31 Questions
What is a monohybrid cross?
A cross that tracks the inheritance of a single trait
What does true-breeding mean?
Pure breeding with all offspring of the same variety
What is the F1 generation?
Offspring of the P generation
What is the significance of Gregor Mendel's work?
He studied segregation of traits in the garden pea and published his theory of inheritance in 1865
What is the frequency of familial hypercholesterolemia in Afrikaner populations in South Africa?
1 in 100
In which regions of Quebec is the frequency of myotonic dystrophy 1 in 550?
Charlevoix and Saguenay–Lac Saint Jean
What is the probability that children born to a heterozygous and a normal parent will receive the mutant gene?
$50%$
Incompletely dominant inheritance is observed in which disorder?
Achondroplasia
Which type of inheritance demonstrates a vertical pedigree pattern, equal disease frequency and severity between males and females, and variable expressivity?
$X$-linked dominant inheritance
'Pure Dominant Inheritance' is characteristic of which disorder?
$\text{Huntington disease}$
'Incompletely Dominant Inheritance' results in what ratio of homozygous normal, heterozygous mutant, and homozygous mutant offspring?
$1:2:1$
What is the frequency of myotonic dystrophy in the Charlevoix and Saguenay–Lac Saint Jean regions of northeastern Quebec?
1 in 550
What are typical features of autosomal dominant conditions?
Vertical pedigree pattern, equal disease frequency between males and females, variable expressivity
Which type of inheritance demonstrates a generally equal disease frequency and severity between males and females?
Autosomal dominant inheritance
What is the probability that children born from two heterozygous parents will be sick due to an autosomal dominant disorder?
3/4
Which term refers to a male with an abnormal allele for a gene located on the X chromosome and no other copy?
Hemizygous
What do homozygous individuals have at a locus?
Two identical alleles
What is the characteristic of single-gene disorders?
They are characterized by patterns of transmission
What does mendelian inheritance patterns depend on?
Chromosomal location of the gene and whether the phenotype is dominant or recessive
What do compound heterozygotes have?
Two different mutant alleles
What is the Law of Segregation?
During gamete formation, each gamete receives one allele for each trait
What did Mendel study in his experiments?
Seven traits or characteristics
What is the significance of Mendel's experiments and discoveries?
Led to an understanding of genetic crosses and the principles of inheritance
What is the F1 generation?
The first filial generation resulting from a cross between purebred parents
What did Mendel's study on pea plants lead to?
An understanding of genetic crosses and the principles of inheritance
What is the Law of Dominance?
Inheritance of contrasting traits results in only one form being expressed in the offspring
What did Mendel do to generate pure lines in his experiments?
Selected plants with different phenotypes for two years
What is the significance of Mendel's reciprocal crosses?
They provided insights into how traits are inherited from both male and female parents
What is the Law of Independent Assortment?
Alleles for different traits are distributed to the sex cells independently
What did Mendel observe about the F1 generation resulting from reciprocal crosses?
It was identical to the purple-flowered parent, regardless of which parent was used in the reciprocal cross.
What did Mendel find about self-crossing F1 generation plants?
No relevant information provided
Study Notes
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A phenotype can be normal or abnormal in an individual, and the genotype can be homozygous, heterozygous, or compound heterozygous.
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Homozygous individuals have two identical alleles at a locus, while heterozygous individuals have one wild-type and one mutant allele.
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Compound heterozygotes have two different mutant alleles.
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Hemizygous refers to a male with an abnormal allele for a gene located on the X chromosome and no other copy.
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Single-gene disorders are characterized by patterns of transmission and affect approximately 1 in 300 neonates, causing 7% of pediatric hospitalizations.
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Mendelian disorders can exhibit pleiotropy, meaning a single gene defect can result in multiple diverse phenotypic effects.
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Pedigrees are used to establish patterns of transmission in families.
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Mendelian inheritance patterns depend on the chromosomal location of the gene and whether the phenotype is dominant or recessive.
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Dominant inheritance patterns include incompletely dominant and codominant, while recessive inheritance patterns include codominance in the ABO blood group system.
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An estimated 50% of all known mendelian disorders are inherited as autosomal dominant traits, some of which have high incidence, such as adult polycystic kidney disease.
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Mendel's experiments with pea plants (Pisum sativum) in the late 1800s:
- Peas were chosen due to their small size, ease of growth, availability in various varieties, and ability to self-fertilize or be cross-pollinated.
- Mendel studied seven traits or characteristics in his experiments.
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Mendel's methods:
- Selected plants with different phenotypes for two years to generate pure lines.
- Conducted reciprocal crosses (females x males and males x females) with the purple-flowered and white-flowered plant lines.
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Mendel's observations:
- The F1 generation (first filial generation) was identical to the purple-flowered parent, regardless of which parent was used in the reciprocal cross.
- When F1 generation plants were self-crossed, they produced the second filial generation (F2 generation) – the birth of modern genetics.
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Mendel's laws of inheritance:
- Law of Dominance: Inheritance of contrasting traits results in only one form (dominant) being expressed in the offspring.
- Law of Segregation: During gamete formation, each gamete receives one allele (hereditary unit) for each trait.
- Law of Independent Assortment: Alleles for different traits are distributed to the sex cells independently.
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Mendel's concepts:
- Dominant and recessive alleles: The dominant allele is expressed when heterozygous (different alleles), while the recessive allele is hidden.
- Segregation of alleles: During gamete formation, alleles separate from each other and are then recombined during fertilization.
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Mendel's experiments and discoveries led to an understanding of genetic crosses and the principles of inheritance.
Test your knowledge of genetic phenotypes and genotypes with this quiz. Explore the concepts of homozygous, heterozygous, and compound heterozygote genotypes and their implications for phenotype expression.
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