6.1.2 - Patterns Of Inheritance (Set A - Variation + Inheritance)

Question 1

Distinguish the definitions of inter and intraspecific variation?

Answer 1

Interspecific variation considers the variation between different species

Intraspecific variation is the variation within a specific species/group

Question 2

Explain what epistasis is?

Answer 2

Epistasis describes an interaction between genes at different loci (affecting a single phenotypic trait)

• gene said to be epistatic when its presence modifies/suppresses the effect of a hypostatic (gene at another locus)

Question 3

Define evolution both at a general and genetic level?

Answer 3

A change in inherited characteristics of a group of organisms over time

• A change in allele frequency over time

Question 4

Explain how variation occurs in plants - use chlorosis as an example?

Answer 4

• most plants are genetically coded to produce large quantities of chlorophyll - chlorosis is where the leaves look pale/yellow and is due to not enough chlorophyll being produced
• most plants which show chlorosis have normal gene coding for chlorophyll production but environmental factors change their phenotype (eg lack of light and mineral deficiencies)

Question 5

Explain how chlorosis can occur in plants?

Answer 5

Most plants which show chlorosis have normal gene coding for chlorophyll production but environmental factors like lack of light which results in the plant having to conserve resources and mineral deficiencies lack of magnesium involved in chlorophyll production and iron needed for cofactor for enzymes, leads to leaves looking pale or yellow and is

Question 6

Explain how variation occurs in animals - use body mass as an example?

Answer 6

Organisms body mass determined by combination of both genetic and environmental factors (majority of cases dramatic variations in size, caused by environmental factors like amount of food and quality of food eaten)

• obesity can be result of genetic make-up - mutations on chromosomes can cause pattern of fat distribution to be altered (obese mouse example)

Question 7

Define genotype?

Answer 7

Combination of alleles an organism inherits for a characteristic (alleles may be the same or different versions of the same gene)

• organisms inherits 2 alleles (one from mother and one from father)

Question 8

Define phenotype?

Answer 8

The observable characteristics of an organism - influenced by the environment which doesn’t change phenotype - referred to as modifications

Question 9

Explain how genetic variation is caused?

Answer 9

created by versions of genes you inherit from parents (are a number of different possible alleles or variants)

• combination they inherit is determined by meiosis and random fusion of gametes which leads to vast genetic variation

Question 10

Outline and define recessive and dominant alleles?

Answer 10

Recessive - allele which will only be expressed if 2 copies of the allele are present (if they have a recessive phenotype you know they have recessive genotype)

Dominant - version of allele which will always be expressed if present (can’t tell genotype from phenotype)

Question 11

Outline and define homozygous and heterozygous?

Answer 11

Homozygous - 2 identical alleles for a characteristic

Heterozygous - 2 different alleles for a characteristic (dominant expressed)

Question 12

Explain what speciation is?

Answer 12

Formation of new species through the process of evolution - organism belonging to new species no longer able to produce fertile offspring with organism belonging to original species

Question 13

Explain 3 events which lead to speciation?

Answer 13

• members of a population become isolated - no longer interbreed with rest of population resulting in no gene flow between 2 groups
• alleles within groups continue to undergo random mutations - environments of each group may be different or change (different selection pressures)
• accumulation of mutations and changes in allele frequencies over generations - leads to large changes in phenotype, no longer able to interbreed (reproductively isolated - now different species)

Question 14

Explain the difference between continuous and discontinuous variation?

Answer 14

With discontinuous variation individuals fall into distinct groups (eg blood groups) normally only 1 or 2 genes involved and the environment has little effect

Continuous variation there are 2 extremes, every degree of variation possible in between (eg height or weight) involve poly genes (controlled by number of genes)

Question 15

Outline the features of continuous variation?

Answer 15

• characteristic that can take any value within a range
• cause of variation is genetic and environment
• controlled by polygenes - number of genes involved
• eg leaf surface area, skin colour and animal mass

Question 16

Outline the features of discontinuous variation?

Answer 16

• characteristic that can only appear in specific values
• variation is caused mostly by genetics
• involves 1 or 2 genes
• examples are blood groups, round and wrinkled pea shape

Question 17

explain what codominance is?

Answer 17

Occurs when 2 different alleles occur for a gene - both are equally dominant

both alleles are expressed in the phenotype of the organism

Question 18

Explain what sex linked genes are?

Answer 18

Some characteristics are determined by genes carried on sex chromosomes - genes called sex linked

• Y chromosome much smaller than X so there are number of gene in the X chromosome males have only one copy of - sex linkage occurs when there is a gene on the X chromosome, not present on the Y chromosome
• males more likely to exhibit recessive disorders like haemophilia

Question 19

Define multiple alleles?

Answer 19

When there are more than 2 different versions of a gene in a population (for example coat colour in rabbits - controlled by single gene but there are 4 different alleles for coat colour)

Question 20

Explain the purpose of a dihybrid cross?

Answer 20

Used to show inheritance of 2 different characteristics caused by 2 genes which may be located on different pairs of homologous chromosomes (each gene can have 2 or more alleles)

• alleles are independent assorted

Question 21

Define autosomal linkage?

Answer 21

Occurs if 2 or more genes are located on the same autosome (non-sex chromosome) the 2 genes are less likely to be separated during crossing over, resulting in the alleles of the linked genes been inherited together

• linked genes cannot undergo normal ‘shuffling’ of alleles during meiosis - expected ratios not produce in offspring

Question 22

Explain what the recombination frequency is - give the equation?

Answer 22

Recombination frequency - measure of the amount of crossing over that happened in meiosis

Recombination frequency - number of recombination offspring / total number offspring

Question 23

Explain what recombination offspring are?

Answer 23

Offspring that have different combinations of alleles than either parent

• closer genes are on a chromosome - less likely they are separated during crossing over - so fewer recombinant offspring produced

Question 24

Explain what epistasis is?

Answer 24

The interaction of genes at different loci which causes one gene to mask the expression of the other in the phenotype

• gene regulation is a form of epistasis with regulatory genes controlling activity of structural genes (eg lac operon)

Question 25

Explain what is meant by locus?

Answer 25

Locus or loci is a precise location of a gene on a chromosome

Question 26

What is meant by epistatic gene?

Answer 26

When a gene suppresses another gene - gene suppressing is called epistatic gene

• gene suppressed is called hypostatic gene

Question 27

Explain what monogenetic inheritance is?

Answer 27

The inheritance of a single gene