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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1:35 minutes

Problem 3b

Textbook Question

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)
A normal male and an albino female have six children, all normal.

Verified step by step guidance

Step 1: Understand the inheritance pattern of albinism. Albinism is a recessive trait, meaning that an individual must inherit two copies of the recessive allele (aa) to express the condition. A person with one dominant allele (A) and one recessive allele (a) will be phenotypically normal but is a carrier.

Step 2: Analyze the phenotypes of the parents. The male is normal, so his genotype could be either homozygous dominant (AA) or heterozygous (Aa). The female is albino, meaning her genotype must be homozygous recessive (aa).

Step 3: Consider the offspring's phenotypes. All six children are normal, which suggests that none of them inherited two recessive alleles (aa). This provides information about the father's genotype.

Step 4: Use a Punnett square to test possible parental genotypes. If the father is homozygous dominant (AA), all offspring will inherit at least one dominant allele (A) and will be normal. If the father is heterozygous (Aa), there is a 50% chance for each child to inherit the recessive allele (a) from both parents, which would result in albinism. Since all children are normal, the father is likely homozygous dominant (AA).

Step 5: Summarize the genotypes. The father's genotype is AA, and the mother's genotype is aa. The offspring's genotype must be heterozygous (Aa), as they inherit one dominant allele (A) from the father and one recessive allele (a) from the mother.

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Key Concepts

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

Recessive Traits

Recessive traits are characteristics that only manifest when an individual has two copies of the recessive allele. In the case of albinism, the trait is caused by a recessive allele, meaning that an individual must inherit this allele from both parents to express the condition. If an individual has one dominant allele, the dominant trait will be expressed instead.

Genotype vs. Phenotype

Genotype refers to the genetic makeup of an individual, specifically the alleles they carry, while phenotype is the observable expression of those genes. For example, a person with one dominant allele for normal pigmentation and one recessive allele for albinism will have a normal phenotype but a heterozygous genotype. Understanding the distinction between these terms is crucial for analyzing inheritance patterns.

Punnett Squares

Punnett squares are a tool used in genetics to predict the possible genotypes of offspring from a cross between two parents. By mapping out the alleles contributed by each parent, one can visualize the probability of different genotypes and phenotypes in the offspring. This method is particularly useful for understanding simple Mendelian traits, such as albinism.

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