CH11

CH11

Fig. 1. Difference between the outcomes from blending and from particulate inheritance. In post-Mendelian terms, we assume a single diallelic locus, and hence three diploid genotypes (AA, blue; Aa, green; aa, yellow). Under particulate inheritance, the population's variability is preserved from generation to generation. In contrast, the conventional wisdom of Darwin's day saw offspring inherit a blend of parents' characteristics, here represented as the average of the two parental shadings. The result is that the variability diminishes in successive generations (the variance is halved each generation if mating is at random) SCIENCE MAGAZINE B. MAY

Figure 11.2

Parentalgeneration(P)

Stamens

First filialgenerationoffspring(F1)

Carpel

Technique

Results

1

2

3

4

5

Why are peas so great to work with?

Figure 11.4

Allele for purple flowers

Pair of homologouschromosomes

Allele for white flowers

Locus for flower-color gene

Review of terms….What is a locus? What are alleles?

• Is this individual with these chromosomes in their cells homozygous or heterozygous?• What is the genotype? • If purple flower allele is dominant, what is the phenotype?

Figure 11.3-3

P Generation

Experiment

(true-breedingparents)

F1 Generation

F2 Generation

(hybrids)

Purple flowers White flowers

All plants had purple flowers

What Self- or cross-pollination

705 purple-floweredplants

224 white-floweredplants

So all F1 are Pp

What are the genotypes of the gametes of these Pp plants?

Figure 11.6 Phenotype

1

Genotype

Purple

Purple

Purple

White

Ratio 3:1

PP (homozygous)

Pp (heterozygous)

Pp (heterozygous)

pp (homozygous)

Ratio 1:2:1

2

3

1

1

Figure 11.3-3

P Generation

Experiment

(true-breedingparents)

F1 Generation

F2 Generation

(hybrids)

Purple flowers White flowers

All plants had purple flowers

Self- or cross-pollination

705 purple-floweredplants

224 white-floweredplants

Imagine crossing a pea heterozygous at the loci for flower color (white versus purple) and seed color (yellow versus green) with a second pea homozygous for flower color (white) and seed color (yellow). What types of gametes will the first pea produce?

• two gamete types: white/white and purple/purple• two gamete types: white/yellow and purple/green• four gamete types: white/yellow, white/green, purple/yellow,

and purple/green• four gamete types: white/purple, yellow/green, white/white,

and purple/purple• one gamete type: white/purple/yellow/green

Imagine crossing a pea heterozygous at the loci for flower color (white versus purple) and seed color (yellow versus green) with a second pea homozygous for flower color (white) and seed color

(yellow). What types of gametes will the first pea produce?

• two gamete types: white/white and purple/purple• two gamete types: white/yellow and purple/green• four gamete types: white/yellow, white/green,

purple/yellow, and purple/green• four gamete types: white/purple, yellow/green, white/white,

and purple/purple• one gamete type: white/purple/yellow/green

For this cross assume white is dominant and yellow is dominant…. What different offspring will you get????

Figure 11.8

YR yr

YR

yr

YYRR

yyrr

YyRr

YyRr

Experiment

Predictions

P Generation

F1 Generation

Predictedoffspring inF2 generation

Gametes

YYRR yyrr

YyRr

Results

EggsEggs

Sperm

Spermor

Hypothesis ofdependent assortment

Phenotypic ratio 3:1

Hypothesis ofindependent assortment

¾ ¼

½ ½

½

½

¼

¼

¼

¼

¼¼¼¼

YR yr

Phenotypic ratio approximately 9:3:3:1

Phenotypic ratio 9:3:3:1

YR yr

YR

yr

YYRR

yyrr

YYRr YyRr

Yr yR

Yr

yR

YyRR

YYRr YYrr YyrrYyRr

YyRR YyRr yyRryyRR

YyRr Yyrr yyRr

315 108 101 32

9 163 16

3 161 16

Twins…EACH of you should respond to each question on paper after you have a discussion in your group about your response!

1. Why are twins raised in different households considered so valuable to biologists?

2. What is heritability? (they talk about height in this article)

FYI these graphs are not a result of twin analyses but are a result of studying inheritance through regression statistics.

3. Which graphs show hi, medium and low heritability?

4. What might a graph with the actual heritability of height look like? Draw one!

5. If heritability is high like .8 does that mean the environment is not important?

6. Why do we freak out when we learn the heritability of IQ is something like .75? Historical connections?

7. What are we learning from situations where identical twins differ in specific substantial ways despite being raised in the same household? (autism example)

8. So what is epigenetics?

9. There are several analogies towards the end of the article-what were they?

http://erinjenne.blogspot.com/2011_02_01_archive.html

Figure 11.10-2

½ ½

P Generation

F1 Generation

Gametes

Gametes

WhiteCWCW

PinkCRCW

RedCRCR

CWCR

CWCR

Today…..What is this called?

Is this blending inheritance???

Albinism in humans occurs when both alleles at a locus produce defective enzymes in the biochemical pathway leading to melanin.

Given that heterozygotes are normally pigmented, which of the following statements is/are correct?

• One normal allele produces as much melanin as two normal alleles.

• Each defective allele produces a little bit of melanin.• Two normal alleles are needed for normal melanin

production.• The two alleles are codominant.• The amount of sunlight will not affect skin color of

heterozygotes.

Imagine a locus with four different alleles for fur color in an animal. The alleles are named Da, Db, Dc, and Dd. If you

crossed two heterozygotes, DaDb and DcDd, what genotype proportions would you expect in the offspring?

• 25% DaDc, 25% DaDd, 25% DbDc, 25% DbDd

• 50% DaDb, 50% DcDd

• 25% DaDa, 25% DbDb, 25% DcDc, 25% DdDdDcDd

• 50% DaDc, 50% DbDd

• 25% DaDb, 25% DcDd, 25% DcDc, 25% DdDd

When a disease is said to have a multifactorial basis, it means that

• both genetic and environmental factors contribute to the disease.

• it is caused by a gene with a large number of alleles.

• it affects a large number of people. • it has many different symptoms. • it tends to skip a generation.

Figure 11.12

¼

¼

¼

¼

¼ ¼¼¼ BE Be

BE

be

BBEE

bbee

BbEE BbEe

bE be

bE

Be

BBEe

BbEE bbEE bbEeBbEe

BBEe BbEe BbeeBBee

BbEe bbEe Bbee

9 : 4: 3

Eggs

Sperm

BbEe BbEeWhat is this called????

What is going on????

Figure 11.13

Eggs

Sperm

AaBbCc AaBbCc

Phenotypes:

0Number ofdark-skin alleles: 1 2 3 4 5 6

1 64 1 646 64 6 64 1 6415 64 15 6420 64

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 81 8 1 8 1 8 1 81 81 8 1 8