Lecture 12: Genetics II: Mendel's Laws of Independent Assortment and Linked Genes

Question 1

dihybrid cross

Answer 1

the mating of parental varieties differing in 2 characters

Question 2

result of a dihybrid cross

Answer 2

2 hypotheses are possible:
* dependent assortment
* independent assortment

Question 3

Mendel’s dihybrid cross and his findings

Answer 3

• Mendel counted 556 F2 seeds from a cross between a plant producing round and yellow seeds with a plant that produced wrinkled green seeds. He considered each character separately before considering both together.
• Mendel’s dihybrid cross supported the hypothesis that each pair of alleles segregates independently of the other pairs during gamete formation
• thus, the inheritance of one character has no effect on the inheritance of another

Question 4

law of independent assortment

Answer 4

• Mendel discovered that during gamete formation, the alleles of different genes segregate independently of one another
• meaning that the inheritance of one trait does not influence the inheritance of another trait and
• all possible combinations of alleles are equally likely to occur

Question 5

testcross

Answer 5

a mating between
* an individual of dominant phenotype (but unknown genotype) and
* a homozygous recessive individual

Question 6

rule of multiplication

Answer 6

the probability of a compound event is the product of the separate probabilities of the independent events

Question 7

chromosome theory of inheritance

Answer 7

• genes are located at loci (“specific positions”) on chromosomes
• the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns
• in 1900, Walter Sutton and Theodore Boveri first linked the behavior of chromosomes during meiosis to behavior of Mendelian factors
• it is chromosomes that undergo segregation and independent assortment during meiosis and account for Mendel’s laws

Question 8

linked genes

Answer 8

• are located close together on a chromosomes
• tend to be inherited together
• violate Mendel’s second law

Question 9

Thomas Hunt Morgan

Answer 9

• studied the fruit fly Drosphilia melanogaster
• determined that some genes were linked based on the inheritance patterns of their traits

Question 10

crossing over

Answer 10

crossing over can
* separate linked genes
* produce gametes with recombinant gametes
* produce offspring with recombinant phenotypes

Question 11

recombinant frequency

Answer 11

the percentage of recombinant offspring among the total

Question 12

recombinant offspring

Answer 12

offspring that have a different combination of characteristics than their parents

Question 13

origin of linkage maps

Answer 13

• Alfred H. Sturvtevant conducted studies of crossing over using the fruit fly Drosophila melanogaster
• developed a method for mapping the relative gene locations, which resulted in the creation of linkage maps

Question 14

linkage maps

Answer 14

• a diagram that shows the relative positions of genes on a chromosome, based on how often they are inherited together during cell division, indicating which genes are closer to each other and which are further apart
• essentially, it’s a visual representation of the genetic “distance” between different genes on a chromosome, determined by how frequently they recombine during meiosis