Week 12 Mendelian Inheritance

What is inheritance?

The acquisition of traits by their transmission from parent to offspring.

What hypothesis about inheritance was proposed until the late 1800s?

Pangenesis, which suggested that 'seeds' produced by all parts of the body were inherited.

What is blending inheritance?

The idea that hereditary traits blended together in offspring and were passed to subsequent generations.

Who is known as the 'Father of modern genetics'?

Gregor Mendel.

What plant did Mendel use for his genetic studies?

Garden Pea (Pisum sativum).

What are the advantages of using Garden Pea for genetic studies?

Genetic variation, many varieties with visible characteristics, and ease of self-fertilization.

What are true-breeding lines?

Lines that exhibit the same traits from generation to generation.

What is a single factor cross?

A genetic cross that follows the variants of only one character.

What are the generations involved in a single factor cross?

P generation (true-breeding parents), F1 generation (first-generation offspring), and F2 generation (offspring of F1 self-fertilization).

What ratio of traits did Mendel observe in the F2 generation?

A 3:1 ratio of dominant to recessive traits.

What are the two forms of traits according to Mendel?

Dominant and recessive.

What does a dominant trait represent in Mendel's studies?

A trait that is seen in a true-breeding (homozygous) parent and its F1 HYBRID.

What does a recessive trait represent?

A trait that is seen in a true-breeding (homozygous) parent but is masked in the F1 hybrid.

What does genotype refer to?

The genetic composition of an individual.

What is the difference between homozygous and heterozygous?

Homozygous has two identical alleles (e.g., TT or tt), while heterozygous has two different alleles (e.g., Tt).

What is phenotype?

The observable characteristics or traits of an organism resulting from its genotype.

What is a Punnett square used for?

To predict the outcome of genetic crosses.

What is the expected genotype ratio from a cross between two heterozygous tall plants?

1:2:1 ratio of TT, Tt, and tt.

What is the expected phenotype ratio from the same cross?

3:1 ratio of tall to dwarf phenotypes.

What is Mendel's Law of Segregation?

Two copies of a gene segregate from each other during gamete formation, so each gamete receives only one allele.

What does it mean for alleles to separate during gamete formation?

Each sperm and egg receives only one allele from each gene.

If a short-haired male guinea pig (S) is mated with a long-haired female (s), what is the genotype of their long-haired offspring?

The long-haired offspring must be homozygous recessive (ss).

Can the offspring of a short-haired male and a long-haired female guinea pig be long-haired?

No, the offspring cannot be long-haired if the male is homozygous dominant (SS) or heterozygous (Ss).

What is a testcross used for?

To distinguish between homozygous dominant and heterozygous genotypes.

What is the outcome of crossing a dominant phenotype with a homozygous recessive individual?

The phenotypes of the offspring are examined to determine the genotype of the dominant parent.

What does the presence of a recessive trait in offspring indicate?

It indicates that the parent was heterozygous.

What is the predicted phenotype ratio for linked assortment?

3:1 ratio of phenotypes.

What is the predicted phenotype ratio for independent assortment?

9:3:3:1 ratio of phenotypes.

What does Mendel's Law of Independent Assortment state?

The alleles of different genes assort independently during gamete formation.

What is pedigree analysis used for?

To analyze the inheritance of human traits over generations.

Why is pedigree analysis important for studying genetic diseases?

It helps determine whether a mutant allele is dominant or recessive.

What is Cystic Fibrosis and how is it inherited?

A recessive genetic disorder caused by a mutant CFTR allele, with carriers being phenotypically normal.

What is Huntington Disease?

A dominant genetic disorder with symptoms appearing later in life.

Pairs of chromosomes found in both sexes, containing most genes are called

autosomes

What are sex chromosomes?

Distinctive pairs of chromosomes that differ between males and females.

How many chromosomes do humans have?

46 chromosomes total, consisting of 22 pairs of autosomes and one pair of sex chromosomes.

What determines sex in humans?

The presence of the Y chromosome, which causes maleness.

What are X-linked traits?

Traits associated with genes found on the X chromosome.

Why do X-linked recessive diseases occur more frequently in males?

Males are hemizygous for X-linked genes, having only one copy.

What is Hemophilia A?

An X-linked recessive disease characterized by excessive bleeding due to a defective clotting protein.

What did Morgan's Drosophila experiments demonstrate?

The connection between eye color and sex, establishing that the eye color gene is located on the X chromosome.

What is a wild-type allele?

The prevalent (most common) allele in a population that typically encodes a functional protein.

What is the difference between dominant and recessive alleles at the molecular level?

Dominant alleles produce functional proteins, while recessive alleles may not produce functional proteins.

What is incomplete dominance?

A genetic scenario where the heterozygote exhibits a phenotype that is intermediate between the two homozygous phenotypes.

What is codominance?

A situation where a single individual expresses both alleles, resulting in both traits being visible in the phenotype.

What is the norm of reaction?

The phenotypic range seen in individuals with a particular genotype under different environmental conditions.

Traits influenced by multiple genes and environmental factors, such as height.

What are complex traits?

What is epistasis?

A gene interaction where the alleles of one gene mask the expression of alleles from another gene.

Inheritance of traits that show continuous variation and are determined by multiple genes.

What is polygenic inheritance?

How did Mendel's experiments contribute to our understanding of inheritance?

His experiments established foundational principles of heredity, including dominant and recessive traits.

What is the significance of the CFTR gene in Cystic Fibrosis?

It encodes a chloride channel, and mutations disrupt chloride and water movement, leading to thick mucus.

What is the expected outcome of a cross between a heterozygous female and an unaffected male for an X-linked recessive trait?

Sons have a 50% chance of being affected; daughters cannot be affected.

What is the genotype of individuals with Roberts Syndrome?

It is characterized by a rare genetic disorder, often requiring pedigree analysis to determine inheritance.