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Exploring Other Patterns of Genetics: Dominance and Recessiveness

In this lesson, we delve into the complexities of genetic inheritance beyond simple Mendelian patterns. We'll explore autosomal dominant and recessive traits, understanding how they manifest in phenotypes and genotypes. Students are encouraged to share their homework for review, facilitating a deeper comprehension of how genes influence traits. We will analyze examples and discuss the implications of various genetic patterns, preparing students for more advanced topics in genetics.

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Exploring Other Patterns of Genetics: Dominance and Recessiveness

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  1. Other Patterns of Genetics

    Do Now: Take out your homework so that I can check it for completion.
  2. Autosomal dominant / recessive 1.      In rabbits the allele for black coat color (B) is dominant over the allele for brown coat color (b).  What is the genotypic ratio and phenotypic ratio be for a cross between an animal homozygous for black coat color and one homozygous for brown coat color? Homozygous black parent Genotype ratio: 100% Bb Phenotype ratio: 100% black Homozygous brown parent
  3. Autosomal dominant / recessive 2.      White (W) hair in sheep is caused by the dominant gene while black (w) hair is recessive.  A heterozygous white male and a black female are parents of a black lamb.  What is the probability that their next lamb will be white?  What are the genotypic and phenotypic ratios? Heterozygous white 50% chance next lamb will be white Genotype ratio: 1:1 Ww:ww Phenotype ratio: 1:1 whtie:black Black
  4. Incomplete Dominance 1.      Yellow coat color in guinea pigs is produced by the homozygous genotype, YY, and cream color by the heterozygous genotype, Yy.  White is produced by the homozygous genotype, yy.  What genotypic ratios are produced by matings between cream colored guinea pigs?  Describe the phenotypic ratio.  cream Genotype ratio: 1:2:1 YY:Yy:yy Phenotype ratio: 1:2:1 yellow:cream:white cream
  5. #3… ooops
  6. Codominance 1.      In shorthorn cattle, the hybrid between red and white is roan, having red and white hairs intermingled.  If a roan is bred with a white, what will the phenotypic ratio be? Roan Phenotype ratio: 1:2:1 red:roan:white White
  7. Multiple Alleles 1.      Suppose a man with homozygous A blood marries a woman with AB blood.  What blood types would you expect to find among their children? Homozygous A A or AB only! AB
  8. Multiple Alleles 2.      A man of type AB blood is married to a woman of type O and he questions the legitimacy of her child, who has type O blood.  What should the legal judgment be? Type O He is NOT the daddy! AB
  9. SEX linkage A woman who is a carrier for the colorblindness trait is planning to have a child with a colorblind man. What % of their male children should they expect to be colorblind? What about their female children? Carrier f. 50% of males will be colorblind 50% of females will be colorblind, 50% will be carriers. Colorblind m.
  10. New Skill: Dihybrid cross Dihybrid crosses study the inheritance of two traits simultaneously.
  11. Mendel’s “Laws” of Heredity The two basic mechanisms of these genetic crosses are explained on the next two slides. It is important to note that these “laws” work under certain conditions: Each gene is on a different chromosome The organisms are diploid
  12. Law of Segregation A pair of factors is segregated (separated) during the formation of gametes (sex cells) Y y For example: 50% Of Gametes 50% Of Gametes
  13. Law of Independent Assortment Factors (alleles) for different characteristics are distributed independently from one another. T T t t Y Y y y For example: 25% Of Gametes 25% Of Gametes 25% Of Gametes 25% Of Gametes
  14. It’s all about the Chromosomes The two “laws” of heredity are due to the separation of homologous chromosomes during meiosis, when gametes are made.
  15. Dihybrid Gametes Pea plant cross: PpYy x PpYy Gametes: reproductive haploid cells (sperm and egg) One individual heterozygous for 2 traits can produce 4 (2n, where n= number of different genes)possible combinations of alleles. YP Yp yP yp
  16. Try a Dihybrid Cross! Predict the outcome of a dihybrid cross between two pea plants heterozygous for both flower color and seed color (PpYy)
  17. Dihybrid Punnett Square PY Py pY py PY Py pY py
  18. Ratios? How many of each? Purple flowers + yellow seeds : Purple flowers + green seeds : White flowers + yellow seeds: White flowers + green seeds: 9:3:3:1
  19. The Dwarf and the Albino 2: Dwarfism is caused by a dominant allele (D) in humans, and albinism is caused by a recessive allele (a). If a man heterozygous for dwarfism and albinism reproduces with an albino woman who is not a dwarf, what is the probability they will have an albino dwarf child?
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