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Understanding Homozygous and Heterozygous Traits in Genetics

Learn the differences between homozygous and heterozygous genotypes through Punnett Squares and eye color inheritance. Explore the probabilities of trait distributions in offspring generations.

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Understanding Homozygous and Heterozygous Traits in Genetics

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  1. Homozygous & Heterozygous • Homo-means the same as • Homozygous--a genotype that has two identical alleles. Homozygous dominant-AA Homozygous recessive-- aa

  2. Homozygous & Heterozygous • Hetero—means difference between two • Heterozygous—a gene has two different alleles(one dominant allele & one recessive allele). AaTt

  3. Punnett Squares

  4. Is there anyway to predict what the distribution of traits will be in the F₃ generation? Turn to your shoulder partner to think about this question.

  5. Let’s see if we can figure out if any of the larkeys will have gray eyes in the F₃ generation • We know that if one parent is homozygous dominant for eye color (EE), all the offspring will have red eyes because they will inherit the dominant allele for eye color. The likelihood of gray eyes is 0%.

  6. We know if both parents are homozygous recessive for the eye color gene (ee), the offspring will all have gray eyes because the only allele either parent can contribute is the recessive allele. The likelihood of gray eyes is 100 %.

  7. What happens when both parents are heterozygous for eye color (Ee & Ee), or one parent is heterozygous and the other is homozygous recessive (Ee & ee)?

  8. A diagram called a Punnett Square Start with a square and divide it in half both ways

  9. Female E e E e Male There were 4 ways the alleles can combine-EE, Ee, Ee, ee 3 combinations produce the dominant trait- EE, Ee, and Ee 1 produces the recessive trait-ee

  10. Female E e E e Male 3 out of every 4 offspring produced will have red eyes 1 out of 4 will have gray eyes 3:1—On average the ratio of red eyes to gray eyes 75% chance of red eyes 25% chance of grey eyes

  11. What happens with one heterozygous parent and one homozygous recessive parent? Female E e e e Male

  12. Female E e e e Male 2 combinations contain the dominant red-eye allele, 2 do not Eye color is a 50/50 chance (ratio of 2 : 2 ) On average, half (50%) of the offspring will have red eyes, and half will have gray eyes

  13. Let’s Practice fossweb.com Middle School 6-8 Populations & Ecosystems Multimedia wiggs / science

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