Genetics - Week 3

Question 1

Are genes that are physically linked and close together likely to undergo recombination?

Answer 1

unlikely to undergo recombination because there are few opportunities to cross over

Question 2

Are genes that are physically linked and far apart likely to undergo recombination?

Answer 2

more likely to undergo recombination because there are more opportunities to cross over

Question 3

What are methods of fertilization?

Answer 3

• crossing over

- independent assortment

Question 4

What is self-fertilization?

Answer 4

combination of one’s own gametes to produce offspring by crossing over or independent assortment

• no resulting offspring will be genetically identical to the parent

Question 5

Why is self-fertilization not asexual reproduction?

Answer 5

gametes with half the ploidy level of the parental cell are produced

Question 6

What is asexual reproduction?

Answer 6

offspring arise from a single parent (ie. not via fusion of gametes)

Question 7

What are the pros of sexual reproduction?

Answer 7

more genetic variation, easier to adapt to environment

Question 8

What are the cons of sexual reproduction?

Answer 8

• have to actually find a mate
• requires more energy and time
• takes longer to produce offspring

Question 9

What are the pros of asexual reproduction?

Answer 9

faster to produce offspring

Question 10

What are the cons of asexual reproduction?

Answer 10

less genetically variable offspring

Question 11

What is a genotype?

Answer 11

genetic make-up (or set of genes, combination of alleles) of an organism/individual

Question 12

What is a phenotype?

Answer 12

any observable characteristics (traits) of an organism/individual as a result of its genotype and interaction with the environment

Question 13

What are homozygotes?

Answer 13

(in diploid organisms) carry two copies of same allele for a particular gene

Question 14

What are heterozygotes?

Answer 14

(in diploid organisms) carry different alleles

Question 15

What is a test cross?

Answer 15

crossing of an individual with an unknown genotype with an individual with a homozygous recessive genotype

Question 16

What are true breeding organisms (purebreds)?

Answer 16

homozygotes

Question 17

What are non-true breeding organisms?

Answer 17

heterozygotes

Question 18

What is incomplete dominance?

Answer 18

traits blend together

Question 19

What is co-dominance?

Answer 19

both traits appear

Question 20

What is a wild type?

Answer 20

refers to the most common form of the allele or phenotype, or the original allele/phenotype that was observed in

Question 21

What is a mutant?

Answer 21

refers to the less common and/or newer version of a gene/trait, that has arisen through mutation

Question 22

Describe the chromosomes in humans.

Answer 22

humans have 46 chromosomes in each diploid cell:

• 44 autosomes (22 pairs)
• 2 sex chromosomes (X and Y)
• X (female) is bigger than Y (male)

Question 23

What are physically linked genes?

Answer 23

genes are on the same chromosome

Question 24

What are sex linked genes?

Answer 24

genes are on one of the sex chromosomes (either X-linked or Y-linked)

Question 25

What are X-linked genes?

Answer 25

X chromosomes in a female act like homologous autosomes (homozygous/heterozygous)

• males only have one X chromosome (neither homozygous nor heterozygotes)

Question 26

What is a carrier?

Answer 26

heterozygotes which have a copy of the allele responsible for the gene of interest

Question 27

What are the 4 modes of inheritance?

Answer 27

• autosomal dominant
• autosomal recessive
• X-linked dominant
• X-linked recessive

Question 28

What may indicate sex-linkage of a trait?

Answer 28

if you see that the distribution of a trait varies between the male & female parents/offspring

Question 29

What are Punnett Squares used for?

Answer 29

to determine what the possible phenotypes and genotypes from fusing of gametes (crosses)

Question 30

How do you approach cross questions?

Answer 30

• clearly state the symbols for each allele
• look at the offspring data (F1 & F2) for hints regarding modes of inheritance (ie. are there differences between the sexes?)
• provide a prediction for your hypothesis using Punnett Squares (or comparable methods using frequencies)
• provide evidence to support your prediction using the frequencies (actual numbers) provided for the resulting F1 or F2 progeny that is provided

Question 31

How do you solve pedigree questions?

Answer 31

have a hypothesis, then, usually:

• if a trait skips no generations: DOMINANT
• unequal sex ratio: SEX-LINKED (on X chromosome)
• if more males than females affected: X-LINKED RECESSIVE
• if more females than males affected: X-LINKED DOMINANT
• if the trait is not seen in parents, but is seen in their children (at least one): RECESSIVE
• if a certain cross is not possible (due to genotypes): eliminates a mode of inheritance