7 Genetics & Ecosystems- Genetics

Question 1

What is a gene and its function?

Answer 1

-A section of DNA, located on its locus
-Base sequence of each gene carries genetic info that determines sequence of amino acids in a protein

Question 2

What are alleles?

Answer 2

-Different variations of a gene; diploid organisms have 2 alleles, 1 on each chromosome

Question 3

What is a genotype and what does it consist of?

Answer 3

-An organism’s underlying genetic makeup
-consists of both physically visible & non-expressed alleles

Question 4

What is a phenotype and what is it determined by?

Answer 4

-The observable traits expressed by an organism
-determined by interaction between its genetic constitution & the environment

Question 5

When are dominant and recessive expressed in the phenotype of an organism?

Answer 5

-Dominant; always expressed
-recessive; only expressed if there’s 2 copies of the allele

Question 6

What are co-dominant alleles?

Answer 6

Alleles both expressed in the heterozygote

Question 7

What are homozygotes?

Answer 7

-Organisms w/ 2 copies of same allele
-Can be homozygous dominant/recessive

Question 8

What are heterozygotes?

Answer 8

Organisms that have different alleles for a gene

Question 9

What is a monohybrid cross and what does it allow?

Answer 9

-When 2 parents that differ in only 1 characteristic breed
-Allow genotype and phenotype of offspring to be predicted

Question 10

What is the first step of constructing a monohybrid cross?

Answer 10

identifying the parental genotypes

Question 11

What are the resulting gamete alleles from a monohybrid cross, what does this represent?

Answer 11

-Gametes= haploid, so only 1 allele from each parent is found in the gametes.
-All possible combinations of parental alleles should be identified; represents meiotic segregation into haploid gametes

Question 12

What is the F1 offspring and how many offspring combinations does a monohybrid cross produce?

Answer 12

-F1 offspring= first generation of offspring.
-produces 4 different combinations of possible offspring

Question 13

What is the F2 offspring?

Answer 13

the second generation of offspring

Question 14

In what 2 ways can a monohybrid cross be drawn?

Answer 14

-Genetic diagrams
-punnett squares

Question 15

What is a dihybrid cross?

Answer 15

When 2 parents that differ in 2 characteristics breed

Question 16

What is the law of independent assortment and what does it mean?

Answer 16

-Mendel proved that genes don’t influence each other w/ regard to sorting of alleles into gametes
-means that genes separate independently of each other when gametes are made.
-combination of alleles can be shown in a dihybrid cross

Question 17

How many gamete allele combinations for each homozygote are possible in a dihybrid cross?

Answer 17

1

Question 18

What is the F1 offspring result in a dihybrid cross?

Answer 18

-all the F1 offspring have the same genotype
-law of segregation predicts each gamete in F1 generation has equal probability of receiving any allele
-means there are 4 possible combinations of gametes produced by the F1 offspring

Question 19

What is the F2 offspring result in a dihybrid cross?

Answer 19

-When F1 offspring breed, the 4 possible gametes from 1 individual can combine w/ any of 4 possible gametes from other individual.
-total possible combinations in the F2 generation= 16.

Question 20

What is the expected ratio for when 2 dihybrid heterozygotes breed?

Answer 20

9:3:3:1

Question 21

What is codominance and what can it influence?

Answer 21

-where both alleles for same characteristic are simultaneously expressed in heterozygote.
-neither of the alleles are recessive.
-can influence the outcome/phenotypic ratio of monohybrid & dihybrid crosses.

Question 22

What is an example of co-dominance?

Answer 22

-sickle-cell anaemia, 2 alleles for sickle-cell anaemia;
H^N- normal haemoglobin. (Homozygotes)
H^S- sickle haemoglobin. (Homozygotes)
-people who have 1 H^N allele & H^S allele (heterozygotes) have both normal haemoglobin & sickled haemoglobin.
H^N & H^S= codominant.

Question 23

What is linkage and what does it show?

Answer 23

-when genes that are close to one another on a chromosome are likely to be inherited together
-shows that some allele combinations aren’t inherited independently of each other

Question 24

What is Mendel’s law of independence assortment and why is this not always the case?

Answer 24

-states that genes don’t influence sorting of alleles into gametes; isn’t always the case.
-some allele combinations aren’t inherited independently of each other.
-genes located close to each other on same chromosome= more likely to be inherited as a pair (linkage)

Question 25

What are autosomes and how are they arranged?

