Genetic crosses 9-2

What proportion of the offspring will be dominant for both traits ?

9/16

A genetic cross performed many times produce 798 long-stemmed plants and 266 short-stemmed plants. The probability of obtaining short-stemmed plant in a similar cross is

A- 266/1,064

The appearance of organisms is its

B-phenotype

In a dihybrid cross between an individual with the genotype RRYY and an individual with the genotype rryy, all of the offspring will have the genotype

C- RrYy

A mono hybrid cross of two individuals that are heterozygous for a trait exhibiting complete dominance would probably result in phenotype ratio of

C-3 dominant : 1 recessive

To determine the genotype of an individual that shows the dominant phenotype , you would cross that individual with one that is

D- homozygous recessive

If the probability that a specific trait will appear in the F2 generation is 0.25 , how many individuals would be expected to show the trait in an F2 generation consisting of 80 individuals ?

0.25•80 individuals =20 individuals

What proportion of the offspring will be homozygous dominant for both traits ?

1/16

What proportion of the offspring will be homozygous recessive for both traits ?

1/16

What proportion of the offspring will have the same genotype as their parents ?

1/4

Complete dominance

Heterozygous and dominant homozygous individuals have the same phenotype . For example , in a pea plant , the P allele is completely dominant over the p alleles , so both PP and Pp plants have purple flowers

What is the difference between a homozygous individual and a heterozygous individual ?

In a homozygous individual , both alleles of a pair are the same ; in a heterozygous individual , the two alleles of a pair are different

Some animals , such as cows , normally produce only one offspring from each mating . If a cow showed a dominant phenotype , why would a typical testcross be a difficult way to determine the genotype of that animal ?

In a testcross , the dominant phenotype would appear in all of the offspring if the cow were homozygous dominant but in only about 50% of the offspring , if the cows were heterozygous with only one individual per F1 generation , distinguishing between these two possibilities would take a long time , until a calf with the recessive phenotype was born .

incomplete dominance

Neither allele is completely dominant over the other and both influence the phenotype . For example , in four o'clocks , neither the R or r allele is completely dominant , so Rr plants have pink flowers

Codominance

Neither allele is dominant or recessive ;both are expressed in heterozygotes . For example , in roan horses , red hairs are produced by the R allele and white hairs are produced by the R allele