Chapter 8: Mendelian Genetics

Question 1

How did people think of Genetics at first? What was the blending of inheritance theory?

Answer 1

The belief that two parents offsprings would have intermediate traits or phenotypes from that of their parents. Such as two kinds of paint that you blend together. This could not have been possible though because we would eventually get more and more homogeneous over time

Question 2

What did Mendel find from his experiments?

Answer 2

His theory was of “particular inheritance” .He found that there was a heritable factor such as a gene that must be present in round seeds in order for them to appear round

Question 3

What is a locus?

Answer 3

It is a physical location on a chromosome.

Question 4

What does Mendel’s law of segregation state?

Answer 4

1) The gametes of an individual with identical alleles at a locus will all have that allele
2) Half of the gametes of an individual with two different alleles at a locus will have one allele and the other half will have the other allele
3) Each individual carries two alleles for each trait such as eye color
4) Gametes carry only allele for each trait

Question 5

What is the chemical basis of dominance?

Answer 5

Genes mostly determine phenotypes by making proteins such as enzymes with certain functions. Dominant genes will code for these proteins and actually produce the protein but recessive genes produce either a nonfunctional mutant protein or no protein at all

Question 6

What is a test cross?

Answer 6

crossing the organism that you want to find their unknown genotype with a homozygous recessive organism

Question 7

What is the law of independent assortment?

Answer 7

Alleles at each locus segregate independently of other alleles at other loci during metaphase 1 of Meiosis. This can only occur if the alleles are on different chromosomes. CONCERNS a DIHYBRID CROSS

Question 8

What is the ratio for independent assortment?

Answer 8

9:3:3:1 ratio

Question 9

What is the ratio for dependent assortment?

Answer 9

3:1 when they are on the same chromosomes

Question 10

What is linkage

Answer 10

when the alleles are very close together on the same chromosome, so they are inherited together

Question 11

Two events are independent of each other if the outcome of one event does not affect the outcome of another

Question 12

To determine the probability that two independent events will both occur

Answer 12

You must multiply Pr ( A and B) = Pr(A) x Pr(B)

Question 13

To determine the probability that either one of two independent events occur

Answer 13

You must add Pr (A or B ) = Pr(A) + Pr(B)

Question 14

Suppose you toss a fair coin once. What is the probability that you will get either a head or a tail?

Answer 14

1. Pr (Head or tail) = Pr(head) + Pr(tail) = 1/2+1/2 = 1

Question 15

Suppose you toss a fair coin three times. What is the probability that you will get three heads?

Answer 15

(1/2)^3 . This is because each flip is an independent event. So each coin flip is 1/2 x 1/2 x 1/2

Question 16

What is the probability of flipping heads twice in a row?

Answer 16

1/4

Question 17

What is the probability of flipping one heads and one tails?

Answer 17

Pr(One heads in two flips) = 1/4 +1/4 =1/2

Question 18

What are the phenotypic ratios for a monohybrid cross between Rr and Rr?

Answer 18

It is a 3:1 phenotypic ratio

Question 19

What is a dihybrid cross?

Answer 19

Any cross involving more than one locus

Question 20

How do you deal with dihybrid crosses?

Answer 20

Divide both traits into their own separate monohybrid crosses. For example, with pea shape (R is round and the dominant trait and r is wrinkled), and with pea color (Y is yellow which is the dominant trait and y is green which is the recessive trait)

Question 21

What is complete dominance ?

Answer 21

This is when the dominant trait shows up as the phenotype. A heterozygote will look just like a homozygous dominant plant

Question 22

What is incomplete dominance?

Answer 22

The heterozygotes are going to demonstrate a phenotype that’s different from the parents who are homozygous dominant and homozygous recessive. It is going to be an intermediate phenotype

Question 23

What is codominance?

Answer 23

a situation in which both alleles at a locus affect the phenotype in distinguishable ways, and there is no intermediate between the two. For example, the M/N locus which codes for antigens on red blood cells. MM will code the M antigen but not the N antigen. MN will code for both the M antigen and the N antigen

Question 24

An example of multiple alleles

Answer 24

The ABO gene is coded for by three different alleles. Ia, Ib, and i and therefore there are 6 different possible genotypes

Question 25

of possible genotypes =

Answer 25

n + (n(n-1)/2)

Question 26

What is pleiotropy?

Answer 26

occurs when a single gene affects multiple phenotypic traits. For example, think Albinism. A single gene codes for being Albino but it affects many phenotypic traits such as hair, eyes and skin. Another example is the SRY locus on the Y chromosome which has a number of effects on the phenotypic traits related to maleness

Question 27

What is epistasis ?

Answer 27

occurs when an allele at one locus affects the phenotypic expression of an allele at a second locus. For example, there is a gene at a locus that codes for specific color pigment such as black and there is another gene at another locus that codes for the actual pigment deposition and whether a color will show.

Question 28

How many possibilities are present with a dihybrid cross?

Answer 28

16

Question 29

What is polygenic inheritance?

Answer 29

A trait that is affected by multiple loci such as skin color and your predisposition to acquiring certain diseases

Question 30

How to go about organizing a dihybrid cross:

Answer 30

1) You have two crosses AABB and aabb 2) You must start the table by putting the possible combinations of A and B such as AB 3) Inside the table is where you will have AaBb or the letters back together without any recombination

Question 31

What are discrete traits

Answer 31

Often only controlled by one or two genes

Question 32

What are continuous traits often known as polygenic traits

Answer 32

are often controlled by more than one gene. controlled by multiple genes

Question 33

What are environmental effects that can have an effect on genetics?

Answer 33

Many traits are not completely determined by genes. Some examples of these traits include skin color, height and weight.

Question 34

What is the norm of reaction?

Answer 34

a range of phenotypes that is shown on a graph. It shows how the phenotype of an organism with the same genotype changes as the environment changes

Question 35

What is a pedigree?

Answer 35

It shows heritable characters in parents and offspring over multiple generations in order to determine a humans genotype. Females are represented by circles. Males are represented by squares and horizontal lines show mating between a male and a female