Genetics and Inheritance Quiz

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Questions and Answers

What type of inheritance does a trait transmitted from one dominant gene exemplify?

Autosomal dominant (correct)

Co-dominance

Autosomal recessive

Sex-linked dominant

What comprises the smallest unit of DNA?

Chromatid

Chromosome

Gene

Nucleotide (correct)

Which of the following disorders is NOT commonly associated with autosomal dominant inheritance?

Polycystic kidney disease

Familial hypercholesterolaemia

Huntington’s disease

Cystic fibrosis (correct)

What type of inheritance did Gregor Mendel's studies primarily focus on?

Mendelian inheritance Signup and view all the answers

Which aspect of genetic predisposition is true?

It increases the likelihood of developing a disease. Signup and view all the answers

What does co-dominance refer to in genetic inheritance?

Both dominant alleles are expressed Signup and view all the answers

What is described by the term 'genotype'?

The unique sequence of DNA Signup and view all the answers

In Mendel's first experiment, what was the genotype of the tall plants crossed?

TT Signup and view all the answers

In a Punnett's Square, if both parents are carriers for an autosomal recessive disorder, what is the probability that their child will be affected?

1/4 Signup and view all the answers

Which of the following is true regarding dominant and recessive traits?

A dominant trait can mask a recessive trait. Signup and view all the answers

Which of the following describes sex-linked inheritance?

Located on the sex chromosomes Signup and view all the answers

What does the term 'epistasis' refer to in genetic interactions?

A condition where one gene masks the expression of another Signup and view all the answers

What type of DNA is primarily located in the mitochondria?

Mitochondrial DNA Signup and view all the answers

Which statement accurately describes mutations?

Mutations can lead to various disease states. Signup and view all the answers

Which of these characteristics does NOT typically follow Mendelian inheritance?

Human skin color Signup and view all the answers

How does a mutation in the genotype affect the organism?

It may change the observable traits (phenotype). Signup and view all the answers

What type of point mutation involves a base being added or deleted from the DNA sequence?

Frameshift mutation Signup and view all the answers

Which point mutation results in a change to a stop codon, leading to a truncated protein?

Nonsense mutation Signup and view all the answers

Which type of mutation does NOT alter the amino acid sequence due to redundancy in the codon code?

Silent mutation Signup and view all the answers

In which point mutation does only one amino acid coding get disturbed?

Missense mutation Signup and view all the answers

Which gross mutation involves the loss of a chunk of DNA from a chromosome?

Deletion Signup and view all the answers

What is a common consequence of frameshift mutations?

Truncated or altered protein Signup and view all the answers

What type of mutation is characterized by a single base being replaced without addition or deletion?

Missense mutation Signup and view all the answers

Which of the following statements about gross mutations is true?

They can involve deletions, insertions, and translocations. Signup and view all the answers

Which type of disorder is most commonly associated with the X chromosome?

X-linked recessive disorders Signup and view all the answers

What is a characteristic symptom of Fragile X syndrome?

Long face Signup and view all the answers

What distinguishes X-linked dominant disorders from X-linked recessive disorders?

No common conditions are inherited this way Signup and view all the answers

What are point mutations?

Mutations that involve a change in the base sequence Signup and view all the answers

Which of the following is NOT a cause of mutations?

Normal cellular metabolism Signup and view all the answers

What is the primary distinction between mutants and wild types?

Wild types exhibit the usual phenotype for that species Signup and view all the answers

What is a significant factor concerning the inheritance of X-linked recessive disorders?

Affected males pass the disorder to all daughters Signup and view all the answers

What is the primary function of the p53 gene?

To regulate apoptosis Signup and view all the answers

Which cancer types have been associated with damage to the p53 gene?

Sarcomas, adrenal tumours, and breast cancer Signup and view all the answers

What kind of disorder is Duchenne muscular dystrophy classified as?

X-linked recessive disorder Signup and view all the answers

What type of mutation is described as the insertion of extra bases from another part of a chromosome?

Gross mutation - insertion Signup and view all the answers

What role do telomeres play in cellular biology?

They protect chromosomes from degradation Signup and view all the answers

What is the function of telomerase in cancer cells?

To extend telomere length Signup and view all the answers

Which of the following disorders is caused by a translocation mutation?

Down syndrome Signup and view all the answers

What happens to the genes during an inversion mutation?

A gene rotates and is reinserted upside down Signup and view all the answers

What is the lifetime risk of breast cancer for females?

1 in 8 Signup and view all the answers

Which syndrome is associated with a higher risk of colorectal cancer?

