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Ch. 8 class notes HEREDITY • Heredity - Ch. 8 class notes HEREDITY • Heredity - The passing of characters (traits) from parents to offspring Ch. 8 class notes HEREDITY • Heredity - The passing of characters (traits) from parents to offspring • Genetics - Ch. 8 class notes HEREDITY • Heredity - The passing of characters (traits) from parents to offspring • Genetics - the study of heredity • Gregor Mendel (1822-1884) – Determined mechanism of inheritance – parents transmit discrete inheritable factors (genes) that remain as separate factors from one generation to the next. This disproved the “blending” hypothesis of the time. – Worked with the garden pea plant to study heredity • Genes – • Genes – sequence of triplets on DNA • Genes – sequence of triplets on DNA • Humans have about – • Genes – sequence of triplets on DNA • Humans have about – 23,000 genes • Genes – sequence of triplets on DNA • Humans have about – 23,000 genes • Each chromosome contains • Genes – sequence of triplets on DNA • Humans have about – 23,000 genes • Each chromosome contains many genes • • • • Genes – sequence of triplets on DNA Humans have about – 23,000 genes Each chromosome contains many genes Like the chromosomes they are part of, • • • • Genes – sequence of triplets on DNA Humans have about – 23,000 genes Each chromosome contains many genes Like the chromosomes they are part of, genes occur in pairs of two. • • • • Genes – sequence of triplets on DNA Humans have about – 23,000 genes Each chromosome contains many genes Like the chromosomes they are part of, genes occur in pairs of two. – Alleles - • • • • Genes – sequence of triplets on DNA Humans have about – 23,000 genes Each chromosome contains many genes Like the chromosomes they are part of, genes occur in pairs of two. – Alleles - alternate forms of a gene • • • • Genes – sequence of triplets on DNA Humans have about – 23,000 genes Each chromosome contains many genes Like the chromosomes they are part of, genes occur in pairs of two. – Alleles - alternate forms of a gene • Each pair of alleles controls • • • • Genes – sequence of triplets on DNA Humans have about – 23,000 genes Each chromosome contains many genes Like the chromosomes they are part of, genes occur in pairs of two. – Alleles - alternate forms of a gene • Each pair of alleles controls one trait • Body cells contain • Body cells contain both alleles of a pair. • Body cells contain both alleles of a pair. • Gametes contain only • Body cells contain both alleles of a pair. • Gametes contain only one allele of a pair. • Body cells contain both alleles of a pair. • Gametes contain only one allele of a pair. • Traits are passed on when gametes unite in fertilization. For each trait, the offspring gets one allele of the pair from the mom and one allele of the pair from the dad. • Types of Alleles • Types of Alleles – Dominant alleles – • Types of Alleles – Dominant alleles – expressed in the appearance of the trait. • Types of Alleles – Dominant alleles – expressed in the appearance of the trait. Mendel’s example: • Types of Alleles – Dominant alleles – expressed in the appearance of the trait. Mendel’s example: purple flower color – Recessive alleles – – Recessive alleles – not expressed when paired with a dominant allele – Recessive alleles – not expressed when paired with a dominant allele Mendel’s example: – Recessive alleles – not expressed when paired with a dominant allele Mendel’s example: white flower allele How did Mendel determine this??? Looking closer at Mendel’s work Parents 1st true-breeding true-breeding X purple-flower peas white-flower peas 100% purple-flower peas generation (hybrids) 100% self-pollinate 2nd generation 75% purple-flower peas 25% white-flower peas 3:1 Mendel collected data for 7 pea traits What did Mendel’s findings mean? • Some traits mask others – purple & white flower colors are separate I’ll speak for both of us! traits that do not blend • purple x white ≠ light purple • purple masked white – dominant allele • Makes functional protein – affects characteristic allele producing functional protein mutant allele malfunctioning protein • masks other alleles – recessive allele • no noticeable effect • allele makes a non-functioning protein homologous chromosomes • Genotypes and Phenotypes • Genotypes and Phenotypes Genotype– tells what • Genotypes and Phenotypes Genotype– tells what types of alleles are in a pair (dominant, recessive or one of each). • Genotypes and Phenotypes Genotype– tells what types of alleles are in a pair (dominant, recessive or one of each). • Phenotype – • Genotypes and Phenotypes Genotype– tells what types of alleles are in a pair (dominant, recessive or one of each). • Phenotype – the appearance of the trait (ex. – purple flowers or white flowers) • Genotype phenotype. • Genotype determines phenotype. • How are Genotypes written? • How are Genotypes written? – Genotypes are usually two-letter symbols (one for each allele). The letter used is usually the first letter of the dominant trait. • How are Genotypes written? – Genotypes are usually two-letter symbols (one for each allele). The letter used is usually the first letter of the dominant trait. • Dominant alleles • How are Genotypes written? – Genotypes are usually two-letter symbols (one for each allele). The letter used is usually the first letter of the dominant trait. • Dominant alleles are written in capital letters. • How are Genotypes written? – Genotypes are usually two-letter symbols (one for each allele). The letter used is usually the first letter of the dominant trait. • Dominant alleles are written in capital letters. • Recessive alleles • How are Genotypes written? – Genotypes are usually two-letter symbols (one for each allele). The letter used is usually the first letter of the dominant trait. • Dominant alleles are written in capital letters. • Recessive alleles are written in lowercase letters Types of genotypes: Types of genotypes: Homozygous - Types of genotypes: Homozygous - when both alleles are the same Types of genotypes: Homozygous - when both alleles are the same Heterozygous – Types of genotypes: Homozygous - when both alleles are the same Heterozygous – when the alleles of a pair are different • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white PP – • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white PP – homozygous dominant • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white PP – homozygous dominant pp – • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white PP – homozygous dominant pp – homozygous recessive • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white PP – homozygous dominant pp – homozygous recessive Pp - • Example: Purple flower color is dominant to white flower color in pea plants. P – purple p - white PP – homozygous dominant pp – homozygous recessive Pp - heterozygous • Genotype / Phenotype examples: Earlobe trait – Free earlobes – F Attached earlobes – f Rabbit fur - Brown fur – B White fur - b Genotypes FF Ff Phenotypes Free earlobes attached earlobes bb brown fur Bb Genotypes FF Ff ff bb BB or Bb Bb Phenotypes Free earlobes Free earlobes attached earlobes white fur brown fur brown fur • The Punnett Square Diagram that can predict the outcome of cross. Aaaaah, phenotype & genotype can have different ratios Punnett squares Pp x Pp 1st generation (hybrids) % genotype male / sperm female / eggs P p PP 25% 75% Pp P PP % phenotype 50% Pp Pp p Pp pp pp 25% 25% 1:2:1 3:1 • Patterns of Inheritance • Patterns of Inheritance – Autosomal dominant • Patterns of Inheritance – Autosomal dominant • Trait caused by: • Patterns of Inheritance – Autosomal dominant • Trait caused by: dominant allele on an autosome • Patterns of Inheritance – Autosomal dominant • Trait caused by: dominant allele on an autosome – Example: • Patterns of Inheritance – Autosomal dominant • Trait caused by: dominant allele on an autosome – Example: Huntington’s disease • Patterns of Inheritance – Autosomal dominant • Trait caused by: dominant allele on an autosome – Example: Huntington’s disease Freckles • Patterns of Inheritance – Autosomal dominant • Trait caused by: dominant allele on an autosome – Example: Huntington’s disease Freckles Widow’s peak – Autosomal recessive – Autosomal recessive • Trait caused by a – Autosomal recessive • Trait caused by a recessive allele on an autosome – Autosomal recessive • Trait caused by a recessive allele on an autosome – Example: – Autosomal recessive • Trait caused by a recessive allele on an autosome – Example: Cystic fibrosis – Autosomal recessive • Trait caused by a recessive allele on an autosome – Example: Cystic fibrosis Albinism – Autosomal recessive • Trait caused by a recessive allele on an autosome – Example: Cystic fibrosis Albinism Hitchhiker’s thumb – Incomplete dominance • When neither allele is fully dominant – Heterozygote phenotype is intermediate – Example: flower color in snap dragons – Sex-linked Recessive – Sex-linked Recessive • Trait caused by recessive allele on the – Sex-linked Recessive • Trait caused by recessive allele on the X chromosome – Sex-linked Recessive • Trait caused by recessive allele on the X chromosome Example: – Sex-linked Recessive • Trait caused by recessive allele on the X chromosome Example: color blindness – Sex-linked Recessive • Trait caused by recessive allele on the X chromosome Example: color blindness Hemophilia – Sex-linked Recessive • Trait caused by recessive allele on the X chromosome Example: color blindness Hemophilia Muscular dystrophy Genotypes of sex-linked traits include the chromosomes: Genotypes of sex-linked traits include the chromosomes: XhXh Genotypes of sex-linked traits include the chromosomes: XhXh XhY Genotypes of sex-linked traits include the chromosomes: XhXh XhY Males get more sex-linked recessive conditions than females do. Why???