Class Notes 4 - Genetics and Inheritance 2

Question 1

what is a gene?

Answer 1

a specific region of a chromosome/DNA that is capable of determining the development of a specific trait through the coding for a regulation of a polypeptide or RNA product.

Question 2

what is an allele?

Answer 2

a particular variation of a gene e.g., gene for flower colour in pea plants : F= purple flowers and f= white flowers. F/f represents flower colour.

Question 3

what is a dominant trait/ allele?

Answer 3

an allele or trait that is expressed over its recessive form. E.g., Purple flowers expressed over white.

Question 4

what is a recessive allele/trait?

Answer 4

an allele or trait that is only expressed in the absence of a dominant allele. E.g., white flowers only if ‘ff’.

Question 5

what is a phenotype?

Answer 5

the trait/characteristic that is expressed (or often visible). E.g., purple flowers vs. white flowers

Question 6

what is a genotype?

Answer 6

the combination of alleles that gives rise to the phenotype. E.g., ‘FF’ or ‘Ff’ = purple flowers vs. ‘ff’ = white flowers.

Question 7

what is homozygous?

Answer 7

having the same alleles, e.g., ‘FF’ or ‘ff’

Question 8

what is heterozygous?

Answer 8

having diferent alleles, e.g., ‘Ff’.

Question 9

what is the parent generation?

Answer 9

homozygous individuals that produce the F1 generation

Question 10

what is the F1 generation?

Answer 10

heterozygous offspring arising from two homozygous individuals.

Question 11

what is the F2 generation?

Answer 11

offspring arising from two heterozygous (F1) individuals

Question 12

what are the three basic patterns of inheritance being studied?

Answer 12

complete dominance
co-dominance and incomplete dominance
epistasis

Question 13

what is complete dominance? give example

Answer 13

one allele completely masks the presence of the other. E.g., flower colour in pea plants.

Question 14

what is a monohybrid cross?

Answer 14

crosses involving only one trait.

Question 15

what is a dihybrid cross?

Answer 15

crosses involving two traits.

Question 16

what do you have to assume in dihybrid crosses?

Answer 16

non-linkage. E.g., Flower colour and seed shape are found on diferent chromosomes, i.e., not linked on the same chromosomes.

Question 17

what is the null hypothesis?

Answer 17

any deviation from the expected outcome is probably due to chance.

Question 18

what is the discussion ?

Answer 18

the null hypothesis is Accepted/supported OR rejected. the chi square value of ____ is less/more than the critical value of ____ at 5% probability level. therefore, the deviation from the expected outcome seen in these results has at least a 5% probability of being due to chance/ not due to chance. Therefore, the deviation between the observed and expected results is not significant/ is significant.

Question 19

what is a test cross?

Answer 19

when an individual expressing the dominant phenotype (e.g., F-R-) is crossed with a recessive individual in order to determine whether, or not, the dominant individual is homozygous or heterozygous for the traits.

Question 20

what is linkage?

Answer 20

linkage is when genes for different traits are formed on the same chromosome.

Question 21

what happens when cross over occurs?

Answer 21

the majority of the gametes in a AaBb meiosis with the linkage pattern A to B and a to b are AB and ab. however, when cross over occurs, some of the gametes will have the recombinant chromatids, with Ab and aB.

Question 22

what is the name of the point of cross-over?

Answer 22

chiasma

Question 23

what happens when you cross a normal linkage parent with a normal linkage parent where some recombinant linkage has occurred?

Answer 23

The ratio of dominant both traits to recessive both traits is 3:1, however, a small number will produce offspring showing one dominant trait and one recessive trait. these, however, make up a very small number of the offspring as they result from the recombinant linkage.

Question 24

what is sex linkage?

Answer 24

sex linkage refers to genes that are located on (or linked to) the sex chromosomes. Typically this involves the X chromosome.

Question 25

what is an example of a sex linkage disorder?

Answer 25

haemophilia - a condition where a person’s blood does not go through normal clotting processes.

Question 26

what is the genotype for a carrier female?

Answer 26

xNxn

Question 27

what is the genotype for a normal male?

Answer 27

xNy

Question 28

what is the genotype for an affected male?

Answer 28

xny

Question 29

what is codominance?

Answer 29

with codominance, the two parental phenotypes are both expressed or represented in the phenotype of the heterozygous individual. with codominant traits we typically see a case there are more than two alleles (e.g., one dominant one recessive). this gives rise to the term ‘multiple alleles’.

Question 30

what is an example of multiple alleles?

Answer 30

Blood type, A,B and O

Question 31

Know the blood type diagram.

Answer 31

see book

Question 32

what is the RH factor?

Answer 32

> blood types are denoted in terms of ‘positive or negative’.
the RH factor includes 50 different antigen groups.
the antigen typically considered when regarding blood transfusions (and blood genetics) is the D antigen.
therefore, we say that a person is either O+ or O-, we are only considering the D antigen.

Question 33

What is an antigen?

Answer 33

an antigen results in an immune response - in this case unwanted blood clotting when a person receives the wrong blood type in a transfusion.

Question 34

how is the RH factor inherited?

Answer 34

the RH factor is inherited separatly from the ABO alleles. The Rh factor has two alleles: Rh+ and Rh-. Rh+ is dominant to Rh-.

Question 35

what is another example of codominance?

Answer 35

flower colour, such as FwFw x FrFr = FrFw (showing both red and white petals)

Question 36

what is incomplete dominance?

Answer 36

with incomplete dominance, the heterozygous individual (e.g., offspring) shows a phenotype that is intermediate to the parental homozygous phenotypes. i.e., a ‘blending effect’. In other words, a new phenotype is produced.

Question 37

what is an example of incomplete dominance?

Answer 37

flower colour in snapdragons

Question 38

what is epistasis?

Answer 38

epistasis is a type of gene interaction where the phenotype expression of one gene alters the expression of another independently inherited gene.

Question 39

what is an example and explanation of epistasis?

Answer 39

coat colour in dogs.
>there is a gene that denotes coat colour - black coats are dominant over brown (B/b)
>however, there is also a second gene that determines whether or not black or brown pigment will be deposited into the hair.
>the dominant allele (E) determines that pigment will be deposited, whereas the recessive allele (e) determines that neither that neither black or brown pigment will be deposited. So if a lab is ‘ee’ their coat colour will be yellow. >So the gene that determines whether or not pigment will be deposited, i.e., E/e is said to be epistatic to the gene that determines black or brown pigment, i.e., B/b

Question 40

what is the ratio in the lab coat colour?

Answer 40

9:3:4
Black:brown:yellow