Chapter 14Mendel and the Gene Idea

[Mendelian genetics: The scientific study of heredity and hereditary variation]

van Leeuwenhoek (17th century)de Graaf (17th century)Early 19th century – blending theory

X?

14.2Crossing pea plants (“genetic crosses”) – Gregor Mendel(19th century)

Discrete heritable factors

14.3Mendel tracked heritable characters for three generations

Both purple and white=flowered plants appear in the F2 generation in a ratio of approximately 3:1

Sweet pea flowers

14.4 Alleles, alternative versions of a gene

Table 14.1 Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants

14.5 Mendel’s law of segregation (Layer 1)

14.5 Mendel’s law of segregation (Layer 2)

14.6 Genotype versus phenotype

Round and wrinkled peas

SS or Ss

ss

14.7A testcross

14.8Testing two hypotheses for segregation in a dihybrid cross.

Do alleles sort independently?

Recombinant phenotypes

14.9 Segregation of alleles and fertilization as chance events

1) Black fur in mice (B) is dominant to brown fur (b). Short tails (T) is dominant to long tails (t). What proportion of the progeny of the cross BbTt multiply BBtt will have black fur and long tails?

A) 6/16B) 8/16C) 9/16D) 3/16E) 1/16

2) Tallness (T) is dominant to dwarfness (t), while red (R) flower color is dominant to white (r). The heterozygous condition results in pink (Rr) flower color. A dwarf red snapdragon is crossed with a plant homozygous for tallness and white flowers. What are the genotype and phenotype of the F1 individuals?

A) TtRr - tall and pinkB) ttRr - dwarf and pinkC) TtRr - tall and redD) TTRR - tall and redE) ttrr - dwarf and white

14.10 Incomplete dominance in snapdragon color

Carnation

Pleiotropic effects of the sickle-cell allele in a homozygoteSingle gene multiple effects

14.14 The effect of environment of phenotype

Norm of reaction for a genotype:The range of phenotypic possibilities due to environmental influence

AcidAlkaline

14.13.A simplified model for polygenic inheritance of skin color.(Mating between individuals who are heterozygous for all three genes)

Three separately-inherited genes affect the darkness of skin

Multiple genes single effect

14.11.Multiple alleles for the ABO blood groups.

Blood types are the result from various combinations of three different alleles (IA, IB and i)

14.15 Pedigree analysis

14.15 Pedigree analysis

Large families provide excellent case studies of human genetics

AlbinismCystic fibrosisHuntington’s disease

14.19Testing a fetus for genetic disorders

See Chapter 14 Review (p. 282-283)

• Concept 14.1. Two laws of inheritance (Mendel)

• Concept 14.2. Applying the law of probability to Mendelian genetics.

• Concept 14.3. Inheritance patterns are often more complex than predicted by Mendelian genetics.

• Concept 14.4. Many human traits follow Mendelian patterns

• Also look at tips for solving genetic problems (p. 283).