Principles of Heredity Exercise 45 Principles of Heredity

Objectives Allele, gene Genotype, phenotype Homozygous, heterozygous Recessive, dominant, incomplete dominance Sex-linked traits Punnet Squares

Genetics Gene: a hereditary, functional segment of DNA Chromosomes contain DNA Each chromosome contains many genes Each gene has instructions for constructing a specific protein Pair of chromosomes GENE GENE

Genotype Your 46 chromosomes in each somatic cell & the genes present on them Combination of your parents’ genotypes Fig. 29-15

Phenotype Genotype = the “blueprint or plans” The instructions found in your genotype determine your anatomical and physiological characteristics, your phenotype. Hair color, eye color, foot size, etc. Genotype = the “blueprint or plans” Phenotype = the finished “building”

Genetics Alleles: various forms of any one gene Allele for brown eyes Two chromosomes in a pair can have different alleles for the one gene EXAMPLE: This gene controls the trait eye color From Mother From Father Allele for blue eyes

If both chromosomes of the pair carry the SAME allele of a particular gene, you are HOMOZYGOUS for the trait affected by that gene. This allele will be expressed in your phenotype: Allele for brown eyes From Mother You have brown eyes From Father Allele for brown eyes

If each chromosome of the pair carries a DIFFERENT allele of a particular gene, you are HETEROZYGOUS for the trait affected by that gene. Allele for brown eyes From Mother You have ??? eyes From Father Allele for blue eyes

If you are HETEROZYGOUS for the trait affected by that gene, your phenotype is determined by recessive and dominant alleles: A DOMINANT allele will be expressed in the phenotype, regardless of what the other allele is. *denoted by uppercase letters A RECESSIVE allele will be expressed in the phenotype ONLY if the same allele is present on BOTH CHROMOSOMES of a homologous pair. *denoted by lowercase letters

If you are HETEROZYGOUS for the trait affected by that gene, your phenotype is determined by recessive and dominant alleles: Eye color: Brown = dominant Blue = recessive Allele for brown eyes From Mother B You have BROWNeyes From Father b Allele for blue eyes

If you are HOMOZYGOUS for the trait affected by that gene, your phenotype is determined: Eye color: Brown = dominant Blue = recessive Allele for brown eyes From Mother B You have BROWN eyes From Father B Allele for brown eyes

If you are HOMOZYGOUS for the trait affected by that gene, your phenotype is determined: Eye color: Brown = dominant Blue = recessive Allele for blue eyes From Mother b You have BLUE eyes From Father b Allele for blue eyes

INCOMPLETE DOMINANCE: Heterozygous alleles produce a phenotype that is different from both phenotypes when the alleles are homozygous Sickle-cell anemia: Homozygous “A” alleles  normal shape RBCs Homozygous “S” alleles  sickled RBCs Heterozygous AS  do not develop anemia, but have RBCs that will sickle in low oxygen levels AA SS AS A From Mother You have both RBCs From Father S

Sex Chromosomes Appear different from each other X chromosome—larger Carried by all eggs Carried by some sperm Y chromosome—determines the male sex Carried by some sperm, no eggs Normal female pair: XX Normal male pair: XY Fig. 29-15

Sex-Linked (X-linked) Traits In most cases, there’s no corresponding allele on the Y chromosome Color-blindness Normal Vision Dominant allele (C) on X chromosome XC Red-Green Color-blindness Recessive allele (c) on X chromosome Xc

Sex-Linked (X-linked) Traits Normal vision Color-blind Females: XCXc heterozygous XCXC homozygous dominant XcXc homozygous recessive Males: XCY heterozygous XcY homozygous

MATERNAL ALLELES (for eye color) PATERNAL ALLELES (for eye color) Punnet Squares Box diagram depicting which alleles come from each parent Allows prediction of the offspring’s genotypes and phenotypes MATERNAL ALLELES (for eye color) b b All offspring (100%) from homozygous dominant father & homozygous recessive mother will be HETEROZYGOUS for the trait. Bb B PATERNAL ALLELES (for eye color)

Genotypes, Phenotypes Bb Genotype: Bb Phenotype: Brown eyes Eye color: Brown = dominant Blue = recessive Genotype: Bb Phenotype: Brown eyes MATERNAL ALLELES b b Bb B PATERNAL ALLELES

Genotypes, Phenotypes BB Bb Genotype: BB or Bb Phenotype: Brown eyes Eye color: Brown = dominant Blue = recessive Genotype: BB or Bb Phenotype: Brown eyes MATERNAL ALLELES B b BB Bb 50% offspring will be HETEROZYGOUS for the trait. 50% offspring will be HOMOZYGOUS dominant. B PATERNAL ALLELES

Genotypes, Phenotypes Bb bb Genotype: Bb or bb Eye color: Brown = dominant Blue = recessive Genotype: Bb or bb Phenotype: Brown eyes or Blue eyes MATERNAL ALLELES b b Bb bb 50% offspring will be HETEROZYGOUS for the trait. 50% offspring will be HOMOZYGOUS recessive. B b PATERNAL ALLELES