Chapter 5 Flashcards
What is the maternal affect
Inheritance pattern where the genotype of the mother directly determines the phenotype of her offspring
What is a general explanation of how maternal affect is possible
Maturing oocytes are surrounded by maternal cells that provide them with nutrients
The nurse cells are diploid whereas as the oocytes become haploid
Is a mother is heterozygous then the haploid oocyte can develop either the dominant or recessive gene
During maternal affect what happens if the sperm fertilizing the egg has a Dominant allele
It is irrelevant because the expression of the sperm will be too late to change early embryonic development
What kind of role does maternal effect genes play in early steps of embryosis
Cell division, cleavage pattern
Accumulation of maternal effect gene products before fertilization allows early steps of embryogenesis to pursue very quickly
What is epigenetic inheritance
Modification occurs to the nuclear gene or chromosome that alters gene expression
Does epigenetic inheritance change the DNA sequence
No and it’s reversible
Expression is not permanently changed over the course of multiple generations
What is the purpose of dosage compensation
Offset differences in the number of active sex chromosomes
What is a Barr body
Highly condensed structures in interphase nuclei of somatic cells (highly condensed X chromosome)
How does dosage compensation occur in mammals
Inactivation of a single X chromosome is females
Chromosome condensation
When does X chromosome inactivation occur
In early development
DNA becomes highly compacted and most genes on the inactivated X cannot be expressed
What happens when the inactivated X chromosome is replicated during cell division
Both copies remain highly compacted and inactive
It is passed on to all future somatic cells
In mammalian cells how many X chromosomes remain active
One
Additional X chromosomes are converted to Barr bodies
What does X chromosome inactivation in mammals depend on
The X inactivation center and Xist
What is Xist
A gene that makes a gene product
What is Xic
A short region on the X chromosome that is termed the X inactivation center
Each X chromosome must have an Xic region for inactivation to occur