Classic Mendelian Genetics 2

Question 1

Normal body cells have a ……… number of chromosomes

Answer 1

Diploid

Meaning each cell contains 2 of each chromosome (1 from the mother and 1 from the father)

Question 2

A pair of homologous chromosomes

Answer 2

A pair of chromosomes that are the same size and have the same genes although they may have different variations of these genes (alleles)

Question 3

How many pairs of chromosomes do dogs and humans have?

Answer 3

dogs = 39 pairs
humans = 23 pairs
In humans’ pair 23 are the sex chromosomes (X & Y)

Question 4

Autosomes

Answer 4

Non-sex chromosomes
Unlike autosomes the sex chromosomes DONT carry the same genes, so they are NOT considered homologous

Question 5

Gonad

Answer 5

Organ that produces sex cells & hormones

Question 6

What does it mean if a trait is sex-linked

Answer 6

Trait that is carried on the X or Y chromosomes which are involved in determining sex of animals

Question 7

What are the genotypes for male and females?

Answer 7

Females have the genotype = XX (homomorphic)
Males have the genotype = XY (heteromorphic)

Question 8

True OR False
The X chromosome contains several thousands of genes, but the Y chromosome only has 53 protein-coding genes

Answer 8

TRUE

Question 9

Sry

Answer 9

Sex-determining region of the Y chromosome (a single gene)
Encodes for a protein called the Testis-determining factor (TDF)

Question 10

So, what does it mean if the Sry gene is present?

Answer 10

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.

Question 11

Genes carried on the …. chromosome is said to be sex-linked

Answer 11

X
As females have 2 X chromosomes, they may be homozygous OR heterozygous for X chromosome alleles.

Question 12

What is Sex-linked inheritance

Answer 12

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

Question 13

How is the Genetic Sex determined?

Answer 13

By the presence or absence of the Y chromosome

Question 14

Sry

Answer 14

Sex-determining region of the Y chromosome. Encodes a protein also called Testis-determining factor (TDF)

Question 15

What happens if the Sry gene is present?

Answer 15

Means you end up with this testis-determining factor (protein). Then this has an effect on undifferentiated gonads to produce testis

Question 16

True or False
The X chromosome carries many more genes than the Y chromosome

Answer 16

True

Question 17

Lyonisation

Answer 17

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)

Question 18

Dosage Compensation

Answer 18

Lyonisation causes only the genes of 1 X chromosome are expressed in each cell just as in males

Question 19

Barr body

Answer 19

The inactive X chromosome in a female somatic cell

Question 20

Autosomal dominant inheritance

Answer 20

• 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