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Questions and Answers
Which of the following is a key difference between autosomal dominant and autosomal recessive inheritance patterns?
Which of the following is a key difference between autosomal dominant and autosomal recessive inheritance patterns?
- Autosomal dominant traits are located on sex chromosomes, while autosomal recessive traits are located on autosomal chromosomes.
- Autosomal dominant traits skip generations, while autosomal recessive traits are present in every generation.
- Autosomal dominant traits only affect males, while autosomal recessive traits only affect females.
- Autosomal dominant traits require only one copy of the gene for expression, while autosomal recessive traits require two copies. (correct)
In a scenario where a true breeding tall pea plant is crossed with a true breeding dwarf pea plant, what is the expected outcome in the F1 generation, according to Mendel's experiments?
In a scenario where a true breeding tall pea plant is crossed with a true breeding dwarf pea plant, what is the expected outcome in the F1 generation, according to Mendel's experiments?
- All offspring will be tall. (correct)
- There will be a 1:1 ratio of tall to dwarf offspring.
- All offspring will be dwarf.
- All offspring will be of medium height.
How does Mendel's Law of Independent Assortment apply to genes located on the same chromosome?
How does Mendel's Law of Independent Assortment apply to genes located on the same chromosome?
- Genes on the same chromosome assort independently only during mitosis.
- Genes on the same chromosome assort independently, similar to genes on different chromosomes.
- Genes on the same chromosome assort independently depending on the sex of the organism.
- Genes on the same chromosome are always inherited together, violating the Law of Independent Assortment. (correct)
What information can be deduced from a pedigree chart?
What information can be deduced from a pedigree chart?
In an autosomal recessive inheritance pattern, what is the likelihood of an affected child having two unaffected parents?
In an autosomal recessive inheritance pattern, what is the likelihood of an affected child having two unaffected parents?
Why are X-linked recessive traits more commonly observed in males than in females?
Why are X-linked recessive traits more commonly observed in males than in females?
For an X-linked dominant trait, which of the following statements is always true?
For an X-linked dominant trait, which of the following statements is always true?
If a female is a carrier for an X-linked recessive trait, what is the probability that her son will inherit the trait?
If a female is a carrier for an X-linked recessive trait, what is the probability that her son will inherit the trait?
What is the mode of inheritance if only males are affected and all sons of affected fathers are also affected?
What is the mode of inheritance if only males are affected and all sons of affected fathers are also affected?
In incomplete dominance, if a red flower (RR) is crossed with a white flower (WW), what is the phenotype of the offspring?
In incomplete dominance, if a red flower (RR) is crossed with a white flower (WW), what is the phenotype of the offspring?
How does co-dominance differ from incomplete dominance?
How does co-dominance differ from incomplete dominance?
What is the genotype of an individual who is hemizygous for a particular gene?
What is the genotype of an individual who is hemizygous for a particular gene?
In the context of genetics, what does the term 'true breeding' refer to?
In the context of genetics, what does the term 'true breeding' refer to?
According to Mendel's Law of Segregation, what happens to alleles during gamete formation?
According to Mendel's Law of Segregation, what happens to alleles during gamete formation?
Which of the following is an example of a sex-linked condition?
Which of the following is an example of a sex-linked condition?
Why is X-linked recessive inheritance not passed from father to son?
Why is X-linked recessive inheritance not passed from father to son?
What is a key characteristic of autosomal dominant inheritance as observed in pedigree analysis?
What is a key characteristic of autosomal dominant inheritance as observed in pedigree analysis?
How do male and female gametes contribute alleles to offspring during fertilization?
How do male and female gametes contribute alleles to offspring during fertilization?
What is the expected phenotypic ratio in the offspring of a monohybrid cross when both parents are heterozygous for a trait, assuming complete dominance?
What is the expected phenotypic ratio in the offspring of a monohybrid cross when both parents are heterozygous for a trait, assuming complete dominance?
