Chapter 9 Student 2015 Part 3

9.8 CONNECTION: Genetic traits in humans can be tracked through family pedigrees  Mendel’s laws apply to inheritance of many human traits.  Wild-type traits, those prevailing in nature, are not necessarily specified by dominant alleles. © 2012 Pearson Education, Inc.

Figure 9.8A Dominant Traits Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe

9.8 CONNECTION: Genetic traits in humans can be tracked through family pedigrees  A pedigree shows the inheritance of a trait in a family through multiple generations, © 2012 Pearson Education, Inc.

Figure 9.8B First generation (grandparents) Second generation (parents, aunts, and uncles) Third generation (two sisters) Female Male Attached Free Ff ff Ff ff FF or Ff

9.9 CONNECTION: Many inherited disorders in humans are controlled by a single gene  Inherited human disorders can show either 1.Autosomal recessive disorder – heterozygous parents are carriers of the disease-causing allele, and » Ex. Cystic fibrosis – the probability of inheritance increases with inbreeding 2.Autosomal dominant disorders – one dominant allele is needed to show disease and » Achondroplasia » Huntington’s disease © 2012 Pearson Education, Inc.

VARIATIONS ON MENDEL’S LAWS © 2012 Pearson Education, Inc.

9.11 Incomplete dominance results in intermediate phenotypes  Mendel’s pea crosses always looked like one of the parental varieties, called complete dominance.  incomplete dominance: the appearance of F 1 hybrids falls between the phenotypes of the two parental varieties. neither allele is dominant over the other and expression of both alleles occurs. Example: cross a red flower with a white flower © 2012 Pearson Education, Inc.

Figure 9.11A P generation F 1 generation F 2 generation Gametes Eggs Sperm  Red RR White rr Pink hybrid Rr R R R R r r r r RR rR Rrrr

Codominant alleles Both alleles are expressed, see both characteristics. Erminette chickens What did this chickens parents look like? What were their genotypes?

9.12 Many genes have more than two alleles in the population (multiple alleles)  Human ABO blood group phenotypes involve three alleles for a single gene.  The four human blood groups, A, B, AB, and O, result from combinations of these three alleles. © 2012 Pearson Education, Inc.

9.13 A single gene may affect many phenotypic characters  Pleiotropy occurs when one gene influences many characteristics.  Sickle-cell disease is a human example of pleiotropy. © 2012 Pearson Education, Inc.

Figure 9.13B An individual homozygous for the sickle-cell allele Produces sickle-cell (abnormal) hemoglobin The abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickled cell The multiple effects of sickled cells Damage to organs Other effects Kidney failure Heart failure Spleen damage Brain damage (impaired mental function, paralysis) Pain and fever Joint problems Physical weakness Anemia Pneumonia and other infections

9.14 A single character may be influenced by many genes  Polygenic inheritance: a single phenotypic character results from the additive effects of two or more genes.  Human skin color © 2012 Pearson Education, Inc.

Figure 9.14 P generation F 1 generation F 2 generation Eggs Sperm Skin color Fraction of population aabbcc (very light) AABBCC (very dark) AaBbCc  

9.15 The environment affects many characters  Many characters result from a combination of heredity and the environment. For example, skin color /sunlight, susceptibility to diseases Intelligence/ experieces  Only genetic influences are inherited.  ABO blood type vs blood count © 2012 Pearson Education, Inc.

THE CHROMOSOMAL BASIS OF INHERITANCE © 2012 Pearson Education, Inc.

9.16 Chromosome behavior accounts for Mendel’s laws  The chromosome theory of inheritance states that genes occupy specific loci (positions) on chromosomes and chromosomes undergo segregation and independent assortment during meiosis. © 2012 Pearson Education, Inc.

9.16 Chromosome behavior accounts for Mendel’s laws  Mendel’s laws correlate with chromosome separation in meiosis. The law of segregation depends on separation of homologous chromosomes in anaphase I. The law of independent assortment depends on alternative orientations of chromosomes in metaphase I. © 2012 Pearson Education, Inc.

9.17 SCIENTIFIC DISCOVERY: Genes on the same chromosome tend to be inherited together  Bateson and Punnett studied plants that did not show a 9:3:3:1 ratio in the F 2 generation. What they found was an example of linked genes, which are located close together on the same chromosome and tend to be inherited together.  Linked alleles can be separated by crossing over, forming recombinant gametes. © 2012 Pearson Education, Inc.

Figure 9.17 The Experiment Purple flower Long pollen  PpLl PhenotypesObserved offspring Prediction (9:3:3:1) Purple long Purple round Red long Red round The Explanation: Linked Genes Parental diploid cell PpLl Meiosis P L p l Most gametes Fertilization Sperm Most offspring Eggs 3 purple long : 1 red round Not accounted for: purple round and red long P L p l