Lynch syndrome Signup and view all the answers

Which syndrome is associated with gene duplication on chromosome 12?

Pallister Killian syndrome Signup and view all the answers

What percentage of breast cancer cases are attributed to BRCA1 and BRCA2 mutations in familial cases?

About 60% Signup and view all the answers

What is a key characteristic of chronic myelogenous leukaemia?

Involves chromosome translocation Signup and view all the answers

What is a potential consequence of a gross mutation involving frameshift?

Truncated protein production Signup and view all the answers

What genetic inheritance pattern is characterized by familial adenomatous polyposis?

Autosomal dominant Signup and view all the answers

Which of the following accurately describes gross mutations?

Include insertions, translocations, inversions, and duplications Signup and view all the answers

Study Notes

Nutritional Biochemistry

Course title: DIET413/BHCS1019
Lecturer: Dr Nathaniel Clark FHEA RNutr MRSB
Email: [email protected]

Previously...

DNA is made of nucleotides
Nucleotides consist of a nitrogenous base, a pentose sugar, and a phosphate group
Polynucleotide chains are formed through phosphodiester bonds connecting the phosphate group and sugar between nucleotides
DNA coils around histone proteins to condense into chromatin
The DNA code is transcribed and translated to form proteins (phenotype)
These processes are highly controlled through enzyme action
DNA is also found in mitochondria, which produces proteins for respiration
Various disease states are caused by mutations to the genome

Learning Outcomes

Outline genetic inheritance (autosomal and sex inheritance)
Describe different types of mutations
Determine how DNA damage can be repaired
Briefly consider some types of cancer

Genotype and Phenotype

Genotype: The unique DNA sequence of an organism
Phenotype: The effect of a mutation on the organism
Changes in genotype can affect phenotype
Inheritable phenotypes are based on genotype

Mendelian Inheritance

Based on work by Gregor Mendel (1822-1884)
Proposed factors (genes) controlling traits are in pairs (one from each parent)
Each factor can be dominant or recessive
Dominant factors (heterozygous) mask recessive factors (homozygous)

Mendelian Inheritance - Experiments

First experiment crossed homozygous tall plants (TT) with homozygous short plants (tt), producing all tall plants (F1)
Second experiment crossed hybrid tall plants (Tt), producing a ratio of 3 tall plants to 1 short plant (F2)

Mendelian Inheritance - Punnett's Square

Visual representation of trait inheritance patterns
Displays possible allele combinations in offspring

Mendelian Inheritance - Limitations

Dominance doesn't always apply to all traits
Some traits exhibit blending inheritance
Co-dominance occurs when two dominant alleles are expressed together (e.g., blood type)
Non-allelic gene interaction (epistasis) occurs when the presence or absence of one gene affects the expression of another

Patterns of Inheritance

Autosomal inheritance: Traits controlled by genes located on non-sex chromosomes
Sex-linked inheritance: Traits controlled by genes located on sex chromosomes (X and Y)
Autosomal dominant: Affected individual has at least one dominant allele, so an affected parent can pass on the trait to their children
Autosomal recessive: Affected individual has two recessive alleles, so both parents must carry the allele to pass it on to their children
Sex-linked dominant: Trait determined by a dominant allele on the X chromosome
Sex-linked recessive: Trait determined by a recessive allele on the X chromosome

Autosomal Dominant Inheritance

Trait or disorder carried on a dominant gene
Easily seen using a Punnett square
Examples: Familial hypercholesterolaemia, Polycystic kidney disease, Huntington’s disease

Autosomal Recessive Inheritance

Trait or disorder carried on a recessive allele
Both parents must carry the allele to pass it on to their child
Examples: Haemochromatosis, Cystic fibrosis

Activity

Calculating the probability of offspring inheriting haemochromatosis given parental genotypes

Sex-linked Disorders

Alleles carried on X or Y chromosomes
Most sex-linked disorders arise from alleles on the X chromosome
Only one copy of the X chromosome in each individual
X-linked recessive: Affected male (XhY), often passed down from a carrier female (XhX)
X-linked dominant rare.