Which of the following statements accurately describes the relationship between alleles and dominance?
Which of the following statements accurately describes the relationship between alleles and dominance?
Which of the following is true regarding carriers of X-linked recessive traits.
Which of the following is true regarding carriers of X-linked recessive traits.
Given two parents, one is heterozygous for trait A, which is autosomal dominant, and the other is homozygous recessive. What is the probability that the child will express trait A?
Given two parents, one is heterozygous for trait A, which is autosomal dominant, and the other is homozygous recessive. What is the probability that the child will express trait A?
For colorblindness to be expressed in an X-linked recessive inheritance for females, what must the genotypes of her parents be?
For colorblindness to be expressed in an X-linked recessive inheritance for females, what must the genotypes of her parents be?
True or False: An affected child can have unaffected parents in an autosomal dominant inheritance.
True or False: An affected child can have unaffected parents in an autosomal dominant inheritance.
Which of the following patterns indicates an X-linked dominant inheritance?
Which of the following patterns indicates an X-linked dominant inheritance?
Flashcards
Haploid Gamete
Haploid Gamete
A cell that contains one set of chromosomes (half the usual number).
Zygote
Zygote
The resulting cell when male and female gametes fuse during fertilisation. Contains two alleles for each gene.
Hemizygous
Hemizygous
Having only one allele for a gene (e.g., males for genes on sex chromosomes).
Homozygous
Homozygous
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Heterozygous
Heterozygous
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Autosomal Gene
Autosomal Gene
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Autosomal Dominant
Autosomal Dominant
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Autosomal Recessive
Autosomal Recessive
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Mendel’s Law of Segregation
Mendel’s Law of Segregation
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Mendel’s Law of Independent Assortment
Mendel’s Law of Independent Assortment
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Pedigree Charts
Pedigree Charts
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Autosomal Recessive (Pedigree)
Autosomal Recessive (Pedigree)
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Autosomal Dominant (Pedigree)
Autosomal Dominant (Pedigree)
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Sex Linkage
Sex Linkage
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X-Linked Dominant
X-Linked Dominant
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X-Linked Recessive
X-Linked Recessive
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Trends of X-Linked Conditions
Trends of X-Linked Conditions
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Y-Linked Inheritance
Y-Linked Inheritance
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Incomplete Dominance
Incomplete Dominance
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Co-dominance
Co-dominance
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X-linked Recessive Inheritance Pattern
X-linked Recessive Inheritance Pattern
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Y-linked Dominant Inheritance
Y-linked Dominant Inheritance
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X-linked Dominant Inheritance
X-linked Dominant Inheritance
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Sex-linked allele notation
Sex-linked allele notation
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Dominance is Relative
Dominance is Relative
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Study Notes
- Gametes are haploid, possessing one allele per gene.
- After fertilization, the zygote has two alleles for each gene, except males, who have one allele for genes on sex chromosomes due to their unpaired XY chromosomes.
Allele Combinations
- Homozygous: Maternal and paternal alleles are the same.
- Heterozygous: Maternal and paternal alleles are different.
- Hemizygous: Males have only one allele for genes on sex chromosomes.
Autosomal Inheritance
- Autosomal genes are inherited from the 22 sets of autosomal chromosomes.
- Autosomal dominant: One copy of the gene is needed for expression.
- Autosomal recessive: Two copies of the gene are needed for expression.
Mendel's Principles
- Each parent contributes one version (allele) of each gene/characteristic.
- Alleles are passed down through generations predictably.
- Alleles can be homozygous or heterozygous.
- Dominant alleles are expressed in heterozygotes, while recessive alleles are hidden (Law of Dominance).
- During gamete formation, allele pairs separate, and each gamete gets one allele (Law of Segregation).
- Mendel crossed true-breeding tall and dwarf pea plants then crossed two of the offspring.
Mendel’s Laws of Dominance and Segregation
- Alleles segregate into gametes, with each gamete carrying one allele.
