Partial or complete blocks in capillary circulation
433
Normal red
434
blood cell
435
Sickled red
436
blood cell
437
Thus
affected individuals tend to have pain
438
vision problems and other symptoms
439
The sickle cell allele is at fairly high frequency in
440
parts of Africa where malaria is found
441
in!
442
< 0.1
443
0.1-0.19
444
0.2-0.99
445
1.0-4.9
446
5.0-9.9
447
10.0-18.9
448
2 19.0
449
Births with a pathological Hb disorder per 1
000 live births
450
Copyright ©The McGraw-Hill Companies
Inc. Permission required for reproduction or display
451
• Malaria is caused by a protozoan
Plasmodium
452
-
453
•
454
This parasite undergoes its life cycle in two main parts
455
One inside the Anopheles mosquito
456
The other inside red blood cells
457
• Malaria is caused by a protozoan
Plasmodium
458
This parasite undergoes its life cycle in two main parts
459
One inside the Anopheles mosquito
460
The other inside red blood cells
461
Life Cycle of the Malaria Parasite
462
sexual stage:
463
male or female
464
camerocutes
465
Torm
466
5 mosquito
467
stages
468
blood cell
469
= ne mosquio consumes
470
the pagastie during blood
471
The mosquito injects the
472
paraste when roles
473
ookinete
474
oocyst
475
6
476
late
477
mosquito
478
stage
479
human 2
480
liver stage
481
sporozoites
482
human
483
Red blood cells of heterozygotes
are likely to rupture when infected by
484
Plasmodium sp.
485
This prevents the propagation of the parasite
486
• HAHS individuals have an "advantage" over because they do not
487
suffer from sickle cell anemia and are more resistant to malaria.
488
Schizogonic cycle
489
Remember that:
490
AA
491
Invasion
492
• HbSHbS
= suffer from
493
sickle cell anemia
494
• HbAHbA
= are less
495
resistant to Malaria
496
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3499995/pdf/mjhid-4-1-e2012065.pdf
497
AS
498
Selective sickling
499
of parasitised
500
AS red cells
501
Selective phagocytosis
502
of sickled parasitised AS red cells
503
Toololall lo Ivialalla
504
http://www.ncbi.nlm.nih.gov/pmc/artic
505
AS red cells
506
Selective phago....
507
O Cd 0 > sicked parasitisee
508
What pattern of inheritance do you observe in the
509
pedigree chart in the next slide?
510
How did you reach that conclusion?
511
Who are carriers?
512
Who are affected?
513
Affected
514
with DMD
515
- Unaffected
516
presumed heterozygote
517
III-
518
1
519
II-
520
1
521
III-
522
2
523
I-1
524
I-2
525
II-
526
2
527
III-
528
3
529
II-
530
3
531
II-
532
4
533
III-
534
4
535
II-
536
5
537
III-
538
5
539
II-
540
6
541
III-
542
6
543
III-
544
7
545
III-
546
8
547
IV-
548
IV-
549
2
550
IV-
551
3
552
IV-
553
IV-
554
4
555
5
556
IV-
557
6
558
IV-
559
7
560
Human Pedigree for Duchenne muscular dystrophy-Affected individuals are shown
561
with filled symbols. Female carriers are shown with half-filled symbols.
562
X-linked Genes
563
Human Pedigree for Duchenne muscular dvstronhv-Affected individuals are shown
564
with filled symbol $ @ • OTt ? dO>bols.
565
X-linked Genes
566
Many species have males and females that
567
differ in their sex chromosome composition
568
Certain traits are governed by genes on the sex
569
chromosomes
570
Question 1: A X-linked recessive trait that leads to disease will
571
affect males or females the most? Complete a Punnett Square to
572
answer this question.
573
• Question 3: Complete a Punnett Square
574
Consider a cross between an affected female
575
golden retriever (XdXd) and unaffected male
576
(XDY). What offspring would you expect?
577
Affected offspring?
578
Carriers?
579
Reverse the genotype of the aft
580
does the outcome differ from the scenario
581
above?
582
Reciprocal Cross
583
Sex Chromosomes and Traits
584
• Sex-linked genes are those found on one of the two types of sex
585
chromosomes
but not both
586
• X-linked
587
Males are more likely to be affected
588
• Y-linked
589
Transmitted from father to son
590
-
591
Males are the only ones affected
592
-
593
Sex Chromosomes and Traits
594
Pseudoautosomal inheritance refers to the very few genes found
595
on both X and Y chromosomes
596
Found in homologous regions needed for chromosome pairing
597
Pseudo (fake)
598
Mic2
599
gen
600
e
601
Y
602
Mic2
603
gen
604
e
605
The following pedigree chart represent a disorder that runs in a family.
606
A. What pattern of inheritance better explains the observed pattern? (autosomal dominant
autosomal recessive or
607
&-linked recessive
Y-linked recessive or Y-linked dominant? Explain in detail how did you reach to that
608
The following pedigree chart represent a disorder that runs in a family.
609
A. What pattern of inheritance better explains the observed pattern? (autosomal dominant
autosomal recessive or
610
&-linked recessive
Y-linked recessive or Y-linked dominant? Explain in detail how did you reach to that
611
conclusion.
612
Note: Carriers are not represented in half-filled
613
becouse the
614
1-1
615
1-2.
616
parent con be
617
a corier
618
auto somaldominal
619
at least and parent will
620
be affected
621
II-1
622
II-2
623
II-3
624
11-4
625
III-1
626
III-2
627
III-3
628
III-4
629
III-5
630
IV-1
631
IV-2
632
IV-3
633
IV-4
634
IV-5
635
IV-6
636
Sex-influenced Traits
637
•
638
Traits where an allele is dominant in one sex but recessive in the
639
opposite sex.
640
Alleles are not found on sex chromosomes. Most sex-influenced
641
traits are autosomal
642
•
643
Sex-influenced does not mean sex-linked
644
Sex-influenced Traits
645
Example: Pattern of baldness in humans
646
Tt
647
Sex-influenced Traits
648
Example: Pattern of baldness in humans
649
Caused by an autosomal gene
650
Allele B is dominant in males
but acts as recessive in females who are
651
heterozygous.
652
in male determine by dominant allele
653
Genotype
654
Phenotype
655
Phenotype
656
in Males
657
in Females
658
BB
659
Bb
660
bald BB
661
bald (BB)
662
bald Bb
663
nonbald Bb
664
bb
665
nonbald bb
666
nonbald (66)
667
in female determine by recessive allele
668
Sex-influenced Traits
669
Pattern baldness appears to be related to the production of
670
Sex-influenced Traits
671
Pattern baldness appears to be related to the production of
672
testosterone
673
Baldness results from overexpression of a gene that converts
674
testosterone to 5-a-dihydrotestosterone (DHT) which binds to cellular
675
receptors and alters expression of many genes (e.g. on the scalp)
676
Females heterozygotes (Bo) are not bald
677
Homozygous women (BB) will have a significant thinning of the hair
678
relatively late in life
679
Sex-influenced Traits
680
• Example: Pattern of baldness in humans
681
-
682
Caused by an autosomal gene
683
Allele B is dominant in males
but acts as recessive in females who are
684
heterozygous.
685
Genotype
686
BB
687
Bb
688
bb
689
Phenotype
690
in Males
691
bald
692
bald
693
nonbald
694
Phenotype
695
in Females
696
bald
697
nonbald
698
nonbald
699
Exercise:
700
- <
701
•
702
Exercise:
703
What might be the phenotypic outcome (% of bald
704
specify their sex) of a cross between a
705
heterozygous bald male and a heterozygous
706
female. Complete a Punnett Square.
707
bal
708
male
709
6
710
female
711
BB
712
M → bald
713
F→ bold
714
Bb
715
M → bald
716
F → no bald
717
bB
718
M → bald
719
f-no bald
720
bb
721
M→ no bald
722
= → nobald
723
bE
724
4
725
4
726
0.5
727
75
728
25
729
and
730
IV-1
731
IV-L
732
IV-3
733
-<1
734
is not because
735
is not shouting the
736
shenatype
737
GENE INTERACTIONS
738
• Two or more different genes influence the outcome of a
739
single trait
740
E.g. height
weight and pigmentation are affected by many
741
different genes in combination with environmental factors
742
The term epistasis describes the situation in which a gene can mask the
743
phenotypic effects of another gene
744
Epistatic interactions often arise because two (or more) different proteins
745
participate in a common cellular function
746
For example
an enzymatic pathway
747
Enzyme
748
Enzyme
749
Colorless
750
precursor
751
Colorless
752
intermediat
753
e
754
P
755
- Purple
756
pigmen
757
The recessive c allele encodes
758
an inactive enzyme
759
PP
760
The recessive p allele encodes
761
an inactive enzyme
762
PP
763
If an individual is homozygous for either recessive allele
764
It will not make any functional enzyme C or enzyme P
765
Therefore
the flowers remain white
766
no intramediat the color will
767
not work
768
A Cross Involving a Two-Gene Interaction Can
769
Produce two distinct phenotypes
770
Inharitance of flower color in the ewaat non
771
It will not make any functional enzyme C or/enzyme P
772
Therefore
the flowers 0>
773
no inteamed at the color will
774
not work
775
A Cross Involving a Two-Gene Interaction Can
776
Produce two distinct phenotypes
777
• Inheritance of flower color in the sweet pea
778
-
779
Lathyrus odoratus normally has purple flowers
780
Bateson and Punnett obtained several true-breeding
781
varieties with white flowers
782
They carried out the following cross
783
-
784
P: True-breeding purple X true-breeding white
785
F1: Purple flowered plants
786
F2: Purple- and white-flowered in a 3:1 ratio
787
These results were not surprising
788
Copyright ©The McGraw-Hill Companies
Inc. Permission required for reproduction or display
789
But these results were
790
White variety #1
791
White variety #2
792
Complementation: Each
793
recessive allele (c and p)
794
is complemented by a
795
wild-type allele (C and P).
796
This phenomenon indicates
797
that the recessive alleles
798
are in different genes.
799
Complementation
800
F2 generation
801
Recessive Epistasis:
802
Homozygosity
803
for the recessive allele
804
of either gene results in
805
a white phenotype
thereby
806
masking the purple
807
(wild-type) phenotype.
808
Both gene products
809
encoded by the wild-type
810
alleles (C and P) are
811
needed for a purple
812
phenotype.
813
Thus
the F2 generation contained purple and white flowers in a ratio of
