Foundations of Medical Science: Genetics and Inheritance

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Questions and Answers

What is a potential consequence of taking a normal dose of warfarin?

Increased heart rate

Reduced risk of stroke

Excessive blood clotting

Excessive bleeding (correct)

What is the main purpose of genotyping in personalized medicine?

To identify genetic variants that affect drug response (correct)

To develop targeted therapies

To determine the patient's blood type

To diagnose genetic disorders

What is the term for the protein-DNA complex that makes up chromatin?

Centromere

Histone

Nucleosome (correct)

Chromatin fiber

How many chromosomes are present in a normal human cell?

46 Signup and view all the answers

What is the term for the study of the genetic component of a cell through the visualization and analysis of chromosomes?

Cytogenetics Signup and view all the answers

What is the normal karyotype of a female?

46 XX Signup and view all the answers

What is the term for the point at which two identical chromatids are joined?

Centromere Signup and view all the answers

What is the purpose of G-banding in cytogenetics?

To visualize chromosomes during metaphase Signup and view all the answers

What is the main difference between the number of chromosomes in mitosis and meiosis?

Mitosis has 46 chromosomes, while meiosis has 23 chromosomes Signup and view all the answers

What occurs during prophase I of meiosis?

Homologous pairs of chromosomes exchange DNA by crossing over Signup and view all the answers

What is the result of one round of DNA replication and one round of chromosomal segregation?

Production of 2 cells with 46 chromosomes Signup and view all the answers

During which stage of mitosis do chromosomes line up at the centre of the spindle?

Metaphase Signup and view all the answers

What is the chromosome number of the cells produced during meiosis?

Haploid (n) Signup and view all the answers

What is the location of the alpha globin gene?

16p13.3 Signup and view all the answers

What is the term for the full complement of all the genes in the genome?

Genotype Signup and view all the answers

What is the result of a gene or combination of genes?

Phenotype Signup and view all the answers

What type of disorder is associated with a single gene?

Monogenic disorder Signup and view all the answers

What is the term for the study of how genetic variations affect response to drugs?

Pharmacogenetics Signup and view all the answers

What is the enzyme responsible for the metabolism and detoxification of drugs?

Cytochrome P450 Signup and view all the answers

What is the result of a genetic variation in the CCR5 gene?

Immunity to HIV infection Signup and view all the answers

What is the consequence of having a specific variant of the CYP450 gene?

Reduced efficiency in metabolism of drugs Signup and view all the answers

What is the term for the physical characteristics of an organism that result from the interaction of its genes and the environment?

Phenotype Signup and view all the answers

What is the probability of a carrier mother having an affected son?

50% Signup and view all the answers

What is a characteristic of an autosomal recessive trait in a pedigree?

The trait often skips a generation Signup and view all the answers

What is the primary advantage of using twins in studying the genetic component of diseases?

Identical twins are genetically identical Signup and view all the answers

What can be inferred from a higher concordance rate in monozygotic twins compared to dizygotic twins?

The disease has a strong genetic component Signup and view all the answers

What is the function of the CFTR protein in cells?

It pumps Cl- ions out of the cell Signup and view all the answers

What is the genotype of an individual who is a carrier of cystic fibrosis?

Cc Signup and view all the answers

What type of disorders are influenced by both genetic and environmental factors?

Multifactorial disorders Signup and view all the answers

What is the probability of a child inheriting cystic fibrosis if both parents are carriers?

1/4 Signup and view all the answers

What is the term for the study of the genetic component of a complex trait?

Quantitative genetics Signup and view all the answers

What is the name of the most common mutant allele of the CFTR gene?

CFTRD508 Signup and view all the answers

What is the probability of a non-carrier mother having an affected son?

0% Signup and view all the answers

What is the normal function of the CFTR protein?

To pump Cl- ions out of the cell Signup and view all the answers

What can be inferred from a concordance rate of 70% for diabetes (type II) in monozygotic twins?

Diabetes (type II) has a strong genetic component Signup and view all the answers

What is the reason for the difference in concordance rates between monozygotic and dizygotic twins?

Different genetic factors Signup and view all the answers

What is the genotype of an individual who is affected by cystic fibrosis?

cc Signup and view all the answers

What is the carrier rate of the mutant CFTR allele in northern Europe?

