Non-Mendelian Inheritance and Gene Linkage

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Questions and Answers

What is responsible for the inheritance of genes that are located close to each other on the same chromosome?

Epistasis

Independent assortment

Linkage (correct)

Incomplete dominance

Which of the following describes co-dominance?

A blend of traits appearing in the offspring

A recessive trait is completely masked

Both parental traits being expressed simultaneously (correct)

A single trait being influenced by multiple genes

What is the phenotypic ratio expected from a cross between two heterozygous pink flowers in incomplete dominance?

3:1

1:1

2:1:1

1:2:1 (correct)

How many chromosomes do human male gametes contain?

23 Signup and view all the answers

Which statement about sex-linked traits is true?

Males express X-linked recessive traits if they inherit one affected X chromosome. Signup and view all the answers

Which example correctly illustrates polygenic inheritance?

Height influenced by multiple genes Signup and view all the answers

What is the inheritance pattern of blood types in humans?

Multiple alleles and co-dominance Signup and view all the answers

In dihybrid crosses, what is the typical phenotypic ratio?

9:3:3:1 Signup and view all the answers

Which statement about sex-linked genes is correct?

Females inherit one X-linked gene from each parent. Signup and view all the answers

What type of inheritance best describes the variation in human skin color?

Polygenic inheritance Signup and view all the answers

What is the chromosomal composition of a normal female?

XX Signup and view all the answers

Which condition is caused by a deficiency of a specific enzyme?

Phenylketonuria (PKU) Signup and view all the answers

What process is used to analyze chromosome structure?

Karyotyping Signup and view all the answers

What is the result of non-disjunction during meiosis?

Aneuploidy Signup and view all the answers

What is the condition called when an organism has three copies of a chromosome?

Trisomy Signup and view all the answers

Which of the following is a sex-influenced trait?

Baldness Signup and view all the answers

How many autosomal chromosomes do humans possess?

44 Signup and view all the answers

What is the primary cause of sickle cell anemia?

Amino acid substitution Signup and view all the answers

What indicates an organism with more than three sets of chromosomes?

Polyploidy Signup and view all the answers

Which gene defect leads to the inability of blood to clot?

Hemophilia Signup and view all the answers

Study Notes

Non-Mendelian Inheritance

Incomplete dominance: Traits are neither dominant nor recessive; a blend of traits occurs. Example: crossing a red flower with a white flower produces pink flowers. Offspring phenotype ratio of a cross between heterozygous pink flowers is 1:2:1 (red:pink:white).
Co-dominance: Both traits are expressed. Example: black and white parents can produce black and white offspring.
Multiple alleles: Many genes affect a trait; examples include height and blood type.
Polygenic inheritance: Many genes contribute to a characteristic (e.g., skin color, hair color, height). This variation in genotype results in a bell-shaped curve in the population.

Gene Linkage

Genes located on the same chromosome are linked and tend to be inherited together.
The closer genes are on a chromosome, the stronger the linkage.
In a dihybrid cross, linked genes deviate from a 9:3:3:1 phenotypic ratio.

Sex-Linked Genes

Carried on the sex chromosomes (primarily the X chromosome).
X-linked traits:
- Females inherit one X from each parent. A recessive mutated gene requires two copies for expression; a single copy makes the female a carrier.
- Males inherit one X from their mother and a Y from their father. If the X chromosome has a mutated gene, the male will express the trait; males are not carriers.
Examples of X-linked recessive traits: color blindness and hemophilia.
X-linked genes are passed from fathers to daughters only.
Males are affected more often by sex-linked traits than females.

Sex-Influenced Traits

Genes present in both sexes but appear more frequently in one sex due to hormonal influences.
Example: Baldness.

Karyotypes

Laboratory procedure analyzing chromosome size, shape, and number during metaphase.
Humans have 46 chromosomes (44 autosomes + 2 sex chromosomes).
Male: XY, Female: XX.
Gametes (sperm and ova) have 23 chromosomes.

Non-Disjunction

Error during meiosis where homologous chromosomes fail to separate.
Results in aneuploidy (abnormal chromosome number).
Trisomy: having three copies of a chromosome. Down syndrome (trisomy 21) is an example.
Triploid (3n): organism with three sets of chromosomes.
Polyploidy: organism with more than three sets of chromosomes.

Gene Defects

Hemophilia: Inability of blood to clot.
Phenylketonuria (PKU): Deficiency in a specific enzyme.
Sickle cell anemia: Substitution of glutamic acid with valine in hemoglobin, leading to abnormal RBC shape and impaired oxygen transport.
Tay-Sachs disease: Mutation in a lysosomal enzyme.

Blood Groups

Blood type inheritance: A and B are dominant; AB is co-dominant; O is recessive.

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Description

This quiz covers non-Mendelian inheritance patterns, including incomplete dominance, co-dominance, multiple alleles, and polygenic inheritance. It also delves into gene linkage and sex-linked genes, showcasing how these concepts affect heredity and traits in populations.