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

2. Mendel's Laws of Inheritance

Pedigrees

Genetics

2. Mendel's Laws of Inheritance

Pedigrees

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1:21 minutes

Problem 15e

Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

One child of female I-3 has albinism. What is the probability that any of the other four children are carriers of the allele for albinism?

Verified step by step guidance

Step 1: Understand the inheritance pattern of albinism. Albinism is typically inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the recessive allele (one from each parent) to express the trait. A carrier has one dominant allele and one recessive allele but does not express the trait.

Step 2: Analyze the pedigree. Female I-3 must be a carrier of the recessive allele for albinism because one of her children has albinism. This means that her genotype is heterozygous (Aa). The father of the children must also be heterozygous (Aa) or homozygous recessive (aa) for the child to inherit two recessive alleles.

Step 3: Determine the possible genotypes of the children. Using a Punnett square, cross the genotypes of the parents (Aa x Aa if both are heterozygous). The possible genotypes of the children are: AA (not a carrier), Aa (carrier), and aa (affected). The probabilities are 25% AA, 50% Aa, and 25% aa.

Step 4: Exclude the child with albinism from the calculation. Since one child is already known to have the genotype aa, focus on the remaining four children. For each of these children, the probability of being a carrier (Aa) is 50%, based on the Punnett square.

Step 5: Conclude that the probability of any of the other four children being carriers of the allele for albinism is 50%. This probability applies independently to each child, as genetic inheritance is random for each offspring.

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Key Concepts

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

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance patterns of traits through generations in a family. It helps identify whether a trait is dominant or recessive, and can indicate the likelihood of individuals being carriers of specific alleles. In this case, understanding the pedigree is crucial to determine the inheritance of albinism.

Autosomal Recessive Inheritance

Albinism is typically inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the recessive allele (one from each parent) to express the trait. Carriers possess one copy of the recessive allele and one dominant allele, which does not manifest the trait. Recognizing this pattern is essential for calculating the probability of the other children being carriers.

Probability in Genetics

Probability in genetics involves calculating the likelihood of certain genotypes or phenotypes occurring in offspring based on parental genotypes. In this scenario, understanding the genetic makeup of the parents and the known child with albinism allows for the application of probability rules, such as the Punnett square, to estimate the chances that the other children are carriers of the albinism allele.

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Textbook Question

Mendel crossed peas having green seeds with peas having yellow seeds. The F₁ generation produced only yellow seeds. In the F₂, the progeny consisted of 6022 plants with yellow seeds and 2001 plants with green seeds. Of the F₂ yellow-seeded plants, 519 were self-fertilized with the following results: 166 bred true for yellow and 353 produced an F₃ ratio of 3/4 yellow: 1/4 green. Explain these results by diagramming the crosses.

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Textbook Question

Nail–patella syndrome is an autosomal disorder affecting the shape of nails on fingers and toes as well as the structure of kneecaps. The pedigree below shows the transmission of nail–patella syndrome in a family along with ABO blood type.

Explain why III-6 has nail–patella syndrome and III-8 does not. Give genotypes for these two individuals.

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Textbook Question

Using N and n to represent alleles at the nail–patella locus and Iᴬ, Iᴮ and i to represent ABO alleles, write the genotypes of I-1 and I-2 as well as their five children in generation II.

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Textbook Question

Consider this human pedigree for a vision defect.

What is the most probable mode of inheritance of the disease? Identify any discrepancies between the pedigree and your proposed mode of transmission, and provide possible explanations for these exceptions.

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

What is the probability that female I-3 is a heterozygous carrier of the allele for albinism?

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

The female I-1 and her mate, male I-2, had four children, one of whom has albinism. What is the probability that they could have had a total of four children with any other outcome except one child with albinism and three with normal pigmentation?

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

Using allelic symbols of your choice, identify the genotypes of the male and his two mates in generation I.

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

What is the most likely mode of transmission of albinism in this family?

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The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.One child of female I-3 has albinism. What is the probability that any of the other four children are carriers of the allele for albinism?

Key Concepts

Pedigree Analysis

Autosomal Recessive Inheritance

Probability in Genetics

Watch next

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

One child of female I-3 has albinism. What is the probability that any of the other four children are carriers of the allele for albinism?