Chapter 14 Part II Chromosomes Chapter 14 Part II Chromosomes and Genesand Genes

• Incomplete dominance, codominance, multiple alleles, epistasis, polygenic inheritance, the chromosomal theory of inheritance, sex chromosomes, linked genes, and chromosomal mutations are covered in this chapter.

12-1 Mendelism and the Genotype12-1 Mendelism and the Genotype

A Incomplete Dominance and Codominance

1 Incomplete Dominance: offspring show traits intermediate between 2 parental phenotypes.- Red x white = pink- One allele only partially

dominant to partner

2 Codominance: pattern of inheritance in which both alleles of a gene are expressed- Ex: A person with AB blood

12-1 Mendelism and the Genotype12-1 Mendelism and the Genotype

B Genes that interact

1 More than one pair of genes may interact to produce the phenotype

C Epistasis1 Epistasis: absence of expected phenotype as a

result of masking expression of one gene pair by the expression of another gene pair.

a Homozygous recessive masks effect of dominant allele at another locus.

b Ex: albino animals (aa) for melanin production prevent expression of hair and eye color

D. Pleiotropy

D. Pleiotropy

E Multiple Allele

a There may be more than 2 alleles for one locus, but each individual inherits only two alleles

b Ex: Blood Type ABO gives 4 possible phenotypes: A, B, AB, O

F Polygenic Inheritance

a Polygenic Inheritance: occurs when a trait is controlled by several diff. Allelic pairs at diff. loci

b Ex: Seed color and skin color

12-1 Mendelism and the 12-1 Mendelism and the GenotypeGenotype

G Environment and Phenotype

a Both temperature and environment affect phenotype

b ex: plants like primrose and animals like Siamese cats and Himalayan rabbits

12-2 Mendelism and 12-2 Mendelism and ChromosomesChromosomes

A Chromosomal Theory of Inheritance

1 Both chromo’s and alleles are paired in diploid cells

2 Chromo’s and alleles of each pair separate during meiosis so gametes have 1/2.

3 Chromo’s and alleles separate individually; gametes contain all combinations.

4 Fertilization restores diploid chromo # and pairs alleles.

B Sex Chromosomes1 Autosomes - non-sex chromo’s that

are the same # and kind in between sexes

2 Sex Chromosomes determine if the individual is male or female

3 Males produce X-containing or Y-containing gametes, males determine sex

4 X-linked Gene is any gene located on X chromosome

12-2 Mendelism and 12-2 Mendelism and ChromosomesChromosomes

C Sex-Linked Problems

1 X-linked alleles are designed as superscript to X chromosome

2 Heterozygous females are carriers; they do not show the trait but can pass it on.

3 Males are never carriers but express the one allele on the X chromosome

4 One form of color-blindness is X-linked

12-3 Chromosomal Mutations12-3 Chromosomal Mutations

AChanges in Chromo #

1 Monosomy: indiv. only has one particular type of chromosome

2 Trisomy

3 Nondisjunction: failure

4 Polyploidy: offspring end up with more than two complete sets of chromo’s.

Changes in Chromosomal Changes in Chromosomal StructureStructure

A Environmental Factors

1 Inversion

2 Translocation

3 Deletion

4 Duplication