1:25 Signup and view all the answers

What is the reason why the mutant CFTR allele may have conferred a selective evolutionary advantage?

It conferred a unknown advantage Signup and view all the answers

What is a characteristic of an autosomal dominant trait?

The trait is frequent in each generation Signup and view all the answers

Study Notes

Inherited Disease

Genotype: the full complement of all genes in the genome
Phenotype: the functional consequence of a gene (or combination of genes)
Genetic diseases are caused by the inheritance of variants of genes (mutations) that have abnormal functions
Monogenic disorders: associated with single gene (e.g. cystic fibrosis)
Polygenic disorders: associated with many different genes (e.g. Type II diabetes)

Pharmacogenetics

Cytochrome P450 enzymes: a common pathway for the metabolism and detoxification of drugs
CYP450 enzymes: particularly important for drug metabolism
Variants of the CYP450 gene: encode enzymes with different activities
Patients with specific variants: have reduced efficiency in metabolism of drugs
Genotyping of variants: can be useful part of therapy
Personalized medicine: prescribing a drug based on an individual's genotype

Packaging of DNA

DNA is packaged in the nucleus with positively charged histone proteins
DNA + histones = chromatin
Octamer of histones: forms a core with the DNA around the outside
Histone octamer + DNA = nucleosome
Nucleosomes form a chromatin fibre
Chromatin fibre loops out of a central nuclear matrix protein to create individual chromosomes

Human Karyotype

46 chromosomes (23 from each parent)
Cells are diploid (2n)
22 pairs of autosomes
1 pair of sex chromosomes
Staining chromosomes at Metaphase with Giemsa dye: produces alternating light and dark bands characteristic of each chromosome
Normal female karyotype: 46 XX
Normal male karyotype: 46 XY
Chromosome 1: largest
Chromosome 22: smallest

Organisation of Chromosomes

After DNA replication: each chromosome consists of two identical chromatid linked together at the centromere
Arms of chromosomes: often different lengths (short (p) and long (q))
Location of genes: can be specified based on the G-banding pattern and the arm of the chromosome (e.g. alpha globin genes: 16p13.3)

Mitosis and Meiosis

Mitosis: production of 2 cells, with 46 chromosomes (diploid: 2n) that are genetically identical
Involves one round of DNA replication and one round of chromosomal segregation
Meiosis: production of 4 cells, with 23 chromosomes (haploid: n) that are genetically variable
Involves one round of DNA replication and two rounds of chromosomal segregation

Modes of Inheritance

Autosomal recessive: trait is rare in pedigree, trait often skips a generation, trait affects males and females, trait is transmitted by either sex
Autosomal dominant: trait is frequent in pedigree, individuals are affected in each generation
X-linked (recessive): trait affects males more than females

Cystic Fibrosis

Caused by a mutation of the Cystic fibrosis transmembrane conductance regulator (CFTR) gene
Locus (chromosomal location) of the gene: on chromosome 7
Sequence variation of a gene: called an allele
Genome contains extensive gene polymorphism – some of these alleles are non-functional and are called mutant alleles or mutants
Normal functional allele: called the wildtype allele
There are >500 mutant alleles of CFTR, the most common is CFTRD508 (deletion of codon 508)

Inheritance Patterns

Autosomal recessive: 3 normal and 1 cystic fibrosis (typical ratio of progeny from two heterozygote carriers)
Autosomal dominant: all male offspring are unaffected and all female offspring are carriers (typical ratio of progeny from non-carrier mother and affected father)

Complex Disorders

Most human characteristics are polygenic (controlled by genes at more than one locus) e.g. height
Many disease states are multifactorial (both polygenic and influenced by the environment) e.g. obesity, diabetes, cardiovascular disease
Twin studies: can assess the contribution of genetic versus environmental factors
Concordance rates: can provide useful insights into the contribution of genetics (e.g. rheumatoid arthritis, schizophrenia, multiple sclerosis, diabetes, cancer)

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Description

This quiz covers the basics of genetics, including chromosomal inheritance, human karyotype, and gene variants. It is designed for students of medical science.