Genetics MT #1 - Chapter 5:

A male with Klinefelter syndrome (XXY) would have how many Barr bodies in his cells?

1

Despite the fact that human males are XY and human females are XX, they have equal expression of many genes on their sex chromosomes. This phenomenon is called .

DC

Epigenetic changes to a chromosome are permanent modifications that remain over the lifetime and later generations of the organism. True False

False Epigenetic changes to a chromosome modify the chromosome during oogenesis, spermatogenesis or embryogenesis, but are not permanent over the course of many generations.

In Drosophila, an X-linked gene confers an apricot eye color. Which of the following would have a very similar phenotype? Homozygous females and homozygous males Heterozygous females and homozygous males Heterozygous females and hemizygous males Homozygous females and hemizygous males

Homozygous females and hemizygous males

predict the outcome of crosses for genes that exhibit a maternal effect pattern of inheritance

In genetics, a maternal effect pattern of inheritance occurs when the phenotype of the offspring is determined by the genotype of the mother rather than the offspring's own genotype. This typically happens because the mother provides certain cytoplasmic components or maternal factors that influence the development or expression of genes in the offspring. When predicting the outcome of crosses involving genes that exhibit a maternal effect pattern of inheritance, the genotype of the mother plays a crucial role. Offspring inherit cytoplasmic components and maternal factors from their mother, which can affect their phenotype. Let's say we have a gene, Gene X, that exhibits a maternal effect pattern of inheritance. The gene has two alleles, A and a. The phenotype of the offspring depends on the genotype of the mother. If the mother is homozygous dominant (AA) for Gene X, then all offspring, regardless of their own genotype, will express the dominant phenotype. If the mother is heterozygous (Aa) for Gene X, then all offspring will express the dominant phenotype because they inherit at least one dominant allele from the mother. If the mother is homozygous recessive (aa) for Gene X, then all offspring will express the recessive phenotype, regardless of their own genotype. In crosses involving genes with maternal effect inheritance, the genotype of the offspring might not directly correspond to their phenotype because the phenotype is determined by factors inherited from the mother. Therefore, understanding the genotype and phenotype of the mother is essential for predicting the outcomes of such crosses!!

describe the process of X chromosome inactivation in mammals

Initiation of XCI: XCI is initiated early in embryonic development. The decision of which X chromosome will be inactivated is random and occurs independently in each cell. This random inactivation leads to a mosaic pattern of X chromosome activity in female tissues. X-inactivation center (Xic): The X-inactivation center (Xic) is a region on the X chromosome that contains regulatory elements involved in the initiation and maintenance of XCI. Xic is essential for the choice of which X chromosome will be inactivated and for the spreading of inactivation along the chromosome. Xist gene expression: The X-inactivation process is regulated by a long non-coding RNA called X-inactive-specific transcript (Xist), which is located within the Xic. During XCI, one of the X chromosomes is chosen for inactivation, and Xist is upregulated on this chromosome. Xist RNA coats the inactive X chromosome in cis and recruits chromatin-modifying complexes to induce gene silencing. Silencing of the inactive X chromosome: Once Xist RNA coats the chosen X chromosome, it undergoes extensive chromatin remodeling, resulting in the condensation of the chromosome into a transcriptionally inactive structure known as a Barr body. The Barr body is a densely stained structure visible in the nucleus of cells undergoing XCI. It represents the inactivated X chromosome and contains highly compacted heterochromatin. Maintenance of XCI: Once established, XCI is stably maintained through cell divisions. Daughter cells inherit the same inactive X chromosome pattern as the parent cell. The inactive X chromosome remains condensed and transcriptionally silent throughout the lifespan of the cell and its descendants. Escape from XCI: While most genes on the inactive X chromosome are silenced, some genes may escape XCI and remain active. These genes are typically

At an early stage of embryonic development in female mammals, random inactivation of one X chromosome occurs in each somatic cell. This is know as the hypothesis.

Lyon

The concept that dosage compensation in mammals occurs by the inactivation of a single X chromosome in females was proposed by the geneticist in 1961.

