Sex-linked and mitochondrial inheritance

Question 1

True or false : sex determination in humans is based on the sex chromosomes only

Answer 1

False, it is also linked to genes

Question 2

Around how many weeks does sexual differentiation occur in humans ?

Answer 2

7th week of the embryo development

Question 2

Define heterogametic

Answer 2

Produces gametes with different chromosome composition

Question 3

Describe the role of the Y chromosome in sex determination

Answer 3

the Y chromosome is responsible for:
- The development of testes
- inhibits the formation of female reproductive organs
- Contains genes for maleness and fertility

Question 4

What does it mean when we say that Y and X contain hemizygous regions ?

Answer 4

Regions that have no homologue : only one copy of the genes on those regions in a normal diploid cell

Question 5

What are the PAR regions ?

Answer 5

Regions on the Y and X chromosome that share homology, have a pattern of inheritance that is indistinguishable from genes on autosomes, and allowing pairing, recombination and segregation during meiosis

Question 6

Describe the SRY (Sex determining region)

Answer 6

Only on the Y chromosome.
- Responsible for male sex determination
- Becomes active at 7 weeks in XY embryos
- Codes for a testis-determining factor (TDF) (transcription factor)
- Causes the undifferentiated gonadal tissue of the embyo to form testes
- Activates the gene for Mullerian inhibiting substances (MIS)

Question 7

What’s the role of the Mullerian inhibiting substances (MIS) ?

Answer 7

• MIS protein causes regression of cells in the Müllerian duct
• Prevents the formation of the female reproductive tract

Question 8

How is it possible to have human males with a XX genotype and human females with a XY genotype ??

Answer 8

human males with XX : one X chromosome has a region of the Y attached and contains SRY

Human females with XY : Y is missing the SRY gene (or it’s mutated)

Question 9

X-linked inheritance affects mainly males or females ?

Answer 9

Males

Question 10

True or false : fathers do not contribute to the X-linked phenotype

Answer 10

True

Question 11

explain how we get very different results when doing reciprocal crosses with traits that are x-linked recessive ?

Answer 11

If the male carries the X chromosome with the trait, none of the offsprings are affected (females are carriers but not affected)

If the female carries the X chromosome with the trait, every male offsprings will be affected and the female offsprings will be carriers

Question 12

Explain dosage compensation

Answer 12

Balancing of the dose of X chromosome gene expresison in females and males

Question 13

What are the 3 hypotheses concerning dosage compensation ?

Answer 13

1. One copy of each X-linkedgene could be inactivated in females
2. Each X-linked gene could work twice as hard in males as it does in females (X is hyperactivated in males)
3. Each X-linked gene could work half as hard in females as it does in males (female X’s are hypoactivated)

Question 14

Which dosage compensation hypothese corresponds to mammals ?

Answer 14

1. One copy of each X-linked gene could be inactivated in females

Question 15

Explain how X inactivation happens

Answer 15

One of the two X chromosomes is inactivated at random when the embryo is a few thousand cells by:
- the addition of methyl groups to the DNA
- Condensation of the X chromosome into the Barr bodies preventing transcription

Question 16

What are Barr bodies ?

Answer 16

Condensated form of the X chromosome that was inactivated (prevents transcription)

Question 17

True or false : a heterozygous female can express 2 different phenotypes for the X chromosome simultaneously

Answer 17

True
(genetic mosaic : one cell may inactivate the paternal X chromosome and the other may inactivate the maternal chromosome)

Question 18

Does mitochondria have a circular or linear genome ?

Answer 18

Circular

Question 19

Do chloroplasts have a circular or linear genome ?

Answer 19

Circular

Question 20

Are mitochondria and chloroplasts inherited maternally or paternally or both ?

Answer 20

Maternally only

Question 21

Define anisogamy

Answer 21

Males produce a lot of gametes that are very small
Females produce few gametes that are a lot bigger

Question 22

How do we know that chloroplasts inheritance is only through the maternal side ?

Answer 22

By doing reciprocal crosses, we see very different results wether the gene/trait of interest is on the paternal or maternal chromosome

Question 23

In chlamydomonas reinhardtii , the chloroplasts contains how many copies of the genome ?

Answer 23

75

Question 24

Who discovered the maternal inheritance of mitochondria ?

Answer 24

Mary Mitchell and Herschel Mitchell (1952)

Question 25

How can we recognize mitochondrial inheritance in a Pedigree ?

Answer 25

- Children from an affected mother are all affected (both sons and daughters) - Affected sons have unaffected children (only transmitted by women)

Question 26

Name one example of a disease inherited through mitochondria

Answer 26

Myoclonic Epilepsy Ragged-Red fiber disease (MERRF)

Question 27

True or false : in some species, the phenotype of the offsprings can be determined by the genotype of the parent producing the egg, regardless of the phenotype of that parent

Answer 27

True (nuclear maternal inheritance)

Question 27

Around how many genes does the mitochondrial genome usually contain in all species ?

Answer 27

10-100

Question 28

True or false : the mitochondrial genome contains introns

Answer 28

False

Question 29

True or false : the mitochondrial genome does not contain histone proteins

Answer 29

True

Question 30

Are repeated sequences frequent or rare in the mitochondrial genome ?

Answer 30

Rare

Question 31

Why is the mitochondrial DNA mutation rate 10x the nuclear rate ?

Answer 31

Because the mitochondrial DNA can be damaged by many ROS (reactive oxygene species) (free radicals)

Question 32

How many genes does the mitochondrial genome contains in humans ?

Answer 32

37

Question 33

What's the number of DNA copies in vertebrates and in plants' mitochondrial genome ?

Answer 33

Vertebrates : 5-10 Plants : 20-40

Question 34

Describe the composition of the human mtDNA (mitochondrial DNA)

Answer 34

37 genes: - 2 rRNAs (ribosomal RNAs) - 22tRNAs (transfer RNAs) - 13 proteins for oxidative respiration

Question 35

Complete : mitochondria needs to be in a ___ to survive

Answer 35

Eukaryotic cell

Question 36

A lot of genes were transmitted from the mitochondria to the nucleus by which transfer ?

Answer 36

Horizontal gene transfer

Question 37

What's a haplotype?

Answer 37

Group of alleles that are inherited together from a single parent

Question 38

What's a haplogroup ?

Answer 38

Group of similar haplotypes that share a common ancestor with a SNP mutation

Question 39

How can we use mtDNA (mitochondrial DNA) to define maternal haplogroups/ancestry?

Answer 39

Because the mitochondria does not do recombination or repair mechanisms, you see a lot of mutations accumulate. From that, we can go back in the ancestry to see when they all shared the same haplogroup (= common ancestors)

Question 40

True or false : Y-chromosomes can be used to define paternal haplogroups/ancestry

Answer 40

true

Question 41

Describe nuclear maternal inheritance

Answer 41

the phenotype of the progeny can be determined by the **genotype** of the parent producing the egg, regardless of the phenotype of that parent | THIS ONE YOU NEED TO KNOW BY HEART