Genetics Understanding Heredity How traits are passed from
- Slides: 8
Genetics: Understanding Heredity (How traits are passed from parent to offspring)
Dominant and Recessive Alleles • Alleles are the different versions of a gene. o Ex/ Gene = height in pea plants • One version (allele) codes for a tall stem • One version (allele) codes for a short stem • Dominant allele – version of the trait that always shows up if it is present • Recessive allele – version of the trait that only shows up if the dominant allele is not present
How do alleles control traits? • Organisms inherit one allele from each parent (two copies in total) • Symbols are used to represent alleles o Capital letters represent dominant alleles o Lower case letters represent recessive alleles Ex/ Tall stem = T (dominant) Short stem = t (recessive)
• Homozygous: When an organism inherits two of the SAME alleles for a trait o Homozygous dominant = TT o Homozygous recessive = tt • Heterozygous: When an organism inherits two different alleles for a trait (Ex/ Tt)
• If T = tall and t = short: o TT = tall o Tt = tall (dominant covers recessive) o tt = short § The allele combination is called an organisms genotype (Ex/ Tt) § The physical expression of the trait is called the phenotype (Ex/ Tall)
Practice: • Determine if the following allele combinations are homozygous or heterozygous: • • • HH Uu Xx PP dd Rr
• What would be the phenotype for the following genotypes: • B = brown fur • BB = • Bb = • bb = tan fur
• Come up with the symbols to represent the following trait: • Blue flowers are dominant to white flowers o Blue: o White: • Then, show the Genotype and Phenotype for: o Homozygous dominant: o Heterozygous: o Homozygous recessive:
