Chapter 14 Mendel and the Gene Idea
p 272 Ch 14 Genetics Problems (17) – due Nov. 4p 291 Ch 15 Genetics Problems (14)
- The answers are in the back of the book!!!!- I need to get the impression that you have worked out the problems &
not copied the correct answer!!
1. What do you know about genetics?- Mendel – Father of Genetics – peas
Chapter 14 Mendel and the Gene Idea
1
5
4
3
2
Removed stamensfrom purple flower
Transferred sperm-bearing pollen fromstamens of white flower to egg-bearing carpel of purple flower
Parentalgeneration(P)
Pollinated carpelmatured into pod
Carpel(female)
Stamens(male)
Planted seedsfrom pod
Examinedoffspring:all purpleflowers
Firstgenerationoffspring(F1)
APPLICATION By crossing (mating) two true-breedingvarieties of an organism, scientists can study patterns ofinheritance. In this example, Mendel crossed pea plantsthat varied in flower color.
TECHNIQUETECHNIQUE
When pollen from a white flower fertilizeseggs of a purple flower, the first-generation hybrids all have purpleflowers. The result is the same for the reciprocal cross, the transferof pollen from purple flowers to white flowers.
TECHNIQUERESULTS
P generation
F1 Generation
P Generation
(true-breeding parents) Purple
flowersWhiteflowers
F1 Generation (hybrids)
All plants hadpurple flowers
F2 Generation
EXPERIMENT True-breeding purple-flowered pea plants andwhite-flowered pea plants were crossed (symbolized by ). Theresulting F1 hybrids were allowed to self-pollinate or were cross-pollinated with other F1 hybrids. Flower color was then observedin the F2 generation.
RESULTS Both purple-flowered plants and white-flowered plants appeared in the F2 generation. In Mendel’sexperiment, 705 plants had purple flowers, and 224 had whiteflowers, a ratio of about 3 purple : 1 white.
Chapter 14 Mendel and the Gene Idea
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?- Mendel – Father of Genetics – peas- Allele – alternate form of a gene that gives different traits- Dominant allele
- gives a visible trait with only 1 copy- A
- Recessive allele - gives a visible trait with 2 copies- a
Allele for purple flowers
Locus for flower-color gene
Homologouspair ofchromosomes
Allele for white flowers
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics?
- Mendel – Father of Genetics – peas- Allele – alternate form of a gene that gives different traits- Dominant allele
- gives a visible trait with only 1 copy- A
- Recessive allele - gives a visible trait with 2 copies- a
- Homozygous - 2 copies of the same allele- AA or aa
- Heterozygous- 1 copy of each allele- Aa
- True breeders - parents who mate & always yield the same genetic offspring- AA x AA or aa x aa
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics?
- Mendel – Father of Genetics – peas- Allele – alternate form of a gene that gives different traits- Dominant allele - Recessive allele - Homozygous - Heterozygous- True breeders
- parents who mate & always yield the same genetic offspring- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest- Dihybrid – organism that is heterozygous for 2 genes of interest- Genotype – genetic make up of an organism (its alleles)- Phenotype – physical traits exhibited – based on genotype
3
1 1
2
1
Phenotype
Purple
Purple
Purple
White
Genotype
PP(homozygous)
Pp(heterozygous)
Pp(heterozygous)
pp(homozygous)
Ratio 3:1 Ratio 1:2:1
Figure 14.6 Phenotype versus genotype
Test corrections- Staple corrections behind- Tuck scantron inside- Place in box
Can transport tomorrow – all day & 4:30
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics?
- Mendel – Father of Genetics – peas- Allele – alternate form of a gene that gives different traits- Dominant allele - Recessive allele - Homozygous - Heterozygous- True breeders
- parents who mate & always yield the same genetic offspring- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest- Dihybrid – organism that is heterozygous for 2 genes of interest- Genotype – genetic make up of an organism (its alleles)- Phenotype – physical traits exhibited – based on genotype- Law of Segregation – each allele in a pair seegregates into a different
gamete during gamete formation (Anaphase I)
P Generation
F1 Generation
P p
Appearance:Genetic makeup:
Purple flowerPP
White flowerspp
Purple flowersPp
Appearance:Genetic makeup:
Gametes:
Gametes:
Each true-breeding plant of the parental generation has identicalalleles, PP or pp.
Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele.
Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple-flower allele is dominant, allthese hybrids have purple flowers.
When the hybrid plants producegametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele.
Figure 14.5 Mendel’s law of segregation
P Generation
F1 Generation
P p
Appearance:Genetic makeup:
Purple flowerPP
White flowerspp
Purple flowersPp
Appearance:Genetic makeup:
Gametes:
Gametes:
Each true-breeding plant of the parental generation has identicalalleles, PP or pp.
Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele.
Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple-flower allele is dominant, allthese hybrids have purple flowers.
When the hybrid plants producegametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele.
Figure 14.5 Mendel’s law of segregation
P Generation
F1 Generation
F2 Generation
P p
P p
P p
P
p
PpPP
ppPp
Appearance:Genetic makeup:
Purple flowerPP
White flowerspp
Purple flowersPp
Appearance:Genetic makeup:
Gametes:
Gametes:
F1 sperm
F1 eggs
1/21/2
Each true-breeding plant of the parental generation has identicalalleles, PP or pp.
Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele.
Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple-flower allele is dominant, allthese hybrids have purple flowers.
When the hybrid plants producegametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele.
This box, a Punnett square, shows all possible combinations of alleles in offspring that result from an F1 F1 (Pp Pp) cross. Each square represents an equally probable product of fertilization. For example, the bottomleft box shows the genetic combinationresulting from a p egg fertilized bya P sperm.
Random combination of the gametesresults in the 3:1 ratio that Mendelobserved in the F2 generation. 3 : 1
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics?
- Mendel – Father of Genetics – peas- Allele – alternate form of a gene that gives different traits- Dominant allele - Recessive allele - Homozygous - Heterozygous- True breeders
- parents who mate & always yield the same genetic offspring- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest- Dihybrid – organism that is heterozygous for 2 genes of interest- Genotype – genetic make up of an organism (its alleles)- Phenotype – physical traits exhibited – based on genotype- Law of Segregation – each allele in a pair segregates into a different
gamete during gamete formation (Anaphase I)- Testcross – breeding an organism of unknown genotype with a
homozygous recessive
Dominant phenotype,unknown genotype:
PP or Pp?
Recessive phenotype,known genotype:
pp
If PP,then all offspring
purple:
If Pp,then 1⁄2 offspring purpleand 1⁄2 offspring white:
p p
P
P
Pp Pp
PpPp
pp pp
PpPpP
p
p p
APPLICATION An organism that exhibits a dominant trait,such as purple flowers in pea plants, can be either homozygous forthe dominant allele or heterozygous. To determine the organism’sgenotype, geneticists can perform a testcross.
TECHNIQUE In a testcross, the individual with theunknown genotype is crossed with a homozygous individualexpressing the recessive trait (white flowers in this example). By observing the phenotypes of the offspring resulting from this cross, we can deduce the genotype of the purple-flowered parent.
RESULTS
Figure 14.7 The Testcross
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics?
- Mendel – Father of Genetics – peas- Allele – alternate form of a gene that gives different traits- Dominant allele - Recessive allele - Homozygous - Heterozygous- True breeders
- parents who mate & always yield the same genetic offspring- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest- Dihybrid – organism that is heterozygous for 2 genes of interest- Genotype – genetic make up of an organism (its alleles)- Phenotype – physical traits exhibited – based on genotype- Law of Segregation – each allele in a pair segregates into a different
gamete during gamete formation (Anaphase I)- Testcross – breeding an organism of unknown genotype with a
homozygous recessive- Law of Independent Assortment – each pair of alleles separates
independently during gamete formation when genes for 2 traits are on different homologous chromosomes (Metaphase I)
YYRRP Generation
Gametes YR yr
yyrr
YyRrHypothesis ofdependentassortment
Hypothesis ofindependentassortment
F2 Generation(predictedoffspring)
1 ⁄2 YR
YR
yr
1 ⁄2
1 ⁄2
1 ⁄2 yr
YYRR YyRr
yyrrYyRr
3 ⁄4 1 ⁄4
Sperm
Eggs
Phenotypic ratio 3:1
YR1 ⁄4
Yr1 ⁄4
yR1 ⁄4
yr1 ⁄4
9 ⁄163 ⁄16
3 ⁄161 ⁄16
YYRR YYRr YyRR YyRr
YyrrYyRrYYrrYYRr
YyRR YyRr yyRR yyRr
yyrryyRrYyrrYyRr
Phenotypic ratio 9:3:3:1
315 108 101 32 Phenotypic ratio approximately 9:3:3:1
F1 Generation
Eggs
YR Yr yR yr1 ⁄4 1 ⁄4 1 ⁄4 1 ⁄4
Sperm
RESULTS
CONCLUSION The results support the hypothesis of independent assortment. The alleles for seed color and seed shape sort into gametes independently of each other.
