Genetics L28

Question 1

What is the life span of red blood cells?

Answer 1

120 days

Question 2

Which cells do not get replaced?

Answer 2

CNS neurons , cardiac muscle , corneal endothelial cells, retinol ganglion cells

Question 3

Why do cells differ if most cells contain the entire genotype?

Answer 3

Cells differ as only a few genes are turned on in each cell

Question 4

What does it mean for a cell to be diploid?

Answer 4

Contain 2 copies of each chromosome

Question 5

What is a haploid?

Answer 5

Contains 1 copy of each chromosome (gametes)

Question 6

What is a zygote?

Answer 6

2 gametes that fuse together.

Question 7

How are male gametes formed?

Answer 7

Spermatogenesis

Question 8

How are eggs formed?

Answer 8

Oogenesis

Question 9

How are haploid gametes formed?

Answer 9

Meiosis

Question 10

What is the process of meiosis?

Answer 10

The same as mitosis except it happens twice and produces 4 haploid daughter cells.

Here exceptions lie in prophase 1 - during prophase 1 genetic recombination occurs (bits of chromosome break off and join other chromosomes).

The other exception is during metaphase 1 independant assortment occurs (here maternal and paternal chromosomes can be facing either pole randomly).

The last exception is random fertilisation - here any out of almost 14,000,000 sperm could fertilise any egg within the woman’s lifetime.

Question 11

What is non-disjunction?

Answer 11

When the tetrads have joined in the middle but then have not been pulled apart and so both chromosomes go to one side. This leads to some daughter cells having an extra chromosome.

Question 12

What is trisomy?

Answer 12

having three copies of the same chromosome. Usually caused dy non-disjunction.

Question 13

What is down syndrome?

Answer 13

Trisomy 21 ( an exra chromosome of chromosome 21)

Question 14

What is edwards syndrome?

Answer 14

Trisomy 18

Question 15

What is patau’s syndrome?

Answer 15

Trisomy 13

Question 16

Can sex chromosomes be subject to non disjunction?

Answer 16

Yes i.e. women could only have one X chromosome ( Turner’s syndrome).

Possession of XXX known as metafemale syndrome.

Possession of XXY known as kleinfelter’s syndrome.

Question 17

Why is it wrong to think of a ‘gene for a disease’?

Answer 17

Because theres not genes for disease its more so that it was a gene with a beneficial function that has mutated.

i.e. some genes that cause disease may also have other beneficial function( e.g. the gene that causes sickle cell anaemia also protects against malaria).

Question 18

Make sure u can still do punnet squares

Answer 18

!!!

Question 19

Not all traits are simply dominant and recessive … what else can they be?

Answer 19

Many traits can show/be intermediate inheritance. This means that when there is an SS phenotype the individual is completely fine, when there is a ss phenotype the individual has the full blown disease for example sickle cell anaemia however when they are Ss not only are they carriers but also show symptoms of the disease they are carrying so e.g. in this case they would have slight breathing problems.

Question 20

What is an example of an ocular trait that has sex linked inheritance?

Answer 20

The possesion of a green sensitive visual pigment. If the allele on the X chromosome in males is dominant their vision is normal , if the alelle on the X chromosme is recessive the male experiences red/green colour blindness ( deutranopia).

Question 21

What is polygenic inheritance?

Answer 21

Traits that are affected by mutliple genes as well as environment i.e. some genes such as the one for freckles are only expressed i certain conditions i.e. sunlight.

Question 22

What are the different types of mutation?

Answer 22

Point mutations - one base is swapped for another via a mistake in DNA replication.

Frameshift mutations - insertion , deletion or inversion od a single base causing the whole length of the DNA to be read wrong. As it is typically read in threes.