Students will be able to answer their genetic questions using other inheritance patterns.

Transcription

1 Chapter 9 Patterns of Inheritance Figure 9.0_ Chapter 9: Big Ideas Mendel s Laws Variations on Mendel s Laws PowerPoint Lectures for Campell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey 0 Pearson Education, Inc. Lecture y Edward J. Zalisko The Chromosomal Basis of Inheritance Sex Chromosomes and Sex-Linked Genes Ojective Students will e ale to answer their genetic questions using other inheritance patterns. Review A locus (plural, loci) is the specific location of a gene along a chromosome. Homozygous individuals have the same allele on oth homologues. Heterozygous individuals have a different allele on each homologue. 0 Pearson Education, Inc. Figure 9.4 Figure 9.7 F genotypes B female B male P Gene loci a B Dominant allele Formation of eggs Formation of sperm Homologous chromosomes B Sperm P Genotype: PP aa B Homozygous Homozygous for the for the dominant recessive allele allele a Recessive allele Heterozygous, with one dominant and one recessive allele F genotypes B B B B Eggs ( ) 4 4 B 4 4

2 9.6 Geneticists can use the testcross to determine unknown genotypes Dominant Traits will e shown, ut you may not know if the organism is Homozygous Dominant or Heterozygous. A testcross uses a homozygous recessive mate to determine the genotype. 0 Pearson Education, Inc. Figure 9.6 What is the genotype of the lack dog? Testcross Genotypes B_? Two possiilities for the lack dog: BB or B VARIATIONS ON MENDEL S LAWS Gametes B B B B Offspring All lack lack : chocolate Sometimes there isn t just one dominant or recessive 0 Pearson Education, Inc. Incomplete Dominance Figure 9.A_ P generation Red RR Gametes R r White rr

3 Figure 9.A_ Figure 9.A_3 F generation Sperm F generation Pink hyrid Rr R R RR rr r Gametes R r Eggs r Rr rr 9. Incomplete dominance results in intermediate phenotypes Incomplete dominant is not lending ecause the parent phenotypes reappear from two middle (pink) individuals. Q U E S T I O N S 0 Pearson Education, Inc. Codominance Example of Codominance: Sickle Cell Disease BOTH TRAITS Sickle-cell Disease Changes in hemogloin cause red lood cells to change to a sickle shape (Cshaped). 3

4 Figure 9.3A Sickle-Cell Disease The changes to the hemogloin make it difficult to transport oxygen ecause they lock circulation Sickle-Cell Disease Heterozygotes have a higher resistance to malaria. This leads to a higher fitness leading to more offspring that carry the trait. Codominance two alleles are present at the same time. Human lood group phenotypes involve three alleles for a single gene. 0 Pearson Education, Inc. Figure 9._ Blood Group (Phenotype) A Genotypes I A I A or I A i Carohydrates Present on Red Blood Cells Carohydrate A Figure 9._ Blood Group (Phenotype) A Antiodies Present in Blood Anti-B Reaction When Blood from Groups Below Is Mixed with Antiodies from Groups at Left O A B AB B I B I B or I B i Carohydrate B B Anti-A AB O I A I B ii Carohydrate A and Carohydrate B Neither AB O None Anti-A Anti-B 4

5 Polygenetic inheritance - many genes. Many characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes. Human skin color, eye color, height, and fingerprints are examples. 0 Pearson Education, Inc. Figure 9.4_ P generation F generation aacc AABBCC (very light) (very dark) AaBCc AaBCc Figure 9.4_ F generation Eggs Sperm

6 Fraction of population Figure 9.4_3 0 Height 5 6 Skin color Rait Coat Color 4 possile alleles 0 genotypes 4 phenotypes 6

7 Epistasis Interaction etween alleles in which one allele hides the effects of another allele Epistasis Ex: Larador Coat Color Two genes with two alleles control coat color Dark color amount ased on the allele Dominant E determines if the dark pigment is present Dominant B determines how dark the pigment will e Figure 9.5A 9.5 The environment affects many characters Many characters result from a comination of heredity and the environment. For example, skin color is affected y exposure to sunlight, susceptiility to diseases, such as cancer, has hereditary and environmental components, and identical twins show some differences. Only genetic influences are inherited. Siamese Cats - Fur Pigment The dark pigment is only seen on cool regions of the cat. The cat is light in warm regions. 0 Pearson Education, Inc. 7