Mary Lyon

Who first proposed the phenomenon of X inactivation? James Watson Gregor Mendel Carl Correns Mary Lyon

Mary Lyon

explain how X chromosome inactivation may affect the phenotypes of female mammals

Mosaicism: XCI leads to a mosaic pattern of gene expression in female tissues. Since which X chromosome is inactivated is random and occurs independently in each cell, some cells will express genes from the paternal X chromosome, while others will express genes from the maternal X chromosome. This mosaicism can result in phenotypic variability between cells within the same individual. Genetic diseases: XCI can influence the expression of X-linked genetic diseases in female mammals. In females heterozygous for X-linked mutations, XCI may result in cells expressing either the wild-type allele or the mutant allele. The severity of the disease phenotype can vary depending on the proportion of cells expressing the mutant allele. Some X-linked diseases may exhibit milder or more variable phenotypes in females due to XCI . X-linked gene dosage: XCI ensures that the dosage of X-linked genes is balanced between males and females. However, since only one X chromosome is active in each cell, females effectively have half the dosage of X-linked gene products compared to males. This dosage difference can influence phenotypic traits controlled by X-linked genes, such as hormone regulation, immune function, and neural development. Gene expression variability: XCI can lead to variability in gene expression levels among different tissues and cell types in female mammals. Depending on which X chromosome is inactivated in a particular cell lineage, the expression levels of X-linked genes may differ between tissues. This variability can contribute to differences in phenotype between tissues and may influence traits such as coat color in mammals.

Heteroplasmy

Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease ex: a plant cell could contain some chloroplasts that make chlorophyll and others that don't

The coat color of the calico cat shown in the image is best explained by Blank______. pleiotropy the Lyon hypothesis the paternal effect the maternal effect codominance

The Lyon Hypothesis Reason: X chromosome inactivation is a random process that occurs early on in development. This is what accounts for the variegated phenotype

explain the molecular mechanisms of imprinting

The combination of DNA methylation, histone modifications, and noncoding RNA-mediated mechanisms results in the selective expression of either the maternal or paternal allele of imprinted genes. Depending on the gene and its regulatory elements, the maternal or paternal allele may be silenced through epigenetic modifications, while the opposite allele remains transcriptionally active.

Which of these statements are true of genes that follow a Mendelian inheritance pattern? The genes are influenced by expression of maternal genes in the egg. The genes segregate independently. The genes are transmissible from generation to generation. The genes segregate during gamete formation. Expression of genes in the offspring directly influences their traits.

The genes segregate independently. The genes are transmissible from generation to generation. The genes segregate during gamete formation. Expression of genes in the offspring directly influences their traits.

mechs of dosage comp in different species

XX, XY mammals (one of the X chromosomes in somatic cells of females is inactivated.) XX, XY marsupial (kangaroos, koala; the X from male is inactivated) dresophila XX, XY (exp in males is doubled) elegans (worms) XX and XO

The short region on the X chromosome that plays an important role in X chromosome inactivation is the . (Use an abbreviation.)

Xic

define genomic imprinting

a pattern of inheritance that involves a change in a single gene or chromosome during gamete formation. It implies a type of marking process that has a memory.

What is a Barr body?

an inactivated X chromosome in mammalian somatic cells

define maternal effect

an inheritance pattern for certain nuclear genes in which the genotype of the female parent directly determines the phenotypic traits of the offspring

The inactivated X chromosome in somatic cells of mammals is called a(n) .

barr body

predict the outcome of crosses involving GI

cannot use a Punnett square! instead, you must know if the offspring expresses the allele that is inherited from the female or male parent AND you need to know which allele was inherited from the female parent and which was inherited from the male

Two copies of the apricot allele in the female fruit fly produce a phenotype that is similar to that produced by one copy in the male. This is an example of the phenomenon of .

dosage compensation

What accounts for equal expression of genes on the sex chromosomes despite the fact that males and females have an unequal complement of sex chromosomes?

dosage compensation

A type of change in which a temporary alteration to a chromosome modifies gene expression but is not permanent over many generations is called change.

epigenetic ("dosage compensation")

Epigenetic changes to a chromosome are permanent modifications that remain over the lifetime and later generations of the organism.

false

extranuclear inheritance occurs due to

genetic material found in chloroplasts and mitochondria

Genes that follow a Mendelian inheritance pattern obey Mendel's law of and Mendel's law of .

i. segregation ii independent assortment

What is the primary role of the region on the X chromosome called Xic?

inactivation of the X chromosome (X inactivation center)

A female with Turner syndrome (XO) would have how many Barr bodies in her cells? Multiple choice question. Two One Three None

none

explain the mechanism of maternal effect at the molecular and cellular levels

oocytes receive gene products that affect early developmental stages of the embryo

define epigenetics

study of mechanisms that lead to changes in gene expression that can be passed from cell to cell and are reversible but do NOT involve a change in the DNA sequence