Patterns of Inheritence

Question 1

What is a genotype?

Answer 1

The genetic makeup of an organism.

Question 2

What is phenotype?

Answer 2

The physical expression of genes and its interaction with the environment

Question 3

What does homozygous mean?

Answer 3

A pair of homologous chromosomes carrying the same alleles for a single gene.

Question 4

What does heterozygous mean?

Answer 4

A pair of homologous chromosomes carrying 2 different alleles for a single gene.

Question 5

What is a recessive allele?

Answer 5

An allele only expressed if no dominant allele is present.

Question 6

What is a dominant allele?

Answer 6

An allele that will always be expressed in the phenotype

Question 7

What is Codominance?

Answer 7

Both alleles are equally dominant and expressed.
Blood type = IB, IO

Question 8

What are multiple alleles?

Answer 8

More than 2 alleles for a single gene

Question 9

What is sex linkage?

Answer 9

A gene whose locus is on the X chromosome.
XR Xr
XR Y

Question 10

What is autosomal Linkage?

Answer 10

Genes located on the same chromosome (not sex chromosome)
Aa Bb

Question 11

What is epistasis?

Answer 11

When one gene modifies or masks the expression of a different gene at a different locus
EE Bb

Question 12

What is monohybrid inheritence?

Answer 12

Genetic inheritance cross of characteristics determined by one gene.
B or b

Question 13

What is Dihybrid inheritence?

Answer 13

Genetic inheritance cross for a characteristic determined by two genes

Question 14

What example is commonly used in dihybrid crosses?

Answer 14

Mendel and his peas. One gene codes for shape and the other for colour

Question 15

What do you need to show in dihybrid crosses?

Answer 15

1. Parental phenotype
2. Parental genotype
3. Possible Gametes
4. Offspring genotype
5. Offspring phenotype
6. Poroportion of each phenotype

Question 16

What is the offspring genotype when homozygous dominant is crossed with homozygous recessive?

Answer 16

All offspring are heterozygous (F1 gen)

Question 17

In a dihybrid cross what is the offspring phenotype ratio when parents are heterozygous?

Answer 17

9:3:3:1

Question 18

When do you NOT get a 9:3:3:1 ratio in a heterozygous dihybrid cross?

Answer 18

Autosomal linkage or crossing over occurs in meisosis

Question 19

What is crossing over in meisosis?

Answer 19

The non sister chromatids of a homologous pair overlap, break off and sections are swapped. This creates a new combination of alleles in the gametes. So, the predicted gametes may differ.

Question 20

What is autosomal linkage?

Answer 20

When two genes are on the same chromosome, so not independently assorted. (Not X or Y). This impacts predicted gametes, by reducing it from 4 possible genotype options to 2. The ratio is 3:1

Question 21

Why do extra unexpected phenotypes show up even when autosomal linkage occurs?

Answer 21

Because of crossing over during meiosis making new allele combinations in gametes. However, the resulting phenotypes are low in number because crossing over is rare.

Question 22

What statistical tests needs to be used to count how many individuals fit into a category and investigate differences?

Answer 22

Chi squared. It is used to investigate differences in frequencies of what we expect and actually observe.

Question 23

How would you structure a null hypothesis?

Answer 23

There is no significant difference between the expected and observed values (eg frequency of the colour of corn kernels).

Question 24

What is the equation of chi sqaured?

Answer 24

(observed value - expected value)^2 / Expected

Question 25

How do you find degrees of freedom?

Answer 25

Number of categories - 1

Question 26

What do you say when your chi squared value is less than the critical value?

Answer 26

The calculated chi squared value of — is less than the critical value of — at p=0.05. This means there is a more than 5% probability that the results are due to chance.
There null hypothesis can be accepted. There is no significant difference between the observed and expected results.

Question 27

What is the Hardy-Weinberg principle and what is it used for?

Answer 27

It is used to predict the allele frequencies in a population.
p2 + q2 + 2pq = 1
p + q = 1
p= frequency of dominant allele
q= frequency of recessive allele
p2= frequency of homozygous dominant genotype
q2= frequency of homozygous recessive genotype
2pq= frequency of heterozygous genotype-

Question 28

What is a gene pool?

Answer 28

All the alleles of all the genes within a population at one time.

Question 29

What is a population?

Answer 29

All the individuals of one species in one area at one time.

Question 30

What is allele frequency?

Answer 30

The proportion of an allele within the gene pool.

Question 31

What ae the 3 types of natural selection?

Answer 31

Stabilising, Directional and Disruptive.

Question 32

What is disruptive selection?

Answer 32

Individuals with alleles coding for either extreme trait are more likely to survive an pass on the alleles. So allele frequency changes. More individuals with extreme alleles and less with middling trait. This continuing can lead to speciation

Question 33

What is directional selection?

Answer 33

Only one of the extremes has the selective advantage. Usually occurs when there is a chang in the environment. The modal trait changes. Eg, antibiotic resistance in bacteria.

Question 34

What is stabilising selection?

Answer 34

The modal trait has the selective advantage. There is no change in environment so the modal trait remains the same. Standard deviation decreases as individuals with extreme traits decrease.

Question 35

What is speciation?

Answer 35

The creation of a new species when one original population is reproductively isolated. They cannot breed together. So differences in gene pools increase to the point that they are so genetically different that reproduction would result in infertile offspring. They are now 2 different species.

Question 36

What are the two causes of reproductive isolation?

Answer 36

Allopatric (geographical) and sympatric (because of changes in reproductive mechanism). Sympatric is usually due to behavioural changes.

Question 37

What is genetic drift?

Answer 37

The idea that there is a change in allele frequency in a population between generations. As this always occurs, substantial genetic drift results in evolution. The smaller a population the bigger the impact allele frequency changes have. This is why evolution is more rapid in smaller populations.

Question 38

What are genetic bottlenecks?

Answer 38

Caused by events that kill most of a population (e.g over hunting), creating a small gene pool. Mnay gene alleles are lost and the remaining breeding population passes o the same alleles. This results in lack of genetic diversity. Diseases that exist in the population are more likely to be passed on.

Question 39

What is the founder effect?

Answer 39

A few individuals from an existing population relocate to an isolated area. This results in a small gene pool over many generations.

Question 40

What is natural selection?

Answer 40

Individuals in a population show wide range of variations in phenotype due to genetic and environmental factors. Most of genetic variation is due to mutation.
Predation, disease and competition = selection pressures.
Organisms with phenotypes that provide selective advantage are likelyu to survive and reproduce, passing on their favourable alleles to the next generation. The effect is a change in allele frequency (evolution)

Question 41

What is artificial slection?

Answer 41

Humans select plants or animals with favourable characteristics and deliberately breed them together. This manipulates the gene pool - more favourable alleles more common and non favourable alleles less common.

Eg dog breeds with cuter features like pug’s flat face.
Ethical issues - many pugs have medical issues due to flat nose structure.

Question 42

What are gene banks?

Answer 42

Stores of biological samples (plant seeds, animal semen and eggs). As selective breeding usually involves inbreeding, these are used to help increase genetic diversity by outbreeding. This reduces frequency of homozygous recessive genes in the offspring.