8 Environmental Influences on Phenotype Artic Fox - Coat Color Himalayan Rait Black pigment is present in fur when the temperature falls elow 33 0 C When hair is shaved and an ice pack is placed in the area, the new fur will grow in lack. Flower Genes. Acidity of Soil Organism s phenotype changes ecause of environmental cause not ecause of genetic cause Manx Mutations A change in DNA, which can change the phenotype of an organism. A mutation can e caused y environmental factors, such as pollution and medicine.

9 Chimera This can result in male and female organs, two different lood types, or sutle variations in form. How can twin e orn with different skin colors? Animal chimeras are produced y the merger of multiple fertilized eggs. Identical Twins (Monozygotic): One zygote splits Fraternal Twins (Dizygotic) : two different eggs are fertilized y two different sperm at the same time. Twin Studies Twin studies allow for genetic and environmental influences to e studied. 9

10 How can this e? Think outside of just humans. Biology Brainteaser A male has no father and cannot have sons, ut he has a grandfather and can have grandsons. Humans Other Animals have different Sex Chromosomes XX-X Female: XX Male: X ZZ-ZW Female: ZW Male: ZZ ** Mothers decide the sex Haplodiploidy Males develop from nonfertilized eggs. Females develop from fertilized eggs. Example: Cats Calico Cat is a tortoiseshell expressing an additional genetic condition known as piealding. A pieald animal has patches of white (no pigment) fur. Orange: Inactive Black allele on X (Sex Chromosome) Black: Inactive Orange allele on X (Sex Chromosome) AND Piealding: White on Autosomal This is controlled y a completely separate autosomal gene. 0

11 Terms Affected: Allele(s) for disease/disorder present AND phenotype is disease/disorder Unaffected: no allele(s) for disease/disorder, so phenotype is normal Carrier: Allele(s) for disease/disorder present, ut NOT phenotype is disease/disorder 9. Sex-linked genes exhiit a unique pattern of inheritance Sex-linked genes are located on either of the sex chromosomes. Many recessive diseases are inherited on the X sex chromosome. 0 Pearson Education, Inc. Common Sex Linked Traits: Red-Green Color Blindness Common Sex Linked Traits: Duchenne Muscular Dystrophy Recessive sexlinked disorder Color lindness is more common in males ecause they have an Y. Color Blind Test nd/ Recessive Sex-linked Disorder Muscular dystrophy Muscle degenerate leading to death usually y 0 years old pgcdk (5 minutes) Common Sex Linked Traits: Hemophilia Recessive sex-linked disorder Blood doesn t clot In the 0 th Century, hemophiliacs were ale to live due to the discovery of clotting factors. Many died from lood-orne viruses until 990s. 9. CONNECTION: Genetic traits in humans can e tracked through family pedigrees A pedigree shows the inheritance of a trait in a family through multiple generations, demonstrates dominant or recessive inheritance, and can also e used to determine genotypes of family memers. 0 Pearson Education, Inc.

12 Figure 9. Figure 9.B Queen Victoria Alice Alert Alexandra Louis Czar Nicholas II of Russia Alexis Female Male Hemophilia Carrier Normal First generation (grandparents) Second generation (parents, aunts, and uncles) FF or Ff Third generation (two sisters) Female Male Attached Free Ff Ff ff Ff ff ff Ff Ff ff ff FF or Ff 9.9 CONNECTION: Many inherited disorders in humans are controlled y a single gene The most common fatal genetic disease in the United States is cystic firosis (CF), resulting in excessive thick mucus secretions. The CF allele is recessive and carried y aout in 3 Americans. Dominant human disorders include achondroplasia, resulting in dwarfism, and Huntington s disease, a degenerative disorder of the nervous system. 0 Pearson Education, Inc.