Answer 25

-all the chromosomes except the sex chromosomes (X and Y).
-arranged in pairs; homologous chromosomes (1 from the father and 1 from the mother), consist of same genes in same order along chromosome.
-there is some variation if chromosomes have different alleles but genes are the same.

Question 26

What is recombination and when does it not occur?

Answer 26

-When gametes are produced by meiosis, multiple sections of homologous chromosomes are exchanged
-If 2 genes are located in close proximity on same chromosome, they’re more likely to be exchanged together, not separated in recombination
-genes= more likely to be transmitted to gamete together

Question 27

How does sex linkage differ from autosomal linkage?

Answer 27

Takes place in sex chromosomes

Question 28

How do sex chromosomes differ from autosomes?

Answer 28

they are non-homologous; don’t consist of the same genes in the same order along the chromosome.

Question 29

What is hemizygosity/X-linked genes?

Answer 29

-that there’s no role of dominance & recessiveness.
-if a recessive gene is inherited on the X chromosome, it’ll always be present in the phenotype as it’s the only allele present.
-males only have 1 copy of an allele for X-linked genes.

Question 30

What is haemophilia and how is it an example of an X-linked disorder?

Answer 30

-a blood disorder that is X-linked
-humans males only need to inherit 1 recessive mutant X allele to be affected by the disorder but females must inherit 2 copies of the recessive allele.
-this means haemophilia= more common in males.
-females can be carriers for the disorder when they’re heterozygous.

Question 31

What are homologous chromosomes and what do they consist of?

Answer 31

-Chromosomes in diploid organisms
-consist of the same genes in the same order.
-the only variation between homologous chromosomes is in the alleles.
-2 alleles can be present for 1 gene

Question 32

What are multiple alleles and what do they provide?

Answer 32

-Although only 2 alleles can be present in an organism, there could be multiple different alleles for a single gene.
-have a dominance hierarchy
-provide many different genotype combinations.
-creates large variation at the population level.

Question 33

What is epistasis and is it dominant or recessive?

Answer 33

-when a gene at one locus inhibits the expression of a gene at another locus.
-can be dominant or recessive.
-alleles that are being masked= hypostatic to epistatic alleles.
-often involves pathway where expression of one gene= dependent on the function of another gene.

Question 34

What is recessive epistasis?

Answer 34

-where the epistatic allele (the allele that masks another gene) is recessive.
-means two copies of the epistatic allele must be present for expression of the hypostatic allele to be affected.

Question 35

What is dominant epistasis?

Answer 35

-where the epistatic allele is dominant.
-means only one copy of the epistatic allele must be present for expression of the hypostatic allele to be affected.

Question 36

What is chi-squared used for in genetics?

Answer 36

-to compare the goodness of fit of observed data with expected data in phenotypic ratios
-tests if the difference between observed and expected values is due to chance.

Question 37

What are the requirements for chi-squared to be used?

Answer 37

-Variation= discrete not continuous; data are in categories (e.g. Aa and aa).
-Data show absolute numbers (whole), normally frequencies.

Question 38

What is the null-hypothesis and why is it used in genetics?

Answer 38

-Before using chi-squared, null hypothesis is stated;
‘There is no significant difference between observed and expected data, the difference is due to chance’.
-used to reject or accept the null hypothesis.

Question 39

What is the Chi-squared equation?

Answer 39

χ=Σ (O−E)²/E

O = observed values.
E = expected values

Question 40

What are the steps in calculating chi-squared?

Answer 40

-expected values need to be calculated; predicted using genetic diagrams (phenotypic ratios)
-compare expected values w/ observed values & use numbers in equation; calculate chi-squared value
-calculate degrees of freedom = the number of categories (e.g. phenotypes) − 1.
-find critical value that corresponds to degrees of freedom in probability distribution table at 0.05 significance level.

Question 41

When do you accept or reject the null hypothesis?

Answer 41

-if chi-squared value < critical value= accept null hypothesis, difference between observed & expected data—> due to chance.
-if the chi-squared value > critical value= reject null hypothesis, difference between observed & expected data—> NOT due to chance.
- ^means we would get this chi-squared value <5% of cases (very unlikely)