Chrom and Gam

Question 1

What is the defining feature of all evolving living organisms?

Answer 1

ability to reproduce

Question 2

What are the requirements for genes to be functional?

Answer 2

→replicate
→separate its 2 copies at mitosis- eliminating mutations
→maintain itself between generations

Question 3

How can the same gene be specific?

Answer 3

→ by having alternative promotors

Question 4

Give an example of a protein that uses different promotors depending on the tissue

Answer 4

→CYP19A1

Question 5

What are the products of alternative splicing called?

Answer 5

→isoforms

Question 6

How can the protein be modified once made?

Answer 6

→Post-translational modification eg phosphorylation,

→Glycosylation i.e. adding on carbohydrates to protein, making protein more stable and soluble

Question 7

What happens to FSH as women age?

Answer 7

→more variants of FSH which are not as effective

Question 8

What are the DNA requirements for sexual reproduction?

Answer 8

→Fusion of haploid cells (gametes) to create unique diploid progeny

Question 9

What are the advantages of sexual reproduction?

Answer 9

→Prevents the accumulation of genetic mutations
→Increase in genetic diversity
→Maintenance occurs because of the advantage of genetic variability

Question 10

What are the numbers of gene in the X and Y chromosomes?

Answer 10

X chromosome → 1000 working genes
Y chromosome → 86 working genes

Question 11

What is a gamete?

Answer 11

→a haploid cell specialised for sexual fusion

Question 12

What are gametes formed from?

Answer 12

→formed from germ line cells: primordial germ cells
→progenitors of both sperm and egg that migrate into the gonad and then differentiate to either male or female gametes

Question 13

What happens to the two chromosomes during S-phase as replication happens?

Answer 13

→remain attached to each other

Question 14

What is a chromatin?

Answer 14

→uncondensed form of DNA

Question 15

What happens in prophase?

Answer 15

→chromatin condense to form chromosomes as DNA wraps around histones
→when DNA is condensed it cannot be replicated and gene activity is shut down
→nuclear membrane begins to break down
→mitotic spindle forms (duplicated during interphase)

Question 16

What happens in metaphase?

Answer 16

→mitotic spindles attach to the chromosomes at the equator

Question 17

What happens in anaphase?

Answer 17

→the sister chromatids of each chromosome begin to separate
→spindle fibres pull chromosomes to each pole

Question 18

What happens in telophase?

Answer 18

→a nuclear envelope forms around each group of chromosomes at each pole
→mitotic spindle disassembles

Question 19

What are the two important sources of genetic variation?

Answer 19

→crossing over recombination during prophase I
→independent assortment during metaphase I

Question 20

What is a difference between meiosis I and meiosis II?

Answer 20

→no interphase or replication in meiosis II

Question 21

Why is meiosis advantageous?

Answer 21

→random distribution of male and female homologous chromosomes
→chromosomal crossing over
→keeps the number of chromosomes constant between generations

Question 22

Compare mitosis and meiosis

Answer 22

mitosis
→one cell division
→produces two diploid cells
→somatic cells
→growth and repair
→no Exhange of genetic material
→daughter cells genetically similar

Question 23

Describe crossing over

Answer 23

→Corresponding pieces of chromatids of maternal and paternal homologues (non-sister chromatids) are exchanged during synapsis when the homologues are aligned side by side.

Each of the affected chromatids has a mixture of maternal and paternal genetic information

Question 24

Why does crossing over not occur between X and Y chromosomes?

Answer 24

→They are hemizygous to each other & so recombination proved harmful
→PAR allows the X & Y chromosomes to pair and properly segregate during meiosis in males

Question 25

What allows X and Y chromosomes to pair and properly segregate during meiosis in males?

Answer 25

→PAR
→found on P-arm on X and Y chromosome

Question 26

What is aneuploidy?

Answer 26

gain or loss of chromosomes from the normal 46

Question 27

What is the common cause for spontaneous miscarriages?

Answer 27

aneuploidy- 47 chromosomes

Question 28

What is a main cause of aneuploidy?

Answer 28

abnormal spindle pulling

failure of meiosis-specific cohesions release

Question 29

What is non-disjunction?

Answer 29

failure of homologous chromosome to separate during MI or sister chromatids to separate during MII, resulting in extra or missing chromosomes

Question 30

What are the viable trisomies?

Answer 30

Trisomy 21 (aka Down’s syndrome, 1:750 births)
Trisomy 18 (Edwards syndrome)
Trisomy 13 (Patau syndrome)

Question 31

Which type of aneuploidy is more viable?

Answer 31

sex chromosome

Turner- 45X

Klinefelter- 47 XXY

Question 32

Describe Turner’s syndrome

Answer 32

45X

caused by complete or partial absence of 2nd sex chromosome

phenotype=short stature, primary amenorrhea, webbed neck (classic Turners)
candy cane aortic arch

Question 33

Describe the Klinefelter syndrome

Answer 33

caused by presence of two X and one Y chromosome

variable phenotype=taller than average, small testes producing reduced testosterone, infertility, curved pinky fingers

Question 34

What risk increases with maternal age and why

Answer 34

risk of trisomy
Recombination failure

Premature homologue separation

Premature sister chromatid separation due to loss of cohesion between sister centromeres

Question 35

Why does oogenesis result in one egg and polar bodies?

Answer 35

unequal cytokinesis