Lecture 2

Question 1

What’s the blending hypothesis

Answer 1

Theory that suggests that traits from parents get mixed (like fluid) in offspring, the point of fluid analogy being that they cannot be separated/recovered again, every child has a new irreversible phenotype

Question 2

Briefly describe mendels method

Answer 2

Mendel crossbred pure bred plants (to get purebred plants he breeded them until failure and then used a test cross to make sure) and studied the phenotypic expression
He noted the results then crossbred the F1 plants and found the phenotype of the original parents in at least some of the plants
He did this in large quantities for more accurate results

Question 3

How did Mendel prevent self pollination

Answer 3

He cut the anther off of the flower such that it couldn’t self pollinate (would affect the result)

Question 4

How was the blending theory disproved by Mendel

Answer 4

He crossbred his pure bred pea plants (white and purple flowers) and their offspring were not a mix of the parents (pale purple) but rather purely purple
But since we dont know everything that goes into determining petal color, thats not enough
Mendel cross bred teh F1 generation, and he got the original phenotype back, something that is explicitly said to not be possible in the blending theory (where a child’s phenotype is a fluid mix of both parents)

Question 5

What’s a monohybrid cross

Answer 5

The cross between two parents that evaluates one gene/trait (two alleles), this has nothing to do with whether its homo or heterozygous

Question 6

What trait results did Mendel get from his monohybrid cross of F1 pea plants

Answer 6

He got about a 3:1 ratio, dominant : recessive, suggesting that blending theory is not accurate and that there are alleles (versions of genes) that dominate another, thus why a recessive allele will only be expressed/visually represented if the dominant allele is not present
Note: at the time he didnt know about genes and alleles, but he could tell that the “grandparent” phenotype was being expressed in F2, so it must’ve somehow gone undetected in F1 but still stayed if it showed up in F2

Question 7

What step in a monohybrid cross of the F1 generation has a 50% chance

Answer 7

The creation of gametes by meiosis, if a plant is heterozygous for for flower color, then theres a 50% chance that it’ll pass on either the white petal or purple petal allele, 50% due to the nature of meiosis producing 2 copies of each allele present, in this case 1 recessive and 1 dominant

Question 8

What’s a test cross

Answer 8

It’s when you cross an individual having an unknown genotype for a certain trait with a tester individual, which is recessive. The idea is that the offspring will tell you what the unknown parent is
If it was heterozygous and is crossed with a tester: we get 50/50 in terms of phenotypes
If it was homozygous and its crossed with a tester: we get fully dominant phenotype

Question 9

What does it mean for a gene to be haplosufficient

Answer 9

It means that if theres a loss of function mutation in one allele (say dad) then the wild type (normal) allele from mom can compensate for the other allele, basically doing the work for both of them

Question 10

Haplosufficiency in recessive diseases

Answer 10

If a gene is haplosufficient and its paired with a recessive or non-functional allele, it will compensate and result in a normal/healthy phenotype
We call these individuals carriers, they’re heterozygous and aren’t directly affected, but if two carriers have an offspring, theres a chance that it wont have a good allele to take over, and they end up expressing the disease

Question 11

Cystic fibrosis (what goes wrong)

Answer 11

Affects cells that produce mucous, sweat and digestive juices, its recessive and carrier are unaffected so it is a haplosufficient gene
Specifically: its a mutation in the CFTR (cystic fibrosis transmembrane receptor)
Note: two carriers of CF have a 1/4 chance of producing an offspring affected by CF

Question 12

What is an allele

Answer 12

An allele is a variation of a particular gene, so genes for flower colours are all in the same place, same chromosome, but petals may come out purple, white, pink, wtv. It’s a different version of a gene