Classic Mendelian Genetics 2 Flashcards
Normal body cells have a ……… number of chromosomes
Diploid
Meaning each cell contains 2 of each chromosome (1 from the mother and 1 from the father)
A pair of homologous chromosomes
A pair of chromosomes that are the same size and have the same genes although they may have different variations of these genes (alleles)
How many pairs of chromosomes do dogs and humans have?
dogs = 39 pairs
humans = 23 pairs
In humans’ pair 23 are the sex chromosomes (X & Y)
Autosomes
Non-sex chromosomes
Unlike autosomes the sex chromosomes DONT carry the same genes, so they are NOT considered homologous
Gonad
Organ that produces sex cells & hormones
What does it mean if a trait is sex-linked
Trait that is carried on the X or Y chromosomes which are involved in determining sex of animals
What are the genotypes for male and females?
Females have the genotype = XX (homomorphic)
Males have the genotype = XY (heteromorphic)
True OR False
The X chromosome contains several thousands of genes, but the Y chromosome only has 53 protein-coding genes
TRUE
Sry
Sex-determining region of the Y chromosome (a single gene)
Encodes for a protein called the Testis-determining factor (TDF)
So, what does it mean if the Sry gene is present?
So the presence of the Sry gene means you end up with the Testis-determining factor (protein). This then has an effect on the undifferentiated gonads to produce testis.
Genes carried on the …. chromosome is said to be sex-linked
X
As females have 2 X chromosomes, they may be homozygous OR heterozygous for X chromosome alleles.
What is Sex-linked inheritance
As females have 2 X chromosomes, they may be homozygous OR heterozygous for X chromosome alleles.
Males with XY chromosomes have only one copy of a gene - they are Hemizygous
This difference generates a special type of inheritance called sex-linked inheritance
How is the Genetic Sex determined?
By the presence or absence of the Y chromosome
Sry
Sex-determining region of the Y chromosome. Encodes a protein also called Testis-determining factor (TDF)
What happens if the Sry gene is present?
Means you end up with this testis-determining factor (protein). Then this has an effect on undifferentiated gonads to produce testis
True or False
The X chromosome carries many more genes than the Y chromosome
True
Lyonisation
During embryonal development, one of each X chromosome is randomly inactivated in female cells. This process is called lyonisation. This causes half of the female cells to have an active Xm chromosome and half an active Xp chromosome. This means that only the gemes of 1 X chromosome are expressed in each cell just like in males (DOSAGE COMPENSATION)
Dosage Compensation
Lyonisation causes only the genes of 1 X chromosome are expressed in each cell just as in males
Barr body
The inactive X chromosome in a female somatic cell
Autosomal dominant inheritance
- Every affected individual has at least one affected parent
-An affected individual has at least 50% chance of transmitting the trait
-Males and females should be affected with equal frequency
-2 affected individuals may have unaffected offspring
