Chapter 14 Mendel and the Gene Idea p 272 Ch 14 Genetics Problems (17) – due Nov. 4 p 291 Ch 15 Genetics Problems (14) - The answers are in the back of

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


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.



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


- 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




- 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


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


Purple flowerPP

White flowerspp

Purple flowersPp


Gametes:

Gametes:





Figure 14.5 Mendel’s law of segregation

P Generation

F1 Generation

F2 Generation

P p

P p

P p

P

p

PpPP

ppPp


Purple flowerPP

White flowerspp

Purple flowersPp


Gametes:

Gametes:

F1 sperm

F1 eggs

1/21/2





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




- 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




- 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?


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)


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

Documents

Chapter 14 Mendel and the Gene Idea p 272 Ch 14 Genetics Problems (17) – due Nov. 4 p 291 Ch 15 Genetics Problems (14) - The answers are in the back of