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

Inheritance in Diploids and Haploids

Genetics

2. Mendel's Laws of Inheritance

Inheritance in Diploids and Haploids

Previous problemNext problem

1:43 minutes

Problem B.1c

Textbook Question

Answer the following questions for autosomal conditions such as PKU.
If the first child of parents who are both heterozygous carriers of a recessive mutant allele is homozygous recessive, what is the chance the second child of the couple will be homozygous recessive? What is the chance the second child will be a heterozygous carrier of the recessive mutation?

Verified step by step guidance

Identify the genotype of the parents: Since both parents are heterozygous carriers of a recessive mutant allele, their genotypes can be represented as

A a

, where

A

is the normal allele and

a

is the recessive mutant allele.

Determine the possible genotypes of their children using a Punnett square: Cross

Aa

(mother) with

Aa

(father) to find the genotypic ratio of offspring. The possible genotypes are

AA

Aa

, and

aa

Calculate the probability of the second child being homozygous recessive (

aa

): From the Punnett square, the chance of

aa

is 1 out of 4, or 25%. This probability is independent of the first child's genotype because each child's genotype is an independent event.

Calculate the probability of the second child being a heterozygous carrier (

Aa

): From the Punnett square, the chance of

Aa

is 2 out of 4, or 50%.

Summarize the results: The chance the second child is homozygous recessive is 25%, and the chance the second child is a heterozygous carrier is 50%, regardless of the first child's genotype.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait is expressed only if an individual inherits two copies of a mutant allele, one from each parent. Carriers have one normal and one mutant allele but typically do not show symptoms. For two heterozygous carriers, each child has a 25% chance of being affected, 50% chance of being a carrier, and 25% chance of being unaffected.

Independent Assortment and Probability in Genetics

Each child’s genotype is determined independently according to Mendelian genetics, meaning the outcome for one child does not affect the probabilities for the next. Thus, even if the first child is homozygous recessive, the chance for the second child to inherit the same genotype remains the same as the initial probability.

Genotype Probabilities for Offspring of Carrier Parents

When both parents are heterozygous carriers, the possible genotypes for each child are: 25% homozygous recessive (affected), 50% heterozygous carrier (unaffected but carrier), and 25% homozygous dominant (unaffected, non-carrier). These probabilities apply independently to each child regardless of previous offspring’s genotype.

Watch next

Master Diploid Genetics with a bite sized video explanation from Kylia

Start learning

Related Videos

Related Practice

Multiple Choice

Which of the following correctly describes the genetic makeup of a haploid set and a diploid set in a eukaryotic cell?

views

Multiple Choice

Which of the following describes an acrocentric chromosome?

In diploid organisms there are _______ chromosomal copies. In haploid organisms there is _______ chromosomal copy.

After a diploid cell undergoes meiosis, it divides to produce…

Answer the following questions for autosomal conditions such as PKU.

Parents who are each heterozygous carriers for a recessive mutant allele have a child who does not have the condition. What is the chance this child is a heterozygous carrier of the condition?

365

views

Textbook Question

Answer the following questions for autosomal conditions such as PKU.

If both parents are heterozygous carriers of a mutant allele, what is the chance that their first child will be homozygous recessive for the mutation?

326

views

Textbook Question

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

The low-methionine diet must be maintained throughout life to manage homocystinuria. Why do you think this is the case?

326

views

Textbook Question

Why do you think eating a low-methionine diet is critical to controlling homocystinuria?

634

views

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap