Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

3. Extensions to Mendelian Inheritance

Variations of Dominance

Genetics

3. Extensions to Mendelian Inheritance

Variations of Dominance

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2:54 minutes

Problem 6

Textbook Question

The ABO and MN blood groups are shown for four sets of parents (1 to 4) and four children (a to d). Recall that the ABO blood group has three alleles: I^A, I^B and i. The MN blood group has two codominant alleles, M and N. Using your knowledge of these genetic systems, match each child with every set of parents who might have conceived the child, and exclude any parental set that could not have conceived the child.

Verified step by step guidance

Step 1: Determine the possible ABO genotypes of each set of parents based on their blood groups. Recall that the ABO blood group alleles are I^A, I^B, and i, where I^A and I^B are codominant and i is recessive. For example, a parent with blood group O must have genotype ii, blood group A could be I^AI^A or I^Ai, blood group B could be I^BI^B or I^Bi, and blood group AB must be I^AI^B.

Step 2: Determine the possible MN genotypes of each set of parents. Since M and N are codominant alleles, a parent with blood group M must be MM, with N must be NN, and with MN must be MN.

Step 3: For each child, analyze their ABO blood group and determine which parental genotypes could produce that blood group. Use Punnett squares or allele combinations to check if the child's ABO blood group is possible from the parents' genotypes. For example, a child with blood group AB must inherit I^A from one parent and I^B from the other.

Step 4: Similarly, analyze the MN blood group of each child and determine which parental MN genotypes could produce the child's MN blood group. Since M and N are codominant, a child with MN must inherit M from one parent and N from the other.

Step 5: Combine the ABO and MN results to match each child with the sets of parents who could have conceived them. Exclude any parental set where either the ABO or MN blood group inheritance is not possible based on the genotypes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

ABO Blood Group Inheritance

The ABO blood group system is determined by three alleles: I^A, I^B, and i. I^A and I^B are codominant, meaning both can be expressed if present, while i is recessive. Blood types A, B, AB, and O result from different allele combinations, with O being homozygous recessive (ii). Understanding parental genotypes helps predict possible offspring blood types.

MN Blood Group and Codominance

The MN blood group is controlled by two codominant alleles, M and N. Individuals with genotype MM express M antigen, NN express N antigen, and MN express both antigens. Since both alleles are equally expressed, offspring inherit one allele from each parent, allowing prediction of possible MN phenotypes.

Genetic Compatibility and Exclusion

By comparing the blood groups of parents and children, one can determine if a parental pair could have conceived a child based on possible allele combinations. If a child's blood type cannot be derived from the parents' genotypes, that parental set is excluded. This principle is used in paternity testing and genetic counseling.

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Textbook Question

With regard to the ABO blood types in humans, determine the genotype of the male parent and female parent shown here:

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Female parent: Blood type A; father type B

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Two genes interact to produce various phenotypic ratios among F₂ progeny of a dihybrid cross. Design a different pathway explaining each of the F₂ ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F₂ progeny produced by crossing wild-type F₁ organisms with the genotype RrTt.

13/16 white : 3/16 green

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