X-linked Recessive Disorders

Transmission depends on whether the mother or father is carrying the allele
Examples: Fragile X syndrome, Haemophilia, Duchenne muscular dystrophy

X-linked Dominant Disorders

Very rare, no common conditions inherit this way
Difference in offspring relative risk (1 in 4 versus 1 in 2 for daughters)

Mutations

Changes in DNA sequence
Base sequence on DNA determines protein structure
Genome consists of approximately 3 billion base pairs, distributed across 23 chromosomes (ranging from 50 to 300 million base pairs)
Potential for mutations to occur

Mutants versus Wild Types

Wild type: Organism with usual phenotype for the species
Mutant: Organism whose phenotype has changed due to mutation
Mutations occur in two forms: point mutations (involving a single base change) or gross mutations (involving larger stretches of DNA)

Point Mutations

The consequences of point mutations are based on an understanding of triplet coding
Main types:
Silent mutations
Frameshift mutations
Missense mutations
Nonsense mutations

Point Mutations - Silent

Wrong nucleotide occurs, but it doesn’t change the amino-acid sequence.
Redundancy in the codon code: DNA sequence and corresponding amino acid remain the same, even with a different nucleotide.
Polymorphisms are where these mutations occur in organisms

Point Mutations - Frameshift

A base is lost or added
Results in incorrect triplet code, disrupting amino acid sequence
Serious impact on the encoded protein and can lead to mutant phenotypes

Point Mutations- Missense

A single base is replaced
Only the amino acid is disturbed
Structure of the final protein is slightly altered

Point Mutations - Nonsense

The misplaced base causes the triplet code to become a stop codon
No corresponding amino acid can be added when the stop codon is encountered
Protein becomes truncated/incomplete

Gross Mutations (Deletions, Insertions, Translocation, Inversion, Duplication)

Substantial alterations to DNA, particularly long DNA sequences
Deletions: Loss of a gene or part of a gene
Insertions: Extra bases inserted into the DNA sequence
Translocations: Parts of chromosomes are exchanged
Inversions: Sections of DNA are reversed
Duplications: Extra copies of a gene or part of a gene

DNA Damage and Response

DNA is constantly under attack
Agents can either directly damage bases (point mutations) or break the phosphodiester backbone (gross mutations)
Repair mechanisms exist for many types of mutations, but are not perfect

Repair Mechanisms (Base Pair Excision, Nucleotide Excision, Mismatch Repair)

Processes through which DNA may be repaired

Cancer

Cell growth and differentiation are controlled by hormones and growth factors acting on cell surface receptors
Genome damage in specific areas (introns, exons), is a factor linked to issues with cell regulation leading to disease
Lifestyle and environmental factors (smoking, diet, alcohol, obesity, radiation) contribute to cancer
DNA damage to growth control genes (proto-oncogenes), and tumor suppressor genes contribute
Cancer due to telomere damage, disruption with telomerase

Proto-oncogenes

Genes involved in normal cell growth and division
Can become oncogenes through mutations, promoting uncontrolled cell growth and development

p53

A tumor suppressor gene involved in regulating cell division and apoptosis (cell death)
Damage to p53 can result in uncontrolled cell proliferation and increased risk of cancer

Telomeres

Protective caps at the ends of chromosomes
Telomere shortening occurs with each cell division
Telomerase enzyme can maintain telomere length

Cancer Etiology: Variation In Cancer Risk Among Tissues Can Be Explained By The Number Of Stem Cell Divisions

Correlation between cancer risks and total stem cell divisions
Implication that random mutations during DNA replication in normal cells are a major factor in the development of certain cancers.

Cancer From Our Environment

Studies of twins to estimate contributions from inherited genes /environmental factors in cancer development, highlighting the significant effect of inherited genes on the risk of some cancers (prostate, colorectal, and breast)

Breast Cancer (BRCA Genes)

Most breast cancer is sporadic (not inherited)
Inherited cases are often linked to BRCA1/BRCA2 gene mutations that impair DNA repair
Prophylactic mastectomy is a possible intervention to reduce breast cancer risk.

Colorectal Cancer (HNPCC)

Genetic predisposition accounts for some cases (Lynch syndrome, HNPCC)
Lynch syndrome: Inherited disorder increasing risk of colon and rectum cancers
Other causes: Familial adenomatous polyposis which accounts for less than 1% of cases

Familial Adenomatous Polyposis (FAP)

Autosomal dominant condition characterized by multiple polyps, frequently in the colon
If not treated, colorectal cancer will develop by middle age
Risk of upper gastrointestinal cancers is also associated with FAP

Summary

Mendelian inheritance is a system describing how traits are inherited and expressed
DNA sequence can be altered in multiple ways
Errors not fixed by repair mechanisms can lead to disease like cancer

Revision Session

Split into two parts for different exam categories: Dietitians (11-12) and Nephrologists (12-1)

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Description

Test your knowledge on different types of genetic inheritance, including Mendelian, co-dominance, and sex-linked traits. This quiz covers key concepts such as genotypes, phenotypes, and genetic disorders. Perfect for students studying genetics!