EXPERIMENT Two true-breeding pea plants—one with yellow-round seeds and the other with green-wrinkled seeds—were crossed, producing dihybrid F1 plants. Self-pollination of the F1 dihybrids, which are heterozygous for both characters, produced the F2 generation. The two hypotheses predict different phenotypic ratios. Note that yellow color (Y) and round shape (R) are dominant.
Figure 14.8 Do the alleles for seed color and seed shape sort into gametes dependently (together) or independently?
Chapter 14 Mendel and the Gene Idea
Rr
Segregation ofalleles into eggs
Rr
Segregation ofalleles into sperm
R r
rR
RR
R1⁄2
1⁄2 1⁄2
1⁄41⁄4
1⁄41⁄4
1⁄2 r
rR r
r
Sperm
Eggs
1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?
- 0 = never will happen- 1 = always happens- Consider a coin….
- Probability of heads = 0.5- Probability of tails = 0.5
3. What is the rule of multiplication?- prob. of RR offspring from
Rr x Rr- R (½ ) x R (½) = ¼ - Prob. of rr offspring from
Rr x Rr- r (½) x r (½) = ¼
4. What is the rule of addition?- Prob. of Rr offspring from
Rr x Rr- R (½) x r (½) = ¼ (1st parent gives R)- R (½) x r (½) = ¼ (2nd parent gives R)- ¼ + ¼ = ½ Rr offspring - Only when Rr x Rr make Rr
Let’s practice…..
PpYyRr x Ppyyrr
1. ppyyRr = ?2. ppYyrr = ?3. Ppyyrr = ?
4. PPyyrr = ?5. ppyyrr = ?
½ · ½ · ½ · 1 · ½ · 1 = 1/16½ · ½ · ½ · 1 · ½ · 1 = 1/16(½ · ½) + (½ · ½) · ½ · 1 · ½ · 1 = ½ · ½ · 1 · ½ · 1 = 1/8 ½ · ½ · ½ · 1 · ½ · 1 = 1/16 ½ · ½ · ½ · 1 · ½ · 1 = 1/16
1/161/161/8
1/161/16
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?
- Heterozygous phenotype is in between the 2 homozygous phenotypes
- snapdragons- 1:2:1 for phenotype = genotype
P Generation
F1 Generation
F2 Generation
RedCRCR
Gametes CR CW
WhiteCWCW
PinkCRCW
Sperm
CR
CR
CR
Cw
CR
CRGametes1⁄2 1⁄2
1⁄2
1⁄2
1⁄2
Eggs1⁄2
CR CR CR CW
CW CWCR CW
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?
- Phenotype shows both alleles being expressed- Both alleles can be detected- Blood typing – glycoprotein on RBC- Blood typing also shows
multiple alleles (more than 2 allelic variations at a gene locus)
Chapter 14 Mendel and the Gene Idea
Tay-Sachs disease – brain cells cannot metabolize a certain lipid because of an enzyme deficiency
Phenotype seen - dd (homozygous recessive)
- consider Dd - appear normal – 1 copy sufficient- biochemically – incomplete dominance – less enzyme activity
can be detected….in between DD and dd- molecularly – codominant – both normal enzyme & mutant
enzyme can be detected
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?7. What is pleiotropy?
- 1 gene with multiple effects- Sickle cell allele- RBC form a sickle shape (“C”) when oxygen deprived causing blood
flow problems leading to fatigue, pain, brain damage, 8. What is epistasis?
