Genetics- Patterns of Inheritance

Question 1

What are the causes of genetic variation?

Answer 1

• Genetic differences
• Environmental influences
• Usually a combination of both

Question 2

Features of continuous variation:

Answer 2

• Normal distribution curve
• Polygenic inheritance
• Environmental influences

Question 3

Features of discontinuous variation:

Answer 3

• Mostly genetic
• Controlled by alleles of one gene or a very small number of genes
• Qualitative
• Small number of distinct classes or categories

Question 4

What are the causes of genetic variation?

Answer 4

-Independent assortment
-Crossing over
-Mutations
-Random Fertilisation
-

Question 5

What is the Mendelian ratio for a monohybrid cross?

Answer 5

3:1

Question 6

What is the Mendelian ratio for a dihybrid cross?

Answer 6

9:3:3:1

Question 7

What is Epistasis?

Answer 7

Occurs when there are multiple alleles of two or more genes interacting with one another to control one phenotypic trait. The presence of one genes suppresses the expression of another gene

Question 8

What is a hypostatic gene?

Answer 8

One that is suppressed

Question 9

What is an epistatic gene?

Answer 9

Gene that suppresses the expression of another

Question 10

How does crossing over cause genetic variation?

Answer 10

In Prophase I, sections of DNA on sister chromatids become entangled and break off and rejoin, resulting in exchange of DNA. This means that new combinations of alleles are created.

Question 11

How does independent assortment create variation?

Answer 11

During metaphase I, the chromosomes line up on the metaphase plate in random order, independently of each other. This can result in many different combinations of alleles facing the poles of the cell so when it divides, each cell contains varied genetic information

Question 12

How does random fertilisation create variation?

Answer 12

Gametes contain different alleles for genes therefore when gametes fuse, new combinations of alleles are formed. Also, multiple sperm compete to fuse with the egg so any combination can be created this way.

Question 13

How do mutations create variation?

Answer 13

Changes in base sequence means that bonds are broken and reformed changing the specific 3D tertiary shape. This means that proteins may not be able to carry out their function therefore affecting the phenotype.

Question 14

What does the Chi-squared test?

Answer 14

Measures the size of difference between the results you get and those expected, and whether that difference is significant or not.

Question 15

How to work out expected number for Chi Squared test?

Answer 15

Total number x ratio of each phenotype

Question 16

What is polygenic inheritance?

Answer 16

A single phenotype is controlled by two or more genes at different loci

Question 17

What does the recombination frequency measure?

Answer 17

The amount of crossing over that has happened in meiosis

Question 18

Recombination frequency equation:

Answer 18

Number of recombiant offspring/Total number of offspring x100

Question 19

What can the recombination frequency be used for?

Answer 19

Recombination frequency for a number of characteristics coded for by genes on the same chromosome can be used to map the genes on the chromosome. RF of 1% relates to a distance of one map unit on a chromosome

Question 20

What is co-dominance?

Answer 20

Both alleles are dominant and expressed in the phenotype. Alleles are independent and the phenotype results from full expression of both alleles

Question 21

Why is blood group an example of co-dominance?

Answer 21

Both A and B are co-dominant over O.

Question 22

What is the Rhesus factor?

Answer 22

People who are rhesus positive have antigen D on their RBC. R+ is dominant over R-

Question 23

How is sex determined?

Answer 23

23rd pair of chromosomes in humans are the sex chromosomes, which are both different. Females have two X chromosomes while males have one X and one Y chromosome. The Y chromosome only contains a gene which will cause the embryo to develop as a male. Therefore, the sex of the offspring is determined by whether the sperm fertilising the egg contains an X or Y chromosome

Question 24

What is sex-linkage?

Answer 24

Some characteristics are determined by genes carried on sex chromosomes. As the Y chromosome is much smaller than the X chromosome, there are a number of genes that males do not have a copy of. Therefore, any characteristic caused by a recessive allele on the section of the X chromosome, which is missing in the Y chromosome, will occur more frequently in males. Females, however, will often have a dominant allele present in their cells

Question 25

What is an example of a sex-linked genetic disorder?

Answer 25

Haemophilia is a condition where patients have blood which clots incredibly slowly due to the absence of a protein blood-clotting factor. This condition affect males more as if they have a recessive allele on their X chromosome, they cannot have a corresponding dominant allele on the Y chromosome and so will develop the condition

Question 26

What is recessive epistasis?

Answer 26

If the presence of two recessive alleles at a gene loci leads affects the expression of a gene

Question 27

What is dominant epistasis?

Answer 27

If a dominant allele has an effect on expression of another gene

Question 28

What is population genetics?

Answer 28

Investigates how allele frequencies within populations change over time

Question 29

What is a gene pool?

Answer 29

Total of all genes in a population at any given time

Question 30

What is genetic drift?

Answer 30

Change in allele frequency due to the random nature of alleles being passed on from parents to their offspring. In some cases, the existence of a particular allele can disappear from a population all together. Occurs more frequently in small populations

Question 31

What is the founder effect?

Answer 31

When a small population is separated from the main population and geographically isolated. This leads to a much smaller gene pool so any alleles that were rare in the original population will suddenly have a much higher frequency in the offspring

Question 32

What is stabilising selection?

Answer 32

An example of natural selection where alleles that are in the extremes (e.g. very high or low birth weight) reduce in frequency as they are less likely to survive. Therefore, there is an increase in the frequency of ‘average’ alleles.

Question 33

What is directional selection?

Answer 33

Occurs when there is a change in the environment and the ‘normal’ phenotype is no longer advantageous. Organisms with rare alleles and extreme phenotypes are positively selected and therefore the allele frequency shifts towards the extreme phenotype and evolution eventually occurs.

Question 34

What is a genetic bottleneck?

Answer 34

Where few individuals within a population survive an event or change, thus reducing the gene pool. Only the alleles of the surviving members of the population are able to be passed on to offspring

Question 35

What is selective breeding?

Answer 35

When animals or plants with favourable characteristics are chosen to be bred

Question 36

Why may crops be selectively bred?

Answer 36

• Increased yield
• Resistance (drought, disease, wind)
• Improve taste
• Desired nutrients
• Longer shelf life

Question 37

What are the pros of aritificial selection?

Answer 37

• Produce higher yields to meet demands of growing population
• Friendlier and prettier pets?
• Produce animals that produce more milk, meat, eggs, etc.

Question 38

What are the cons of artificial selection?

Answer 38

• Loss of genes in a population
• Animal discomfort (cows with large udders struggle to walk and some chicken are too heavy to stand and are forced to lay down)
• Can lead to inbreeding, which causes health problem in offspring