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Questions and Answers
What is the key observation in the Law of Uniformity?
What is the key observation in the Law of Uniformity?
- Only dominant alleles are expressed in the F1 generation
- Traits blend in the F1 generation
- All offspring in the F1 generation are homozygous
- The characteristics do not blend and can reappear in later generations (correct)
What is the principle behind the Law of Independent Assortment?
What is the principle behind the Law of Independent Assortment?
- The genes controlling different traits are inherited independently (correct)
- The distribution of one pair of alleles influences the distribution of another pair
- Autosomal dominant traits are always expressed
- Sex-linked traits are always recessive
How many human traits or disorders are known to follow Mendelian principles?
How many human traits or disorders are known to follow Mendelian principles?
- Over 50,000
- Over 5,000
- Over 16,000 (correct)
- Over 1,000
What is the characteristic of the ABO blood system?
What is the characteristic of the ABO blood system?
What determines the type of Mendelian inheritance?
What determines the type of Mendelian inheritance?
What is the probability of a child inheriting an autosomal dominant trait from an affected parent?
What is the probability of a child inheriting an autosomal dominant trait from an affected parent?
What is the requirement for a recessive trait to manifest?
What is the requirement for a recessive trait to manifest?
What is the characteristic of an autosomal recessive disorder?
What is the characteristic of an autosomal recessive disorder?
What is the reason for X-linked recessive traits not being clinically manifested in females?
What is the reason for X-linked recessive traits not being clinically manifested in females?
Why are men more likely to be affected by X-linked recessive diseases?
Why are men more likely to be affected by X-linked recessive diseases?
What is the characteristic of a Y-linked gene?
What is the characteristic of a Y-linked gene?
What is the purpose of a Punnett square?
What is the purpose of a Punnett square?
What is the first step in using a Punnett square?
What is the first step in using a Punnett square?
What is the characteristic of an X-linked recessive trait in women?
What is the characteristic of an X-linked recessive trait in women?
What is the inheritance pattern of a Y-linked gene?
What is the inheritance pattern of a Y-linked gene?
What is hypertrichosis of the ear?
What is hypertrichosis of the ear?
What is the ratio of smooth to rough peas in the F2 offspring?
What is the ratio of smooth to rough peas in the F2 offspring?
What is the term Mendel used to describe the units of inheritance?
What is the term Mendel used to describe the units of inheritance?
What is the result of multiplying two 3:1 ratios in a dihybrid cross?
What is the result of multiplying two 3:1 ratios in a dihybrid cross?
What is the condition for a recessive allele to be expressed?
What is the condition for a recessive allele to be expressed?
What is the term for the alleles that can be expressed in the presence of another allele?
What is the term for the alleles that can be expressed in the presence of another allele?
What happens to the gene pairs during gamete production?
What happens to the gene pairs during gamete production?
What is the term for an individual with two identical alleles at the same locus?
What is the term for an individual with two identical alleles at the same locus?
What is the law that states genes occur in pairs and separate during gamete production?
What is the law that states genes occur in pairs and separate during gamete production?
Study Notes
Laws of Inheritance
- Law of Uniformity: When two homozygotes with different alleles are crossed, all offspring in the F1 generation are identical and heterozygous.
- Law of Independent Assortment: The distribution of one pair of alleles into gametes does not influence the distribution of another pair; genes controlling different traits are inherited independently.
Mendelian Inheritance in Humans
- Mendelian principles apply to over 16,000 human traits or disorders.
- The human ABO blood system is an example of a simple Mendelian inheritance:
- A and B alleles are dominant to the O allele.
- A or B alleles are codominant (both traits are expressed).
Types of Mendelian Inheritance
- Autosomal dominant: A trait or disorder that manifests in the heterozygous state; 1 in 2 (50%) chance of inheriting it and being similarly affected.
- Autosomal recessive: A trait or disorder that manifests only when the mutant allele is present in a double dose (homozygosity); individuals heterozygous for the mutant allele are healthy.
- X-linked recessive: A trait that is not clinically manifested when a normal copy of the gene is present; fully evident in men, but women are rarely affected unless homozygous for the mutant allele.
- Y-linked inheritance: Few genes are involved in primary sex determination or development of secondary male characteristics; a Y-linked gene will manifest in all men carrying it, regardless of dominance or recessiveness.
Punnett Square
- Used to predict genotypes and phenotypes of offspring.
- Steps:
- Determine parent genotypes.
- Write down the cross (mating).
- Draw a Punnett square.
- "Split" letters of the genotype for each parent and put them outside the square.
- Determine possible genotypes of the offspring by filling in the square.
Dihybrid Cross
- Analyzes two characters simultaneously.
- Plants used as parental lines produced smooth yellow seeds and wrinkled green seeds.
- Ratios obtained: 9:3:3:1, resulting from multiplying two 3:1 ratios (one for color and one for form).
Dominance and Recessiveness
- Recessive traits are not expressed in heterozygotes; two copies of the allele are required for expression.
- Dominant traits are governed by an allele that can be expressed in the presence of another, different allele; dominant alleles prevent expression of recessive alleles in heterozygotes.
Law of Segregation
- Genes occur in pairs (like chromosomes).
- During gamete production, members of each gene pair separate.
- During fertilization, the full number of chromosomes is restored (allele pairs are reunited).
- Homozygous: same allele at the same locus on both members of a chromosome pair (e.g., TT, tt).
- Heterozygous: two different alleles at the same locus on a chromosome pair.
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Description
Quiz on Mendel's laws, including the Law of Uniformity and the Law of Independent Assortment, which describe how alleles are inherited and expressed in offspring.