6.1.2 - Pattern Of Inheritance

Question 1

Define sex linkage

Answer 1

X chromosome is much larger and has many more genes not present on the Y: they are not homologous
Sex linked - when the allele that codes for it is located on a sex chromosome
Males only have one allele for sex linked genes as they have one X chromosome meaning they only have one copy
Disorders caused by a recessive allele with an x locus will be much more common e.g haemophilia and colour blindness

Question 2

Define an allele

Answer 2

Different version of a gene. Most plants and animals have two alleles of each gene
Represented using letters

Question 3

Define genotype

Answer 3

The alleles an organism has

Question 4

Define both homozygote and heterozygote

Answer 4

Homozygote - an organism that carries two copies of the same alleles of a gene BB or bb
Heterozygote - an organism that carries two different alleles of a gene

Question 5

Define co dominance

Answer 5

Both alleles are expressed in the phenotype when present in the genotype
Neither one is recessive

Question 6

What is a locus

Answer 6

Fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair

Question 7

What is special about phenotype formed as a result of a gene which has co dominate alleles

Answer 7

Codominant alleles are equally dominant,heterozygous individual would display a phenotype chases by the expression of both alleles

Question 8

Explain the difference between the phenotype and genotype of an oak tree

Answer 8

Phenotype - the displayed characteristics of the oak tree

Genotype - the alleles present for each characteristic

Question 9

What is the difference between continuous and discontinuous variation

Answer 9

Continuous - characteristic which can take any value within a range, affected by environmental and genetic factors
Discontinuous - characteristic which can take only specific values , affected by only genetic factors

Question 10

State the difference between monogenic and dihybrid inheritance

Answer 10

Monogenetic inheritance is the study of the inheritance of one gene whereas,dihybrid inheritance is the study of the inheritance of two genes

Question 11

Define autosomal linkage

Answer 11

When the genes that are linked are found on one of the other pairs of chromosomes

Question 12

Define recombination frequency

Answer 12

Measure of the amount of crossing over that has happened in meiosis

Question 13

What is the equation for recombination frequency

Answer 13

Recombination frequency = no of recombinant offspring/total number of offspring

Question 14

Describe epistasis

Answer 14

Interaction between genes at a different loci, affecting a single phenotypic trait
Genes may work antagonistically or in a complementary fashion

Question 15

When is a gene said to be epistatic

Answer 15

When it’s presence modifies or suppresses the effect of a gene at another locus
Hypostatic gene

Question 16

Define recessive epistasis

Answer 16

The presence of homozygous recessive allele at first locus prevents the expression of another allele at a second locus
Hypostatic genes are essentially redundant if the epistatic locus is homozygous recessive

Question 17

What factors affect evolution

Answer 17

Mutation - necessary for the existence of different alleles
Sexual selection to an increase in frequency of allleles which code for characteristics that improve mating success
Gene flow - movement of alleles between populations, immigration and emigration
Genetic drift - due to random nature of mutation
Natural selection - increase number of individuals that have characteristics that improve their chances of survival

Question 18

Define genetic bottleneck

Answer 18

Large reduction in gene pool which last for at least one direction

Question 19

Explain why evoloution does not occur within single organims but groups of organims

Answer 19

Evoloution is change in allele frequency, alleles do not change within organism, single organsima do not adapt

Question 20

Arounf the world,humans dhose their partners for a wide variety of reaons. Explain why this might affect any conclusion about human evoloution drawn using the Hardy- Weinberg principle

Answer 20

HW principle assumes a stable, iso,ages breeding population of dipiloid organimss wirh random mating,no mutations, no selection pressure. Human - mating is not random.

Question 21

Eukaryotes

Question 22

Define speciation

Answer 22

Formation of new species through the process of evolution.

Question 23

Define Allopatric speciation

Answer 23

A form of speciarion where some members of a population are seperated from the rest of the group by a physical barrier e.g river or sea

Question 24

Define sympatric speciation

Answer 24

Speciation that occurs within population that share the same habitat

Question 25

Describe with examples, the difference between pre zygotic and post zygotic reproductive barriers

Answer 25

Pre- zygotic reproductive isolation before fertilisation stage , geographical behaviuoral, seasonsal Post zygotic reproductive isolation after fertilisation

Question 26

Name how outbreeding reduces the problems caused by inbreeding

Answer 26

Introduce new alleles, new alleles can be beneficial, increased genetic variation