- Gene at 1 locus alters the phenotypic expression of a gene at a 2nd locus
BC bC Bc bc1⁄41⁄41⁄41⁄4
BC
bC
Bc
bc
1⁄4
1⁄4
1⁄4
1⁄4
BBCc BbCc BBcc Bbcc
Bbcc bbccbbCcBbCc
BbCC bbCC BbCc bbCc
BBCC BbCC BBCc BbCc
9⁄163⁄16
4⁄16
BbCc BbCc
Sperm
Eggs
Figure 14.11 An example of epistasis
B = black coatb = brown coatC = pigmentc = no pigment
In order to have color,the cells must have pigment.
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?7. What is pleiotropy?8. What is epistasis?9. What is polygenic inheritance?
- An additive effect of 2 or more genes on a single phenotype- Opposite of pleiotropy- Skin pigmentation
AaBbCc AaBbCc
aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC
20⁄64
15⁄64
6⁄64
1⁄64
Fra
cti o
n o
f p
rog
en
y
Figure 14.12 A simplified model for polygenic inheritance of skin color
Skin pigmentation controlled by 3 separate genes
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?7. What is pleiotropy?8. What is epistasis?9. What is polygenic inheritance?10. Can the environment influence phenotype?
- Plants – leaf shape, size, greenness – depend on wind, sunlight, rain nutrition – Figure 50.9
- Us – height, weight, exercise – depend on nutrition
- Hydrangea color depends on soil acidity- Multifactorial – many factors,genetic & environmental influence phenotype
Ww ww ww Ww
wwWwWwwwwwWw
WWor
Ww
ww
First generation(grandparents)
Second generation(parents plus aunts
and uncles)
Thirdgeneration
(two sisters)
Ff Ff ff Ff
ffFfFfffFfFF or Ff
ff FForFf
Widow’s peak No Widow’s peak Attached earlobe Free earlobe
(a) Dominant trait (widow’s peak) (b) Recessive trait (attached earlobe)
Figure 14.14 Pedigree analysis
Pedigree analysis - follows specific traits over generations of a family
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?7. What is pleiotropy?8. What is epistasis?9. What is polygenic inheritance?10. Can the environment influence phenotype?11. What are some recessively inherited human disorders?
- Only seen as dd, Dd are considered carriers- Cystic fibrosis – caused by a defect in a Cl- channel protein in lungs
which leads to a mucus build up because an increase in Cl- concentration
- 1 in 2500 Caucasians of European descent- 1 in 25 (4%) carriers- Sickle-cell disease
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?7. What is pleiotropy?8. What is epistasis?9. What is polygenic inheritance?10. Can the environment influence phenotype?11. What are some recessively inherited human disorders?12. What are some dominantly inherited alleles?
- Achondroplasia - form of dwarfism- 1 in 25,000
- Huntington’s disease- degenerative disease of the nervous system- lethal dominant- phenotype visible between 35 – 45 yrs old- 1 in 10,000
Chapter 14 Mendel and the Gene Idea1. What do you know about genetics? Terms to know…2. How does genetics reflect probabilities?3. What is the rule of multiplication?4. What is the rule of addition?5. What is incomplete dominance?6. What is codominance?7. What is pleiotropy?8. What is epistasis?9. What is polygenic inheritance?10. Can the environment influence phenotype?11. What are some recessively inherited human disorders?12. What are some dominantly inherited alleles?13. How do doctors test for genetic anomalies?
- amniocentesis- chorionic villus sampling (CVS)
(a) Amniocentesis
Amnioticfluidwithdrawn
Fetus
Placenta Uterus Cervix
Centrifugation
A sample ofamniotic fluid canbe taken starting atthe 14th to 16thweek of pregnancy.
(b) Chorionic villus sampling (CVS)
Fluid
Fetalcells
Biochemical tests can bePerformed immediately onthe amniotic fluid or lateron the cultured cells.
Fetal cells must be culturedfor several weeks to obtainsufficient numbers forkaryotyping.
Severalweeks
Biochemicaltests
Severalhours
Fetalcells
Placenta Chorionic viIIi
A sample of chorionic villustissue can be taken as earlyas the 8th to 10th week ofpregnancy.
Suction tubeInserted throughcervix
Fetus
Karyotyping and biochemicaltests can be performed onthe fetal cells immediately,providing results within a dayor so.
Karyotyping
Figure 14.17 Testing a fetus for genetic disorders