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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2:20 minutes

Problem 1b

Textbook Question

How do we know whether an organism expressing a dominant trait is homozygous or heterozygous?

Verified step by step guidance

To determine whether an organism expressing a dominant trait is homozygous (AA) or heterozygous (Aa), we can perform a test cross. A test cross involves crossing the organism in question with another organism that is homozygous recessive (aa) for the same trait.

Set up the Punnett square for the test cross. If the organism in question is homozygous dominant (AA), all offspring will express the dominant trait because they will inherit one dominant allele (A) from the parent in question and one recessive allele (a) from the homozygous recessive parent.

If the organism in question is heterozygous (Aa), the Punnett square will show a 1:1 ratio of offspring expressing the dominant trait (Aa) and the recessive trait (aa). This is because there is a 50% chance of passing on the dominant allele (A) and a 50% chance of passing on the recessive allele (a).

Observe the phenotypes of the offspring. If all offspring express the dominant trait, the organism in question is likely homozygous dominant. If there is a mix of dominant and recessive phenotypes, the organism is heterozygous.

Repeat the test cross with a larger sample size if necessary to confirm the results, as small sample sizes may not accurately reflect the expected ratios due to random chance.

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Key Concepts

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

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations, based on the principles established by Gregor Mendel. It includes concepts such as dominant and recessive alleles, where dominant traits are expressed in the phenotype even if only one copy of the allele is present. Understanding these principles is crucial for determining the genetic makeup of organisms exhibiting dominant traits.

Homozygosity vs. Heterozygosity

Homozygosity refers to having two identical alleles for a particular gene, while heterozygosity involves having two different alleles. When an organism expresses a dominant trait, it could be either homozygous dominant (two dominant alleles) or heterozygous (one dominant and one recessive allele). Distinguishing between these two states is essential for predicting inheritance patterns in offspring.

Test Cross

A test cross is a breeding experiment used to determine the genotype of an organism expressing a dominant trait. By crossing the organism with a homozygous recessive individual, the offspring's phenotypes can reveal whether the dominant organism is homozygous or heterozygous. The ratio of dominant to recessive offspring provides insight into the genetic composition of the parent organism.