- Offspring inherit one allele from each parent.
- Dominant alleles are always expressed.
- Heterozygous parents produce offspring with a 3:1 dominant to recessive ratio.
Mendel’s Law of Independent Assortment
- Two traits are inherited independently if their genes are on different chromosomes.
- Genes on the same chromosome are inherited together.
- Mendel’s dihybrid crosses showed independent inheritance.
- Independent assortment is due to chromosome behavior during meiosis.
Mendelian Ratios
- Mendel determined ratios of trait expression in pea plants across generations.
- Mendelian ratios apply across all living things.
Pedigree Charts
- Inheritance patterns help trace genetic conditions in families using pedigree charts.
- Pedigree charts depict individual genotypes.
- They determine trait dominance/recessiveness.
- Pedigree charts predict trait likelihood in future generations.
Pedigree Analysis: Autosomal Recessive
- Affects males and females equally.
- Affected children can have unaffected parents.
- Affected parents only have affected children.
Pedigree Analysis: Autosomal Dominant
- Affects males and females equally.
- Affected children must have at least one affected parent.
- Unaffected children can have affected parents.
Beyond Mendelian Ratios
- Not all inheritance follows the 3:1 Mendelian ratio.
- Discoveries by Beadle & Tatum linked genes to protein synthesis.
Non-Mendelian Inheritance
- Sex linkage, co-dominance, incomplete dominance, and multiple alleles exist.
Sex Linkage
- A gene is located on a sex chromosome (X or Y).
- Sex-linked conditions are usually X-linked.
- Females can be homozygous or heterozygous, having two X chromosomes.
- X-linked dominant traits are more common in females.
- Males are hemizygous for X-linked traits, having one X chromosome.
- X-linked recessive traits are more common in males.
X-linked Conditions
- Only females can be carriers for recessive diseases.
- Males inherit X-linked traits from their mothers.
- Females cannot inherit X-linked recessive conditions from unaffected fathers.
Sex-Linked Examples
- Red-green color blindness and hemophilia are X-linked recessive conditions, more common in males.
- Alleles for sex-linked traits are written as superscripts to the sex chromosome (X).
Sex-Linked Allele Notation
- Haemophilia: XH = unaffected, Xh = affected
- Colour blindness: XA = unaffected, Xa = affected
Y-Linked Inheritance
- This is the inheritance of genes on the Y chromosome.
- Only males are affected.
- Y-linked genes are transmitted from father to son.
- The Y chromosome is generally smaller than the X chromosome, and carries fewer genes.
- Besides the genes for sperm development, the Y chromosome also carries genes other than for sex determination.
X-Linked Dominant
- Affects males & females
- Does not skip a generation
- All daughters are affected from affected fathers
X-Linked Recessive
- Unaffected mother can have affected son
- Not passed from father to son
- Affected fathers have carrier daughters
Y-Linked Dominant
- Only males affected
- All sons affected
Incomplete Dominance
- A blending of features occurs when two alleles are expressed.
- One allele is not completely dominant over the other.
- Example: pink snapdragons from white and red alleles.
- Alleles are written as superscripts next to the letter chosen to represent the gene, with capital letters still representing the dominant trait like CR.
Co-dominance
- Both alleles are expressed, creating a new phenotype, where both (dominant) alleles are expressed.
- Hybrids (heterozygotes) have one allele for each trait and are a combination of the homozygotes.
- Codominance has both alleles expressed, while incomplete dominance is a blend of the two phenotypes.
- Alleles are written as superscripts next to the genes.
- Because both alleles are expressed they are both given a capital letter.
- Different alleles also have different capital letters as both alleles are dominant.
Dominance and Recessiveness
- An allele isn't inherently dominant or recessive.
- Dominance/recessiveness is relative to another allele.
- Either one allele is dominant and the other is recessive, or the two alleles are codominant.
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