24 Questions
What happens to one of the two X chromosomes in each cell during embryonic development in human and some other female species?
One of the two X chromosomes is randomly inactivated
What is a good phenotypic example of X inactivation?
A tortoise shell cat
The inactive X chromosome can be seen as a ___________ in the nucleus.
Barr body
A female who is heterozygous for a particular gene located on the X chromosome will always express the dominant trait.
False
What is the result of X inactivation in a female mammal?
Some cells express one trait, while others express a different trait
X inactivation occurs in all cells of a female mammal.
False
Match the following terms with their descriptions:
X inactivation = A process where one of the two X chromosomes is randomly inactivated during embryonic development Mosaic = A mixture of cells expressing different traits Barr body = A visible structure in the nucleus representing the inactive X chromosome
What is the result of X chromosome inactivation in the tortoise shell cat?
A mix of orange and black fur
What is the purpose of pedigree analysis in human genetics?
To describe the inheritance patterns of particular traits
A recessive allele codes for a malfunctioning protein.
True
What is the significance of pedigree analysis in understanding human inheritance?
Pedigree analysis helps to trace and describe the inheritance patterns of particular traits in families across generations.
If an individual lacks a particular phenotypic trait, but both parents have the trait, then the parents must be _____________ for that gene.
heterozygous
What is the characteristic of heterozygotes in recessive traits?
They have a normal phenotype
Albinism is a life-threatening genetic disorder.
False
Match the following genetic disorders with their characteristics:
Albinism = Relatively mild genetic disorder Cystic fibrosis = Life-threatening genetic disorder Widow's peak = Recessively inherited trait
What is the significance of identifying the inheritance pattern of a trait as dominant or recessive?
Identifying the inheritance pattern of a trait as dominant or recessive helps in predicting the risk of passing the trait to future offspring.
What is the main characteristic of X-linked genes?
They follow a specific pattern of inheritance
A recessive X-linked trait is more common in females than in males.
False
What is the term for genes found on the Y chromosome?
Y-linked genes
A gene that is located on either sex chromosome is called a _______________ gene.
sex-linked
Match the following types of genes with their characteristics:
Autosomal genes = Located on autosomes, can be dominant or recessive X-linked genes = Located on the X chromosome, can be dominant or recessive Y-linked genes = Located on the Y chromosome, responsible for sex determination
What is the number of genes identified on the human Y chromosome?
78
X-linked genes are only responsible for sex determination.
False
For a recessive X-linked trait to be expressed in a female, she needs _______________ copies of the allele.
two
Study Notes
X-Inactivation in Female Mammals
- In human females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development
- This leads to mosaicism, where a female is heterozygous for a particular gene located on the X chromosome
- Example: tortoise shell cat, which demonstrates X-inactivation
Mendelian Inheritance
- Autosomal dominant or recessive traits: gene loci on autosomes can be dominant or recessive
- X-linked dominant or recessive traits: gene loci on the X chromosome can be dominant or recessive
- Y-linked traits: genes on the Y chromosome, involving hemizygous alleles
- Sex-linked genes: genes located on either sex chromosome
Inheritance of X-Linked Genes
- X chromosomes have genes for many characters unrelated to sex
- Y-linked genes are related to sex determination
- X-linked genes follow a specific pattern of inheritance
- For a recessive X-linked trait to be expressed, a female needs two copies of the allele (homozygous), while a male needs only one copy of the allele (hemizygous)
- X-linked recessive disorders are more common in males than in females
Pedigree Analysis
- Pedigree analysis reveals Mendelian patterns in human inheritance
- Inheritance patterns of particular traits can be traced and described using pedigree analysis
- Information about the presence/absence of a particular phenotypic trait is collected from as many individuals in a family as possible and across generations
- Pedigrees can be used to make predictions about future offspring
Practice creating and interpreting Punnett squares to predict the probability of inheritance of traits. Complete the crosses to determine the genotypes and phenotypes of offspring.
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