BIO- Genetics

Question 1

Gene

Answer 1

Sequence of DNA that codes for a given trait

Question 2

Alleles

Answer 2

Variations of a gene

Dominant or recessive

Question 3

Homologues

Answer 3

Copies of the same chromosome
Same set of genes
Can have different alleles

Question 4

Locus (loci)

Answer 4

Specific place on a chromosome where a gene occurs

Question 5

Recessive

Answer 5

Both alleles must be recessive for the phenotype to be expressed

Question 6

Gain of function mutations

Answer 6

Mutated protein can do something the original protein could not
Usually dominant
Doesn’t mean advantageous –> Huntington’s Disease

Question 7

Loss of function mutation

Answer 7

Mutated protein can no longer perform the function of the original protein
Usually recessive

Question 8

Homozygous

Answer 8

2 copies of the same allele

Ex: RR or rr

Question 9

Homozygous dominant

Answer 9

RR

Question 10

Homozygous recessive

Answer 10

rr

Question 11

Heterozyogous

Answer 11

Have one copy each of two different alleles

Ex: Rr

Question 12

Hemizygous

Answer 12

Only one copy of a give allele i present
Can occur due to nondisjunction in an organism with aneuploidy
Ex: can occur with regard to genes on the X and Y chromosome in male humans

Question 13

Parent generation homozygous dominant (RR) and homozygous recessive (rr) –>

Answer 13

F1 generation –> all heterozygotes –> Rr

Question 14

Cross F1 generation with itself (Rr x Rr)

Answer 14

Genotypes 1:2:1 ratio
25% homozygous dominant (RR)
50% heterozygous (Rr or rR)
25% homozygous recessive (rr)

Phenotype 3:1 ratio

Question 15

Test Cross

Answer 15

Used to tell whether an organism with a dominant trait is Homozygous dominant (RR) or Heterozygous (Rr) by test crossing it with a Homozygous recessive (rr) organism

Homozygous dominant (RR) offspring --> 100% dominance
Heterozygous (Rr) offspring --> 50% dominance

Question 16

Wild-Type

Answer 16

Refers to the default phenotype or genotype that is present in most members of a species, in contrast to mutation

Question 17

Complete Dominance

Answer 17

One copy of the dominant gene is enough to induce the dominant phenotype
No phenotypic difference between homozygous dominant individuals and heterozygotes

Question 18

Codominance

Answer 18

When two dominant alleles can be expressed at the same time

Ex: ABO blood typing –> AB
Ex: B for black fur, W for white –> BW for black and white spots

Question 19

Incomplete dominance

Answer 19

Occurs when a heterozygote displays a blended phenotype

Ex: Snapdragon flower
Homozygous snapdragon flower (red or white)
Heterozygotes have blended phenotype of pink

Question 20

Penetrance

Answer 20

Refers to the likelihood that the carrier of a given genotype will manifest the corresponding phenotype

Ex: BRCA1 gene –> 80% risk of developing breast cancer –> BCRA1 gene has an 80% penetrance

Question 21

Expressivity

Answer 21

The intensity or extent of variation in the phenotype

Mutations of human diseases –> could be thought of as the severity of the condition

Question 22

Penetrance vs. Expressivity

Answer 22

Penetrance: yes/no question, does an organism express a certain phenotype or not?
Expressivity: grey area question, how much of an effect does a mutation have on the phenotype?

Question 23

Law of Independent Assortment

Answer 23

No link between inheritance of an allele of the R gene and inheritance of the allele of the P gene

Alleles of genes on different chromosomes will be inherited independently due to the random orientation of the homologous pairs on the metaphase plate in Metaphase I of meiosis

Alleles of genes on the same chromosome will be inherited independently assorted due to crossing over during Prophase I of meiosis

Question 24

Chiasmata

Answer 24

points of crossing over on the chromosome

Question 25

Obey the Law of Independent Assortment

Answer 25

When the recombination frequency (theta) is greater than 50% then the genes in questions

Question 26

Recessive mutations

Answer 26

Can skip generations, but don’t have to

Question 27

Dominant mutations

Answer 27

Cannot skip generations

Question 28

Sex-linked Inheritance

Answer 28

takes place for genes located on the X chromosome

Question 29

X-linked Inheritance

Answer 29

Asymmetry in the sex of affected individuals

Affect males much more since only one X from mother