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Biology EOC Element Review – SB3a,b (Heredity)
Scenario:
The diagram below represents sexual reproduction in humans.
GSE Elements Addressed:
SB3a. Use Mendel’s laws (segregation and independent assortment) to ask questions and define problems that explain the role of meiosis in reproductive variability. b.
SB3b. Use mathematical models to predict and explain patterns of inheritance. (Clarification statement: Students should be able to use Punnett squares (monohybrid and dihybrid crosses) and/or rules of probability, to analyze the following inheritance patterns: dominance, codominance, incomplete dominance.)
1. How will the child’s genotype and phenotype relate to those of the parents?
2. The arrows labeled A and B represent meiosis. Explain the two key roles of meiosis in sexual reproduction.
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● Key Vocabulary:
3. Mendel’s Laws
a. Explain Mendel’s law of independent assortment.
b. Identify the allele combinations in the cross above that represent Mendel’s Law of Independent Assortment.
c. Cross two non-parental offspring from the cross above and determine the probability of producing offspring that share the parental phenotypes you chose.
Summary (What are the key ideas that you learned or reviewed in this scenario?)
All Answers 1
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Below are answers and explanations tied to the GSE elements SB3a,b (Mendelian inheritance and meiosis).
1) How will the child’s genotype and phenotype relate to those of the parents?
- For each gene the child inherits one allele from the mother and one allele from the father, so the child’s genotype is a combination of parental alleles.
- If a parent is homozygous (AA or aa) it always gives the same allele to a child; if heterozygous (Aa) it may give either allele.
- The child’s phenotype depends on those alleles plus the mode of inheritance: with simple dominance a single dominant allele produces the dominant phenotype; with incomplete dominance the heterozygote shows an intermediate trait; with codominance both alleles are expressed.
- Therefore a child may have the same genotype/phenotype as a parent, a different genotype with the same phenotype (e.g., AA vs Aa), or a different phenotype depending on combinations and probabilities.
2) The arrows labeled A and B represent meiosis. Explain the two key roles of meiosis in sexual reproduction.
- Produce haploid gametes: meiosis reduces the chromosome number from diploid (2n) to haploid (n) so that fertilization restores the species’ diploid number.
- Generate genetic variation: meiosis creates new allele combinations via (1) crossing over (recombination) between homologous chromosomes and (2) independent assortment (random separation) of different chromosome pairs; random fertilization further increases variation.
Key vocabulary (important terms)
- allele, genotype, phenotype, homozygous, heterozygous, dominant, recessive, codominance, incomplete dominance, meiosis, gamete, crossing over (recombination), independent assortment, segregation, Punnett square, probability, dihybrid/monohybrid cross.
3) Mendel’s Laws
a. Explain Mendel’s law of independent assortment.
- Mendel’s law of independent assortment states that alleles of different genes (located on different chromosomes or far apart on the same chromosome) segregate into gametes independently of one another. As a result, the inheritance of an allele for one trait generally does not affect the inheritance of an allele for a different trait, producing new combinations of traits in offspring.
b. Identify the allele combinations in the cross above that represent Mendel’s Law of Independent Assortment.
- For a typical dihybrid heterozygote AaBb, the four possible gamete allele combinations produced by independent assortment are: AB, Ab, aB, and ab. Those four gamete types illustrate independent assortment.
c. Cross two non-parental offspring from the cross above and determine the probability of producing offspring that share the parental phenotypes you chose.
- Example setup (classic dihybrid example): Let S = round (dominant), s = wrinkled (recessive); Y = yellow (dominant), y = green (recessive). Parental cross: SSYY (round yellow) × ssyy (wrinkled green) → F1 all SsYy. The F2 from SsYy × SsYy include parental phenotypes (round yellow and wrinkled green) and two non-parental recombinant phenotypes (round green and wrinkled yellow).
- Pick two non-parental offspring (recombinants) and cross them, for example:
- Offspring 1: Ss yy (round green)
- Offspring 2: ss Yy (wrinkled yellow)
- Gametes:
- Ss yy produces S y or s y (Sy and sy)
- ss Yy produces s Y or s y (sY and sy)
- Offspring genotypes (4 equal possibilities): SsYy, Ssyy, ssYy, ssyy → corresponding phenotypes: round yellow, round green, wrinkled yellow, wrinkled green.
- Probability of producing each phenotype = 1/4 (25%). Thus probability of producing an offspring that matches either original parental phenotype:
- round yellow (parent 1) = 25%
- wrinkled green (parent 2) = 25%
- either parental phenotype = 50%.
