Testcrosses

Question 1

What is a testcross?

Answer 1

an individual with a dominant phenotype and an unknown genotype is bred with a homozygous recessive individual and then look at the offspring to determine the unknown genotype

Question 2

What is incomplete dominance?

Answer 2

neither gene is dominant over the other so the 2 traits are blended together

Question 3

Give an example of incomplete dominance.

Answer 3

When a red snapdragon is crossed with a white snapdragon, neither gene is dominant, so there is a blending of the two colors. A pink snapdragon is created.

Question 4

How do you represent incomplete dominance in characters?

Answer 4

C superscript-r C superscript-w. The superscripts vary with the traits.

Question 5

When a homozygous red radish plant is crossed with a homozygous white radish plant, purple radishes result. What kind of crossing is this? And what is the phenotypic and genotypic ratio of a cross between 2 plants from the F1 generation of the cross described above?

Answer 5

a) incomplete dominance
b) the F1 generation is the result of the 1st cross. These plants would be purple: CrCw. Crossing to of these plants together would develop a Punnett square like this:
Cr Cw
Cr CrCr CrCw
Cw CrCw CwCw
The phenotypic ratio of this cross is:
1 red: 2 purple: 1 white
The genotypic ratio of this cross is:
1 CrCr: 2 CrCw: 1 CwCw

Question 6

What is codominance?

Answer 6

Both traits are expressed

Question 7

Example of codominance.

Answer 7

roan cow. White fur and red fur combined to create a blotchy cow (a roan cow)

Question 8

Compare and contrast codominance and incomplete dominance.

Answer 8

1. described in same characters, cross them in the same way

2. incomplete is a blending, co = both traits are expressed

Question 9

What is a hybrid? a monohyrbid cross? a dihybrid cross?

Answer 9

hybrid- combination of genes, creating F1 generation
monohybrid- looking at one gene/trait, simple Punnett square
dihybrid- comparing two traits

Question 10

Give an example of a dihybrid cross.

Answer 10

yellow round peas and green wrinkled peas
YYRR- yellow round
yyRR- green round
Punnet square with 16 boxes

Question 11

What are multiple alleles?

Answer 11

more than 2 possible alleles for a particular trait

Question 12

Give an example of them.

Answer 12

Blood type-
I(A)
I(B)
i
codominance- I(A)I(B)
different variations- I(A)I(A) or I(A)i for type A blood, same for B, look above for AB, ii for O blood

Question 13

What is pleiotropy?

Answer 13

multiple phenotypic effects of a gene

Question 14

Give an example of pleiotropy.

Answer 14

sickle cell anemia - red blood cells are shaped like a crescent moon because they don’t carry O2 properly. This causes them to clop in arteries. One change in the DNA causes one amino acid to misshape which causes hemoglobin (the protein that carries O2) to misshape which results in misshapen red blood cells

Question 15

What is epistasis?

Answer 15

a gene at one location affects the phenotypic expression of another gene at a second location

Question 16

Give an example of epistasis.

Answer 16

labs- yellow, brown, black
black- when B and E gene are dominant
brown- when b gene is recessive and E gene is dominant
yellow- when E gene is recessive, it blocks the B gene’s expression so it does not matter if the B gene is dominant or recessive

Question 17

What is the purpose of the A series of genes in a bunny? Describe the genes in the A series.

Answer 17

determines how many colors there will be on a shaft of fur
- A- agouti
- a(t)- tan pattern
- a- self
in order from dominance to recessive-ness
can have any variation of those genes
i.e. Aa(t) = agouti, AA = agouti, Aa = agouti

Question 18

B series (purpose and description)

Answer 18

basic color, B (black), b (brown)

Question 19

C Series

Answer 19

C- full color development (7 pigments: 4 dark/ 3 yellow)
c(chd) - dark chinchilla (5 pigments: 4 dark/ 1 yellow)
c(chl)- light chinchilla (2 pigments: 2 dark/ 0 yellow)
c(h)- himalayan (dark extremeties - tail, nose, ears)
c- albino (color expression blocked completely)

Question 20

D series

Answer 20

D- dense color

d- dilute color

Question 21

E series

Answer 21

incomplete dominance
E(subscript n) - broken
e (subscript n) - solid
E(n)e(n) is when they’re the most mixed.

Question 22

What is polygenic inheritance?

Answer 22

multiple genes control a single phenotypic characteristic, opposite of pleiotropy

Question 23

Example of polygenic inheritance

Answer 23

skin color: AABBCC = more dominant, more dark

aabbcc = more recessive, more light

Question 24

What are multifactorial characters?

Answer 24

traits that are affected by both genes and the environment

Question 25

Give 2 examples of multifactorial characters?

Answer 25

hydrangeas- color affected by temperature

himalayan bunnies- hotter = paler dark spots, colder = spots grow darker

Question 26

What are pedigrees?

Answer 26

family history or tree that explains how genes get passed from one generation to the next

Question 27

What are carriers?

Answer 27

heterozygous for a recessive allele but have the dominant phenotype, recessive allele can be expressed in next generation

Question 28

Why do doctors perform amniocenteses and chorionic villus samplings?

Answer 28

doctors can do these on babies to determine if they have a disease

Question 29

Describe amniocenteses.

Answer 29

amniotic fluid around the baby contains body cells, take some of this out with a needle through the stomach, grow cells, develop karyotype

Question 30

Describe chorionic villus samplings.

Answer 30

suction tube through the cervix, gather some tissue off the chorionic villi of the placenta, grow cells, develop karyotype

Question 31

How did Mendel get lucky?

Answer 31

There were no alternate variations of genes (incomplete, codominance). Only 2 possible pairs of results (yellow/green). law of independent assortment: genes were found on different chromosomes so they separated independently from one another

Question 32

What did the 2 pennies represent?

Answer 32

the parents’ gametes coming together in fertilization to create a zygote

Question 33

When you draw a Punnett square, what do the letters represent?

Answer 33

the possible gametes for your genotype

Question 34

What are Mendel’s 4 important findings?

Answer 34

1. There are “factors” in living things that are inherited by offspring.
2. These “factors” occur in pairs. Today we know these “factors” are genes. The alternate versions of a gene are called alleles.
3. Dominant factors are always expressed. Recessive ones have no effect.
4. the law of segregation- the 2 factors for a trait separate during gamete formation (anaphase).