Chapter 8 part 2: Mendelian Inheritance and Chromosomes

Question 1

What is the chromosome theory of inheritance?

Answer 1

1) Genes have specific loci on chromosomes
2) Alleles at the same locus segregate during Meiosis also known as the law of segregation so that each gamete gets one allele for each trait
3) Alleles on different loci on different chromosomes assort independently of each other

Question 2

Males will only have the white eyes in fruit flies if he has the recessive allele on his X chromosome. The females must have two copies of the recessive gene on both X chromosomes in order to be white eyed

Question 3

Sex linkage

Answer 3

X linked traits include red-green color blindness, hemophilia, and muscular dystrophy. A recessive trait is usually sex linked if the male shows the trait more often the female which is usually because they only have one functional copy of a gene on their X sex chromosome

Question 4

What are some characteristics of X-linked recessive phenotypes:

Answer 4

• They are more common in males than in females
• Affected males pass the mutation on to their daughters. Sons cannot receive the mutation because they contribute the Y chromosome to their sons and the X chromosome to their daughters. The mutation is only on the X chromosome
• Daughters who receive only one recessive allele are heterozygous carriers
• The mutant phenotype can skip generations

Question 5

What is autosomal linkage? What are two important key notes about autosomal linkage?

Answer 5

refers to two genes that reside on the same autosomal chromosome. Linkage between genes reduces genetic variation and crossing over restores some of that genetic variation lost because the genes are linked

Question 6

Linked genes yield half as many phenotypic possibilities as genes that are not linked and experience independent assortment

Question 7

What is the frequency of recombination for genes that are on the same chromosome

Answer 7

Less than 50 percent

Question 8

What causes recombination?

Answer 8

The crossing over of NON-SISTER chromatids at the chiasma

Question 9

What is the result of any one crossover?

Answer 9

Two parental chromosomes such as ABC and abc. And two recombinant chromosomes such as ABc and abC

Question 10

The probability of recombination between loci is a function of the distance between them

Answer 10

The greater the distance between two loci, the greater the possibility that they will recombine

Question 11

For every one percent of recombinants, there is one centimorgan distance (or one map unit) between the two genes

Question 12

Crossover frequency equation:

Answer 12

of recombinant offspring/ Total # of offspring

Question 13

What is the probability of recombination if the genes are on separate chromosomes. Are these three genes on the same chromosomes?

Answer 13

50%. As long as they have percentages of recombination’s that are below 50% they are on the same chromosome

Question 14

Any gene that is greater than 50 centimorgans away from another gene is effectively unlinked and has a recombination rate of 50%

Question 14

What happens when there is a second crossover event.

Answer 14

It restores the parental genotype at loci that are sufficiently far apart. Double crossovers reduce the frequency of recombinant gametes and restore the parental genotype

Question 15

The number of linkage groups decreases at the number of loci rises, why?

Answer 15

because as you add more and more loci, you link together the linkage groups forming larger connected linkage groups

Question 15

What are linkage groups?

Answer 15

These are groups of loci that are linked to one another or groups on the same chromosome with a recombination rate of less than 50%