7.1 Genetics

Question 1

define heterozygous

Answer 1

genotype with two different alleles at a particular locus

Question 2

what does it mean for an allele to be dominant?

Answer 2

it is always expressed in the phenotype

Question 3

what is a genotype?

Answer 3

the combination of alleles an organism contains

Question 4

what does it mean for an organism to be diploid?

Answer 4

is has two copies of each chromosome

Question 5

define codominant

Answer 5

both alleles for a gene in a heterozygous organism are expressed in the phenotype

Question 6

what is a phenotype?

Answer 6

what characteristics an organism has as a result of its genes and the effect the environment has on them

Question 7

define homozygous

Answer 7

genotype with two of the same allele at a particular locus

Question 8

what is a monohybrid cross?

Answer 8

a diagram that shows the likelihood of two different alleles of a single gene being inherited by the offspring of two parents

Question 9

what does it mean for an allele to be recessive?

Answer 9

it is only expressed in the phenotype if two copies are present (homozygous)

Question 10

what does it mean for an organism to be haploid?

Answer 10

it only only has copy of each chromosome

Question 11

what does it mean for a characteristic to be sex-linked?

Answer 11

the allele that codes for them are located on a sex chromosome

Question 12

why are men more likely than females to show recessive phenotypes for characteristics that are sex-linked?

Answer 12

• the Y chromosome is shorter than the X chromosome and therefore carries fewer genes
• so most genes on the sex chromosomes are carried on the X chromosome
• males only have one X chromosome, so often just have one allele for sex-linked genes
• this means the characteristic will be expressed even if it’s recessive

Question 13

what is an autosome?

Answer 13

any chromosome that isn’t a sex-chromosome

Question 14

what combination of sex chromosomes do biological males have?

Answer 14

XY

Question 15

what combination of sex chromosomes do biological females have?

Answer 15

XX

Question 16

what evidence on a pedigree chart suggests that a characteristic in not sex-linked?

Answer 16

an unaffected father with an affected daughter

Question 17

what evidence on a pedigree chart suggests that a characteristic is sex-linked?

Answer 17

only males are affected

Question 18

define autosomal linkage

Answer 18

when two or more genes are positioned on the same autosome, they are unlikely to be separated by crossing over during meiosis, so are often inherited together

Question 19

define dihybrid inheritance

Answer 19

the inheritance of two different genes that determine two phenotypes on two different chromosomes

Question 20

define epistatis

Answer 20

the relationship between genes where the allele of one gene affects the expression of a different gene

Question 21

define monohybrid inheritance

Answer 21

the inheritance of one gene