5,3 Continued

Question 1

In many cases, two or more genes are responsible for determining phenotypes. What is this called, and what is it?

Answer 1

• epistasis

- The phenotype expression of a gene at one Locus affects a gene at another locus (location on xme)

Question 2

Give an example of epistasis. (2)

Answer 2

• coat colour in labs and some mice

- One gene codes for pigment and a second gene determines whether or not that pigment will be deposited into the Hair

Question 3

What is polygenic inheritance?

Answer 3

• The effect of two or more genes acting on a single Phenotype
  Ex. Height, human skin colour

Question 4

What are sex-linked genes? (2)

Answer 4

A gene located on either the X or Y xme

- note that it’s the same for y-linked and x-linked, but very few y linked genes so less disorders

Question 5

Who can fathers pass their x-linked alleles to, and why? (2)

Answer 5

• only to their daughters, none to sons

- because dads give Y to sons

Question 6

Who can mothers pass their x-linked alleles to?

Answer 6

Both daughter and sons

Question 7

If an x-linked trait is due to a recessive allele, how can females express the trait?

Answer 7

• females can only express trait if they are homozygous

Question 8

If an x-linked trait is due to a recessive allele, how can males express the trait? What are they referred as, and what is the disadvantage? (3)

Answer 8

• since males will only have one X-chromosome, they will express the trait if they inherit the trait from their mother
• they are called hemizygous. (Hetero doesn’t apply)
• thus, makes are more likely to have an x-linked disorder

Question 9

And example of an X-linked disorder is Duchenne muscular dystrophy. What is that?

Answer 9

• Progressive weakening of muscles

Question 10

An example of an X-linked disorder is hemophilia. What is that?

Answer 10

inability to properly clot blood

Question 11

Example of an X-linked disorder is colour blindness. What is that?

Answer 11

Inability to correctly see colours

Question 12

X-inactivation: females inherit 2 X chromosomes, which is double than males. What occurs in x-inactivation?

Answer 12

1. during development, most of the X chromosome in each cell becomes inactive
2. The inactive X in each cell of a female condenses into a bar body ( only in females btw)
3. This helps to regulate gene dosage in females
   See diagram on page 38

Question 13

Linked genes: genetic recombination. What is genetic recombination?

Answer 13

• production of offspring with a new combination of genes from parents

Question 14

We know that linked genes: genetic recombination is the production of offspring with a new combo of genes from parents. What are parental types, and recombinants?

Answer 14

Parental types: offsprings with the parental phenotype

Recombinant: offspring with the phenotypes that are different from the parents

Question 15

Mendel also observed recombinants during his crosses. What does 50% recombination mean?

Answer 15

• indicates genes are unlinked, or on different chromosomes

Question 16

What would happen if Mendel did not choose to cross pea plants?

Answer 16

He would not have made discoveries about linked and unliked genes, etc. because pea plants randomly assort

Question 17

What are linked genes?

Answer 17

• genes located near each other on the same chromosome that tend to be inherited together

Question 18

Meiosis and random fertilization generate ____ _____ in offspring due to three things. What are they?

Answer 18

• genetic variation
  1. Independent assortment of chromosomes
  2. Crossing over in meiosis I
  3. Any spermicide can fertilize any egg

Question 19

Linked genes show parental phenotypes in offspring at higher than 50%. Why does this happen?

Answer 19

• during crossing over, chromosomes from one paternal chromatid and one maternal chromatid exchange corresponding segments