Genetics: Lethal Alleles and Inheritance Patterns

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Questions and Answers

What are lethal alleles?

When the recessive or dominant (heterozygous or homozygous) genotype results in the death of the organism.

What is the ratio of recessive lethal alleles?

3:0 instead of 3:1.

What is the ratio for dominant lethal alleles?

0:1 instead of 3:1.

What is epistasis?

When one specific allele controls the function of another. Signup and view all the answers

What is the ratio for epistasis?

9:3:4 instead of 9:3:3:1. Signup and view all the answers

What are multiple alleles?

When dominant alleles can coexist to create a phenotype while still overpowering a recessive allele. Signup and view all the answers

What is sex-linked inheritance?

Genes located at the sex chromosomes. Signup and view all the answers

What is X-linked inheritance?

Genes passed through the X chromosome. Signup and view all the answers

When is the sex of an organism determined?

After 6-8 weeks when the SRY (sex-determining region of the Y) is activated. Signup and view all the answers

Is the X chromosome responsible for the genes for sex determination?

False Signup and view all the answers

Does the father carry the gene for the male reproductive system?

False Signup and view all the answers

If affected fathers have only affected daughters, what is the most probable inheritance pattern?

X-linked dominant. Signup and view all the answers

If affected mothers have only affected sons, what is the most probable inheritance pattern?

X-linked dominant. Signup and view all the answers

What is transcription?

Process of converting DNA to RNA. Signup and view all the answers

What is translation?

Process of converting RNA to protein. Signup and view all the answers

What is responsible for transcription?

RNA polymerase. Signup and view all the answers

What is the difference between the coding and template strand?

5’ to 3’ is the coding strand, while 3’ to 5’ is the template strand. Signup and view all the answers

How does RNA start?

With methionine (TAC) in the template strand. Signup and view all the answers

What are the three 'Stop' codons?

ATT, ACT, ATC. Signup and view all the answers

How does transcription/translation differ between prokaryotes and eukaryotes?

In prokaryotes, mRNA is immediately available, while in eukaryotes, it is first processed. Signup and view all the answers

What is left out in translation but not in transcription? How many of them are there?

Exons, introns – 1. Signup and view all the answers

What are codons?

Triplet of nitrogenous bases that make up the genetic code. Signup and view all the answers

How are mRNA oriented?

mRNA molecules are always oriented in the 5’ to 3’ direction. Signup and view all the answers

What strand does RNA polymerase use to transcribe?

The template strand. Signup and view all the answers

What makes for a nonheritable mutation?

A non-inheritable mutation occurs in somatic cells. Signup and view all the answers

What are SNPs?

Single nucleotide polymorphism. Signup and view all the answers

What is a germline?

Sex cells. Signup and view all the answers

What are the two types of SNPs?

Base substitutions and frameshift mutation. Signup and view all the answers

What are the three types of base substitutions, and what do they entail?

Missense mutations, nonsense mutations, silent mutation. Signup and view all the answers

Give an example as to why missense mutations can be so drastic.

Serine can easily turn into proline, leading to a significant change in the structure of the protein. Signup and view all the answers

What is the basis of frameshift mutation?

It is the insertion or deletion of a nitrogenous base. Signup and view all the answers

What is a Large Chromosomal Rearrangement (LCRs)?

A mutation with a much larger effect than SNPs, affecting 1000+ nucleotides. Signup and view all the answers

What is deletion (LCRs)?

The removal of a segment of a gene that can cause disastrous effects. Signup and view all the answers

What is duplication (LCRs)?

Occurs if a segment is broken from one chromosome and inserted into its homologue. Signup and view all the answers

What is translocation (LCRs)?

Occurs if the broken segment is attached to a different nonhomologous chromosome. Signup and view all the answers

Study Notes

Lethal Alleles

When the recessive or dominant (heterozygous or homozygous) genotype results in the death of the organism
Recessive lethal alleles result in a 3:0 phenotypic ratio instead of the expected 3:1.
Dominant lethal alleles result in a 0:1 phenotypic ratio instead of the expected 3:1.

Epistasis

One specific allele controls the function of another
Results in a 9:3:4 phenotypic ratio instead of the expected 9:3:3:1.

Multiple Alleles

Dominant alleles can coexist to create a phenotype while still overpowering a recessive allele (e.g., blood types)
Multiple genes can be necessary to confer a single trait.

Sex-Linked Inheritance

Genes located at the sex chromosomes
X-linked inheritance refers to genes passed through the X chromosome.

Sex Determination

Determined after 6-8 weeks of development when the SRY (sex-determining region of the Y) is activated, leading to testes development.
The X chromosome is not solely responsible for sex determination; most genes governing sex structures are found on autosomal chromosomes.
The mother carries the genes coding for the penis structure, illustrating that possession of a gene doesn't necessarily equate to its expression.

Inheritance Patterns

If a trait skips a generation, the most likely inheritance pattern is recessive.
If affected fathers have only affected daughters, the most probable inheritance pattern is X-linked dominant.
If affected mothers have only affected sons, the most probable inheritance pattern is X-linked dominant.

Transcription and Translation

Transcription: The process of converting DNA to RNA
Translation: The process of converting RNA to protein
RNA polymerase is responsible for transcription.
The coding strand is 5' to 3', while the template strand is 3' to 5' and serves as the template for transcription.
Transcription starts with methionine (TAC) in the template strand.
The stop codons in the template strand (3' to 5') are ATT, ACT, and ATC.
In prokaryotes, mRNA is immediately available and translated into proteins; in eukaryotes, it is first processed (pre-mRNA à mRNA) before translation.
Exons are included in both transcription and translation, while introns are only present in transcription.
Codons: triplets of nitrogenous bases that make up the genetic code.
mRNA molecules are always oriented in the 5' to 3' direction.
RNA polymerase utilizes the template strand for transcription.

Mutations

Nonheritable mutations occur in somatic cells, whereas heritable mutations are present in the allele.
Single nucleotide polymorphisms (SNPs) impact only one gene but can involve alterations in more than one nucleotide.
Germline refers to sex cells.

Types of SNPs

Base substitutions: Changes in a single nucleotide, resulting in missense, nonsense, or silent mutations.
- Missense mutation: A change in nitrogenous base alters the identity of one amino acid, which can have moderate to deleterious effects due to its impact on the protein's reactive site.
- Nonsense mutation: Generates an early stop codon by switching a nitrogenous base, leading to protein shortening, which can have severe effects.
- Silent mutation: A change in nitrogenous base does not affect the identity of an amino acid, typically having no effect.
Frameshift mutation: Insertion or deletion of a nitrogenous base, altering the reading frame and often leading to a premature stop codon.

Large Chromosomal Rearrangements (LCRs)

Mutations with a larger impact than SNPs, involving changes in 1000+ nucleotides.
Deletion: Removal of a gene segment can severely disrupt normal cell function (e.g., deletion of chromosome 5 causing cri-du-chat disorder).
Duplication: A segment is broken from one chromosome and inserted into its homologue, adding the fragment to the alleles (e.g., hemoglobin).
Translocation: A broken segment attaches to a different nonhomologous chromosome, similar to a crossover in meiosis but involving nonhomologous chromosomes (e.g., Burkitt lymphoma).

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Description

Explore the fascinating concepts of lethal alleles, epistasis, multiple alleles, and sex-linked inheritance in this genetics quiz. Understand how different genotypes can affect phenotypic ratios and inheritance patterns. Test your knowledge on how these mechanisms play a role in genetics and development.