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Set Cornelland Notes on pg. 6.3 up Mendel Heredity Topic: 6.4 Genes, Traits, Alleles •Essential Questions: 1. Explain why an organism’s genes may be homozygous dominant, homozygous recessive, but never heterozygous recessive. 6.4 Genes, 2.1 Atoms, Ions, Traits, Alleles and Molecules 1. Explain why an organism’s genes may be homozygous dominant, homozygous recessive, but never heterozygous recessive. 6.4 Traits, Genes, and Alleles KEY CONCEPT Genes encode proteins that produce a diverse range of traits. 6.4 Traits, Genes, and Alleles • An allele is a gene occurring at a specific locus on a chromosome. – Each parent donates one allele for every gene. – Alleles are represented using letters. X X XX Y XY • 50% Girl X X X XY • 50% Boy 6.4 Traits, Genes, and Alleles • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, a specific position on a pair of homologous chromosomes. *homo =same 6.4 Traits, Genes, and Alleles Punnett Square Vocabulary Review 6.4 Traits, Genes, and Alleles Dominant J A P H B 6.4 Traits, Genes, and Alleles Recessive j a p h b 6.4 Traits, Genes, and Alleles Dominant vs. Recessive n b A j L K Z r 6.4 Traits, Genes, and Alleles • Alleles are represented using letters. – A dominant allele is expressed as a phenotype when at least one allele is dominant. –(AA or Aa) – A recessive allele is expressed as a phenotype only when two copies are present. –(aa) 6.4 Traits, Genes, and Alleles Homozygous AA bb ww LL jj oo aa 6.4 Traits, Genes, and Alleles Heterozygous Aa Bb Ww Ll Jj Oo Mm 6.4 Traits, Genes, and Alleles Heterozygous vs. Homozygous Aa Bb ww LL JJ Pp Oo Mm 6.4 Traits, Genes, and Alleles Homozygous Dominant MM JJ KK NN GG YY DD 6.4 Traits, Genes, and Alleles Homozygous Recessive mm jj kk nn oo yy dd 6.4 Traits, Genes, and Alleles Heterozygous Dominant? Mm Pp Tt Zz Jj Yy Mm 6.4 Traits, Genes, and Alleles Heterozygous Recessive? Yy No such thing as heterozygous recessive. Why? 6.4 Traits, Genes, and Alleles • Homozygous describes two alleles that are the same at a specific locus. –AA or aa. *homo=same – Heterozygous describes two alleles that are different at a specific locus. –Aa *Hetero=different 6.4 Traits, Genes, and Alleles *Both homozygous dominant (AA) and heterozygous (Aa) genotypes yield a dominant phenotype. • Most traits occur in a range and do not follow simple dominant-recessive patterns. 6.4 Traits, Genes, and Alleles Genotype Mm Pp Tt Zz Jj Yy Mm 6.4 Traits, Genes, and Alleles Phenotype 6.4 Traits, Genes, and Alleles • A genotype refers to the makeup (alleles) of a specific set of genes. Genotype: BB or Bb Genotype: bb Genotype CODES FOR Phenotype!!!!!!!!! 6.4 Traits, Genes, and Alleles • A phenotype is the physical expression of a trait. You can see it! Phenotype: Brown Eyes Phenotype: Blue Eyes 6.4 Traits, Genes, and Alleles 6.4 Traits, Genes, and Alleles Genes influence the development of traits. • All of an organism’s genetic material is called the genome. Which of these are Heterozygous? Hh FF KK Jj LL mm Aa AA aa PP Pp WW qq Dd Rr Which of these are Heterozygous? Hh FF KK Jj LL mm Aa AA aa PP Pp WW qq Dd Rr Which of these are Homozygous? Hh FF KK Jj LL mm Aa AA aa PP Pp WW qq Dd Rr Which of these alleles codes for a Dominant trait? Hh FF KK Jj LL mm Aa AA aa PP Pp WW qq Dd Rr Which of these alleles are Dominant? Hh FF KK Jj LL mm Aa AA aa PP Pp WW qq Dd Rr Which of these allele pairs are recessive? Hh FF KK Jj LL mm Aa AA aa PP Pp WW qq Dd Rr