Summary — key ideas reviewed
- Meiosis creates haploid gametes and generates genetic variation through crossing over and independent assortment; segregation of alleles ensures each gamete gets one allele per gene.
- A child’s genotype is a combination of one allele from each parent; phenotype depends on allele interactions and the mode of inheritance (dominant/recessive, incomplete dominance, codominance).
- Mendel’s laws (segregation and independent assortment) explain how allele pairs separate and how alleles for different genes assort into gametes independently, which allows us to use Punnett squares and probability to predict offspring genotype and phenotype frequencies.
1) How will the child’s genotype and phenotype relate to those of the parents?
- For each gene the child inherits one allele from the mother and one allele from the father, so the child’s genotype is a combination of parental alleles.
- If a parent is homozygous (AA or aa) it always gives the same allele to a child; if heterozygous (Aa) it may give either allele.
- The child’s phenotype depends on those alleles plus the mode of inheritance: with simple dominance a single dominant allele produces the dominant phenotype; with incomplete dominance the heterozygote shows an intermediate trait; with codominance both alleles are expressed.
- Therefore a child may have the same genotype/phenotype as a parent, a different genotype with the same phenotype (e.g., AA vs Aa), or a different phenotype depending on combinations and probabilities.
2) The arrows labeled A and B represent meiosis. Explain the two key roles of meiosis in sexual reproduction.
- Produce haploid gametes: meiosis reduces the chromosome number from diploid (2n) to haploid (n) so that fertilization restores the species’ diploid number.
- Generate genetic variation: meiosis creates new allele combinations via (1) crossing over (recombination) between homologous chromosomes and (2) independent assortment (random separation) of different chromosome pairs; random fertilization further increases variation.
Key vocabulary (important terms)
- allele, genotype, phenotype, homozygous, heterozygous, dominant, recessive, codominance, incomplete dominance, meiosis, gamete, crossing over (recombination), independent assortment, segregation, Punnett square, probability, dihybrid/monohybrid cross.
3) Mendel’s Laws
a. Explain Mendel’s law of independent assortment.
- Mendel’s law of independent assortment states that alleles of different genes (located on different chromosomes or far apart on the same chromosome) segregate into gametes independently of one another. As a result, the inheritance of an allele for one trait generally does not affect the inheritance of an allele for a different trait, producing new combinations of traits in offspring.
b. Identify the allele combinations in the cross above that represent Mendel’s Law of Independent Assortment.
- For a typical dihybrid heterozygote AaBb, the four possible gamete allele combinations produced by independent assortment are: AB, Ab, aB, and ab. Those four gamete types illustrate independent assortment.
c. Cross two non-parental offspring from the cross above and determine the probability of producing offspring that share the parental phenotypes you chose.
- Example setup (classic dihybrid example): Let S = round (dominant), s = wrinkled (recessive); Y = yellow (dominant), y = green (recessive). Parental cross: SSYY (round yellow) × ssyy (wrinkled green) → F1 all SsYy. The F2 from SsYy × SsYy include parental phenotypes (round yellow and wrinkled green) and two non-parental recombinant phenotypes (round green and wrinkled yellow).
- Pick two non-parental offspring (recombinants) and cross them, for example:
- Offspring 1: Ss yy (round green)
- Offspring 2: ss Yy (wrinkled yellow)
- Gametes:
- Ss yy produces S y or s y (Sy and sy)
- ss Yy produces s Y or s y (sY and sy)
- Offspring genotypes (4 equal possibilities): SsYy, Ssyy, ssYy, ssyy → corresponding phenotypes: round yellow, round green, wrinkled yellow, wrinkled green.
- Probability of producing each phenotype = 1/4 (25%). Thus probability of producing an offspring that matches either original parental phenotype:
- round yellow (parent 1) = 25%
- wrinkled green (parent 2) = 25%
- either parental phenotype = 50%.
Summary — key ideas reviewed
- Meiosis creates haploid gametes and generates genetic variation through crossing over and independent assortment; segregation of alleles ensures each gamete gets one allele per gene.
- A child’s genotype is a combination of one allele from each parent; phenotype depends on allele interactions and the mode of inheritance (dominant/recessive, incomplete dominance, codominance).
- Mendel’s laws (segregation and independent assortment) explain how allele pairs separate and how alleles for different genes assort into gametes independently, which allows us to use Punnett squares and probability to predict offspring genotype and phenotype frequencies.
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